Conditioned Reflexes: An Investigation of the Physiological Activity of the Cerebral Cortex

Reprinted photographically in Great Britain in 1928, 1940, 1946, by LOWE & BRYDONE, PRINTERS, LTD., LONDON, from sheets of the first edition Director of Physiological Laboratories in the Russian Academy of Sciences and the Institute of Experimental Medicine, formerly Professor of Physiology at the Military Medical Academy, Petrograd G. V. ANREP, M.D., D.Sc & Lecturer in Physiology in the University rite The Carl F. Shen Monori Library BLLINOIS ny Noa OF OPTOMETRY lichigan Avenue

ProFeEssor Pavrov in his preface to this English edition regards it as lucky for his book that the task of pre- paration fell into my hands; but I consider that the luck was mine, because it was the best way I had of showing my personal regard for my old teacher. Although I had personal contact with the work, the task was not easy, especially on account of the extreme importance of this new field of investigation, not only for physiology itself, but also for all the biological sciences.

Since the present is the first complete discussion rendered out of the Russian into one of the more familiar European tongues, technical terms had to be devised which should in some measure impayé\that fluency to the discussion which one finds in ‘bein text. A terminology has therefore been ad which, after having received the advantage o, <r consider- ation and advice from my friends colleagues at University College, London, I j to answer the purpose sufficiently well.

Professor Pavlov allowed or the sake of clarity, to introduce some modificgfions and additions into the text in order to mak reading lighter for those English and Amerig” readers unfamiliar with the original literatuse @)*this field. This I have done sparingly, patil, Jareful only to expand, but in no sense to weeps original meaning. The pi€Pfration of the English edition was helped by a from the Royal Society, which was sufficient to cover the draft translation of Lectures I-XII; but at: this stage, owing to the difficulty of finding really suitable translators, and desiring not to burden the Royal Society unduly with further costs of translation, I resolved to undertake the revision of the draft trans- lation and the complete translation of the remaining lectures myself. This, with the willing help of Mr. R. A. Nash, a research student in my laboratory, I was able to accomplish. I desire to thank him, and also to express my grateful thanks to my friend Mr. E. L. Ball, who critically read the whole of our manuscript in both

I am deeply sensible of my good fortune that this book should appear in the English language through the assistance of the Royal Society of London. Without their material help the presentation of the book in its English form could not in the first place have been attempted. I desire to express to them my deepest gratitude. I count it a great stroke of luck for the book that the preparation of the English edition was carried out entirely under the supervision of, and in part made by, my young friend Dr. Anrep, formerly an active collaborator in the work described in its pages. Dr. Anrep’s task has not been an easy one, and it has been fraught with responsibility, as practically at every step he has had to adapt a vast new terminology. yin

In the spring of 1924, in a series of lectures delivered at the Military Medical Academy in Petrograd to an audience of medical men and biologists, I attempted to give a full and systematized exposition of our researches upon the activities of the cerebral hemispheres in the dog—researches which had then been in progress for nearly twenty-five years. These lectures were taken down by a steno- grapher with a view to subsequent publication. On looking through the manuscript I found the lectures not entirely satisfactory, and began, therefore, to recast them. This occupied over eighteen months of my leisure, during the whole of which period investigation was being vigorously pushed forward in the laboratories under my direction. As a result of this continued experimentation some of the deductions and interpretations drawn in my lectures had to be considerably modified. However, in the book as it stands at present I intentionally allowed the chapters to remain as they hands at the first revision, incorporating in the later le he new material as it came to hand. In this manner t der is placed in a position to obtain a much clearer idea o natural growth of the subject.

In the lectures I have. restricted Qosition to the purely experimental material, avoiding all r AA to the literature of the subject. A complete treatment of ng fioro would have increased the labour of my task excessively, Méreover, my intention was the simple one of treating the subj Qi an entity from my own personal viewpoint. I am fully aw t not a few of our observations have been in the nature NO confirmation of facts established by other authors. The Kon of priority has been considered of relatively small noooit) since I am fully convinced that the subject lends a sufficient @epe for the full development of initiative of all workers intere in solving its problems. At the same time we are convine at this method of research is destined, in the hands

of other workers, and with new modifications in the mode of experi- mentation, to play a yet more considerable part in the study of the physiology of the nervous system. I have to express my warmest thanks to all my fellow-workers who joined their labour with mine in our common task. If I insti- gated, directed and correlated all our labour, I was myself continually influenced by the vigilance and the resourcefulness of my co-workers. In all cases of team work where there is a continuous interplay of many minds, it is scarcely possible to draw any definite line, saying what belongs to one and what to another. Each, however, has the satisfaction and joy of having borne his part in the common structure.

VII.—THE ANALYSING AND Ea D Ma N, ACTIVITY OF THE CEREBRAL HEMIS ES: (a) THE INITIAL GENERALIZATION OF DITIONED STIMULI. (b) DIFFERENTIAL Ne N - ` 5 = : EXAMPL THE ANALYSIS OF STIMULI. (d) Syari O AND ANALYSIS OF COMPOUND SIMUL- TANE STIMULI. (e) SYNTHESIS AND ANALYSIS Kee SUCCESSIVE STIMULI - - - PROCESSES IN THE CEREBRAL HEMISPHERES (con- tinued) : (b) IRRADIATION AND CONCENTRATION OF INHIBITION OVER THE ENTIRE CORTEX ; (c) [RRA- XITI.—THE CORTEX AS A MOSAIC OF FUNCTIONS: (a) THIS CHARACTER IS ACQUIRED ; (b) VARIABILITY

XVIII.—PatTHOLO ee OF THE CORTEX, RESULT OF HONQHONAL INTERFERENCE (continued) - - RESULT OF SURGICAL INTERFERENCE (continued) : (c) IN THE VISUAL ANALYSER ; (d) IN THE TACTILE CUTANEOUS ANALYSER; (e) OCCURRING AFTER EXTIRPATION OF THE FRONTAL LOBES; (f) IN THE THERMAL CUTANEOUS ANALYSER; (g) ARIS- FORMIS ; (h) IN THE MOTOR ANALYSER - - 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.

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! and others?], the animal becomes not only i able of performing these duties but also incapable even of ing after itself. It becomes in fact a helpless invalid, and ca ng survive unless it be carefully tended. A ;

In man also the highest nervous activity id {pendent upon the structural and functional integrity of ebral hemispheres. As soon as these structures become d'and their functions impaired in any way, so man also na an invalid. He can no longer proceed with his normal dytție but: has to be kept out of the working world of his fellow In astounding contrast „wi he unbounded activity of the cerebral hemispheres stan e meagre content of present-day - physiological TS, erning them. Up to the year 1870,

in fact, there was no physiology of the hemispheres ; they seemed to be out of reach of the physiologist. Inthat year the common physio- logical methods of stimulation and extirpation were first applied to them [Fritsch and Hitzig 1]. 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,? H. Munk °] 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 hemis- pheres, was not touched in any of these investi ns and formed no part of the current physiological knowledg xS

When therefore we ask the questionsaWhat do those facts which have up to the present been at tego of the physiologist explain with regard to the behaviour AA higher animals ? What general scheme of the highest n activity can they give ? or what general rules governing this ity can they help us to formu- late ?—the modern ysikag a himself at a loss and can give no satisfactory reply. The\groblem of the mechanism of this complex structure whicl iC rich in function has got hidden away in a corner, and thig nitea field, so fertile in possibilities for research, has neve adequately explored.

1 Fritsch und Eş itzig, “ Ueber die elektrische Erregbarkeit des Gross- hirns.” Archw Anatomie und) Physiologie, p. 300, 1870. tD: FetgD Functions of the Brain, London, 1876. NS Ueber die Functionen der Grosshirnrinde, Berlin, 1890 and 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.

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 but I will stay to give one fact which strikes me v that even the advocates of psychology do not loo as being in any sense exact. The eminent William James, has in recent years referr triking illustration is provided by Wundt, the celebrated sopher and psychologist, founder of the so-called experime ethod in psychology and himself formerly a physiologist. before the War (1913), on the occasion of a discussion in G s to the advisability of making separate Chairs of Philos and Psychology, Wundt opposed the separation, one of hj ments being the impossibility of fixing a common examination dule in psychology, since every professor had his own special Sas as to what psychology really was. Such testimony seems © ow clearly that psychology cannot yet claim the status of act science.

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,! continuing the classical investi- gations of Sherrington? 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 Bens © t its application has stopped short of the cerebral cortex.

It may be hoped that some of the m Chaple activities of the body, which are made up by a groupi ether of the elementary locomotor activities, and which ente the states referred to in so forth, will soon be demonsgra as reflex activities of the sub- cortical parts of the brain. eo attempt to apply the idea of the reflex to the activiti the hemispheres was made by the Russian physiologist, I, echenov, on the basis of the knowledge available in his da hysiology of the central nervous system. In a pamphlet ed “Reflexes of the Brain,” published in

Russian in 1 attempted to represent the activities of the cerebral hemiSpMeres as reflex—that is to say, as determined. errington, The Integrative Action of the Nervous System, London, 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,! who introduced the concep- tion 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 ;? to the introduction of a new objective terminology to describe animal reactions [ Beer, Bethé cng AE and finally, it led to the investigation by zoologists, Qty g purely objective methods, of the behaviour of the lower, bers of the animal kingdom in response to external pie for example in the classical researches of Jennings.4 ®

Under the influence of these new Ln PR in biology, which appealed to the practical bent of the A@ertean mind, the American School of Psychologists—already i ted in the comparative study of psychology—evinced a co Ta to subject the highest nervous activities of animals to S imental analysis under various 1 Ch. Richet, Réflexes Ps ’ . Réflexes Conditionels. Automatisme Mental. Pavlov’s Jubilee Vo Petrograd, 1925. * Beer, Bethe und Ugxktl, “ Vorschläge zu einer objectivirenden Nomen-

klatur in der ow e des Nervensystems,” Biologisches Centralblaitt, V. xix. p. 517, 189 *H. S. Jennjtigs) The Behavior of Lower Organisms, New York, 1906. specially devised conditions. We may fairly regard the treatise by Thorndyke, The Animal Intelligence (1898),1 as the starting point for systematic investigations of this kind. In these investi- gations 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.

At about the same time as Thorndyke 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 circum- stance : 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 con- junction 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 ga\gn experimental investigation by strictly objective methods. r*this purpose I started to record all the external stimuli g on the animal at the time its reflex reaction was manifes in this particular case the secretion of saliva), at the same recording all changes in

on now for twenty-five yea ears in which numerous fellow- workers on whom I now look sack with tender affection have united the reaction of the animal. Q This was the beginning of = estigations, which have gone with mine in this work hearts and hands. We have of course passed through man es, and only gradually has the subject been opened up a difficulties overcome., At first only a few scattered fact available, but to-day sufficient material has been gathered ether to warrant an attempt to present it in a

more or aCA es a form. At the present time I am in a 75; Orme The Animal Intelligence, An Experimental Study of the 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 col- laborators have taken part. 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 psycho- logical—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. RY

I shall now turn to the description of our materi SS. giving as a preliminary an account of the general concepti f the reflex, of specific physiological reflexes, and of the so d “instincts.” Our starting point. has been Descartes’ idea 2 nervous reflex. This is a genuine scientific conception, £1 it implies necessity. It may be summed up as follows e al or internal stimulus falls on some one or other a and gives rise to a nervous impulse ; this nervous i Q is transmitted along nerve fibres to the central nervous sys and here, on account of existing nervous connections, it give to a fresh impulse which passes along outgoing nerve fibré he active organ, where it excites a special activity of the ar structures. Thus a stimulus appears to be connected of netgsgity with a definite response, as cause with effect. It seems dmious that the whole activity of the organism should conform efinite laws. If the animal were not in exact correspondengeNwith its environment it would, sooner or later,

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 animal threw itself into the fire, then it would quickly perish. The animal must respond to changes in the en- vironment 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.