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| ISBN-13: | 9780486161211 |
|---|---|
| Publisher: | Dover Publications |
| Publication date: | 04/30/2012 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 448 |
| File size: | 11 MB |
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CONDITIONED REFLEXES
An investigation of the physiological activity of the cerebal cortex
By Ivan Petrovich Pavlov, G.V Anrep
Dover Publications, Inc.
Copyright © 2003 Dover Publications, Inc.All rights reserved.
ISBN: 978-0-486-16121-1
CHAPTER 1
LECTURE I
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 incapable of performing these duties but also incapable even of looking after itself. It becomes in fact a helpless invalid, and cannot long survive unless it be carefully tended.
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,
1
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]. 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 hemispheres, was not touched in any of these investigations and formed no part of the current physiological knowledge.
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.
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 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.
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 investigations 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 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. 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 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; to the introduction of a new objective terminology to describe animal reactions [Beer, Bethe and Uexküll]; and finally, it led to the investigation by zoologists, using purely objective methods, of the behaviour of the lower members of the animal kingdom in response to external stimuli—as for example in the classical researches of Jennings.
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 specially devised conditions. We may fairly regard the treatise by Thorndyke, The Animal Intelligence (1898), 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.
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 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.
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 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. 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.
(Continues...)
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Table of Contents
I. THE DEVLOPMENT OF THE OBJECTIVE METHOD IN INVESTIGATING THE PHYSIOLOGICAL ACTIVITIES OF THE CEREBRAL HEMISPHERESCONCEPT OF REFLEX.
VARIETY OF REFLEXES
"SIGNAL-REFLEXES, THE MOST FUNDAMENTAL PHYSIOLOGICAL CHARACTERISTIC OF THE HEMISPHERES"
II. 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
III. 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
IV. INTERNAL INHIBITION OF CONDITIONED REFLEXES :
(a) EXTINCTION
V. INTERNAL INHIBITION (continued):
(b) CONDITIONED INHIBITION
VI. INTERNAL INHIBITION (continued):
(c) DELAY
VII. THE ANALYSING AND SYNTHESIZING ACTIVITY OF THE CEREBRAL HEMISPHERES :
(a) THE INITIAL GENERALIZATION OF CONDITIONED STIMULI
(b) DIFFERENTIAL INHIBITION
VIII. THE ANALYSING AND SYNTHESIZING ACTIVITY OF THE CEREBRAL HEMISPHERES (continued) :
(c) EXAMPLES OF THE ANALYSIS OF STIMULI
(d) SYNTHESIS AND ANALYSIS OF COMPOUND SIMULTANEOUS STIMULI
(e) SYNTHESIS AND ANALYSIS OF COMPOUND SUCCESSIVE STIMULI
IX. THE IRRADIATION AND CONCENTRATION OF NERVOUS PROCESSES IN THE CEREBRAL CORTEX :
(a) THE IRRADIATION AND CONCENTRATION OF INHIBITION WITHIN A SINGLE ANALYSER
X. IRRADIATION AND CONCENTRATION OF NERVOUS PROCESSES IN THE CEREBRAL HEMISPHERES (continued)
(b) IRRADIATION AND CONCENTRATION OF INHIBITION OVER THE ENTIRE CORTEX
(c) IRRADIATION AND CONCENTRATION OF EXCITATION
XI. MUTUAL INDUCTION OF EXCITATION AND INHIBITION :
(a) POSITIVE INDUCTION
(b) NEGATIVE INDUCTION
XII. INTERACTION OF IRRADIATION AND CONCENTRATION WITH INDUCTION
XIII. THE CORTEX AS A MOSAIC OF FUNCTIONS :
(a) EXAMPLES OF THE MOSAIC CHARACTER OF THE CORTEX AND THE MORE OBVIOUS WAYS IN WHICH THIS CHARACTER IS ACQUIRED
(b) "VARIABILITY OF THE PHYSIOLOGICAL PROPERTIES OF DIFFERENT POINTS OF THE CORTEX IN SOME INSTANCES, STABILITY IN OTHERS"
THE CORTEX AS A UNITED COMPLEX DYNAMIC SYSTEM
XIV. THE DEVELOPMENT OF INHIBITION IN THE CORTEX UNDER THE INFLUENCE OF CONDITIONED STIMULI
XV. INTERNAL INHIBITION AND SLEEP AS ONE AND THE SAME PROCESS WITH REGARD TO THEIR INTIMATE MECHANISM
XVI. TRANSITION STAGES BETWEEN THE ALERT STATE AND COMPLETE SLEEP : HYPNOTIC STAGES
XVII. THE DIFFERENT TYPES OF NERVOUS SYSTEM
"PATHOLOGICAL DISTURBANCES OF THE CORTEX, RESULT OF FUNCTIONAL INTERFERENCE"
XVIII "PATHOLOGICAL DISTURBANCES OF THE CORTEX, RESULT OF FUNCTIONAL INTERFERENCE (continued)"
XIX. "PATHOLOGICAL DISTURBANCES OF THE CORTEX, RESULT OF SURGICAL INTERFERENCE :"
(a) GENERAL DISTURBANCES OF THE CORTICAL ACTIVITY
(b) DISTURBANCES OF THE ACOUSTIC ANALYSER
XX. "PATHOLOGICAL DISTURBANCES OF THE CORTEX, 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) ARISING AFTER EXTIRPATION OF THE GYRUS PYRIFORMIS
(h) IN THE MOTOR ANALYSER
XXI. "PATHOLOGICAL DISTURBANCES OF THE CORTEX, RESULT OF SURGICAL INTEREFERENCE (continued):"
ATTEMPT TO CORRELATE THE GENERAL POST-OPERATIVE BEHAVIOR OF THE ANIMALS WITH THE DISTURBANCES IN THE ACTIVITY OF INDIVIDUAL ANALYSERS
XXII. THE GENERAL CHARACTERISTICS OF THE PRESENT INVESTIGATION AND ITS SPECIAL DIFFICULTIES
DISCOVERY OF CERTAIN ERRORS NECESSITATING THE MODIFICATION OF SOME EARLIER INTERPRETATIONS
XXIII. THE EXPERIMENTAL RESULTS OBTAINED WITH ANIMALS IN THEIR APPLICATION TO MAN
BIBLIOGRAPHY
INDEX