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パブロフ 条件反射 解説原文

パブロフ 条件反射 解説原文

記憶理論 パブロフ 条件反射 要約解説

記憶理論 パブロフ 条件反射 要約解説


プロ家庭教師による記憶理論の講座で、パブロフの条件反射の解説です。彼の書籍をインターネットで読めるようにまとめています。

日本語データ
パブロフ・イワン・ペトローヴィチ  (1849-1936)
条件反射:大脳半球の生理的活動の探求 (1927)
ウェブ版編集:矢部祐司(2019)

英語データ
Pavlov, Ivan Petrovich, 1849-1936
Conditioned reflexes: An investigation of the physiological activity of the cerebral cortex (1927)
Translated from Russian into English by G. V. Anrep (1927)
An internet resource developed by Yuji Yabe

プロ家庭教師による難関中学・難関高校・難関大学合格対策カリキュラムを指導依頼できます。

パブロフと条件反射 基本知識


Q:パブロフ博士の本名は何ですか?
A:パブロフ博士の本名は、パブロフ・イワン・ペトローヴィチといい、ロシア出身の科学者です。ロシア人として初めてノーベル賞を受賞されました。

Q:パブロフ博士の問題意識
A:当時の心理学が内観に依存している点を問題にし、生理学の実験により脳の働きを科学的に解明すべきと考えました。身体の他の部位とは異なり、脳は特別に扱われていて、脳の働きをどのように測定するべきか科学的な研究手法を探求しました。

Q:パブロフ博士の研究手法
A:ロシアに実験施設を建てて、犬を用いた動物実験を開始しました。外部からの刺激がどのように犬の脳を刺激して、犬に唾液を催させるかを測定しました。その結果、刺激と反射についての理論をまとめました。パブロフ博士による犬の動物実験は、人々に衝撃を与えたので、パブロフの犬といえば条件反射の代名詞となっています。

Q:パブロフ博士の実験は、どのような内容なのですか?
A:パブロフ博士は、生物への刺激を2種類に分けました。

1つめは無条件刺激(unconditioned stimilus)と呼ばれます。無条件刺激は、生物にあらかじめ備わっている固有の反射を促します。例えば、餌という刺激は、犬に唾液分泌という反射を促します。痛みという刺激は、犬に筋肉の緊張という反射を促します。無条件刺激に対応する反射を、無条件反射(unconditioned reflex)と呼びます。

2つめは、条件刺激(conditioned stimilus)です。条件刺激は、特定の反射とは結びついていません。例えば、ベルの音を聞かせても、唾液分泌は促されません。ところが、条件刺激のベルを鳴らした後に、無条件刺激の餌を見せて、無条件反射の唾液分泌を促していくと、犬に変化が起こります。それまでベルの音を聞かせても、唾液分泌しなかった犬が、ベルの音を聞くだけで、唾液分泌するようになります。もともとは無関係だったベルの音(条件刺激)と唾液分泌(無条件反射)が結びつくことを、条件付(conditioning)と呼びます。

このような条件付の法則をパブロフ博士は発見し、細部をていねいに確認していきました。


Q:パブロフ博士の実験は、どこで実施されたのですか?
A:ロシアのペトログラード(サンクトペテルブルグの別名)にある実験施設です。刺激を厳密に管理するために、専用の建物が用意されました。

Q:パブロフ博士の実験は、それまでの実験とどのように異なるのですか?
A:パブロフ博士の実験は、学習に科学的な根拠を求めました。人間が学習できることは、伝統的に肯定されていましたが、学習の仕組みは科学的に解明されていませんでした。

Q:パブロフ博士の実験は、どのような意義があるのですか?
A:パブロフ博士は、刺激と反射の関係を、人工的に操作できることを実証しました。刺激と反射に秩序を与えることが、学習理論として確立しました。私たちが文字を見て、意味を読み取ることができるのも、刺激と反射の理論に基礎づけられています。

Q:パブロフ博士の条件反射理論は、現代にどのように役立つのですか?
A:パブロフ博士の条件反射理論は、現代では、記憶力の強化を通じて、学習能力向上に役立ちます。他にも、メディア依存対策や広告報道への批判能力となります。条件反射理論によれば、広告による条件刺激は、負の学習とも考えられます。パブロフ博士の確立した理論は、何を記憶するべきか主体的に考えるべきと、私たちに教えてくれます。

Q:パブロフ博士の理論には、どのような限界があるのですか?
A:パブロフ博士の理論の限界は、反射がそのまま理解や記憶とはならなかった点です。

例えば、現代社会では、子供に芸能人の顔(刺激)を見せると、反射が起きます。しかし子供は、芸能人の制度について理解していませんし、芸能人の名前すら覚えていない場合があります。芸能人の顔という刺激に、反射が起きたとしても、刺激がどのようなものか、理解しているわけではありません。

同じように、人間の言葉の刺激に対して、オウムは反射を返すこと(オウム返し)ができますが、オウムが人間の言語を理解しているとは言えません。

このように、反射・記憶・理解には、内容的な差異が指摘できます。現代の試験問題も、反射(択一)・記憶(一問一答)・理解(論述)は、異なる能力として扱います。パブロフの条件反射理論は、小学生から中学生くらいまでの暗記中心カリキュラムまでは有効と考えられます。

テレビ視聴と学力の相関関係も、単純な刺激と反射だけでは、学習が成立しないであろうと示唆しています。


Q:パブロフ博士の実験は、どのような刺激を採用したのですか?
A:実験の刺激として以下を採用しています。しかし、人間に反射を促すものであれば、すべてが条件刺激となりえると述べています。

視覚:ドッグフード・特定の人間・光線
味覚:塩酸・食べられない固形物
嗅覚:バニラ
聴覚:メトロノームの音・特定のヘルツの音・ブザー・車の警笛
触覚:電流・傷


Q:パブロフ博士の実験で、刺激の順番を前後させると、どうなるのですか?
A:パブロフ博士の実験は、無条件刺激(メトロノーム音)の後に、条件刺激(ドッグフード)を提示しました。この場合は、条件付が成功しています。しかし、無条件刺激(ドッグフード)の後に条件刺激(メトロノーム音)を提示すると、条件付は成功しませんでした。このことから、広告は先に覚えさせたい刺激(スポンサー名)を提示して、その後に無条件刺激(強い色や光)を提示するように、制作されています。

Q:パブロフ博士の実験で、刺激の間隔は重要なのですか?
A:刺激の間隔は、条件付に重要です。基本的には、条件刺激のすぐ後に無条件刺激を提示しないと、条件付が起きにくくなります。

Q:パブロフ博士の実験で、条件付の強化とは何ですか?
A:条件付の強化(reinforcement)とは、ひとたび条件付が成立した後で、無条件刺激と条件刺激を再び条件付すると、反射がより強くなることです。いわば、条件付の上乗せができる法則です。この法則は、スポーツやアートの達人が、素晴らしい反応を見せることをよく説明できます。反対に、メディア依存や買物依存も、説明できてしまいます。

Q:パブロフ博士の実験で、無条件刺激と条件刺激では、反射の強さは異なるのですか?
A:条件刺激は、無条件刺激よりも、反射が弱くなることがわかっています。

Q:パブロフ博士の実験で、先行条件付とは何ですか?
A:先行条件付(forward conditioning)とは、条件刺激が無条件刺激より先行する条件付です。

Q:パブロフ博士の実験で、延滞条件付とは何ですか?
A:延滞条件付(delayed conditioning)とは、条件刺激が無条件刺激より遅れて提示される条件付です。延滞時間には内制止が発生し、睡眠に陥る場合もあります。

Q:パブロフ博士の実験で、痕跡条件付とは何ですか?
A:痕跡条件付(delayed conditioning)とは、条件刺激が無条件刺激より遅れて提示される条件付です。条件刺激と無条件刺激はまったく重ならず、条件刺激の終止した後、時間を隔てて、無条件刺激が提示されます。

Q:パブロフ博士の実験で、外制止とは何ですか?
A:外制止(external inhibition)とは、条件付の途中で、条件刺激以外の刺激を提示すると、条件反射が弱められることです。

Q:パブロフ博士の実験で、内制止とは何ですか?
A:内制止(internal inhibition)とは、動物の体内で自然に条件反射が制止されることです。

Q:パブロフ博士の実験で、条件付の消去とは何ですか?
A:条件付の消去(extinction)とは、条件付が成立した後で、条件刺激だけを提示して、無条件刺激を提示しない(無条件反射を起こさない)ようにすると、条件付が弱まり、やがて消去される法則です。いわば、条件刺激に飽きるという法則です。
ただし、ひとたび消去された条件付でも、完全に存在しなくなったわけではく、身体に保存されていることがわかっています。

Q:パブロフ博士の実験で、脱制止とは何ですか?
A:脱制止(disinhibition)とは、消去の進行中に、条件刺激以外の刺激を提示すると、消去しかけた条件反射が復活することです。

Q:パブロフ博士の実験で、般化とは何ですか?
A:般化(generalization)とは、ある条件刺激に対して条件反射を形成すると、それと似ている刺激に対しても条件反射が生じることです。例えば、1000ヘルツ音に条件反射が生じると、800ヘルツ音に対しても条件反射が生じます。

Q:パブロフ博士の実験で、分化条件付とは何ですか?
A:分化条件付(differential conditioning)とは、一方の刺激を条件付し、他方の刺激を消去すると、消去された刺激に般化が及ばなくなることです。

Q:パブロフ博士の実験で、高次条件付とは何ですか?
A:高次条件付(higher order conditioning)とは、条件刺激に対する条件反射が形成されたのち、別の条件刺激に対して次々に条件付することでせう。例えば、音刺激を条件付した後に、さらに音刺激に光刺激を条件付します。

Q:パブロフ博士の実験で、感性前条件付とは何ですか?
A:感性前条件付(sensory pre-conditioning)とは、まだ条件付されていない刺激(中性刺激)同士を、反復して提示した後に、片方を条件刺激として条件付すると、もう片方の刺激にも条件付されることです。

Q:パブロフ博士の実験で、大脳の機能はどのように考えられていたのですか?
A:大脳皮質(cerebral cortex)に結合が起きることで、条件付が生じると考えました。

Q:パブロフ博士の実験で、第一信号とは何ですか?
A:条件反射の第一信号とは、動物にみられる直接経験による条件反射です。

パブロフと条件反射 講義1


The development of the objective method in investigating the physiological activities of the cerebral hemispheres. -- Concept of Reflex. -- Variety of Reflexes. -- Signal reflexes, the most fundamental physiological characteristic of the hemispheres.


大脳半球への好奇心
The cerebral hemispheres stand out as the crowning achievement in the nervous development of the animal kingdom. These structures in the higher animals are of considerable dimensions and exceedingly complex, being made up in man of millions upon millions of cells -- centres or foci of nervous activity -- varying in size, shape and arrangement, and connected with each other by countless branchings from their individual processes. Such complexity of structure naturally suggests a like complexity of function, which in fact is obvious in the higher animal and in man. Consider the dog, which has been for so many countless ages the servant of man. Think how he may be trained to perform various duties, watching, hunting, etc. We know that this complex behaviour of the animal, undoubtedly involving the highest nervous activity, is mainly associated with the cerebral hemispheres. If we remove the hemispheres in the dog [Goltz [l] and others[2]], the animal becomes not only incapable of performing these duties hut also incapable even of looking after itself. It becomes in fact a helpless invalid, and cannot long survive unless it be carefully tended.


大脳半球の生理学の不在
In man also the highest nervous activity is dependent upon the structural and functional integrity of the cerebral hemispheres. As soon as these structures become damaged and their functions impaired in any way, so man also becomes an invalid. He can no longer proceed with his normal duties, but has to be kept out of the working world of his fellow men. In astounding contrast with the unbounded activity of the cerebral hemispheres stands the meagre content of present-day physiological knowledge concerning them. Up to the year 1870,[p. 2] in fact, there was no physiology of the hemispheres; they seemed to be out of reach of the physiologist. In that year the common physiological methods of stimulation and extirpation were first applied to them [Fritsch and Hitzig (3)]. It was found by these workers that stimulation of certain parts of the cortex of the hemispheres (motor cortex) regularly evoked contractions in definite groups of skeletal muscles: extirpation of these parts of the cortex led to disturbances in the normal functioning of the same groups of muscles. Shortly afterwards it was demonstrated [Ferrier [4], H. Munk [5]] that other areas of the cortex which do not evoke any motor activity in response to stimulation are also functionally differentiated. Extirpation of these areas leads to definite defects in the nervous activity associated with certain receptor organs, such as the retina of the eye, the organ of Corti, and the sensory nerve-endings in the skin. Searching investigations have been made, and still are being made, by numerous workers on this question of localization of function in the cortex. Our knowledge has been increased in precision and filled out in detail, especially as regards the motor area, and has even found useful application in medicine. These investigations, however, did not proceed fundamentally beyond the position established by Fritsch and Hitzig. The important question of the physiological mechanism of the whole higher and complex behaviour of the animal which is -- as Goltz showed -- dependent upon the cerebral hemispheres, was not touched in any of these investigations and formed no part of the current physiological knowledge.

脳科学研究が遅れている理由
When therefore we ask the questions: What do those facts which have up to the present been at the disposal of the physiologist explain with regard to the behaviour of the higher animals? What general scheme of the highest nervous activity can they give? Or what general rules governing this activity can they help us to formulate? -- the modern physiologist finds himself at a loss and can give no satisfactory reply. The problem of the mechanism of this complex structure which is so rich in function has got hidden away in a corner, and this unlimited field, so fertile in possibilities for research, has never been adequately explored.[p.3]

The reason for this is quite simple and clear. These nervous activities have never been regarded from the same point of view as those of other organs, or even other parts of the central nervous system. The activities of the hemispheres have been talked about as some kind of special psychical activity, whose working we feel and apprehend in ourselves, and by analogy suppose to exist in animals. This is an anomaly which has placed the physiologist in an extremely difficult position. On the one hand it would seem that the study of the activities of the cerebral hemispheres, as of the activities of any other part of the organism, should be within the compass of physiology, but on the other hand it happens to have been annexed to the special field of another science-psychology.

研究の方法論 心理学の検討
What attitude then should the physiologist adopt? Perhaps he should first of all study the methods of this science of psychology, and only afterwards hope to study the physiological mechanism of the hemispheres? This involves a serious difficulty. It is logical that in its analysis of the various activities of living matter physiology should base itself on the more advanced and more exact sciences -- physics and chemistry. But if we attempt an approach from this science of psychology to the problem confronting us we shall be building our superstructure on a science which has no claim to exactness as compared even with physiology. In fact it is still open to discussion whether psychology is a natural science, or whether it can be regarded as a science at all.

It is not possible here for me to enter deeply into this question, but I will stay to give one fact which strikes me very forcibly, viz. that even the advocates of psychology do not look upon their science as being in any sense exact. The eminent American psychologist, William James, has in recent years referred to psychology not as a science but as a hope of science. Another striking illustration is provided by Wundt, the celebrated philosopher and psychologist, founder of the so-called experimental method in psychology and himself formerly a physiologist. Just before the War (1913), on the occasion of a discussion in Germany as to the advisability of making separate Chairs of Philosophy and Psychology, Wundt opposed the separation, one of his arguments being the impossibility of fixing a common examination schedule in psychology, since every professor had his own special ideas as to what psychology really was. Such testimony seems to show clearly that psychology cannot yet claim the status of an exact science. [p. 4]


研究の方法論 生理学の検討
If this be the case there is no need for the physiologist to have recourse to psychology. It would be more natural that experimental investigation of the physiological activities of the hemispheres should lay a solid foundation for a future true science of psychology; such a course is more likely to lead to the advancement of this branch of natural science.

The physiologist must thus take his own path, where a trail has already been blazed for him. Three hundred years ago Descartes evolved the idea of the reflex. Starting from the assumption that animals behaved simply as machines, he regarded every activity of the organism as a necessary reaction to some external stimulus, the connection between the stimulus and the response being made through a definite nervous path: and this connection, he stated, was the fundamental purpose of the nervous structures in the animal body. This was the basis on which the study of the nervous system was firmly established. In the eighteenth, nineteenth and twentieth centuries the conception of the reflex was used to the full by physiologists. Working at first only on the lower parts of the central nervous system, they came gradually to study more highly developed parts, until quite recently Magnus,[6] continuing the classical investigations of Sherrington[7] upon the spinal reflexes, has succeeded in demonstrating the reflex nature of all the elementary motor activities of the animal organism. Descartes' conception of the reflex was constantly and fruitfully applied in these studies, but its application has stopped short of the cerebral cortex.

It may be hoped that some of the more complex activities of the body, which are made up by a grouping together of the elementary locomotor activities and which enter into the states referred to in psychological phraseology as "playfulness," "fear," "anger," and so forth, will soon be demonstrated as reflex activities of the subcortical parts of the brain. A bold attempt to apply the idea of the reflex to the activities of the hemispheres was made by the Russian physiologist, I. M. Sechenov, on the basis of the knowledge available in his day of the physiology of the central nervous system. In a pamphlet entitled "Reflexes of the Brain," published in Russian in 1863, he attempted to represent the activities of the cerebral hemispheres as reflex -- that is to say, as determined. [p. 5] Thoughts he regarded as reflexes in which the effector path was inhibited, while great outbursts of passion he regarded as exaggerated reflexes with a wide irradiation of excitation. A similar attempt was made more recently by Ch. Richet,[8] who introduced the conception of the psychic reflex, in which the response following on a given stimulus is supposed to be determined by the association of this stimulus with the traces left in the hemispheres by past stimuli. And generally speaking, recent physiology shows a, tendency to regard the highest activities of the hemispheres as an association of the new excitations at any given time with traces left by old ones (associative memory, training, education by experience).

All this, however, was mere conjecture. The time was ripe for a transition to the experimental analysis of the subject -- an analysis which must be as objective as the analysis in any other branch of natural science. An impetus was given to this transition by the rapidly developing science of comparative physiology, which itself sprang up as a direct result of the Theory of Evolution. In dealing with the lower members of the animal kingdom physiologists were, of necessity, compelled to reject anthropomorphic preconceptions, and to direct all their effort towards the elucidation of the connections between the external stimulus and the resulting response, whether locomotor or other reaction. This led to the development of Loeb's doctrine of Animal Tropisms;[9] to the introduction of a new objective terminology to describe animal reactions [Beer, Bethe and Uexküll[10]]; and finally, it led to the investigation by zoologists, using purely objective methods, of the behaviour of thc lower members of the animal kingdom in response to external stimuli-as for example in the classical researches of Jennings.[11]


アメリカの行動主義の心理学について
Under the influence of these new tendencies in biology, which appealed to the practical bent of the American mind, the American School of Psychologists -- already interested in the comparative study of psychology -- evinced a disposition to subject the highest nervous activities of animals to experimental analysis under various [p. 6] specially devised conditions.

ソーンダイクの動物行動実験
We may fairly regard the treatise by Thorndyke [sic], The Animal Intelligence (1898),[12] as the starting point for systematic investigations of this kind. In these investigations the animal was kept in a box, and food was placed outside the box so that it was visible to the animal. In order to get the food the animal had to open a door, which was fastened by various suitable contrivances in the different experiments. Tables and charts were made showing how quickly and in what manner the animal solved the problems set it. The whole process was understood as being the formation of an association between the visual and tactile stimuli on the one hand and the locomotor apparatus on the other. This method, with its modifications, was subsequently applied by numerous authors to the study of questions relating to the associative ability of various animals.

客観的な実験を求めて
At about the same time as Thorndyke[sic] was engaged on this work, I myself (being then quite ignorant of his researches) was also led to the objective study of the hemispheres, by the following circumstance: In the course of a detailed investigation into the activities of the digestive glands I had to inquire into the so-called psychic secretion of some of the glands, a task which I attempted in conjunction with a collaborator. As a result of this investigation an unqualified conviction of the futility of subjective methods of inquiry was firmly stamped upon my mind. It became clear that the only satisfactory solution of the problem lay in an experimental investigation by strictly objective methods. For this purpose I started to record all the external stimuli falling on the animal at the time its reflex reaction was manifested (in this particular case the secretion of saliva), at the same time recording all changes in the reaction of the animal.

25年に渡る実験
This was the beginning of these investigations, which have gone on now for twenty-five years-years in which numerous fellow-workers on whom I now look back with tender affection have united with mine in this work their hearts and hands. We have of course passed through many stages, and only gradually has the subject been opened up and the difficulties overcome. At first only a few scattered facts were available, but to-day sufficient material has been gathered together to warrant an attempt to present it in a more or less systematized form. At the present time I am in a [p. 7] position to present you with a physiological interpretation of the activities of the cerebral hemispheres which is, at any rate, more in keeping with the structural and functional complexity of this organ than is the collection of fragmentary, though very important, facts which up to the present have represented all the knowledge of this subject. Work on the lines of purely objective investigation into the highest nervous activities has been conducted in the main in the laboratories under my control, and over a hundred collaborators have taken part.

ロシアとアメリカの科学者の違い
Work on somewhat similar lines to ours has been done by the American psychologists. Up to the present, however, there has been one essential point of difference between the American School and ourselves. Being psychologists, their mode of experimentation, in spite of the fact that they are studying these activities on their external aspect, is mostly psychological -- at any rate so far as the arrangement of problems and their analysis and the formulation of results are concerned. Therefore -- with the exception of a small group of "behaviourists " -- their work cannot be regarded as purely physiological in character. We, having started from physiology, continue to adhere strictly to the physiological point of view, investigating and systematizing the whole subject by physiological methods alone. As regards other physiological laboratories a few only have directed their attention to this subject, and that recently; nor have their investigations extended beyond the limits of a preliminary inquiry.




反射の整理
I shall now turn to the description of our material, first giving as a preliminary an account of the general conception of the reflex, of specific physiological reflexes, and of the so-called "instincts."

デカルトの反射神経
Our starting point has been Descartes' idea of the nervous reflex. This is a genuine scientific conception, since it implies necessity. It may be summed up as follows : An external or internal stimulus falls on some one or other nervous receptor and gives rise to a nervous impulse; this nervous impulse is transmitted along nerve fibres to the central nervous system, and here, on account of existing nervous connections, it gives rise to a fresh impulse which passes along outgoing nerve fibres to the active organ, where it excites a special activity of the cellular structures. Thus a stimulus appears to be connected of necessity with a definite response, as cause with effect. It seems obvious that the whole activity of the organism should conform to definite laws. If the animal were not in exact correspondence with its environment it would, sooner or later, [p. 8]cease to exist. To give a biological example: if, instead of being attracted to food, the animal were repelled by it, or if instead of running from fire the anial threw itself into the fire, then it would quickly perish. The animal must respond to changes in the environment in such a manner that its responsive activity is directed towards the preservation of its existence. This conclusion holds also if we consider the living organism in terms of physical and chemical science. Every material system can exist as an entity only so long as its internal forces, attraction, cohesion, etc., balance the external forces acting upon it. This is true for an ordinary stone just as much as for the most complex chemical substances; and its truth should be recognized also for the animal organism. Being a definite circumscribed material system, it can only continue to exist so long as it is in continuous equilibrium with the forces external to it: so soon as this equilibrium is seriously disturbed the organism will cease to exist as the entity it was. Reflexes are the elemental units in the mechanism of perpetual equilibration. Physiologists have studied and are studying at the present time these numerous machine-like, inevitable reactions of the organism-reflexes existing from the very birth of the animal, and due therefore to the inherent organization of the nervous system.

生理学における反射の研究
Reflexes, like the driving-belts of machines of human design, may be of two kinds-positive and negative, excitatory and inhibitory. Although the investigation of these reflexes by physiologists has been going on now for a long time, it is as yet not nearly finished. Fresh reflexes are continually being discovered. We are ignorant of the properties of those receptor organs for which the effective stimulus arises inside the organism, and the internal reflexes themselves remain a field unexplored. The paths by which nervous impulses are conducted in the central nervous system are for the most·part little known, or not ascertained at all. The mechanism of inhibitions confined within the central nervous system remains quite obscure: we know something only of those inhibitory reflexes which manifest themselves along the inhibitory efferent nerves. Furthermore, the combination and interaction of different reflexes are as yet insufficiently understood. Nevertheless physiologists are succeeding more and more in unravelling the mechanism of these machine-like activities of the organism, and may reasonably be expected to elucidate and control it in the end. [p. 9]

本能は反射に含まれるか
To those reflexes which have long been the subject of physiological investigation, and which concern chiefly the activities of separate organs and tissues, there should be added another group of inborn reflexes. These also take place in the nervous system, and they are the inevitable reactions to perfectly definite stimuli. They have to do with reactions of the organism as a whole, and comprise that general behaviour of the animal which has been termed "instinctive."

ハーバード・スペンサーの本能の議論
Since complete agreement as regards the essential affinity of these reactions to the reflex has not yet been attained, we must discuss this question more fully. We owe to the English philosopher, Herbert Spencer, the suggestion that instinctive reactions are reflexes. Ample evidence was later advanced by zoologists, physiologists, and students of comparative psychology in support of this. I propose here to bring together the various arguments in favour of this view. Between the simplest reflex and the instinct we can find numerous stages of transition, and among these we are puzzled to find any line of demarcation.

生まれたてのヒナの本能
To exemplify this we may take the newly hatched chick. This little creature reacts by pecking to any stimulus that catches the eye, whether it be a real object or only a stain in the surface it is walking upon. In what way shall we say that this differs from the inclining of the head, the closing of the lids, when something flicks past its eyes ? We should call this last a defensive reflex, but the first has been termed a feeding instinct: although in pecking: nothing but an inclination of the head and a movement of the beak occurs.

本能は反射よりも複雑
It has also been maintained that instincts are more complex than reflexes. There are, however, exceedingly complex reflexes which nobody would term instincts.

嘔吐は複雑な反射
We may take vomiting as an example. This is very complex and involves the co-ordination of a large number of muscles (both striped and plain) spread over a large area and usually employed in quite different functions of the organism. It involves also a secretory activity on the part of certain glands which is usually evoked for a quite different purpose.

本能の分析
Again, it has been assumed that the long train of actions involved in certain instinctive activities affords a distinctive point of contrast with the reflex, which is regarded as always being built on a simple scale. By way of example we may take the building of a nest, or of dwellings in general, by animals. A chain of incidents is linked ;:together: material is gathered and carried to the site chosen ; there it is built up and strengthened. To look upon this as reflex we must [p. 10] assume that one reflex initiates the next following -- or, in other words, we must regard it as a chain-reflex. But this linking up of activities is not peculiar to instincts alone. We are familiar with numerous reflexes which most certainly fuse into chains. Thus, for example, if we stimulate an afferent nerve, e.g. the sciatic nerve, a reflex rise of blood pressure occurs; the high pressure in the left ventricle of the heart, and first part of the aorta, serves as the effective stimulus to a second reflex, this time a depressor reflex which has a moderating influence on the first. Again, we may take one of the chain reflexes recently established by Magnus. A cat, even when deprived of its cerebral hemispheres, will in most cases land on its feet when thrown from a height.

猫の本能
How is this managed? When the position of the otolithic organ in space is altered a definite reflex is evoked which brings about a contraction of the muscles in the neck, restoring the animal's head to the normal position. This is the first reflex. With the righting of the head a fresh reflex is evoked, and certain muscles of the trunk and limbs are brought into play, restoring the animal to the standing posture. This is the second reflex.

本能はどのような仕組みか
Some, again, object to the identification of instincts with reflexes on this ground: instincts, they say, frequently depend upon the internal state of an organism. For instance, a bird only builds its nest in the mating season. Or, to take a simpler case, when an animal is satiated with eating, then food has no longer any attraction and the animal leaves off eating. Again, the same is true of the sexual impulse. This depends on the age of the organism, and on the state of the reproductive glands; and a considerable influence is exerted by hormones (the products of the glands of internal secretion). But this dependence cannot be claimed as a peculiar property of "instincts." The intensity of any reflex, indeed its very presence, is dependent on the irritability of the centres, which in turn depends constantly on the physical and chemical properties of the blood (automatic stimulation of centres) and on the interaction of reflexes.

反射はひとつの器官だけに限定されない
Last of all, it is sometimes held that whereas reflexes determine only the activities of single organs and tissues, instincts involve the activity of the organism as a whole. We now know, however, from the recent investigations of Magnus and de Kleijn, that standing, walking and the maintenance of postural balance in general, are all nothing but reflexes. [p. 11]

反射と本能を区別しない
It follow from all this that instincts and reflexes are alike the inevitable responses of the organism to internal and external stimuli, and therefore we have no need to call them by two different terms. Reflex has the better claim of the two, in that it has been used from the very beginning with a strictly scientific connotation.

反射は神経系の基盤
The aggregate of reflexes constitutes the foundation of the nervous activities both of men and of animals. It is therefore of great importance to study in detail all the fundnmental reflexes of the organism.

本能についてはあまりよく分かっていないが文学的・直観的な分類はある
Up to the present, unfortunately, this is far from being accomplished, especially, as I have mentioned before, in the case of those reflexes which have been known vaguely as " instincts." Our knowledge of these latter is very limited and fragmentary. Their classification under such headings as "alimentary," "defensive," "sexual," "parental" and "social" instincts, is thoroughly inadequate. Under each of these heads is assembled often a large number of individual reflexes. Some of these are quite unidentified; some are confused with others; and many are still only partially appreciated. I can demonstrate from my own experience to what extent the subject remains inchoate and full of gaps. In the course of the researches which I shall presently explain; we were completely at a loss on one occasion to find any cause for the peculiar behaviour of an animal. It was evidently a very tractable dog, which soon became very friendly with us. We started off with a very simple experiment. The dog was placed in a stand with loose loops round its legs, but so as to be quite comfortable and free to move a pace or two. Nothing more was done except to present the animal repeatedly with food at intervals of some minutes. It stood quietly enough at first, and ate quite readily, but as time went on it became excited and struggled to get out of the stand, scratching at the floor, gnawing the supports, and so on. This ceaseless muscular exertion was accompanied by breathlessness and continuous salivation, which persisted at every experiment during several weeks, the animal getting worse and worse until it was no longer fitted for our researches. For a long time we remained puzzled over the unusual behaviour of this animal. We tried out experimentally numerous possible interpretations, but though we had had long experience with a great number of dogs in our laboratories we could not work out a satisfactory solution of this strange behaviour, until it occurred to us at last that it might be the expression of a special freedom reflex, and that the dog simply could not remain quiet when it was constrained in the stand. [p. 12]

自由反射
This reflex was overcome by setting off another against it -- the reflex for food. We began to give the dog the whole of its food in the stand. At first the animal ate but little, and lost considerably in weight, but gradually it got to eat more, until at last the whole ration was consumed. At the same time the animal grew quieter during the course of the experiments: the freedom reflex was being inhibited.
It is clear that the freedom reflex is one of the most important reflexes, or, if we use a more general term, reactions, of living
beings. This reflex has even yet to find its final recognition. In James's writings it is not even enumerated among the special human "instincts." But it is clear that if the animal were not provided with a reflex of protest against boundaries set to its freedom, the smallest obstacle in its path would interfere with the proper fulfilment of its natural functions. Some animals as we all know have this freedom reflex to such a degree that when placed in captivity they refuse all food, sicken and die.


探求反射 あれは何?反射
As another example of a reflex which is very much neglected we may refer to what may be called the investigatory reflex. I call it the "What-is-it?" reflex. It is this reflex which brings about the immediate response in man and animals to the slightest changes in the world around them, so that they immediately orientate their appropriate receptor organ in accordance with the perceptible quality in the agent bringing about the change, making full investigation of it. The biological significance of this reflex is obvious. If the animal were not provided with such a reflex its life would hang at every moment by a thread. In man this reflex has been greatly developed with far-reaching results, being represented in its highest form by inquisitiveness -- the parent of that scientific method through which we may hope one day to come to a true orientation in knowledge of the world around us.

抑制性反射についてもまだよく分かっていない
Still less has been done towards the elucidation of the class of negative or inhibitory reflexes (instincts) which are often evoked by any strong stimulus or even by weak stimuli, if unusual. Animal hypnotism, so-called, belongs to this category.

反射を整理分類したい
As the fundamental nervous reactions both of men and of animals are inborn in the form of definite reflexes, I must again emphasize how important it is to compile a complete list comprising all these
reflexes with their adequate classification. For, as will be shown later on, all the remaining nervous functions of the animal organism are based upon these reflexes. Now, although the possession of such [p. 13] reflexes as those just described constitutes the fundamental condition for the natural survival of the animal, they are not in themselves sufficient to ensure a prolonged, stable and normal existence.

大脳を切除した犬
This can be shown in dogs in which the cerebral hemispheres have been removed. Leaving out of account the internal reflexes, such a dog still retains the fundamental external reflexes. It is attracted
by food ; it is repelled by nocuous stimuli; it exhibits the investigatory reflex, raising its head and picking up its ears to sound. In addition it exhibits the freedom reflex, offering a powerful resistance to any restraint. Nevertheless it is wholly incapable of
looking after itself, and if left to itself will very soon die. Evidently something important is missing in its present nervous make-up. What nervous activities can it have lost? It is easily seen that, in this dog, the number of stimuli evoking reflex reaction is
considerably diminished; those remaining are of an elemental generalized nature, and act at a very short range. Consequently the dynamic equilibrium between the inner forces of the animal system and the external forces in its environment has become elemental as compared with the exquisite adaptability of the normal animal, and the simpler balance is obviously inadequate to life.

唾液分泌
Let us return now to the simplest reflex from which our investigations started. If food or some rejectable substance finds its way into the mouth, a secretion of saliva is produced. The purpose of this
secretion is in the case of food to alter it chemically, in the case of a rejectable substance to dilute and wash it out of the mouth. This is an example of a reflex due to the physical and chemical properties of a substance when it comes into contact with the mucous membrane of the mouth and tongue. But, in addition to this, a similar reflex secretion is evoked when these substances are placed at a distance from the dog and the receptor organs affected are only those of smell
and sight. Even the vessel from which the food has been given is sufficient to evoke an alimentary reflex complete in all its details; and, further, the secretion may be provoked even by the sight of the
person who brought the vessel, or by the sound of his footsteps. All these innumerable stimuli falling upon the several finely discriminating distance receptors lose their power forever as soon as the hemispheres are taken from the animal, and those only which have a direct effect on mouth and tongue still retain their power. The great advantage to the organism of a capacity to react to the former stimuli is evident, for it is in virtue of their action that [p. 14] food finding its way into the mouth immediately encounters plenty of moistening saliva, and rejectable substances, often nocuous to the mucous membrane, find a layer of protective saliva already in the mouth which rapidly dilutes and washes them out. Even greater is their importance when they evoke the motor component of the complex reflex of nutrition, i.e. when they act as stimuli to the reflex of seeking food.

防衛反射
Here is another example -- the reflex of self-defence. The strong carnivorous animal preys on weaker animals, and these if they waited to defend themselves until the teeth of the foe were in their flesh
would speedily be exterminated. The case takes on a different aspect when the defence reflex is called into play by the sights and sounds of the enemy's approach. Then the prey has a chance to save itself by hiding or by flight.

How can we describe, in general, this difference in the dynamic balance of life between the normal and the decorticated animal? What is the general mechanism and law of this distinction? It is pretty evident that under natural conditions the normal animal must respond not only to stimuli which themselves bring immediate benefit or harm, but also to other physical or chemical agencies -- waves of sound, light, and the like -- which in themselves only signal the approach of
these stimuli; though it is not the sight and sound of the beast of prey which is in itself harmful to the smaller animal, but its teeth and claws.

刺激と反射はどのような関係でありえるか
Now although the signalling stimuli do play a part in those comparatively simple reflexes we have given as examples, yet this is not the most important point. The essential feature of the highest activity of the central nervous system, with which we are concerned and which in the higher animals most probably belongs entirely to the hemispheres, consists not in the fact that innumerable signalling stimuli do initiate reflex reactions in the animal, but in the fact that under different conditions these same stimuli may initiate quite different reflex reactions; and conversely the same reaction may be initiated by different stimuli.

大脳は刺激と反射を制御する
In the above-mentioned example of the salivary reflex, the signal at one time is one particular vessel, at another time another; under certain conditions one man, under different conditions another -- strictly depending upon which vessel had been used in feeding and which man had brought the vessel and given food to the dog. This evidently makes the machine-like responsive activities of the [p. 15] organism still more precise, and adds to it qualities of yet higher perfection. So infinitely complex, so continuously in flux, are the conditions in the world around, that that complex animal system which is itself in living flux, and that system only, has a chance to establish dynamic equilibrium with the environment. Thus we see that the fundamental and the most general function of the hemispheres is that of reacting to signals presented by innumerable of interchangeable signification.


注記

[1] F. Goltz, "Der Hund ohne Grosshirn," Pflüger's Archiv, V. li. p.
570, 1892.

[2] M. Rothmann, "Der Hund ohne Grosshirn." Neurologischcs
Celtralblatt, V. xxviii. p. 1045, 1909.

[3] Fritsch und E. Hitzig, "Ueber die elektrische Erregbarkeit des
Grosshirns." Arckiv für (Anatomie und) Physiologie, p. 300, 1870.

[4] D. Ferrier, Functions of the Brain, London, 1876.

[5] H. Munk, Ueber die Functionen der Grosskirnrinde, Berlin, 1890 and 1909.

[6] R. Magnus, Körperstellung, Berlin, 1924.

[7] C. S. Sherrington, The Integrative Action of the Nervous System,
London, 1906.

[8] Ch. Richet, Réflexes Psychiques. Réflexes Conditionels.
Automatisme Mental. Pavlov's Jubilee Volume, Petrograd, 1925.

[9] J. Loeb, Studies in General Physiology, Chicago, 1905.

[10] Beer, Bethe und Uexküll, "Vorschläge zu einer objectivirenden
Nomenklatur in der Physiologie des Nervensystems," Biologisches
Centralblatt,V., xix. P. 517, 1899.

[11] H. S. Jennings, The Behavior of Lower Organisms, New York, 1906.

[12] E. L. Thorndyke[sic], The Animal Intelligence, An Experimental
Study of the Associative Processes in Animals, New York, 1898.



解説

evince 明らかにする
contrivance 装置・発明
cerebral hemisphere 大脳半球
excitatory 興奮性
inhibitory 抑制性
tractable 摂食の
nocuous stimuli 有害刺激
inchoate 初期段階
freedom reflex  自由反射
investigatory reflex 探求反射
alimentary reflex 消化反射
hypnotism 催眠
secretion of saliva 唾液の分泌
mucous membrane 粘膜

パブロフと条件反射 講義2


Technical methods employed in the objective investigation of the
functions of the cerebral hemispheres. -- Response to signals as
reflex action. -- Unconditioned and conditioned reflexes. -- Necessary conditions for the development of conditioned reflexes.

実験の客観性について
In the previous lecture I gave an account of the reasons which led us to adopt, for the investigation of the functions of the cerebral hemispheres, the purely objective method used for investigating the physiological activity of the lower parts of the nervous system. In this manner the investigation of the cerebral hemispheres is brought into line with the investigations conducted in other branches of natural science, and their activities are studied as purely physiological facts, without any need to resort to fantastic speculations as to the existence of any possible subjective state in the animal which may be conjectured on analogy with ourselves.

条件反射が存在する理由
From this point of view the whole nervous activity of the animal must be regarded as based firstly on inborn reflexes. These are regular causal connections between certain definite external stimuli acting on the organism and its necessary reflex reactions. Such inborn reflexes are comparatively few in number, and the stimuli setting them in action act close up, being as a rule the general physical and chemical properties of the common agencies which affect the organism. The inborn reflexes by themselves are inadequate to ensure the continued existence of the organism, especially of the more highly organized animals, which, when deprived of their highest nervous activity, are permanently disabled, and if left to themselves, although retaining all their inborn reflexes, soon cease to exist. The complex conditions of everyday existence require a much more detailed and specialized correlation between the animal and its environment than is afforded by the inborn reflexes alone. This more precise correlation can be established only through the medium of the cerebral hemispheres; and we have found that a great number of all sorts of stimuli always act through the medium of the hemispheres as temporary and interchangeable signals for the comparatively small number of agencies [p. 17] of a general character which determine the inborn reflexes, and that this is the only means by which a most delicate adjustment of the organism to the environment can be established. To this function of the hemispheres we gave the name of " signalization."

実験の方法論
Before passing on to describe the results of our investigation it is necessary to give some account of the purely technical side of the methods employed, and to describe the general way in which the signalizing activity of the hemispheres can be studied. It is obvious that the reflex activity of any effector organ can be chosen for the purpose of this investigation, since signalling stimuli can get linked up with any of the inborn reflexes. But, as was mentioned in the first lecture, the starting point for the present investigation was determined in particular by the study of two reflexes -- the food or "alimentary" reflex, and the "defence" reflex in its mildest form, as observed when a rejectable substance finds its way into the mouth of the animal. As it turned out, these two reflexes proved a fortunate choice in many ways. Indeed, while any strong defence reflex, e.g. against such a stimulus as a powerful electric current, makes the animal extremely restless and excited; and while the sexual reflexes require a special environment -- to say nothing of their periodic character and their dependence upon age -- the alimentary reflex and the mild defence reflex to rejectable substances are normal everyday occurrences.

唾液分泌に限定する理由
It is essential to realize that each of these two reflexes -- the alimentary reflex and the mild defence reflex to rejectable substances -- consists of two distinct components, a motor and a secretory. Firstly the animal exhibits a reflex activity directed towards getting hold of the food and eating it or, in the case of rejectable substances towards getting rid of them out of the mouth; and secondly, in both cases an immediate secretion of saliva occurs, in the case of food, to start the physical and chemical processes of digestion and, in the case of rejectable substances, to wash them out of the mouth. We confined our experiments almost entirely to the secretory component of the reflex: the allied motor reactions were taken into account only where there were special reasons. The secretory reflex presents many important advantages for our purpose. It allows of an extremely accurate measurement of the intensity of reflex activity, since either the number of drops in a given time may be counted or else the saliva may be caused to displace a coloured fluid in a horizontally placed graduated glass tube. It would be much [p. 18] more difficult to obtain the same accuracy of measurement for any motor reflex, especially for such complex motor reactions as accompany reflexes to food or to rejectable substances. Even by using most delicate instruments we should never be able to reach such precision in measuring the intensity of the motor component of the reflexes as can easily be attained with the secretory component. Again, a very important point in favour of the secretory reflexes is the much smaller tendency to interpret them in an anthropomorphic fashion -- i.e. in terms of subjective analogy. Although this seems a trivial consideration from our present standpoint, it was of importance in the earlier stages of our investigation and did undoubtedly influence our choice.

唾液の測定方法
For the purpose of registering the intensity of the salivary reflex all the dogs employed in the experiments are subjected to a preliminary minor operation, which consists in the transplantation of the opening of the salivary duct from its natural place on the mucous membrane of the mouth to the outside skin. For this purpose the terminal portion of the salivary duct is dissected and freed from the surrounding tissue, and the duct, together with a small portion of the mucous membrane surrounding its natural opening, is carried through a suitable incision, to the outside of the cheek in the case of the parotid gland, or under the chin in the case of the submaxillary gland. In this new position the duct is fixed by a few stitches which are removed when the wound has healed. As a result of the operation the saliva now flows to the outside, on to the cheek or chin of the animal, instead of into the mouth, so that the measurement of the secretory activity of the gland is greatly facilitated. It is only necessary for this purpose to adjust a small glass funnel over the opening of thc duct on to the skin, and for this we find a special cement prepared according to a formula of Mendeléev [1] most useful. As an alternative, very suitable and accurate as recording apparatus is a hemispherical bulb which also can be hermetically sealed on to the skin. From the bulb project two tubes, one pointing up and the other pointing down. The latter tube is used for drawing off the saliva which collects during each observation, while the former tube connects by air transmission with a horizontal graduated glass tube filled with coloured fluid. As the saliva flows into the hemispherical bulb the coloured fluid is displaced along the graduated tube, where [p. 19] the amount of secretion can be read off accurately. Further, it is not difficult to fix up an automatic electrically-recording device which will split up the displaced fluid into drops of exactly equal volume and reduce any lag in the movement of the fluid to a minimum.[2]

パブロフ 条件反射 講義2 実験装置

パブロフ 条件反射 講義2 実験装置



FIG.1.:The apparatus used for recording the salivary secretion in experiments on conditioned reflexes.
A:hemispherical bulb which is fixed over the fistula.
aaa: connecting tube leading through the partition separating the animal's room from the experimenter and connecting the bulb A to the registering apparatus B.
bb:tube connecting the bulb with bottle C.
After each observation a vacuum is created in the bottle C by depression of the rubber balloon D.
D:the saliva accumulating in A is thus sucked away.
During the observation A is automatically disconnected from C and connected with the registering apparatus. During the aspirations of the saliva from bulb A the latter is automatically disconnected from the registering apparatus.


ペトログラードの実験施設
To come to the general technique of the experiments, it is important to remember that our research deals with the highly specialized activity of the cerebral cortex, a signalizing apparatus of tremendous complexity and of most exquisite sensitivity, through which the [p.20] animal is influenced by countless stimuli from the outside world. Every one of these stimuli produces a certain effect upon the animal, and all of them taken together may clash and interfere with, or else reinforce, one another. Unless we are careful to take special precautions the success of the whole investigation may be jeopardized, and we should get hopelessly lost as soon as we began to seek for cause and effect among so many and various influences, so intertwined and entangled as to form a veritable chaos. It was evident that the experimental conditions had to be simplified, and that this simplification must consist in eliminating as far as possible any stimuli outside our control which might fall upon the animal, admitting only such stimuli as could be entirely controlled by the experimenter. It was thought at the beginning of our research that it would be sufficient simply to isolate the experimenter in the research chamber with the dog on its stand, and to refuse admission to anyone else during the course of an experiment. But this precaution was found to be wholly inadequate, since the experimenter, however still he might try to be, was himself a constant source of a large number of stimuli. His slightest movements-blinking of the eyelids or movement of the eyes, posture, respiration and so on-all acted as stimuli which, falling upon the dog, were sufficient to vitiate the experiments by making exact interpretation of the results extremely difficult. In order to exclude this undue influence on the part of the experimenter as far as possible, he had to be stationed outside the room in which the dog was placed, and even this precaution proved unsuccessful in laboratories not specially designed for the study of these particular reflexes. The environment of the animal, even when shut up by itself in a room, is perpetually changing. Footfalls of a passer-by, chance conversations in neighbouring rooms, slamming of a door or vibration from a passing van, street-cries, even shadows cast through the windows into the room, any of these casual uncontrolled stimuli falling upon the receptors of the dog set up a disturbance in the cerebral hemispheres and vitiate the experiments. To get over all these disturbing factors a special laboratory was built at the Institute of Experimental Medicine in Petrograd, the funds being provided by a keen and public-spirited Moscow business man.

The primary task was the protection of the dogs from uncontrolled extraneous stimuli, and this was effected by surrounding the building with an isolating trench and employing other special structural devices. Inside the building all the research rooms [p. 21] (four to each floor) were isolated from one another by a, cross-shaped corridor; the top and ground floors, where these rooms were situated, were separated by an intermediate floor. Each research room was carefully partitioned by the use of sound-proof materials into two compartments -- one for the animal, the other for the experimenter. For stimulating the animal, and for registering the corresponding reflex response, electrical methods or pneumatic transmission were used. By means of these arrangements it was possible to get something of that stability of environmental conditions so essential to the carrying out of a successful experiment.

実験の限界
another point should be mentioned-although in this respect the means at our disposal still leave something to be desired. In analysing the exceedingly complex influence of the external environment upon the animal, the experimenter must be able to exercise full control over all the conditions obtaining during the course of any experiment. He should therefore have at his disposal various instruments for affecting the animal by different kinds of stimuli, singly or combined, so as to imitate simple natural conditions. But we were often handicapped by the conditions in which we had to work and by the shortcomings of the instruments at our disposal, for we always found that the cerebral hemispheres were sensitive to far finer gradations of stimulus than we could furnish.

実験を厳密にするために
It is possible that the experimental conditions I have described may raise somewhere the objection of being abnormal and artificial. However it is hardly likely, in view of the infinite variety of stimuli met with under natural conditions, that we shall hit on one that is quite unprecedented in the life of the animal. Moreover, in dealing with any phenomenon of vast complexity it is absolutely necessary to isolate the different single factors involved, so as to
study them independently, or in arbitrary groups in which we can keep the individual units under control. But as a matter of fact the same objection and the same answer apply equally to the whole of animal physiology. For instance, the methods of vivisection and of the study of isolated organs and tissues, which aim at the same isolation of different individual functions, have been constantly employed, and we may safely say that the greater part of the achievements of physiology are due to the successful application of such methods of control. In our experiments it is the whole animal which is placed under a limited number of rigidly defined conditions, and [p. 22] only by this method is it possible to study the reflexes independently of one another.

メトロノームと犬
The foregoing remarks give an idea of our general aim and of the technical side of our methods. I propose to introduce you to the first and most elementary principles of the subject matter of our research by means of a few demonstrations:

Demonstration. -- The dog used in the following experiment has been operated upon as described previously. It can be seen that so long as no special stimulus is applied the salivary glands remain quite inactive. But when the sounds from a beating metronome are allowed to all upon the ear, a salivary secretion begins after 9 seconds, and in the course of 45 seconds eleven drops have been secreted. The activity of the salivary gland has thus been called into play by impulses of sound -- a stimulus quite alien to food. This activity of the salivary gland cannot be regarded as anything else than a component of the alimentary reflex. Besides the secretory, the motor component of the food reflex is also very apparent in experiments of this kind. In this very experiment the dog turns in the direction from which it has been customary to present the food and begins: to lick its lips vigorously.

This experiment is an example of a central nervous activity depending on the integrity of the hemispheres. A decerebrate dog would never have responded by salivary secretion to any stimilus of the kind. It is obvious also that the underlying principle of this activity is signalization. The sound of the metronome is the signal for food, and the animal reacts to the signal in the same way as if it were food; no distinction can be observed between the effects produced on the animal by the sounds of the beating metronome and showing it real food.

食物と犬
Demonstration. -- Food is shown to the animal. The salivary secretion begins after 5 seconds, and six drops are collected in the course of 15 seconds. The effect is the same as that observed with the sounds of the metronome. It is again a case of signalization, and is due to the activity of the hemispheres. That the effect of sight and smell of food is not due to an inborn reflex, but to a reflex which has been acquired in the course of the animal's own individual existence, was shown by experiments carried out by Dr. Zitovich in the laboratory of the late Prof. Vartanov. Dr. Zitovich took several young puppies away from their mother and fed them for considerable time only on milk. When the [p. 23] puppies were a few months old he established fistulae of their salivary ducts, and was thus able to measure accurately the secretory activity of the glands. He now showed these puppies some solid food -- bread or meat -- but no secretion of saliva was evoked. It is evident, therefore, that the sight of food does not in itself act as a direct stimulus to salivary secretion. Only after the puppies have been allowed to eat bread and meat on several occasions does the sight or smell of these foodstuffs evoke the secretion.

The following experiment serves to illustrate the activity of the salivary gland as an inborn reflex in contrast to signalization:

Demonstration. -- Food is suddenly introduced into the dog's mouth; secretion begins in 1 to 2 seconds. The secretion is brought about by the physical and chemical properties of the food itself acting upon receptors in the mucous membrane of the mouth and tongue. It is purely reflex.

This comparatively simple experiment explains how a decerebrate dog can die of starvation in the midst of plenty, for it will only start eating if food chances to come into contact with its mouth or tongue. Moreover, the elementary nature of the inborn reflexes, with their limitations and inadequacy, are clearly brought out in these experiments, and we are now able to appreciate the fundamental importance of those stimuli which have the character of signals.

条件反射の速度は原則として同じ
Our next step will be to consider the question of the nature of signalization and of its mechanism from a purely physiological point of view. It has been mentioned already that a reflex is an inevitable reaction of the organism to an external stimulus, brought about along a definite path in the nervous system. Now it is quite evident that in signalization all the properties of a reflex are present. In the first place an external stimulus is required. This was given in our first experiment by the sounds of a metronome. These sounds falling on the auditory receptor of the dog caused the propagation of an impulse along the auditory nerve. In the brain the impulse was transmitted to the secretory nerves of the salivary glands, and passed hence to the glands, exciting them to active secretion. It is true that in the experiment with the metronome an interval of several seconds elapsed between the beginning of the stimulus and the beginning of the salivary secretion, whereas the time interval for the inborn reflex secretion was only 1 to 2 seconds. The longer latent period was, however, due to some special conditions of the experiment, as will come out more clearly as we proceed. But [p. 24] generally speaking the reaction to signals under natural conditions is as speedy as are the inborn reflexes. We shall be considering the latent period of signalization in fuller detail in a further lecture.

In our general survey we characterized a reflex as a necessary reaction following upon a strictly definite stimulus under strictly defined conditions. Such a definition holds perfectly true also for signalization; the only difference is that the type of thc effective reaction to signals depends upon a greater number of conditions. But this does not make signalization differ fundamentally from the better known reflexes in any respect, since in the latter, variations in character or force, inhibition and absence of reflexes, can also be traced to some definite change in the conditions of the experiment.

Thorough investigation of the subject shows that accident plays no part whatever in the signalizing activity of the hemispheres, and all experiments proceed strictly according to plan. In the special laboratory I have described, the animal can frequently be kept under rigid experimental observation for 1 to 2 hours without a single drop of saliva being secreted independently of stimuli applied by the observer, although in the ordinary type of physiological laboratory experiments are very often distorted by the interference of extraneous and uncontrolled stimuli.

反射の分類 無条件反射と条件反射
All these conditions leave no grounds for regarding the phenomena which we have termed "signalization" as being anything else than reflex. There is, however, another aspect of the question which at a first glance seems to point to an essential difference between the better known reflexes and signalization. Food, through its chemical and physical properties, evokes the salivary reflex in every dog right from birth, whereas this new type claimed as reflex -- "the signal reflex" -- is built up gradually in the course of the animal's own individual existence. But can this be considered as a fundamental point of difference, and can it hold as a valid argument against employing the term "reflex" for this new group of phenomena ? It is certainly a sufficient argument for making a definite distinction between the two types of reflex and for considering the signal reflex in a group distinct from the inborn reflex. But this does not invalidate in any way our right logically to term both "reflex," since the point of distinction does not concern the character of the response on the part of the organism, but only the mode of formation of the reflex mechanism. We may take the telephonic installation as an illustration. Communication can be effected in two ways. [p. 25] My residence may be connected directly with the laboratory by a private line, and I may call up the laboratory whenever it pleases me to do so; or on the other hand, a connection may have to be made through the central exchange. But the result in both cases is the same. The only point of distinction between the methods is that the private line provides a permanent and readily available cable, while the other line necessitates a preliminary central connection being established. In the one case the communicating wire is always complete, in the other case a small addition must be made to the wire at the central exchange. We have a similar state of affairs in reflex action. The path of the inborn reflex is already completed at birth; but the path of the signalizing reflex has still to be completed in the higher nervous centres. We are thus brought to consider the mode of formation of new reflex mechanisms. A new reflex is formed inevitably under a given set of physiological conditions, and with the greatest ease, so that there is no need to take the subjective states of the dog into consideration. With a complete understanding of all the factors involved, the new signalizing reflexes are under the absolute control of the experimenter; they proceed according to as rigid laws as do any other physiological processes, and must be regarded as being in every sense a part of the physiological activity of living beings. I have termed this new group of reflexes conditioned reflexes to distinguish them from the inborn or unconditioned reflexes. The term "conditioned" is becoming more and more generally employed, and I think its use is fully justified in that, compared with the inborn reflexes, these new reflexes actually do depend on very many conditions, both in their formation and in the maintenance of their physiological activity. Of course the terms "conditioned" and "unconditioned" could be replaced by others of arguably equal merit. Thus, for example, we might retain the term "inborn reflexes," and call the new type "acquired reflexes"; or call the former "species reflexes " since they are characteristic of the species, and the latter "individual reflexes" since they vary from animal to animal in a species, and even in the same animal at different times and under different conditions. Or again we might call the former "conduction reflexes "and the latter "connection reflexes."

大脳と反射の関係
There should be no theoretical objection to the hypothesis of the formation of new physiological paths and new connections within the cerebral hemispheres. Since the especial function of the central [p.26] nervous system is to establish most complicated and delicate correspondences between the organism and its environment we may not unnaturally expect to find there, on the analogy of the methods used by the technician in everyday experience, a highly developed connector system superimposed on a conductor system. The physiologist certainly should not object to this conception seeing that he has been used to employing the German conception of "Bahnung," which means a laying down of fresh physiological paths in the centres. Conditioned reflexes are phenomena of common and widespread occurrence: their establishment is an integral function in everyday life. We recognize them in ourselves and in other people or animals under such names as "education," "habits," and "training; " and all of these are really nothing more than the results of an establishment of new nervous connections during the post-natal existence of the organism. They are, in actual fact, links connecting definite extraneous stimuli with their definite responsive reactions.

条件反射と学習能力
I believe that the recognition and the study of the conditioned reflex will throw open the door to a true physiological investigation probably of all the highest nervous activities of the cerebral hemispheres, and the purpose of the present lectures is to give some account of what we have already accomplished in this direction.

刺激の選定
We come now to consider the precise conditions under which new conditioned reflexes or new connections of nervous paths are established. The fundamental requisite is that any external stimulus which is to become the signal in a conditioned reflex must overlap in point of time with the action of an unconditioned stimulus. In the experiment which I chose as my example the unconditioned stimulus was food. Now if the intake of food by the animal takes place simultaneously with the action of a neutral stimulus which has been hitherto in no way related to food, the neutral stimulus readily acquires the property of eliciting the same reaction in the animal as would food itself. This was the case with the dog employed in our experiment with the metronome. On several occasions this animal had been stimulated by the sound of the metronome and immediately presented with food -- i.e. a stimulus which was neutral of itself had been superimposed upon the action of the inborn alimentary reflex. We observed that, after several repetitions of the combined stimulation, the sounds from the metronome had acquired the property of stimulating salivary secretion and of evoking the motor reactions characteristic of the alimentary reflex. The first [p.27] demonstration was nothing but an example of such a conditioned stimulus in action. Precisely the same occurs with the mild defence reflex to rejectable substances. Introduction into the dog's mouth of a little of an acid solution brings about a quite definite responsive reaction. The animal sets about getting rid of the acid, shaking its head violently, opening its mouth and making movements with its tongue. At the same time it produces a copious salivary secretion. The same reaction will infallibly be obtained from any stimulus which has previously been applied a sufficient number of times while acid was being introduced into the dog's mouth. Hence a first and most essential requisite for the formation of a new conditioned reflex lies in a coincidence in time of the action of any previously neutral stimulus with some definite unconditioned stimulus. Further, it is not enough that there should be overlapping between the two stimuli; it is also and equally necessary that the conditioned stimulus should begin to operate before the unconditioned stimulus comes into action.

刺激の順番
If this order is reversed, the unconditioned stimulus being applied first and the neutral stimulus second, the conditioned reflex cannot be established at all. Dr. Krestovnikov performed these experiments with many different modifcations and controls, but the effect was always the same. The following are some of his results: In one case 427 applications were made in succession of thc odour of vanillin together with the introduction of acid into the dog's mouth, but the acid was always made to precede the vanillin by some 5 to 10 seconds. Vanillin failed to acquire the properties of a conditioned stimulus. However, in the succeeding experiment, in which the order of stimuli was reversed, the odour, this time of amyl acetate, became an effective conditioned stimulus after only 20 combinations. With another dog the loud buzzing of an electric bell set going 5 to 10 seconds after administration of food failed to establish a conditioned alimentary reflex even after 374 combinations, whereas the regular rotation of an object in front of the eyes of the animal, the rotation beginning before the administration of food, acquired the properties of a conditioned stimulus after only 5 combinations. The electric buzzer set going before the administration of food established a conditioned alimentary reflex after only a single combination.

Dr. Krestovnikov's experiments were carried out on five dogs, and the result was always negative when the neutral stimulus was [p. 28] applied, whether 10 seconds, 5 seconds or only a single second after the beginning of the unconditioned stimulus. During all these experiments not only the secretory reflex but also the motor reaction of the animal was carefully observed, and these observations always corroborated one another. We thus see that the first set of conditions required for the formation of a new conditioned reflex encompasses the time relation between the presentation of the unconditioned stimulus and the presentation of that agent which has to acquire the properties of a conditioned stimulus.

大脳の状態
As regards the condition of the hemispheres themselves, an alert state of the nervous system is absolutely essential for the formation of a new conditioned reflex. If the dog is mostly drowsy during the experiments, the establishment of a conditioned reflex becomes a long and tedious process, and in extreme cases is impossible to accomplish. The hemispheres must, however, be free from any other nervous activity, and therefore in building up a new conditioned reflex it is important to avoid foreign stimuli which, falling upon the animal, would cause other reactions of their own. If this is not attended to, the establishment of a conditioned reflex is very difficult, if not impossible. Thus, for example, if the dog has been so fastened up that anything causes severe irritation, it does not matter how many times the combination of stimuli is repeated, we shall not be able to obtain a conditioned reflex. A somewhat similar case was described in the first lecture-that of the dog which exhibited the freedom reflex in an exaggerated degree.

初回の条件反射の成立は難しい
It can also be stated as a rule that the establishment of the first conditioned reflex in an animal is usually more difficult than the establishment of succeeding ones. It is obvious that this must be so, when we consider that even in the most favourable circumstances the experimental conditions themselves will be sure to provoke numerous different reflexes -- i.e. will give rise to one or other disturbing activity of the hemispheres. But this statement must be qualified by remarking that in cases where the cause of these uncontrolled reflexes is not found out, so that we are not able to get rid of them, the hemispheres themselves will help us. For if the environment of the animal during the experiment does not contain any powerful disturbing elements, then practically always the extraneous reflexes will with time gradually and spontaneously weaken in strength.

健康状態と条件反射
The third factor determining the facility with which new conditioned reflexes can be established is the health of the animal. A [p. 29] good state of health will ensure the normal functioning of the cerebral hemispheres, and we shall not have to bother with the effects of any internal pathological stimuli.

見慣れない刺激について
The fourth, and last, group of conditions has to dg with the properties of the stimulus which is to become conditioned, and also with the properties of the unconditioned stimulus which is selected. Conditioned reflexes are quite readily formed to stimuli to which the animal is more or less indifferent at the outset, though strictly speaking no stimulus within the animal's range of perception exists to which it would be absolutely indifferent. In a normal animal the slightest alteration in the environment -- even the very slightest sound or faintest odour, or the smallest change in intensity of illumination -- immediately evokes the reflex which I referred to in the first lecture as the investigatory reflex -- "What is it?" -- manifested by a very definite motor reaction. However, if these neutral stimuli keep recurring, they spontaneously and rapidly weaken in their effect upon the hemispheres, thus bringing about bit by bit the removal of this obstacle to the establishment of a conditioned reflex. But if the extraneous stimuli are strong or unusual, the formation of a conditioned reflex will be difficult, and in extreme cases impossible.

強力な電流は何を起こすか
It must also be remembered that in most cases we are not acquainted with the history of the dog before it came into the laboratory, and that we do not know what sort of conditioned reflexes have been established to stimuli which appear to be of the simplest character. But in spite of this we have, in a large number of cases, found it possible to take a strong stimulus which evoked some strong unconditioned response of its own, and still succeed in converting it into a conditioned stimulus for another reflex. Let us take for example a nocuous stimulus, such as a strong electric current or wounding or cauterization of the skin. These are obviously stimuli to vigorous unconditioned defence reflexes. The organism responds by a violent motor reaction directed towards removal of the nocuous stimulus or to its own removal from it. But we may, nevertheless, make use even of these stimuli for the establishment of a new conditioned reflex. Thus in one particular experiment a strong nocuous stimulus --an electric current of great strength -- was converted into an alimentary conditioned stimulus, so that its application to the skin did not evoke the slightest defence reaction. Instead, the animal exhibited a well-marked alimentary conditioned reflex, turning its [p.30] head to where it usually received the food and smacking its lips, at the same time producing a profuse secretion of saliva. The following is a record taken from a research by Dr. Eroféeva:

パブロフ 条件反射 講義2 実験結果

パブロフ 条件反射 講義2 実験結果




複数の刺激は強度の競争関係にある
Similar results were obtained from dogs in which cauterization or pricking of the skin deep enough to draw blood was made to acquire the properties of an alimentary conditioned stimulus. These experiments have been apt to upset very sensitive people; but we have been able to demonstrate, though without any pretension of penetrating into the subjective world of the dog, that they were labouring under a false impression. Subjected to the very closest scrutiny, not even the tiniest and most subtle objective phenomenon usually exhibited by animals under the influence of strong injurious stimuli can be observed in these dogs. No appreciable changes in the pulse or in the respiration occur in these animals, whereas such changes are always most prominent when the nocuous stimulus has not been converted into an alimentary conditioned stimulus. Such a remarkable phenomenon is the result of diverting the nervous impulse from one physiological path to another. This transference is dependent, however, upon a very definite condition -- namely, upon the relative strengths of the two unconditioned reflexes.

どちらの刺激が条件反射に接続されるか
Successful transformation of the unconditioned stimulus for one reflex into the conditioned stimulus for another reflex can be brought about only when the former reflex is physiologically weaker and biologically of less importance than the latter. We are led to this conclusion from s consideration of Dr. Eroféeva's experiments. [p. 31] A nocuous stimulus applied to the dog's skin was transformed into a conditioned stimulus for the alimentary reflex. This, we consider, was due to the fact that the alimentary reflex is in such cases stronger than the defence reflex. In the same way we all know that when dogs join in a scuffle for food they frequently sustain skin wounds, which however play no dominant part as stimuli to any defence reflex, being entirely subordinated to the reflex for food.

無条件反射には階層性がある
Nevertheless there is a certain limit -- there are stronger reflexes than the alimentary reflex. One is the reflex of self-preservation, of existence or non-existence, life or death. To give only one example, it was found impossible to transform a defence reaction into an alimentary conditioned reflex when the stimulus to the unconditioned defence reaction was a strong electric current applied to skin overlying bone with no muscular layer intervening. This signifies that the afferent nervous impulses set up by injury to the bone, and signalizing far greater danger than those set up by injury to the skin, cannot acquire even a temporary connection with the part of the brain from which the alimentary reflex is controlled. Nevertheless, and the whole, the foregoing considerations emphasize the advantage of using the alimentary reflex for most of our experiments, since in the hierarchy of reflexes this holds a very high place.

弱い刺激は弱い条件反射しか接続できない
While, as we have seen, very strong and even specialized stimuli can under certain conditions acquire the properties of conditioned stimuli, there is, on the other hand, a minimum strength below which stimuli cannot be given conditioned properties. Thus a thermal stimulus of 45°C. applied to the skin can be made into an alimentary conditioned reflex, whereas at 38° to 39°C. (approximately 2°C. above the skin temperature in the dog) a thermal stimulus is ineffective [experiments of Dr. Solomonov]. Similarly, while with the help of a very strong unconditioned stimulus it is possible to convert a very unsuitable stimulus -- for example, one which naturally evokes a different unconditioned reflex -- into a conditioned stimulus, it is exceedingly difficult or even impossible with the help of only a weak unconditioned stimulus to transform even a very favourable neutral stimulus into a conditioned stimulus. Even where such a conditioned reflex is successfully established, its occurrence results only in a very small reflex response. Some unconditioned stimuli may be permanently weak, others may display a weakness which is only temporary -- varying with the condition of the animal. As an example of the last we may take food. In the hungry animal food [p. 32] naturally brings about a powerful unconditioned reflex, and the conditioned reflex develops quickly. But in a dog which has not long been fed the unconditioned stimulus has only a small effect, and alimentary conditioned reflexes either are not formed at all or are
established very slowly.

By complying with all the conditions which I have enumerated -- which is not a very difficult task -- a new conditioned reflex is infallibly obtained. We apply to the receptors of the animal rigidly defined stimuli; these stimuli necessarily result in the formation of a new connection in the hemispheres with a consequent development of a typical reflex reaction.

生理学と条件反射
To sum up, we may legitimately claim the study of the formation and properties of conditioned reflexes as a special department of physiology. There is no reason for thinking about all these events in any other way, and it is my belief that in these questions prejudices blunt the intellect and that generally speaking the preconceptions of the human mind stand in the way of any admission that the highest physiological activity of the hemispheres is rigidly determined. The difficulty is mainly due to the tremendous complexity of our subjective states; and, of course, these cannot yet be traced to their primary causations.

パブロフ 条件反射 講義2 動物室

パブロフ 条件反射 講義2 動物室


The animal's section of the double chember
パブロフ 条件反射 講義2 二重室

パブロフ 条件反射 講義2 二重室


Experimenter's section of the double chember
パブロフ 条件反射 講義2 唾液測定

パブロフ 条件反射 講義2 唾液測定


The upper tracing is a record of a conditioned salivary reflex to a tone of 637.5 dv.
The tone lasted 30 seconds-began at the first and ended at the second downward mark.
The third mark shows the beginning of the unconditioned stimulus.
Each mark upwards=1drop =0.01 c.c.
Each bigger mark=to each tenth drop.
Reflex=68 drops.
The lower tracing is a similar record, but the tone is continued for 60 seconds. Reflex =128 drops. (Experiments by Dr. Anrep).

パブロフ 条件反射 講義2 実験施設

パブロフ 条件反射 講義2 実験施設


The special laboratory built for the study of conditioned reflexes, Institute of Experimental Medicine, Petrograd.




【本文注記】

[1] Mendeléef's cement: Colophonium, 50 grammes; ferric oxide, 40 grammes; yellow beeswax, 25 grammes.

[2] In almost all the experiments quoted in these lectures the amount of salivary secretion is, for the sake of uniformity, given in drops. It was, however, only in the very earliest period of the research -- before the separation of the experimenter from the animal was made -- that the actual number of drops falling from a small funnel fixed over the fistula was counted, and only a few of these experiments are given. In the great majority of the experiments the salivary secretion was measured by the displacement of water in a graduated tube or by the electric recorder, allowing much greater accuracy of measurement. The readings so obtained have been converted, in the tables, into drops. Thus, in some experiments it will be noticed that the number of drops is given to an accuracy of one-tenth.


【重要表現】
anthropomorphic 語彙
Parotid gland 耳下腺(じかせん)
submaxillary gland 顎下腺(がっかせん)
funnel 漏斗(ろうと)
jeopardize 危うくする
veritable 真の
vivisection 生体解剖
decerebrate dog 大脳切除された犬

パブロフと条件反射 講義3


The formation of conditioned reflexes by means of conditioned and direct stimuli. -- Agencies which can be used as conditioned stimuli. -- Inhibition of conditioned reflexes: external inhibition.

条件反射を結びつける
In the previous cases a conditioned reflex was obtained by linking up the action of a new stimulus with an unconditioned reflex. It is possible, however, to obtain a conditioned reflex less directly, by linking up yet a further stimulus with a conditioned stimulus which is already firmly established. Let us refer again to our experiment with the metronome. The sound of the beats was a conditioned stimulus so firmly and powerfully established as readily to admit of demonstration in face of the large audience present at my lecture. The effect of the metronome even under such unfavourable conditions was complete and precise. With the help of this strong conditioned stimulus it has been found possible to give still another stimulus conditioned properties like the first. For if some new and more or less neutral stimulus is applied in conjunction with the metronome alone -- i.e. not at the same time giving food -- this new stimulus also acquires the character of an alimentary conditioned stimulus [Drs. Zeljony, Foursikov, Frolov].

二次条件反射
Conditioned reflexes established in this manner are termed secondary conditioned reflexes, and I shall bring to your attention certain precautions which must be observed for the successful establishment of reflexes of this order.

通常は10秒の間隔を開ける
The essential condition is that the new stimulus should be withdrawn some seconds before the primary stimulus is applied. With new stimuli of a medium physiological strength this lapse of time must be not less than ten seconds, while for stronger stimuli the interval must be considerably increased. Any shortening of the indicated minimal interval of time leads to a quite different result, typifying a group of extremely delicate and interesting phenomena in the physiology of the hemispheres, which will be treated in the fifth lecture.

二次条件反射の実験
I shall describe first an experiment conducted by Dr. Frolov illustrating the development of a secondary conditioned reflex: A [p.34] dog has two primary alimentary conditioned stimuli firmly established, one to the sound of a metronome and the other to the buzzing of an electric bell. The appearance of a black square in the dog's line of vision is now used as yet a further stimulus, which is to be given the character of a secondary conditioned stimulus. The black square is held in front of the dog for ten seconds, and after an interval of fifteen seconds the metronome is sounded during 30 seconds. In the table given below the square is presented for the tenth time.

パブロフと条件反射 講義3 実験1924年

パブロフと条件反射 講義3 実験1924年




Prior to these experiments the appearance of the black square had no secretory effect at all. As seen from the above table the conditioned reflex of the second order is measured even at this early stage of its development by 5½ drops (2.5 plus 3) during 25 seconds.

消化反射は三次までは不可能
It was found impossible in the case of alimentary reflexes to press the secondary conditioned stimulus into our service to help us in the establishment of a new conditioned stimulus of the third order.

防衛反射も四次までは不可能
Conditioned reflexes of the third order can however be obtained with the help of the second order of conditioned reflexes in defence reactions such as that against stimulation of the skin by a strong electric current. But even in this case we cannot proceed further than a conditioned reflex of the third order.

三次反射の実験
I shall describe the results of an experiment of Dr. Foursikov illustrating a conditioned reflex of the third order: The unconditioned stimulus to a defence reaction in a dog was given by the application of an electric stimulus to the skin over the front paw. A mechanical stimulation of the skin over the hind paw to which the dog was formerly quite indifferent had been converted by the usual procedure into a conditioned stimulus of the first order, while for the establishment [p. 35] of the second order of reflex a sound of bubbling water had been employed. By combining with the sound of bubbling water a tone, previously indifferent, of 760 double vibrations per second, a conditioned stimulus of the third order was now established. In these conditioned reflexes, passing from the first to the third order, the latent period progressively increases. In the same order we pass from the strongest to the weakest conditioned defence reflex. All these conditioned reflexes were maintained by Dr.Foursikov by means of appropriate reinforcement for over a year, but here again many attempts to combine a still further stimulus with the conditioned stimulus of the third order were quite unsuccessful.

条件反射の範囲
So far we have discussed two distinct modes of formation of a conditioned reflex, one in which it is based directly upon an unconditioned reflex and the other in which it is based upon another conditioned reflex which has already been firmly established. There is, however, yet another method of establishing conditioned reflexes. We were led a considerable time ago to perform experiments of the following type: A dog was given a small dose of apomorphine subcutaneously and after one or two minutes a note of a definite pitch was sounded during a considerable time. While the note was still sounding the drug began to take effect upon the dog: the animal grew restless, began to moisten its lips with its tongue, secreted saliva and showed some disposition to vomit. After the experimenter had reinforced the tone with apomorphine several times it was found that the sound of the note alone sufficed to produce all the active symptoms of the drug, only in a less degree [experiments of Dr. Podkopaev]. Unfortunately, Dr. Podkopaev was prevented from pursuing his experiments and extending them by modifcations in technique. However, quite recently, Dr. Krylov, of the Tashkent Bacteriological Laboratory, has made some interesting observations bearing on this matter, in the course of certain serological investigations, when he had occasion repeatedly to inject morphine into dogs hypodermically. It is well known that the first effect of a hypodermic injection of morphine is to produce nausea with profuse secretion of saliva, followed by vomiting, and then profound sleep. Dr. Krylov, however, observed when the injections were repeated regularly that after 5 or 6 days the preliminaries of injection were in themselves sufficient to produce all these symptoms -- nausea, secretion of saliva, vomiting and sleep. Under these circumstances the symptoms are now the effect, not of the morphine acting through [p. 36] the blood stream directly on the vomiting centre, but of all the external stimuli which previously had preceded the injection of morphine. The connection between the morphine itself and the various signals may in this instance be very remote, and in the most striking cases all the symptoms could be produced by the dogs simply seeing the experimenter. Where such a stimulus was insufficient it was necessary to open the box containing the syringe, to crop the fur over a small area of skin and wipe with alcohol, and perhaps even to inject some harmless fluid before the symptoms could bc obtained. The greater the number of previous injections of morphine the less preparation had to be performed in order to evoke a reaction simulating that produced by the drug. Dr. Krylov was able to demonstrate these facts quite easily in my laboratory. In a series of experiments specially adapted to the purpose he showed that the phenomena described are absolutely identical with conditioned reflexes. The experiments readily lend themselves for lecture demonstration.

モルヒネ注射の実験
Demonstration. -- The dog has repeatedly been injected with morphine on previous occasions, and is now held quietly on the table by an attendant who has never had anything to do with injecting the morphine. When the experimenter approaches, the dog gets restless and moistens its lips, and as soon as the experimenter touches the animal, severe nausea and profuse secretion of saliva begin.

This experiment provides a clue to the well-known fact that dogs will eat meat the first time it is offered them, after removal of their parathyroids, or after an Eck fistula and tying of the portal vein, but on all subsequent occasions refuse it. Evidently in these cases the appearance and smell of meat produce of themselves a reaction identical with that produced through direct pathological action in the absence of the parathyroids or the portal circulation, by those toxic substances deriving from digestion of the meat.

条件反射と脳の接続
All this brings us to the important question of the intimate mechanism by which new nervous connections are established in the hemispheres. It is easy to suggest an explanation on the basis of the actual facts as they are known at present. Any unconditioned, or any firmly established conditioned, stimulus undoubtedly evokes a state of nervous activity in some definite part of the brain. Using the generally accepted terminology, let us refer to such areas of the brain as centres, not however thereby implying any idea of anatomical localization. During the period of excitation of such centres [p. 37] all other external stimuli which happen to affect the animal are conducted to these centres, and the paths by which they are conducted through the hemispheres become thereby specially marked out. This is the only possible interpretation of the facts, and upon this interpretation was planned the series of experiments with apomorphine which have just been described as corroborating so thoroughly the experiments of Dr. Krylov with morphine. Arguing that excitations set up in the cells of the cortex were constantly transmitted to the salivary centre when this was reflexly [sic] excited to activity by external agencies, we had to expect a precisely similar phenomenon to take place when the centre was stimulated directly (i.e automatically) by changes in the internal environment due to alterations in the composition of the blood. Excitations set up in the cortex would now also be transmitted to the salivary and to the vomiting centres. This assumption was fully justified in the sequel.

条件反射の接続が2つである場合
The facts dealt with so far reveal another important feature of this mechanism, namely, that such external stimuli as have been from the very birth of the animal transmitted to a definite centre, can, notwithstanding, be diverted and made to follow another route, becoming linked up by the nervous connection to another centre, provided always that this second centre is physiologically more powerful than the first.

This linking up of impulses in different areas of the brain, by the formation of new nervous connections, is the first nervous mechanism we have encountered in our study of the physiology of the hemispheres. The question as to the site where this new nervous connection occurs has not yet been clearly answered. Is it within the cortex exclusively, or does it take place between the cortex and the subcortical areas? Both possibilities are conceivable. In the latter case it must be assumed that when two points, one in the cortex, the other in a subcortical area, are simultaneously excited by different stimuli, a path is established for the transmission of the excitation direct from the former point to the latter. If on the other hand the connection takes place entirely within the cortex, it is necessary to assume either that all the receptor organs (including internal receptors) of the organism are represented in the cortex, in which case impulses originating in different organs during their activity would be transmitted to the corresponding cortical point, which would then enter into connection with a point excited by the external stimulus, or else that stimuli which lead to activity of an organ gain [p. 38] direct representation in the cortex independently of the simultaneous excitation of a subcortical area. Of the two last mentioned alternatives I have reason to believe that the latter represents what probably takes place in the intact brain when the hemispheres are in a state of alertness. In any case it appears that the cells predominantly excited at a given time become foci attracting to themselves the nervous impulses aroused by new stimuli -- impulses which on repetition tend to follow the same path and so to establish conditioned reflexes.

条件反射の媒介
We must now take some account of the agencies which can be transformed into conditioned stimuli. This is not so easy a problem as appears at first sight. Of course to give a general answer is very simple; any agent in nature which acts on any adequate receptor apparatus of an organism can be made into a conditioned stimulus for that organism. This general statement, however, needs both amplification and restriction. We can, in the first place, divide up natural agencies into their ultimate component parts as regards their properties as physiological stimuli. Even a very small single component of such agency may acquire in itself the properties of a conditioned stimulus. Such, for example, may be a very small variation in loudness of a tone, or s small and barely distinguishable variation in luminosity, and so on. In this way alone the number of potentially effective stimuli in nature is extended almost indefinitely, although it is also obvious that a limit is set to the fineness of gradation of such stimuli by the degree of sensitivity and perfection of the peripheral receptor organs of the organism. On the other hand, the animal may be affected by the sum total of numerous elementary stimuli acting together as a whole. For example, in distinguishing facial appearance we take info account simultaneously form, dimensions, shades, colours. We behave very much in the same way when making out our direction in a more or less familiar neighbourhood. Such examples of compound stimuli can be multiplied indefinitely, and when we consider the unlimited possibilities of grouping the very great number of single elementary stimuli, we shall arrive at a very formidable figure. Yet in this case also a limit is undoubtedly imposed by the intrinsic structure of the cerebral hemispheres themselves. But I wish at present only to give some idea of the possible number of conditioned stimuli, leaving a, more detailed discussion of this important matter to a subsequent lecture.

条件刺激としての消滅
So far we have considered only one broad group of conditioned [p. 39] stimuli, namely those derived from the appearance of any natural agency. But the disappearance also of such an agency may become the stimulus to a conditioned reflex. Let us take the following example as an illustration. A metronome is sounding continuously in the experimental laboratory when the dog is brought in. The sound of the metronome is now cut out, and immediately an unconditioned stimulus, say food or a rejectable substance, is introduced. After several repetitions of this procedure it is found that the disappearance of the sound has become the stimulus to a new conditioned reflex [Dr.Zeliony and Dr. Makovsky].

条件刺激としての減少
Not only can the cessation of a stimulus be made the signal to a conditioned reflex, but also a diminution in its strength, if this diminution is sufficiently rapid. The effect of rate of change of some property of a stimulating agent is well brought out in the following experiment by Dr. Zeliony. The sudden stoppage of a powerful pneumatic tuning fork D-2 had been made into the signal for a conditioned alimentary reflex, which was measured by 32 drops of salivary secretion during the test interval; but a gradual damping down of this tone over a period of 12 minutes, though ending in complete extinction, did not yield a single drop of saliva. So we see that not only can the appearance of some external agency act as a conditional stimulus, but its disappearance also, or the rapid weakening of its strength. Thus the number of potential stimuli to a conditioned reflex is once more greatly increased.

条件反射としての空白
The next group of conditioned stimuli can be regarded as a variation, or further development, of the type of stimuli with deferred action which has just been discussed. The stimulus this time is not the actual disappearance of an external agent, but the trace left by the action of this agent on the central nervous system after the agent itself has been removed. The procedure of development of such reflexes is as follows. Any convenient external stimulus is applied to the animal and continued for ½ to 1 minute. After another definite interval of 1-3 minutes, food or a rejectable substance is introduced into the mouth. It is found that after several repetitions of this routine the stimulus will not itself evoke any reaction; neither will its disappearance; but the appropriate reaction will occur after a definite interval, the after-effect of the excitation caused by the stimulus being the operative factor. We have to distinguish this type of reflex from the type described previously, in which the unconditioned stimulus coincided for part of its duration [p. 40] with the conditioned stimulus. The type described in this paragraph is termed a trace conditioned reflex.

痕跡条件反射
I shall describe here an experiment by Dr. Grossman with trace conditioned reflexes : A tactile stimulation of the skin was employed as a stimulus for the trace reflex to injection of acid. The tactile stimulus was applied during one minute and acid was introduced into the mouth after a further period of one minute.

パブロフと条件反射 講義3 実験1909年

パブロフと条件反射 講義3 実験1909年




Trace reflexes may be of different character, depending on the length of pause between the termination of the conditioned stimulus and the appearance of the unconditioned stimulus. When the pause is short, being a matter of only a few seconds, then the trace left by theconditioned stimulus is still fresh, and the reflex is what we may term a short-trace reflex. On the other hand, if a considerable interval, one minute or more, is allowed to elapse between the termination of the conditioned and the beginning of the unconditioned stimulus we have a long-trace reflex. It is important to distinguish all these cases on account of the essential peculiarities exhibited by long-trace reflexes.

We come now to the last of those agents which can be transformed into a conditioned stimulus, and this one is peculiar in that it originates apparently quite regularly and spontaneously. Its operation depends on the fact that every stimulus must leave a trace on the nervous system for a greater or less time a fact which has long been recognized in physiology under the name of after effect. The further agency I wish to introduce to you is no less real, but the clear apprehension of its nature is apt to present some difficulty. [p. 41]

First of all I shall describe an experiment of a general nature. One dog was given food at regular intervals of time; another had acid introduced into the mouth at the same intervals. After this had gone on for a little time it was found that food or acid was no longer necessary to produce the alimentary or mild defence reflex, but that these reflexes appeared spontaneously at the regular intervals of time. This may be illustrated by the following detailed experiment of Dr. Feokritova: A dog is placed in the stand and given food regularly every thirtieth minute. In the control experiments any-one feeding after the first few is omitted, and it is found that despite the omission a secretion of saliva with a corresponding alimentary motor reaction is produced at about the thirtieth minute. Sometimes this reaction occurs exactly at the thirtieth minute, but it may be one or two minutes late. In the interval there is not the least sign of any alimentary reaction, especially if the routine has been repeated a good number of times. When we come to seek an interpretation of these results, it seems pretty evident that the duration of time has acquired the properties of a conditioned stimulus.

The experiment just described may be performed with the following modification. The animal can be given food regularly every thirtieth minute, but with the addition, say, of the sound of a metronome a few seconds before the food. The animal is thus stimulated at regular intervals of thirty minutes by a combination of two stimuli, one of which is the time factor and the other the beats of the metronome. By this manner a conditioned reflex is established to a compound stimulus consisting of the sound plus the condition of the hemispheres at the thirtieth minute, when both are reinforced by food. Further, if the sound is now applied not at the thirtieth minute after the preceding feeding, but, say, at the fifth or eighth minute, it entirely fails to produce any alimentary conditioned reflex. If it is applied slightly later it produces some effect; applied at the twentieth minute the effect is greater; at the twenty-fifth minute greater still. At the thirtieth minute the reaction is of course complete. If the sound is never combined with food except when applied at the full interval, in time it ceases to have any effect even at the twenty-ninth minute and will only produce a reaction at the thirtieth minute -- but then a full reaction. An illustration is given from experiments by Dr.Feokritova: A dog is given food every half-hour, each feeding being preceded by the sound of a metronome, [p. 42] which is continued for thirty seconds; the effect of the metronome is tested at the twenty-ninth minute.

パブロフと条件反射 講義3 実験1911年

パブロフと条件反射 講義3 実験1911年




延長は30分が限界
Of course in the establishment of a conditioned reflex of this type any length of time interval can be employed. No experiments, however, were made with longer intervals than half an hour.

生理的な時間
What is the physiological meaning of these time intervals. In their rôle as conditioned stimuli? Only a tentative approach can be made to a definite answer to such a question at present: Time is measured from a general point of view by registering different cyclic phenomena in nature, such for instance as the rising and setting of the sun or the vibration of the pendulum of a clock. But many cyclic phenomena take place inside the animal's body. In the course of 24 hours the brain receives a very considerable number of stimuli, becomes fatigued, and again restored through sleep. The alimentary canal is periodically filled or emptied; and, in fact, changes in practically all the component tissues and parts of the organism are capable of influencing the cerebral hemispheres. This continuous cycle of direct and indirect influences upon the nervous activity constitutes the physiological basis for the estimation of duration of time. We may consider the following simple case of physiological registration of short intervals of time by the hemispheres. It is well known that a fresh stimulus -- we will take for example an olfactory stimulus -- produces a very definite nervous excitation. This, however, gradually and progressively weakens. The physiological state of the nervous elements, under the influence of the continued stimulation, without doubt undergoes a series of simultaneous and successive changes. The same is true for the reverse condition: When a stimulus is withdrawn the change is perceived for some time very acutely, but quite soon its influence diminishes until we are no longer aware of it. Here again the physiological [p. 43] condition of the nerve cells is, doubtless, undergoing the reverse series of changes. From this point of view we can give an interpretation of the establishment of conditioned reflexes to an interruption of a stimulus, and to a trace of a stimulus, as well as, apparently, to a duration of time. In the experiment described the administration of food was accompanied and followed by a definite activity in a large number of organs, which all underwent e series of definite cyclic changes. All these changes were reflected in the cerebral hemispheres where they fell on appropriate receptive fields, and a definite phase of these changes acquired the properties of the conditioned stimulus.

条件刺激は大量にある
To conclude this part of our discussion I shall suggest the following modification and amplification of our definition of agencies which can become conditioned, viz. that innumerable individual fluctuations in the external and internal environment of the organism may, each and all of them, singly or collectively, being reflected in definite changes in the cells of the cerebral cortex, acquire the properties of a conditioned stimulus.

抑制性反射
We shall now follow out another important group of phenomena. Hitherto we have been dealing with reflexes of a positive character -- i.e. reflexes which ultimately gave rise to positive reactions, both motor and secretory, all of them associated with various processes of excitation in the nervous system. There is, however, another manifestation of nervous activity which is in no way inferior in physiological and vital importance to that positive manifestation which has just been considered. I refer to nervous inhibition. When we come to investigate the highly complex functions of the cerebral hemispheres, we naturally expect to come across inhibitory phenomena, for these are very constantly and very intimately mixed up with the positive phenomena of nervous excitation. But before dealing with these I consider it advisable to give a brief description of inhibition of centres as observed in the field of unconditioned reflexes.

抑制性反射の例
The present state of physiological knowledge enables us to recognize under normal conditions two types of central inhibition. These may be termed direct and indirect, or internal and external respectively. On the one hand we are familiar with the direct inhibitory action of certain afferent nerves, or of certain physical and chemical properties of the blood, upon definite nervous centres controlling respiration, circulation, locomotion and so on. On the [p. 44] other hand, the central nervous system supplies numerous cases of indirect inhibition. In the latter cases inhibition of the activity of a given centre is brought about as the result of an activity of some other centre, which activity has arisen in its turn as a result of excitation from some afferent nerve or from some change in the composition of the blood. Instances of other kinds of inhibition are provided by those complex unconditioned reflexes generally known as "instincts." Thus many insects, especially when in the larval stage, become immobilized and drop down at the slightest touch. This is obviously a case of direct inhibition of the entire nervous apparatus of locomotion. Another example may be taken from the newly hatched chick, which manifests straightway a pecking reflex to the visual stimulus of small objects or patches of light and shade. If, however, a strongly irritant and injurious substance gets taken up, the pecking reflex becomes inhibited immediately and is replaced by a defence reaction leading to a rejection of the irritating substance. This is a result of an interaction of two active centres, and is an example of external inhibition.

条件反射の抑制の実験
Conditioned reflexes are also subject to these two types of central inhibition. Since the indirect or external inhibition of conditioned reflexes does not differ in the least from the corresponding inhibition of unconditioned reflexes I shall take this first. The following is a very simple case, and one of common occurrence in our earlier experiments. The dog and the experimenter would be isolated in the experimental room, all the conditions remaining for a while constant. Suddenly some disturbing factor would arise -- a sound would penetrate into the room; some quick change in illumination would occur, the sun going behind a cloud; or a draught would get in underneath the door, and maybe bring some odour with it. If any one of these extra stimuli happened to be introduced just at the time of application of the conditioned stimulus, it would inevitably bring about a more or less pronounced weakening or even a complete disappearance of the reflex response, depending on the strength of the extra stimulus. The interpretation of this simple case does not present much difficulty. The appearance of any new stimulus immediately evokes the investigatory reflex and the animal fixes all its appropriate receptor organs upon the source of disturbance, pricking up its ears, fastening its gaze upon the disturbing agency, and sniffing the air. The investigatory reflex is excited and the conditioned reflex is in consequence inhibited. [p. 45]

抑制性反射の延長
These extra stimuli have also another important influence. Every stimulus, however rapidly it may disappear, is effective not only while it lasts, but also for some time after its cessation while its after-effect lasts. On account of this, if the conditioned stimulus is applied shortly after the extra stimulus, the reflex reaction will be partly inhibited. Different extra stimuli, whether accidental or deliberate, produce after-effects of different length. Some may still have a powerful after-effect after 2 or 3 minutes, others after 10 or 12 minutes, and still others after several days. These longer after-effects occur especially with alimentary, and gustatory stimuli in general, and in many experiments they have to be taken seriously into account.

条件反射の接続している期間の長さは影響がある
The effect of exciting an extra reflex will, of course, vary according as the conditioned reflex has only freshly been formed or has already been firmly established. It is obvious that an old-established reflex is not likely to be so easily inhibited as a recent one.

他人という刺激
In our old laboratory the neglect to provide against external stimuli often led to a curious complication when I visited some of my co-workers. Having by himself established a new conditioned reflex, working in the room with the dog, the experimenter would invite me for a demonstration, and then everything would go wrong and he would be unable to show anything at all. It was I who presented the extra stimulus: the investigatory reflex was immediately brought into play: the dog gazed at me, and smelled at me, and of course this was sufficient to inhibit every recently established reflex. Another example is very similar. If one experimenter had worked with a dog and established some firm and stable conditioned reflexes, conducting numerous experiments with them, when he handed the animal over to another experimenter to work with, all the reflexes disappeared for a considerable time. The same happened when the dog was changed over from one research room to another.

気配という抑制性刺激
In the case of extra stimuli, which awaken specialized reflex responses, the resulting inhibition is extremely profound. Examples of such extra stimuli are, the sight or sound of game for sporting dogs, of cats for some dogs, rustling under the floor for others, and so on. Not only such specialized stimuli, but also any very strong or unusual stimulus exhibits a prolonged and pronounced inhibitory after-effect. With respect to strong or unusual stimuli dogs can be divided into two groups. Some respond in a manner which may be termed positive, i.e. aggressively -- barking furiously and baring [p. 46] their teeth. Others exhibit a defence reaction of a passive nature -- they try to get free and run away or they stand like lumps of stone absolutely motionless; and sometimes they will shiver violently and crouch down in the stand; or they may urinate, a most unusual occurrence for dogs while in the stand. In these dogs inhibition predominated. This case can also be classified as a type of indirect or external inhibition of conditioned reflexes, for the inhibition originates primarily in other parts of the brain than that where the reflex response is initiated.

一時的な抑制性反射
All the cases of external inhibition which have just been discussed are of a temporary nature; and on this account the stimuli producing these effects are termed temporary inhibitory stimuli. If they act upon the animal repeatedly and are not reinforced with any unconditioned or conditioned stimulus, sooner or later they become lost upon the organism and lose all their inhibitory properties.

犬の抑制性反射の例
An experiment providing an admirable illustration of this condition occurred during the first two lectures, without the audience being aware of it. The dog used for the experiment with the metronome (p.22) had been kept in the lecture theatre during the whole of one lecture previous to the demonstration, while one of my co-workers repeatedly tried the experiment. As a matter of fact the experiment was at first a failure, the reflex being inhibited, and the animal only freed itself graduadly from the inhibitory influence of the unfamiliar surroundings.

Some years ago, when I was delivering a series of lectures on conditioned reflexes, I had to proceed in a similar manner for demonstration of experiments. The dogs were placed in the lecture theatre from the very beginning of the course of lectures, and my co-workers constantly repeated the experiments preliminary to the actual lecture demonstration, and only with this precaution could the experiments be successfully conducted. In this series of lectures, unfortunately, the present unavoidable and unforeseen circumstances have deprived me of these facilities; I shall have to restrict myself to occasional demonstrations, keeping chiefly to a description of experiments and researches conducted in our laboratories.

永続的な抑制性反射
In addition to the temporary external inhibition, a second type of external inhibition can be distinguished. This may be termed permanent external inhibition, since it does not weaken through repetition, but constantly maintains its strength. An example may be found in the reaction to acid. If the dog is given food, even [p. 47] some considerable time before the conditioned stimulus to the acid is applied, this reflex cannot be obtained. What happens is that the alimentary centres inhibit the reaction to acid for a considerable time after they themselves are set into activity, and this happens always, no matter how often the experiment may be repeated. It is therefore a permanent external inhibition which does not undergo any sort of spontaneous extinction. Such cases are not at all rare. If a conditioned reflex is established to introduction of acid, any careless administration -- too much acid, or too concentrated, or applied too often -- produces a severe irritation of the buccal mucous membrane and produces a permanent inhibition of conditioned reflexes which lasts until the pathological condition is removed. Again, the dog may have some laceration of the skin which may be constantly irritated by the supporting loops of the stand. The defence reflex will then become dominant while the conditioned reflexes, and especially the mild defence reflex to acid, will be inhibited. Many more examples of this nature could be quoted.

排尿反射
I will give one or two more. In one case an experiment may be running quite smoothly, and suddenly all conditioned reflexes begin to fail, and finally disappear altogether. The dog is taken out, allowed to urinate, and then all the reflexes return to normal. Evidently stimulation of the centre for urination had inhibited the conditioned reflexes.

欲情反射
Another example may be chosen in the season when the females are in heat. If the males have been housed near the females before the experiment, it is found that all their conditioned reflexes are inhibited in greater or less degree. It is obvious in this case that the inhibition derives from the sexual centres in the hemispheres.

抑制性反射が消えると抑制されていた条件反射が再び活性化する
In face of such numerous potential sources of inhibition we see that our term of "conditioned" reflexes is very appropriate. Yet these conditions can readily be controlled, and the disquieting factors can be eliminated. All of them produce external inhibition, and I should like to give a final summing up of their character: No sooner does any extra nervous excitation occur in the central nervous system than it immediately makes its presence felt in diminishing or abolishing conditioned reflexes, but temporarily only, as long as the causative stimulus or its after-effect is present.




【重要表現】
foci 焦点 focusの複数形
buccal mucous membrane 頬の粘膜

パブロフと条件反射 講義4


Internal inhibition of conditioned reflexes: (a) Extinction.

抑制性反射
Towards the end of the last lecture I discussed external inhibition of conditioned reflexes, as exhibited in numerous cases of temporary clashing between conditioned reflexes and other extra excitatory processes in the brain, and we saw how this clashing led to weakening, more or less profound, and sometimes even to the disappearance of the conditioned reflexes.

内抑制
In the second type of inhibition, which may be termed internal inhibition, the positive conditioned stimulus itself becomes, under definite conditions, negative or inhibitory; it now evokes in the cells of the cortex a process of inhibition instead of the usual excitation. Conditions favouring the development of conditioned reflexes of the negative or inhibitory type are of frequent occurrence, and these reflexes are met with not less frequently than reflexes of the positive or excitatory type.

外抑制と内抑制
The most striking difference between external and internal inhibition is that, whereas under the conditions described in the preceding lecture external inhibition is produced on the very first application of an extra stimulus, internal inhibition on the other hand always develops progressively, quite often very slowly, and in many cases with difficulty.

内抑制の実験
I shall start by describing that form of internal inhibition which was first encountered in our researches, and shall trace the growth of our present conception of its nature.

Demonstration.-- The following is an example of an experiment illustrating the first group of internal inhibitions.

We are taking for this experiment the same dog that was used in the second lecture for the conditioned reflex to the sound of the metronome. In testing the reflex the metronome is sounded for 30 seconds during which the secretion of saliva is measured in drops, and at the same time the interval between the beginning of the stimulus and the beginning of the salivary secretion is recorded. This interval is customarily called the latent period, although as [p. 49] will be seen later some other term might more usefully have been employed. Stimulation by the metronome is not followed in this particular experiment by feeding, i.e. contrary to our usual routine the conditioned reflex is not reinforced. The stimulus of the metronome is repeated during periods of 30 seconds at intervals of two minutes. The following results are obtained:

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




条件反射が弱くなる 消去
The continuation of this experiment must be left over until later on in the lecture when it will be possible to add a further important detail. One detail, however, already stands out quite clearly, namely that repeated application of a conditioned stimulus which is not followed up by reinforcement leads to a weakening of the conditioned reflex. If the experiment had been pushed further there would have come a stage when the reflex would entirely disappear. This phenomenon of a rapid and more or less smoothly progressive weakening of the reflex to a conditioned stimulus which is repeated a number of times without reinforcement may appropriately be termed extinction of conditioned reflexes. Such a term has the advantage that it does not imply any hypothesis as to the exact mechanism by which the phenomenon
is brought about.

天然刺激と人工刺激
Abundant evidence has been collected in our laboratories relating to experimental extinction of conditioned reflexes, but before I can discuss this it is necessary to make a few remarks about the terminology which will be employed. Formerly we made a distinction between "natural" and "artificial" conditioned reflexes, "natural" reflexes being those which appeared to be formed spontaneously as a result of the natural association of, for example, the sight and smell of food with the eating of food itself, or of the procedure of introducing acid or some rejectable substance with the acid or the rejectable substance itself, while "artificial" reflexes were those which could be formed as a result of artificially associating [p. 50] with the food or rejectable substance stimuli which in the ordinary with food or the rejectable course of events have nothing in common substance. At the present time, however, we know that there is not the slightest difference in properties between all these reflexes. I mention this fact here because the numerous experiments of the earlier period of our work were carried out with the "natural" conditioned reflexes, and it is from these that I shall draw many examples in the present lecture. All the numerous artificial stimuli which we now use every day in our experiments were important to us at the time of those experiments because they provided easily controlled, exact, and regularly reproducible stimuli, and because they could be applied to check the correctness of our conception of the mechanism by which natural conditioned reflexes are formed. At present the artificial stimuli predominate in importance because of the vast field of research they have unfolded to us and because they came ultimately to provide the most important material for our investigation.

人工刺激は管理しやすい
The progress of experimental extinction is often subject to fluctuation. The fluctuations of an otherwise smooth curve may be brought about both by external and internal factors. To obtain a smooth curve of extinction of a conditioned reflex it is necessary to maintain the unreinforced conditioned stimulus rightly constant in character and strength; the environing experimental conditions also must remain absolutely constant. Very wide fluctuations in the reflex undergoing experimental extinction are apt to occur in the case of 8 natural conditioned stimulus, for example the presentation of food, which may be held at one time further away from, the animal than at another, or which may be held stationary or slightly moving. With an artificial conditioned stimulus, on the other hand, it is quite easy to obtain an exact repetition of the stimulus and so to avoid this cause of disturbance in the curve of extinction. With regard to
variations in the experimental conditions it is only natural that any marked changes in the environment, such, for example, as any introduction of strong extra stimuli which would produce external inhibition, should also affect the smoothness of the curve of experimental extinction. Such strong stimuli abruptly diminish all conditioned reflexes, including of course reflexes undergoing extinction, but the reflexes reappear when the disturbing stimuli are removed. Even greater interest attaches to the effect of extra stimuli of small intensity: Such stimuli produce a temporary [p. 51] weakening, not of the reflex, but of the progress of the experimental
extinction. An example can be seen in the fifth repetition of the conditioned stimulus in our lecture demonstration (p. 49). The rise in the reaction from 5 drops to 7 drops definitely coincided with some small disturbance produced by the audience. This effect of extra stimuli of small intensity is of great importance for the physiology of the hemispheres, and we shall return to it later in this lecture.

条件反射の消去の速度
Even with stimuli of constant strength, and with constant environing conditions, fluctuations in the curve of experimental extinction are sometimes observed. These fluctuations are of rhythmic character and are evidently due to some internal factors. These factors affect directly the nervous processes involved in experimental extinction, and we shall come across examples on frequent occasions in the further course of our discussion.

条件反射の消去速度は何で変化するのか
The rate of experimental extinction, measured by the period of time during which a given stimulus must be applied at definite regular intervals without reinforcement before the reflex response becomes zero, depends on numerous conditions.

動物の神経構造
First among these come any individual peculiarities of the nervous organization of the animal. Under the same set of external conditions some animals will have the conditioned reflexes rapidly extinguished, while in others the whole process will be much delayed. In excitable dogs the reflexes are mostly slow of extinction, but in quiet animals extinction is rapid.

条件反射の継続期間の長さ
Clearly also the extent to which a reflex has gained a firm footing is an important point: a reflex which has only recently been established-is likely to be less firmly grounded than an older one and is likely to suffer extinction the more quickly.

無条件反射の強度
The rapidity of extinction depends also in a great measure upon the intensity of the unconditioned reflex underlying the conditioned one which is undergoing experimental extinction.

無条件刺激の強度と消去の関係
In this connection the following experiments by Dr. Babkin are of interest:

An unconditioned reflex to a given quantity of 1% extract of quassia introduced into the dog's mouth produces on an average of ten experiments 1.71 c.c. of salivary secretion. A conditioned reflex established on the basis of this unconditioned one produces 0.3 c.c. during one minute of stimulation. A definite quantity of 0.1% aqueous solution of hydrochloric acid evokes in the ame dog an unconditioned reflex measuring on an average of five experiments [p. 52] 52 c.c. The corresponding conditioned reflex gives 0.9 c.c. during one minute of stimulation. The onditioned stimuli are "natural" ones, namely, the presentation of quassia or of acid, as the case may be, at some distance from the animal. Every other condition of the experiment is maintained rigidly constant. The following table illustrates the experimental extinction of each of the two conditioned reflexes in this animal.


パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験





条件刺激の反復の間隔が短いと消去が早い
Yet another important factor in determining the rate of experimental extinction is the length of pause between successive repetitions of the stimulus without reinforcement. The shorter the pause the more quickly will extinction of the reflex be obtained, and in most cases a smaller number of repetitions will be required. The conditions may be illustrated from an experiment by Dr. Babkin:

条件反射の刺激の間隔と消去の実験
The conditioned stimulus was provided by meat powder presented to the dog at a distance for one minute; the stimulus was repeated several times in succession, and was of course not reinforced. The five series of extinctions given below were carried out on the same animal in a single day. Between separate extinctions the dog was given a rest, and the reflex was reinforced by feeding with meat powder.

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




[p. 53]

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験



パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




消却の累計が消却速度に影響する
The final condition which influences the rate of experimental extinction is the number of times the given reflex has been subjected to extinction in the same animal. After each fresh extinction of a conditioned reflex the number of unreinforced [p. 54] conditioned stimuli required to produce the next experimental extinction is less, until in the end a zero reaction results in some dogs from only a single application of the unreinforced conditioned stimulus.

二次消却
A circumstance of special interest is that experimental extinction of any single conditioned reflex results, not only in a weakening of that particular conditioned reflex which is directly subjected to the extinction (primary extinction), but also in a weakening of other conditioned reflexes which were not directly subjected to extinction (secondary extinction). This latter phenomenon involves not only those conditioned reflexes which were based upon a common unconditioned reflex with the primarily extinguished one (homogeneous conditioned reflexes), but also those which were based upon a different unconditioned reflex (heterogeneous conditioned reflexes). Sometimes secondary extinction reaches a profound degree, involving even the unconditioned reflexes. The latter case is illustrated by the following experiment of Dr. Perelzweig:

A given quantity of hydrochloric acid produced on an average in a dog a salivatry secretion of 6 c.c. After several extinctions of the corresponding conditioned defence reflex, in which the conditioned stimulus was tactile, application of the acid itself produced only 3.8 c.c. Even more striking results were obtained in connection with the secondatry extinction of homogeneous conditioned reflexes, and our experiments were mainly concerned with these.

二次消却の程度は一次消却の程度に関係する
In every case of secondary extinction the degree to which the primary experimental extinction is carried is of first importance. A primary experimental extinction of a conditioned reflex which is carried to its final stages smooths out the many small points of difference between secondary extinctions of different conditioned reflexes, but a primary extinction which is carried to only a moderate degree leaves these small differences well pronounced. It may be stated, other things being equal, that the extent to which homogeneous conditioned reflexes undergo secondary extinction is determined by their relative physiological strengths. The strength of a conditioned reflex, in its turn, depends on whether it has long been established, on the number of times it has been refreshed by reinforcement, and on whether or not the reinforcement has been discontinued, and for how long. The extent of secondary extinction depends also on whether, and on how often, the reflex has previously [p. 55] been subjected to experimentalextinction, and on whether or not it is reinforced immediately before the primary extinction is begun.

The greater the strength of the conditioned reflex as compared with the reflex which is subjected to primary extinction, the less does it undergo secondary extinction; on the other hand, if the stronger reflex is subjected to primary experimental extinction the weaker conditioned reflex undergoes complete secondary extinction. The following experiments bearing on this subject were performed by Dr. Babkin :

二次消却と一次消却の関係についての実験
A dog has three conditioned reflexes to acid, one depending on the sound of a buzzer, a second on the sound of a metronome and a third on a tactile stimulation of the skin. Every conditioned stimulus was continued always for 30 seconds. The first experiment shows the relative strengths of the reflexes.


パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験





In the following experiment a primary extinction of the reflex to the metronome was produced by repeating the stimulus at intervals of three minutes.

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




[p. 56]

On primary extinction of the conditioned reflex of medium strength the weaker tactile reflex also was completely extinguished, while the stronger reflex (to buzzer) was still partly active. These results were corroborated by further experiments in which the order of testing the secondarily extinguished reflexes was reversed.

合成刺激
The same dependence of the degree of extinction upon the strength of the conditioned reflexes is seen when the conditioned reflex undergoing extinction is one to a compound stimulus composed of several distinct elements which can be applied either simultaneously or else independently. Primary extinction of the reflex to the compound stimulus is always accompanied by secondary extinction of the reflexes to its individual components. Supposing there are two components of equal physiological Strength, then the primary extinction of the one leads to simultaneous secondary extinction of the other, while the reflex to the compound stimulus is usually considerably diminished. Where, however, the two components of the compound stimulus are unequal in strength, primary extinction of the stronger reflex leads to a complete extinction of the reflex to the weaker component, while extinction of the weaker (unless carried beyond zero) leads only to a partial weakening of the reflex to the stronger component. The primary extinction of the stronger reflex leads also to a complete extinction of the reflex to the compound stimulus. The question of interrelation between the different individual components in a compound stimulus will be discussed further in a future lecture.

In the meantime we must endeavour to find a correct interpretation of the phenomenon of experimental extinction, and we shall find it important in this connection to give attention to a case in which the weaker of the two components in a conditioned reflex is completely overshadowed by the stronger, the weaker when tested separately producing no positive reflex effect. When in such a case the weaker stimulus is applied singly several times in succession, without reinforcement, there results, nevertheless, an extinction not only of the reflex to the stronger stimulus, but also of the reflex to the
compound stimulus. An experiment by Dr. Perelzweig can be taken to illustrate this point:

合成された条件反射の実験
A compound conditioned reflex has been established on a basis of the defence reflex to acid. The individual components of the compound stimulus are a tactile stimulus and a thermal stimulus of 0° C. In the experiment given below the animal is stimulated by [p. 57] the compound stimulus and by its components separately. In every case the stimulus is applied during one minute.

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




This experiment shows that the application of the thermal component, which by itself was ineffective, led when repeated three times without reinforcement to a complete secondary extinction of the stronger tactile component and to a practically complete extinction of the reflex to the compound stimulus.

条件反射の消却は負の値も取りえる
Hitherto, when referring to the degree of extinction, we have only spoken of the extinction as being partial or as being complete, but we shall now have to extend our conception. Not only must we speak of partial or of complete extinction of a conditioned reflex, but we must also realize that extinction can proceed beyond the point of reducing a reflex to zero. We cannot therefore judge the degree of extinction only by the magnitude of the reflex or its absence, since there can still be a silent extinction beyond the zero. This statement rests upon the fact that a continued repetition of an extinguished stimulus' beyond the zero of the positive reflex deepens the extinction still further. Such an extension of our conception serves fully to elucidate the experiment just described, and it explains why the seemingly inactive thermal component when subjected to experimental extinction led to such a profound secondary extinction of the stronger tactile component. The importance of considering the degree of extinction in all experiments thus becomes evident. The methods of determining the degree of extinction when it goes beyond zero will be explained in connection with the question which will next be discussed.

消去の深度
We shall consider what happens to the conditioned reflexes after they have been subjected to experimental extinction and inquire [p. 58] whether they ever regain their original strength. Left to themselves extinguished conditioned reflexes spontaneously recover their full strength after a longer or shorter interval of time, but this of course does not apply to conditioned reflexes which are only just in
process of formation. Such reflexes, being weak and irregular, may require for their recovery after extinction a fresh reinforcement by the underlying unconditioned reflex. However, all those conditioned reflexes which have been fully established invariably and spontaneously return sooner or later to their full strength. This provides one way of determining the depth of extinction; it is measured, other conditions being equal, by the time taken for spontaneous restoration of the extinguished reflex to its original strength. Such time interval may vary for the different reflexes from a few minutes to a number of hours. I shall give a few experiments in
illustration. The first is an experiment by Dr. Babkin:

消去の深度の実験
Presentation of meat powder a short distance away at intervals of three minutes ; the reflex is not reinforced.

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




The second experiment is by Dr. Eliason :

Meat powder is presented a short distance away at intervals of ten minutes; the reflex is not reinforced.

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




It will be interesting now to return to the demonstration given in the earlier part of this lecture and to examine whether there is [p. 59] any spontaneous recovery of the reflex to the metronome which was partially extinguished just twenty-three minutes ago.

消去の自発的復活
Continuation of Demonstration.-- The dog is again subjected to the stimulus of the metronome for 30 seconds: the latent period of the conditioned reflex now comes out at 5 seconds and the salivary secretion is 6 drops. At the last reading the latent period was 13 seconds and the salivary secretion 3 drops. Considerable recovery has therefore taken place spontaneously during the lecture.

消去の復活の速度はどのように決まるのか
The great differences in rapidity of restoration of extinguished reflexes depend on a number of factors. The most important factor is the depth of the preceding extinction. The individual character of an animal and its type of general nervous organization also play an important part. Much depends also on the intensity of. The conditioned reflex which was subjected to experimental extinction; and finally, upon how often the experimental extinction has been repeated. In every case, however, it is possible to accelerate the restoration of an extinguished conditioned reflex. For this purpose it is only necessary to apply the unconditioned stimulus on which the conditioned reflex was built up, either singly, or together with the extinguished conditioned stimulus. This method produces a more or less rapid restoration, according as the conditioned reflex has been extinguished to a greater or less degree. If the extinction has not been carried very far, a single application of the unconditioned stimulus is often sufficient to restore the reflex to full strength; but if the extinction has been made profound, repeated reinforcements are necessary. This means of accelerating the recovery of the extinguished reflex affords another method of measuring the depth of extinction. The further question whether the acceleration in the restoration of an extinguished conditioned reflex is greater when the unconditioned reflex is applied singly, or when it is applied in the form of reinforcement cannot be discussed at present, as it is still under investigation (see Lecture XXII).

消去は抑制に含まれる
All this description of facts about extinction may have proved rather wearisome to the reader, owing to the absence of any underlying uniformity. Nevertheless they served an important purpose in that through a careful consideration of them we were enabled gradually to come upon a solution of the fundamental question as to the intimate nature of experimental extinction. By ruling out one interpretation after another we arrived at the conclusion that [p. 60] extinction must be regarded as a special form of inhibition. That it cannot be regarded as an irreparable destruction of the conditioned reflex, due to disruption of the respective nervous connections, is evidenced by the fact that the extinguished reflexes spontaneously regenerate in course of time. Another possible explanation also suggests itself: may it not be that the experimental extinction is brought about simply by fatigue in some part of the neuro-secretory apparatus involved in the reflex? This is ruled out by the following evidence. The secretory elements in the gland do not become fatigued when the conditioned reflexes are being reinforced, although they continue indefinitely during an experiment to produce a full salivary secretion. Moreover, the restoration of an extinguished reflex is greatly accelerated by a fresh application of the unconditioned stimulus, a still further secretory activity of the gland being readily obtained although the reflex has been deeply extinguished. Neither can there be fatigue in the nervous centres of the secretory reflex. It is sufficient to recall the experiment which the conditioned reflex to the compound stimulus which had two cutaneous components -- tactile and thermal. The thermal stimulus, which was the weaker, could not by itself produce even the slightest positive effect: yet none the less its repeated application brought about a secondary extinction of the stronger tactile stimulus and even of the compound stimulus itself. The extinction of the ineffective thermal stimulus was at no time accompanied by any kind of positive activity of the nervous elements, and it is difficult to conceive that a part of the central nervous system underwent fatigue without previous activity. Again, it would seem that if we were to admit the possibility of any fatigue in the nervous centres, we could expect only the reflex to the thermal stimulus to become fatigued, but we find also an extinction of the reflex to the tactile stimulus which was not brought into activity at any time during the repeated stimulation of the thermal receptors. Thus by a process of elimination we are forced to the conclusion that experimental extinction is based on inhibition, and if we look at the facts which have been described, in the light of this conclusion nearly all of them become perfectly intelligible.

The spontaneous rhythmic fluctuations in the reflexes sometimes observed during the process of experimental extinction can now easily be explained as a manifestation of the struggle which is taking place between the nervous processes of excitation and inhibition [p. 61] before one or other of them gains the mastery. Similarly it becomes quite easy to understand the part played by the individuality of the animal. We have all observed for ourselves how the inhibitory processes in the nervous system of human beings are seldom of the same intensity in any two people, and numerous examples in the further course of these lectures will make it clear that a precisely similar variation obtains in the nervous system of animals.

条件刺激の結びつきが強いほど消去も強くする必要がある
It is clear that the more vigorous a conditioned reflex, or in other words the greater the intensity of the excitatory process, the more intense must be the inhibitory process in order to overcome it, and therefore the greater the number of unreinforced repetitions necessary to bring about complete extinction. Again, it was seen that a repetition of the non-reinforced conditioned stimulus was necessary to produce a sufficient summation of the inhibitory after-effect for complete experimental extinction, and it is reasonable to suppose that the shorter the intervals between successive repetitions of the stimulus the more quickly will the required intensity of the inhibitory process be obtained. This also was found to be the case. As a result of repetitions of experimental extinction on the same animal the zero level of a fresh extinction of the reflex is reached more rapidly. This shows that inhibition like excitation is facilitated by repetition. The fact itself is well known from observation of ourselves and others, but abundant experimental evidence for animals will be afforded during the further course of our study of conditioned reflexes.

The influence exerted by experimental extinction on reflexes other than the one undergoing extinction, including unconditioned reflexes as well as homogeneous and heterogeneous conditioned reflexes, must be regarded as the result of a spreading of the inhibitory process from its point of initiation through the entire nervous structure of the hemispheres. This process will be fully discussed in one of the later lectures.

消去の途中に逸脱があるのはなぜか
We have now to consider in detail still another important feature which has already been noted in passing, but was left unexplained, namely the frequent deviations observed in the curve of experimental extinction. These deviations represent sudden rapid strengthenings in the intensity of the reflex which is undergoing extinction, and they depend on the introduction of any accidental stimuli into the experimental environment. Some extraneous sound or shadow [p. 62] finding its way into the room produces at once a rapid strengthening of the reflex, and of course a similar effect is produced by different extra stimuli which we ourselves apply on purpose in order to study this phenomenon experimentally.

消化反射の消去は30分から60分で再び強くなる
I shall describe first of all an observation which for a long time we were at a loss to interpret. A natural conditioned reflex to meat powder, which, as we know from control experiments, after extinction recovers its initial value spontaneously in something between a half and one hour, is again extinguished to zero.

条件反射の消去からの回復
This time, however, instead of waiting for the spontaneous recovery of the reflex a weak, solution of acid is immediately introduced into the dog's mouth, and after the termination of the secretion produced by the acid (about five minutes) meat powder is again presented at a short distance. This time although nothing like half an hour has elapsed the conditioned alimentary reflex is found to be almost completely restored. At first sight the accelerated recovery of the extinguished reflex seems paradoxical, since we know already that positive conditioned reflexes are always quite definitely specific -- a definite stimulus rigidly evoking a definite reaction -- but in this case a stimulus to an extinguished conditioned alimentary reflex has had its full strength restored through the single application of a stimulus to a heterogeneous unconditioned reflex, namely the defence reflex to acid. And there can be no doubt that although the secretory component of the two reflexes is effected through the same glands yet they are distinctly heterogeneous in nature, since the defence reflex to acid differs sharply from the alimentary reflex to food both as regards the composition of the saliva secreted and as regards the character of the motor response. Without attempting for the present to give any explanation we can designate this observation from a purely matter of fact point of view as consisting of a sudden removal by an extraneous reflex of the inhibitory process set up by experimental extinction.

The whole group of cases of which the above is an illustration have one common feature. In all of them the removal of the inhibition is only temporary, persisting no longer than the extra stimulus responsible for the removal of inhibition and its after-effect.

条件反射の脱制止の実験
It is interesting to mention in this connection a disagreement which arose among the members of the staff in our laboratory before the fact of the restorative effect of acid upon an extinguished [p. 63] alimentary conditioned reflex had been indubitably established. Some of the workers admitted this restorative effect without question, while others disputed it. However, the experimental side of the question turned out to be right in both cases. The cause of the discrepancy was clearly brought out in Dr. Zavadsky's researches. It appeared that previous observers had overlooked the fact that their conditions of experimentation were not fully identical. Those workers who accepted the restorative effect had tested the extinguished conditioned alimentary reflex immediately or only a few moments after the salivary secretion in response to the acid had ceased, while the others had tested the extinguished reflex after allowing a considerable interval of time to elapse. Realizing the difference in the experimental procedure of the two sets of workers Dr. Zavadsky was able in his experiments to obtain all the different stages that had been reported by other workers. Two of his experiments, performed on the same day, are given below.

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




The time interval between the end of the secretion produced by acid and the subsequent testing of the extinguished reflex was in the above experiment 7 minutes 10 seconds.

[p. 64]

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




The time interval between the end of the secretion produced by acid and the subsequent testing of the extinguished reflex was in this experiment 40 seconds.

Seven minutes after the salivary secretion to acid had ceased the restoration of the conditioned alimentary reflex was minimal, only one gland showing any activity. When, however, the reflex was tested only 40 seconds after the salivary secretion to acid had ceased, a considerable restoration of the alimentary conditioned reflex was found, involving both glands.

By this and similar experiments the temporary nature of the restoration of an extinguished reflex in response to other extra stimuli was easily demonstrated. The restorative effect was in no way confined to the administration of acid but was produced also by any other extra stimulus. A further example from Dr. Zavadsky's experiments illustrates this general case. The experiment was conducted on another dog.

[p. 65]

パブロフと条件反射 講義4 実験

パブロフと条件反射 講義4 実験




This experiment leaves no doubt that the extinguished alimentary conditioned reflex is restored both by the actual presence of the extra stimulus (tactile and auditory), and by its after-effect (after-effect of stimulus of my entering the room).

In all the experiments which have just been described the restoration of the extinguished reflexes lasts only for a few minutes, depending on the duration of the extra stimulus and its after-effect. In the case, however, of certain special extra stimuli already mentioned in connection with external inhibition, stimuli which are of a protracted nature, the restorative effect is felt throughout the whole course of experimental extinction, which is therefore never smoothly progressive and can never be brought down to and kept at the zero level of the reflex.

異なる反射が同時に起きる場合
We have now to discuss another important observation bearing on the same point. During the whole period of our work we observed [p. 66] on many occasions the simultaneous existence of several different reflexes, leading of course to an interaction between them which resulted either in predominance of one or another reflex or in their mutual neutralization. Thus, if we make a tactile stimulation of the skin the stimulus to a conditioned reflex, it frequently happens that we are bothered with an interference from the unconditioned reflex response to the cutaneous stimulus itself, in the form of the scratch reflex or some sort of quivering reflex. This may, in rare cases, be so troublesome that the conditioned reflex never reaches a stable value. Exactly the same thing happens sometimes with musical tones of exceedingly high pitch, it being in some dogs impossible to overcome the difficulty of the resulting sharp motor response. All such powerful unconditioned stimuli exercise an external inhibitory influence which perpetually interferes with all positive conditioned reflexes. But it is obvious that these persistent extra reflexes should exert a still more powerful disturbing influence upon the normal course of the inhibitory processes underlying extinction, since inhibition is in every respect more labile than excitation. I shall be giving a number of examples substantiating this statement in a further lecture, when the whole matter will be subjected to a rigorous experimental analysis. All the considerations put forward in this lecture permit us to regard the temporary restoration of the reflex which is in process of extinction, or which is already extinguished, as based upon the removal of an inhibitory process. We therefore describe this phenomenon as a dis-inhibition, a term we shall always use in the future when we wish to denote a temporary removal of inhibition.

脱制止の効果は刺激によって異なるのか
The next question is, whether any distinction can be drawn between the ease of the restoration of an extinguished conditioned reflex resulting from fresh applications of the appropriate unconditioned stimulus, and the case which has just been termed dis-inhibition. Our experiments show that undoubtedly such a distinction does exist. In the first case, when restoration is effected by the special unconditioned stimulus underlying the reflex which has undergone extinction, such restoration is permanent. In the second case, however, when the restoration is effected under the influence of any alien stimulus, such restoration is only temporary. As to the actual reason for this difference it is not possible to say very much upon the experimental evidence available up to the present. There is, however, no doubt that in the first case, just as has already [p. 67] been shown in the second, we are dealing with a removal of inhibition. Any hypothesis of an irreparable destruction of the conditioned reflex in the process of experimental extinction cannot possibly stand for a moment, since in every case of extinction the reflex invariably becomes spontaneously restored in a longer or shorter time.

The question of the difference in the mode of restoration in these two cases probably goes much deeper, involving the intimate nature of the nervous process underlying dis-inhibition. Regarding the nervous mechanism of dis-inhibition we cannot hope at present to approach anything like a fundamental conception, since as yet we know little about the real nature either of the inhibitory process, or of the excitatory process, or of their mutual relations.

I should like, however, specially to direct your attention to one very important feature which repeatedly enforces notice. We have seen that the very same extra stimuli, which, when they evoke strong extraneous reflexes, produce external inhibition of the positive conditioned reflexes, produce, when their effect is weak from the start or weakened by repetition, dis-inhibition of the conditioned reflexes which were made to undergo extinction. Many examples of this will appear in the next lecture. We are now afforded some justification for regarding dis-inhibition, as we did a short while ago, as being the "inhibition of an inhibition. " By this we do not pretend, however, to explain the underlying mechanism of dis-inhibition.

The main conclusion of our discussion of the experimental evidence described in this lecture can be summed up briefly as follows. A stimulus to a positive conditioned reflex can under certain definite conditions readily be transformed into a stimulus for a negative or inhibitory conditioned reflex; this transformation is fairly rapid, smooth and progressive. It becomes obvious therefore that in our further study of the function of the cerebral hemispheres we shall necessarily be dealing not only with positive but also with negative or inhibitory conditioned reflexes.



【重要表現】
tactile 皮膚感覚の
indubitably 議論の余地なく
dispute 論争する
after-effect 余波・後遺症

パブロフと条件反射 講義5


Internal inhibition (continued): (b) Conditioned Inhibition.

内制止の二種類 実験消去
The fourth lecture was devoted entirely to the study of the first type of internal inhibition, which was termed experimental extinction. In extinction the positive conditioned stimulus is temporarily transformed into a negative or inhibitory one by the simple method of repeating it several times in succession without reinforcement.

内制止の二種類 分化消去
In the present lecture we shall consider the second type of internal inhibition, which has also been investigated in some detail.

分化制止の実験の解説
The method of experimentation is as follows. A positive conditioned stimulus is firmly established in a dog by means of the usual repetitions with reinforcement. A new stimulus is now occasionally added, and whenever the combination is applied, which may be at intervals sometimes extending to hours or days, it is never accompanied by the unconditioned stimulus. In this way the combination is gradually rendered ineffective, so that the conditioned stimulus when applied in combination with the additional stimulus loses its positive effect, although when applied singly and with constant reinforcement it retains its full powers.

分化制止
We have been accustomed in our investigations to designate this phenomenon by the name of conditioned inhibition, although this cannot be regarded as especially appropriate since the development of experimental extinction also is subject to equally rigid conditions. The use of this term, in fact, can only be justified by historical consideration. Since we were concerned in this case with the participation of an additional stimulus, the whole phenomenon was confused at first with external inhibition. It was only later when its character of internal, as distinct from external, inhibition became firmly established that the prefix "conditioned" was added. As will be shown further on, this form of inhibition might more appropriately have been termed "differential inhibition."

The process of development of conditioned inhibition presents [p. 69] especial interest. While illustrating the varied complexity of the phenomena involved, it demonstrates at the same time the value of the experimental method as providing a satisfactory means for the analysis of this very complexity into simple general principles. For this reason we shall discuss conditioned inhibition in considerable detail.

分化制止の2つの刺激の時間関係
The first point of importance in the establishment of a conditioned inhibition is its dependence on time relations between the applications of the two stimuli in the inhibitory combination. Conditioned inhibition is developed with comparative ease in all those cases where the duration of the positive stimulus overlaps that of the additional stimulus. In our experiments it is usual to start the additional stimulus a few seconds (generally from 3 to 5) before the positive stimulus, but provided there is an overlap it is immaterial whether the commencement of the additional stimulus precedes, coincides with, or even follows by a few seconds, that of the positive stimulus. If, on the other hand, the additional stimulus is removed as soon as the positive stimulus is applied, so that the two stimuli never coincide, the development of the conditioned inhibition may be a matter of considerable difficulty, and accompanied by restlessness and various defence reactions of the animal.


分化制止は10秒の間隔があると生じない
If, finally, a pause of several seconds is introduced between the termination of the additional stimulus and the beginning of the positive stimulus no inhibition develops at all. On the contrary, in the majority of cases, when this pause reaches a duration of about ten seconds, the additional stimulus itself acquires the properties of a positive stimulus. This has been discussed already as the general method of formation of positive conditioned reflexes of the second order. It is only with exceptionally powerful additional stimuli, such for example as a powerful motor-car hooter, that the pause can be increased to so much as twenty seconds and a conditioned inhibition still be developed. An example from the work of Dr. Frolov will serve to illustrate the latter case :

パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


A motor-car hooter was allowed to act for 10 seconds, when, after a pause of a further 10 seconds, the alimentary conditioned stimulus of the metronome was applied. The first application of the hooter did not in the least diminish the magnitude of the succeeding reflex reaction. When, however, the same combination had been repeated several times in succession, and always without reinforcement, the reflex began gradually to diminish. [p. 70] This diminution persisted even when the pause was lengthened to 20 seconds.

We thus find that the time interval between the two stimuli required to produce either conditioned inhibition, or alternatively a positive conditioned reflex of the second order, varies according to the intensity of the additional stimulus. This contingency of the ultimate significance of the additional stimulus upon the time relations is interesting as evidence of an encounter between the antagonistic processes of excitation and inhibition.

分化制止の大脳での解釈
The following interpretation of the complete difference in the final character assumed by the additional stimulus under so slight a difference in the experimental conditions seems best to agree with the experimental results : When the additional stimulus or its fresh trace loft in the hemispheres coincides with the action of the positive stimulus, there must result some sort of special physiological fusion of the effect of the stimuli into one compound excitation partly differing from and partly resembling the positive one. It will be shown in the seventh lecture, that in response to closely related stimuli, such as neighbouring tones or tactile stimulation of adjacent [p. 71] places of the skin, the same events take place as in the development of conditioned inhibition. If one stimulus with the help of the usual procedure is given positive conditioned properties, the neighbouring stimuli belonging to the group also give at first a positive conditioned reaction, whereas later, on their systematic repetition without reinforcement, they lose their excitatory properties and acquire inhibitory properties instead. This result corresponds exactly with the successful development of conditioned inhibition in the experiment mentioned at the beginning of this lecture. When, however, the additional stimulus is separated from the application of the positive conditioned stimulus by a longer interval, the union in the hemispheres into a single compound excitation does not materialize; instead, the stimuli act upon the hemispheres as two distinctly separate events, and the additional stimulus acquires new properties as a positive conditioned stimulus of the second order. The older conditioned stimulus acts in this case in exactly the same capacity as an unconditioned stimulus in the usual method of establishing conditioned reflexes of the first order. A strong stimulus has a prolonged after-effect; it is, therefore, still capable of being fused by the hemispheres with the conditioned stimulus into a special new compound even after a long interval of time. It is easy to understand from this point of view that in the establishment of conditioned inhibition the interval which can be made between the end of the additional stimulus and the beginning of the positive conditioned stimulus must depend directly upon the strength of the additional stimulus. Whether our interpretation be the correct one or not, the phenomena are encouraging to the experimenter in that in every case he can discern a remarkable regularity in these very complex activities of the cortex.

In addition to the usual results obtained as described above, mention must be made of certain very rare phenomena obtained with some apparently normal animals and with animals in which surgical interference with the hemispheres had produced a condition of obviously increased excitability of the nervous system. In these cases even perfectly synchronous applications of the additional and of the positive conditioned stimuli led not to conditioned inhibition but to the development of a definite positive conditioned reflex of the second order. This generally persisted for a very long time, but later it often happened that the secondary conditioned reflex and also conditioned inhibition were both present simultaneously. [p. 72]

Such a case is represented in the following experiment of Dr. Kasherininova :

Tactile stimulation of the skin was used in this dog as the conditioned stimulus for the defence reflex to acid, and a metronome served for the additional stimulus in an inhibitory combination which, of course, was never reinforced. The twenty-fifth application of the inhibitory combination evoked a secretion of only 3 drops of saliva during one minute, whereas the conditioned stimulus applied singly evoked a secretion of 29 drops during one minute. After thirty-four repetitions of the inhibitory combination the stimulus of the metronome applied singly elicited a salivary secretion of 8 drops, although prior to its participation in the inhibitory combination it had no excitatory effect whatsoever. It is clear, therefore, that the metronome coupled with the tactile stimulus exerted a strong inhibitory influence, but it acquired at the same time some of the excitatory properties of the tactile stimulus, so that when used alone it behaved as a conditioned stimulus of the second order. Though cases such as that just described have been observed but rarely, it is quite possible that a transitory acquisition of weak excitatory properties of the second order is of no infrequent occurrence in the development of conditioned inhibition.

分化制止の細かな差異
The course of development of conditioned inhibition is not always the same. In some cases the first addition of a new stimulus to the positive conditioned stimulus immediately results in a diminution, or even in a complete disappearance, of the conditioned reflex. With successive repetitions of the combination the reflex comes back nearly to its original level and then again falls slowly to zero. In other cases the first few combinations result in an augmentation of the reflex as compared with the normal isolated action of the conditioned stimulus, and only subsequently does the reflex gradually diminish to zero. In yet a third group it is found that an initial diminution in the strength of the reflex is followed by a phase of augmentation above normal and then again the reflex slowly falls to a permanent zero.

分化制止には刺激の強度が影響する
All these different phases which are observed during the establishment of the conditioned inhibition depend entirely upon the intensity of the extraneous reflex which is evoked in the animal by the additional stimulus. The initial diminution of the reflex which occurs in one group during the fist few applications of the combination is due undoubtedly to external inhibition. When the additional stimulus applied singly evokes in the dog a [p.73] strong investigatory reflex it is found that its addition to the positive conditioned stimulus exerts an inhibitory influence from the very start. When on the other hand the stimulus evokes only a mild investigatory reflex, the preliminary phase of diminution of the reflex is absent and the first applications of the combination produce an increase in the reflex. This increase is undoubtedly due to dis-inhibition, since -- as we may state now in anticipation of a future discussion -- the positive effect of the majority of conditioned stimuli in our experimental reflexes is almost invariably preceded by a phase of internal inhibition. The inhibitory process is removed by the investigatory reflex, provided that the latter is not sufficiently strong also to influence the excitatory component of the conditioned reflex. The third group of cases, in which the initial diminution in strength of the reflex is followed by an increase above normal, depends on the gradual weakening through repetition of the extraneous reflex produced by the additional stimulus. The external inhibition brought about by the investigatory reaction is at first strong enough to inhibit the conditioned reflex, but, on weakening, produces only dis-inhibition and so increases the strength of the reflex response. Several examples of this will be given at the end of the present lecture.

どのような種類の刺激も用いられるはずだ
It is obvious that any agent in nature may be used as a stimulus for the development of a conditioned inhibition, supposing of course that the organism is provided with the requisite organs for the perception of such an agent. The records of actual experiments will afford numerous illustrations of the different types of stimuli employed.

遅延した場合の制止
As was mentioned before, not only the actual stimulus but also its trace in the hemispheres can be used for the development of conditioned inhibition. The trace must, however, in all cases be as recent as possible. The establishment of conditioned inhibition when the interval between the stimuli is more prolonged can be brought about only by the use of exceptionally strong additional stimuli. Once, however, the inhibitory combination has been firmly established the pause between the end of the additional stimulus and the beginning of the positive conditioned stimulus may be extended even to so much as one minute without the inhibitory effect of the combination being impaired.

内制止としての時間
Some experiments have been made in which the time interval was itself employed as a stimulus for internal inhibition. [p. 74]

The following experiment by Dr. Krjyshkovski illustrates such cases:
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


A definite tone served as a positive conditioned stimulus to acid, while a tactile stimulation of the skin served for the additional stimulus in the inhibitory combination. The inhibitory combination in this dog had been habitually applied for some other special purpose at the 19th-20th minute after the last introduction of acid. This led to the result that at the 19th-20th minute only a minimal salivary secretion was produced by the action of the positive conditioned stimulus when it was applied singly.


In these experiments the interval of 19 to 20 minutes had itself acquired sufficient inhibitory properties to abolish or greatly reduce the effect of the conditioned stimulus.

制止と回数
The rate of development of conditioned inhibition as well as its completeness (absolute or relative inhibition) also depends upon a number of conditions. Of first importance in this connection is the individuality of the animal, the excitable or inhabitable character of its nervous organization. In some dogs the establishment of a conditioned inhibition takes a long time and never becomes absolute; in other dogs an inhibition becomes completely and firmly established after very few repetitions of the inhibitory combination.

制止と刺激強度
A further important factor is the intensity of the additional stimulus employed in the inhibitory combination. For example, in an experiment by Dr. Mishtovt, a metronome was used for a positive conditioned stimulus to acid, while a thermal stimulation of the skin was employed as the additional stimulus. It was found that with the thermal stimulus at a temperature of 4 to 5° C. the first indication of a conditioned inhibition could be observed only after the 30th application of the inhibitory combination, and the inhibition was not yet complete even after 145 applications. With the use, however, of a thermal stimulus at a temperature of 1° C., in an ex-[p.75]periment performed on the same animal after an interval of four months, only twelve repetitions of the inhibitory combination were required to establish complete inhibition.

制止と刺激の組合せ
The rate of formation of conditioned inhibition depends, again, on the character and the relative intensity of the additional stimulus in comparison with the conditioned stimulus. In some dogs it was found impossible to establish complete inhibition by the addition of a thermal stimulus at 45° C., when the sound of a metronome served as the positive conditioned stimulus. When, however, a visual stimulus was employed as the positive conditioned stimulus in a similar combination, a conditioned inhibition could be readily produced [experiment by Dr. Poursikov].

制止と初回条件付
Finally, it should be mentioned that, although other factors may remain constant, the first establishment of a conditioned inhibition in a dog takes more time than any succeeding one.

I have not up to the present given any conclusive evidence that the phenomenon of conditioned inhibition is really in the nature of an inhibition at all, and is not merely a passive disappearance of the positive conditioned reflex owing to the compound stimulus remaining habitually unreinforced. The proof that the phenomenon actually does represent a real inhibition will be gradually brought out as we proceed with our study of the experimental evidence.

制止する刺激の組合せ
It will be of interest, first of all, to study the nature and ultimate function of the additional stimulus on which conditioned inhibition depends. This can, of course, be determined only by trying out the action of the additional stimulus in different modifications of the experiment: Tested singly after the conditioned inhibition has been fully established it produces no positive effect at all. The action of the additional stimulus can be tested, however, by applying it in combination with some other positive conditioned stimulus with which it has never previously been associated. In such a case the inhibitory properties of the additional stimulus become clearly revealed, the result being an immediate diminution in the positive reflex response. This is true not only in the case of homogeneous reflexes, but also in the case of heterogeneous reflexes, and the inhibitory effect may extend even to the unconditioned reflexes themselves. These facts are clearly exhibited in the following experiment by Dr. Leporsky:

Three alimentary Conditioned reflexes have been established in the dog used for this experiment, the three stimuli being the flash [p. 76] of a lamp, a rotating object, and the tone C sharp of a pneumatic tuning fork. Two independent conditioned inhibitions of the reflex to rotation have also been firmly established, one by the use of tactile stimulation of the skin and the other by the use of a metronome.

In the first experiment the flash of the lamp is for the first time accompanied by a tactile stimulation of the skin:
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


In the second experiment the tone C sharp is for the first time accompanied by the metronome.
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


It will be seen that the additional stimulus when applied for the first time in the new combination produced a diminution almost to zero in the conditioned reflex response. It follows, therefore, that when an additional stimulus is used with an alien homogeneous conditioned reflex its inhibitory property becomes thereby immediately revealed. This same property is seen also when the additional [p. 77] stimulus is combined for the first time with a heterogeneous conditioned reflex, a case which is illustrated in the following experiment:

A dog has a conditioned alimentary reflex which has been established by the use of the metronome, while the addition of a whistle provides a powerful inhibitory combination. Besides this a conditioned reflex to acid has been established in response to tactile stimulation of the skin. The metronome and the tactile stimuli belong therefore to heterogeneous conditioned reflexes, and the positive effect of one of them (i.e. the metronome) is completely inhibited by the sound of the whistle. The whistle is now for the first time combined with the heterogeneous tactile conditioned stimulus [experiment by Dr. Babkin].
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


In all the foregoing experiments it had, of course, to be shown before any particular additional stimulus was used in combination with an alien positive conditioned stimulus that it would not exercise any effect of external inhibition. With this precaution it seems to me that the experiments justify our conclusion that where a conditioned inhibition has been firmly established the additional stimulus itself acquires inhibitory properties which can be manifested outside the parent combination. The additional stimulus is therefore termed in our investigations the conditioned inhibitor.

It is made clear by further experiments that a real inhibitory effect is also produced by the inhibitory combination itself, the inhibitory process persisting as an after-effect which may be detected some considerable time after the stimulus of the inhibitory combination itself has been removed. The inhibitory after-effect exerts its influence not only upon the particular reflex to the conditioned stimulus employed in the combination, but also upon all other conditioned reflexes whether homogeneous or heterogeneous. In this connection we may consider the following experiments: [p. 78]

In the first experiment a rotating object serves as an alimentary conditioned stimulus, and a tone of 30,000 vibrations produced by a Galton's whistle as its conditioned inhibitor [experiment by Dr. Nikolaev].
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


After withdrawal of the stimulation by the inhibitory combination the effect of the positive conditioned stimulus is weakened for several minutes, and only regains its normal strength by degrees.

In the next experiment a rotating object serves as a conditioned stimulus for the defence reflex to acid, and a musical tone serves as a conditioned alimentary stimulus. A tactile stimulus is used as a conditioned inhibitor for the alimentary reflex. [Experiment by Dr. Ponisovsky.]
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


This experiment demonstrates that the heterogeneous conditioned reflex also becomes diminished as a result of the inhibitory after-effect of the combination.

When the inhibitor is applied by itself alone, and not together with the excitatory stimulus in combination with which it was originally developed, it can also be demonstrated to produce an inhibitory after-effect. [p. 79]

制止と刺激強度
The degree to which positive conditioned reflexes are influenced by the conditioned inhibitor varies inversely as their relative physiological strength. An experiment may be taken from a paper by Dr. Leporsky in illustration of this point :

Three independent conditioned alimentary reflexes have been firmly established to a rotating object, to the flash of several electric lamps, and to a musical tone. A tactile stimulation of the skin has been established as a conditioned inhibitor for each of the three reflexes, so that in combination with any one of them separately it reduces the reflex to zero. All three positive stimuli applied together produce a much greater salivary secretion than any one of them applied singly, showing summation of conditioned reflexes. The experiment shows the effect of the application of the conditioned inhibitor in conjunction with the simultaneous action of all three positive stimuli.
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


制止と同時刺激
The conditioned inhibitor, therefore, although it reduced to zero every one of the positive conditioned reflexes taken singly, could only partially inhibit the reflex secretion evoked by all three acting simultaneously (2.27 p.m.).

制止の後遺症
Two further details concerning the inhibitory after-effect remain to be considered. The first is the phenomenon of summation of after-effect. If the inhibitory combination is applied not once only, but several times in succession, so much the more will the strength and duration of the inhibitory after-effect be increased. Two experiments of Dr. Chebotareva, carried out on successive days, serve to illustrate the case in point:

A metronome serves as a conditioned alimentary stimulus, and a rotating object as its conditioned inhibitor. [p. 80]
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


In the first experiment it is seen that the conditioned reflex, which, to start with, was of considerable strength, when tested by a fresh application of the positive conditioned stimulus 1 1/2 minutes after the cessation of a single application of the inhibitory combination (3.52 p.m.), is diminished by half (i.e. from 6 drops to 3). In the second experiment, taking place on the following day, the reflex, when tested 5 1/2 minutes after the second of two successive applications of the inhibitory combination (1.25 p.m.), is diminished by
three-quarters (i.e. from 8 drops to 2).

The second important detail concerning the inhibitory after-effect is that its duration becomes shorter as the experiments proceed from day to day. It may extend in the earlier experiments for something over an hour, but in the course of succeeding experiments gradually becomes reduced to only a few minutes or seconds. The following two experiments of Dr. Nikolaev which were performed, with an interval of over 6 months' continuous experimentation, provide an illustration of the case in question:

A rotating object provides the stimulus to a conditioned alimentary reflex, while a given tone serves as its conditioned inhibitor. In the first experiment the inhibitory after-effect was obvious for over 20 minutes; six months later, after continual practice, it was absent so soon as 3 1/2 minutes after the single application of the inhibitory combination.
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


制止の破壊はできるか
The problem of experimental destruction of the inhibitory properties of the conditioned inhibitor applied singly or in its inhibitory combination is very complex and has not yet been fully worked out. I shall mention, therefore, only some of the better established facts. It is obvious that a complete abolition of the inhibitory properties of the combination should most readily be brought about by reversing the technique employed in its formation -- i.e. by systematically reinforcing the inhibitory combination by the appropriate
unconditioned reflex. An experiment by Dr. Krjishkovski will illustrate this process:

A given tone of a pneumatic tuning fork provides a conditioned stimulus to acid, while a tactile stimulation of the skin serves as the conditioned inhibitor.
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


[p. 82]

It is interesting to note that if alternately with every application of the reinforced inhibitory combinations we repeat the reinforced positive conditioned stimulus, a very considerable retardation in the
progress of destruction of the inhibition is produced. This matter will be subjected to rigorous experimental analysis further on (Lecture XI).

Quite distinct from the above process of gradual weakening of the inhibitory combination is the case in which the disturbance appears suddenly and as suddenly disappears. Extra stimuli belonging to the group of mild external inhibitors, as we may term them, influencing the animal during the action of the inhibitory combination instantaneously restore to something of its normal value the positive conditioned reflex which underwent conditioned inhibition. It is evident that external inhibition has brought about the removal of conditioned inhibition, and that we deal again with the phenomenon of dis-inhibition. These relations may be illustrated by the following experiments of Dr. Nikolaev:
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


[p. 83]

The stimulus to a conditioned alimentary reflex is provided by a rotating object, while a given tone serves as its conditioned inhibitor. Tactile and thermal stimulations of the skin and the sounds of a metronome serve as different extra stimuli.

The above three experiments show that during the time when the extra stimuli (metronome, tactile, or thermal) were acting upon the animal the conditioned inhibition was partially removed, revealing the underlying excitation.

In connection with these observations considerable interest is attached to the following experiment on the same dog, in which it was the intention to introduce an odour as still another dis-inhibiting agent. For this purpose the dog was transferred into another room fitted with a special box for graduating the intensity of odours. The apparatus itself, in addition to its visual effect and the sound of its electric motor, acted upon the animal by blowing a continuous current of air. All these agencies introduced a whole complex of new extra stimuli into the experiment, even without the addition of the odour. The new complex of extra stimuli dis-inhibited the inhibitory combination, but this effect gradually declined as time went on, disappearing completely in an hour and a half after the experiment was started. The following experiment was performed on the day following the last experiment.
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


[p. 84]

The first application of the camphor dis-inhibited the combination, while on the second application this extra stimulus had already lost its dis-inhibiting effect. This rapid disappearance of the effect of the extra stimuli introduced by the new apparatus, and again by the use of the camphor, is the most usual case with extra stimuli which bring about dis-inhibition. The dog employed in this particular experiment was an old laboratory animal and had previously been subjected to numerous extraneous agencies, so that different changes produced now only a transient effect, the animal speedily becoming indifferent to them. This is why the introduction of new conditions into this experiment produced a dis-inhibition right from the very start and never any inhibition of tho positive conditioned reflexes.

Results were quite different in the case of another dog used by Dr. Nikolaev. This dog was fresh to the laboratory and may have possessed also a type of nervous organization which was more easily subjected to inhibition. In this dog a rotating object was used for a conditioned alimentary stimulus, and a tone for its conditioned inhibitor. A metronome provided the extra stimulus.
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


The experiment on the following day gave similar results. On the 18th February, at the beginning of the next experiment, the metronome was applied alone during one minute, the subsequent course of the experiment being shown on the opposite page.

In the experiment of 15th February the sound of the metronome, which served as an extra stimulus, did not produce during its first application the result which would be expected from dis-inhibition (11.41 a.m.). But the very same stimulus of the metronome when [p. 85] applied along with the positive conditioned stimulus used singly produced a complete inhibition (12.14 p.m.). It follows, therefore, that the zero value of the reflex in the first case -- inhibitory combination + metronome -- was not really due to the internal inhibition remaining undisturbed but was due to external inhibition resulting from a very powerful extraneous reflex in response to the first application of the metronome. As a result of several repetitions of the stimulus of the metronome with the inhibitory combination on the 16th February and an application at the beginning of the experiment of 18th February, the stimulus of the metronome was no longer able to produce so powerful an alien reflex and therefore its inhibitory effect upon the positive conditioned component had practically disappeared (12.27 p.m.). However, its dis-inhibitory effect was still retained and could be well seen in the experiment of 18th February (11.32 a.m. and 12.9 p.m.).
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


The terminology used in the interpretation of the foregoing phenomena may seem to be artificial and arbitrary, but it is not possible at a time: when the intimate mechanism is still beyond our powers of analysis to avoid such terms in what is necessarily a schematic representation of the complex nervous processes involved. Our terms serve to describe only the actual state and succession of events.

A dis-inhibition of the inhibitory combination can further be obtained by means of those stimuli which determine a permanent external inhibition (p. 46). The following experiment by Dr. Nikolaev bears out this statement: [p. 85]

A rotating object serves for the conditioned alimentary stimulus, while a tone serves for its conditioned inhibitor.
パブロフと条件反射 講義5 実験

パブロフと条件反射 講義5 実験


In this case the inhibitory after-effect of sodium carbonate, given 4 minutes before, caused a definite dis-inhibition of the reflex (2.44 p.m.).

If an inhibitory combination is applied early within the time of the after-effect left by a very strong extra stimulus, for example a concentrated solution of quinine, no dis-inhibition is obtained. This corresponds exactly with the case of the metronome in the experiment on page 84. However, the dis-inhibiting effect of quinine can be exhibited as clearly as in the case of the metronome, simply by throwing in the inhibitory combination at a later stage, when the strength of the after-effect of the action of the quinine has had time to diminish. On account of the complete accord of the two sets of experiments the description of the experiments with quinine need not be given.

共通の性質
All the experimental evidence which has been dealt with in this lecture establishes conclusively that the nervous processes on which conditioned inhibition depends are identical in character with those of extinctive inhibition. The fundamental condition for their development is the same, namely that there shall be no reinforcement by the unconditioned reflex. In both cases the process develops gradually, being strengthened by repetition. Moreover, the inhibitory after-effect does not limit itself to the particular positive conditioned reflex which undergoes experimental extinction or conditioned inhibition, but in both cases extends to other conditioned reflexes as well, including even those which are of heterogeneous origin. [p. 87]

The final point of resemblance is that in both cases the inhibitory process can be rapidly though temporarily removed, the inhibited reflexes undergoing dis-inhibition on account of external inhibition resulting from alien reflexes to extra stimuli of small intensity. The only point of difference is that in extinctive inhibition it is the positive conditioned stimulus taken by itself which changes its positive significance to an inhibitory one, while in the case of conditioned inhibition the positive conditioned stimulus becomes involved in a new complex and changes its character in conjunction with an additional stimulus.



【重要表現】
pneumatic 空気圧

パブロフと条件反射 用例


[p. 100]:原著のp100ページ


(p. 200):参照例がp200ページにあり


[sic] :原文そのまま  原文の表記に異和感があってもこの表記で正しいという確認のための記号です。ラテン語のsic erat scriptumの省略形です。参考 文法辞典

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