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

In the experiments in w the tactilė stimulus was used the dog showed signs of a gener y citation : at the slightest sound from the experimenter’s ro the animal immediately responded by the peculiar motor nG, Obviously the tactile cutaneous stimulation in this \4 ought about a vigorous and widely irradiated excitation te cortex. ‘The nature of this excitation remained, ha SD, own. It did not seem to be associated with any sexual réfiexes since it was not accompanied by erection of the penis seemed to be something like the common reaction to IKA At any rate it was a sufficiently interesting nervous

this purpose we began to develop internal inhibition in the form of differentiation of tactile stimuli according to their place of applica- tion. On account of initial generalization the application of the tactile stimulus to the shoulder gave some conditioned secretion, and this also was accompanied by the special motor reaction. On repetition of the stimulus without reinforcement the motor and the salivary components of the conditioned reflex disappeared (8 repeti- tions), and this was followed by the disappearance of the special motor reaction (40 repetitions). The stimulation of the place on the thigh continued, however, to evoke the special motor, and the alimentary motor, reaction in succession. A differentiation was now

developed to stimulation of a place on the side of the animal nearer to the thigh. The different stages repeated themselves in the same way as for stimulation on the shoulder, but again the special reaction to stimulation of the thigh did not diminish. Finally a differentiation was developed to a tactile stimulation on the hind paw, and now the special motor reaction in response to the stimulation on the thigh first began to weaken, and then disappeared altogether. At the same time the strength of the salivary reflex to the tactile stimulus took up its usual position in the series of conditioned reflexes as regards the relative strengths of the stimuli producing them, falling from its predominant place to a position below the conditioned reflexes to auditory stimuli.

In this manner we see that the development Gevoera inhibitory areas in the cortical part of the cutan analyser abolished the special cutaneous reflex, at the same preserving, and even rendering normal, the alimentary cu s conditioned reflex. x This example and other observation, est that a gradual development of internal inhibition in the ex should be used for re-establishment of the balance of no conditions in cases of an unbalanced nervous system. The Soa is being used at present on the dog, described in the eigh lecture, which had a narrowly localized functional injury acoustic analyser. Since this region was specially related DN beating of a metronome we resolved to develop a differenti iMDition -of other auditory stimuli related to normal areas of uih analyser. We hope that irradiation of the inhibition» he defective metronome-pcint will have a

normal activa o not know whether similar therapeutic measures (not counting of course general sedatives such as hot baths) are applied in human neurotherapy. We shall now attempt a discussion of borderline states of the nervous system in our dogs, states merging from a normal into a pathological character which, on the analogy of corresponding human states, should in some instances be described as psycho-pathological. These are different hypnotic phases, such as the transition phases between the alert state and sleep, and the passive defence reflex.. We have seen in the sixteenth lecture that the transition of animals from the alert state into sleep is based upon the development in the brain of an inhibitory process which, under the influence of definite stimuli, is initiated in the cortex and reaches different stages of intensity and extensity during the different phases of the developing sleep. Undoubtedly, even at present, the observations made upon animals allow in part of a physiological interpretation of the funda- mental aspects of hypnotism in the human subject.

We shall consider first the conditions under which hypnotic states develop. In animals, as we already know, they appear, as the result of monotonous stimuli of a small and medium intensity repeated for a long time (the most common case in our experiments), more or less gradually, while in the case of stimuli of a considerably greater intensity they appear quickly—a form of animal hypnotism which has been known for a very long time. The stimuli di a, initiating these states, both weak and strong, can also sage ed-by any other stimuli which have conditioned propertiG} respect to the first. In this connection the special mode of fgmp&tion of conditioned reflexes described in the sixth lecture will €é)femembered where the neutral stimulus repeated several time conjunction with the pre-established inhibitory stimulug að Kired inhibitory properties of its own [experiments by Dr. Dofth (p. 106)]. The method of inducing hypnosis in man inv conditions entirely analogous to those which produced PAA our ne The classical method con- sisted in the pertamane tt alled “ passes ”—weak, monotonously |

repeated tactile and muli, just as in our experiments upon animals. At presen more usual method consists in the repetition of some form of(w¢rds, describing sleep, articulated in a flat and monotonous toné*ef voice. Such words are, of course, conditioned stimuli whié ve become associated with the state of sleep. In this man @eny stimulus which has coincided several times with the Kx ment of sleep can now by itself initiate sleep or a hypnotic state. The mechanism is analogous to the inhibitory chain reflexes, which are. similar to the positive conditioned chain reflexes, t.e. reflexes of different orders which have been described in the third lecture [experiments of Dr. Volborth]. Finally, hypnosis in the case of hysteria (in the sense of Charcot) can be obtained by the application of strong and unexpected stimuli, as in the old method of initiating hypnosis in animals. It is obvious that in this respect physiologically weak stimuli may act in the same manner if, on account of a coincidence in time, they have acquired signalling properties in respect to the strong ones. Most of the procedures producing hypnosis become more and more effective the more frequently they are repeated.

One of the first expressions of hypnosis in man is the loss of so-called voluntary movements and the development of a cataleptic state, i.e. maintenance by different parts of the body of the position given to them by external forces. This may best be regarded as an isolated inhibition of the motor analyser which has not descended to the sub-cortical motor centres. Other areas of the cortex may continue to function quite normally. A man in a state of hypnosis may understand what we tell him, may realize what kind of unnatural posture we have given him and may attempt to change it, but is incapable of doing so. The outward signs of the hypnotic state are similar in men and animals. It has already been describe sixteenth lecture how some ‘animals retain their ale

into sub-cortical regions. Other dogs continue act to all the i conditioned stimuli by the secretory compone the reflex only, exhibiting-no motor reaction and not oo food—obviously a case of an isolated inhibition of the ko analyser. Finally, in animals hypnotized by the old meta could often be observed that the body and extremities remain otionless while the animal yet continued to follow everythi th its eyes, and even accepted the food. This is obviously a a still more localized inhibition within the motor ang JENY e local “tonic” (i.e. spinal flexor and extensor) reflexes, KQ are observed in man and animals in some cases, become eystandable only if we postulate complete inhibition of the m analyser of the cortex. When we As) deal with more complicated forms of the hypnotic states viously becomes, for several reasons, difficult, or wv

even impossible, to draw a parallel between man and animals. As already stated, we know only a few of the phases of the hypnotic state, especially as regards their relative intensity, and we have no’ definite idea as to the sequence of their development. We are not familiar with the manner in which these phases manifest themselves under natural conditions of life in animals, since the transition phases were observed not in the natural individual and social sphere of life, but only in the restricted sphere of a laboratory environment. In man, however, we become familiar with these phenomena under more normal conditions of life and we can evoke and investigate them with the help of the most valuable signalling medium— speech. Of course, on account of the extraordinary complexity of the behaviour of man as compared with the higher animals, the latter may not exhibit some of the phases of the hypnotic state seen in man at all. It is, therefore, only those crude and elementary results obtained in the animal which can be used for an attempt at a physiological interpretation of the different hypnotic phases in man. Let us consider the automatism of the hypnotized subject who repeats in a stereotyped fashion the movements of the hypnotist, being able to perform even difficult movements such as balancing along a difficult path. Obviously we deal with a certain degree of inhibition of some parts of the cortex—a state in which the more complicated forms of normal activity are excluded and replaced by responsiveness to immediate stimuli. This i allows

of or even favours the establishment and reinfore t of the physio- logical connections between certain stimuli certain activities, e.g. movements. In this manner, in hypngskNall activities based on merged reflex which in all of us in c d forms and develops the complicated individual and socialge r.. Similarly, some change in the environment, which in on days had repeatedly evoked certain movements affecting,ceftain analysers, in hypnosis calls forth without fail and in eotyped manner the old response. It is a common occurrenge being predominantly preoccupied with some one activity, can simultaneously perform some other activity which \ been practised, t.e. those parts of the cortex involved in thisNefder response, although in a state of partial inhibition thax negative induction, still continue to function in a normal KON er. That this interpretation is somewhere near the RSN me more and more convinced, through observing the

“imitation” are accentuated and we RA revealed the long-sub- diminution in the reactivity of my own brain through my advancing age (my diminished memory of recent events). Moreover, with time I progressively. lose the faculty, when busy with one activity, of performing correctly another also. Apparently the concentrated excitation of some definite point induces, on account of diminished excitability of the cortex, such a strong inhibition of the rest of the cortex that even the conditioned stimuli of the old firmly established reflexes are now below the threshold for excitation. The above described phase of hypnosis in the human subject may perhaps be compared with what I have termed the narcotic phase of transition in dogs, when strong and old reflexes persist while the more recent ones disappear.

Among the various aspects of the hypnotic state in man attention may be drawn to “ suggestion ” so-called and its physiological interpretation. Obviously for man speech provides conditioned stimuli which are just as real as any other stimuli. At the same time speech provides stimuli which exceed in richness and many-sidedness any of the others, allowing comparison neither. qualitatively nor quantitatively with any conditioned stimuli which are possible in animals. Speech, on account of the whole preceding life of the adult, is connected up with all the internal and external stimuli which can reach the cortex, signalling all of them and replacing all of them, and therefore it can call forth all those reactions of the organism which are normally determined by the actual stimuli selves. We can, therefore, regard “ suggestion ” as the most gif\jNe Torm of a typical conditioned reflex in man. The command e hypnotist, in correspondence with the general law, concentzge’ the excitation in the cortex of the subject (which is in a con of partial inhibi- tion) in some definite narrow region, at e time intensifying (by negative induction) the inhibition ate) rest of the cortex and so abolishing all competing effects of Syntemporary stimuli and of. traces left by previously received one This accounts for the large and practically insurmountable j Bence of suggestion as a stimulus during hypnosis as well as gD at it. The command retains its effect after the terminà of hypnosis, remaining independent of other stimuli, bein i{pprmeable to them, since at the time of primary introduction Kuo stimulus into the cortex it was prevented from Se aati ga gi ea with the rest of the cortex. The great number of ey uli which speech can replace explains the fact that we RN Qygest to a hypnotized subject so many different

activities, and influence and direct the activities of his brain. It could be questioned why does suggestion carry in itself such a commanding influence as compared with dreams, which are usually forgotten and only have a very small vital significance ? But dreams are due to traces, generally of very old stimuli, while suggestion is a powerful and immediate stimulus. Moreover, hypnosis depends upon a smaller intensity of inhibition than sleep. Suggestion, therefore, is doubly effective. Still further, suggestion as a stimulus is brief, isolated and complete, and. therefore vigorous, while dreams are generally linked up into chains of various, sometimes inconsistent or antagonistic, traces of stimuli. The fact that it is possible to sug- gest to a hypnotized subject almost anything, however little it may correspond to the physical reality, and to evoke a reaction in opposi- tion to the actual reality—for example, the reaction appropriate’ to a bitter taste when the reality is a sweet taste—this fact, I believe, can be compared with the fact observed in the paradoxical phase of transition in the dog, that weak stimuli have a greater effect than strong ones. The real stimulus from the sweet substance going directly to the corresponding cortical cells should be expected to be much stronger than the substituted verbal stimulus of “ bitter,”

-which goes through auditory cells to the chemical analyser of taste for bitter—just as a conditioned stimulus of the first order is always stronger than one of the second order. The significance of the para- doxical phase is not limited to pathological st uch as those previously observed, and it is highly probab at it plays an e apt to be much more influenced by words than by the actugktacts of the surrounding reality. I hope to be able to produc x enomenon in animals analogous to “ suggestion ” in many hypnosis.

The fact that certain phases 3 ypnotic state in man remain more or less stationary O self in dogs. Similarly, under certain conditions and in elrdence on the individual condition of the nervous system the otic state in man, as in animals, passes The passive det N Netix stands in a definite connection with the hypnotic sta#@. \As I suggested previously (p. 312) the old form of hypnosis in aħiñals may be regarded with reason as a reaction of passive selfreservation, occurring when the animal meets with

some very QOerful or extraordinary external stimulus, and consisting in a SS r less profound immobilization of the animal by means of an inhibition, beginning in the cortical cells representative of all the skeletal muscles (motor analyser). This reflex was often observed j in our experimental animals, of course in different degrees of intensity | and in somewhat different forms, always, however, retaining its fundamental inhibitory character. The variations consisted in a '

smaller or greater diminution of the movements, in a smaller or greater weakening, or in the disappearance, of conditioned reflexes. The passive defence reflex was usually evoked by relatively un- familiar and powerful external stimuli. The relative strength of a stimulus will of course depend on the state of the given nervous system, on its inherent properties, the state of health or disease, and on different periods of life. Animals which have been employed many times in front of a large audience remain quite normal under such conditions, while those which are exposed for the first time enter into a state of powerful inhibition. The exceptional dog described before (p. 402) behaved towards even the slightest changes in the environment as if to strong stimuli, and its activities became deeply inhibited. Some of the dogs which passed through the extraordinary stimulus of the flood entered into a chronic patho- logical state and now became inhibited under the influence of strong conditioned stimuli, which previously had produced a specific con- ditioned effect. Finally, some other dogs become as easily inhibited but only in some definite phases of hypnosis. The following is a

experiments remains fully alert accepts the food fe} Wing the conditioned stimuli quickly and with avidity. By repeete tion of weak conditioned stimuli a certain stag hypnosis is induced in the animal, which soon becomes p ally motionless. When a strong conditioned stimulus is noy ed the animal first turns in the direction from which the, fded/is administered, then turns away without touching it. To Kanal observer the animal looks frightened. A weak conditio Coy is now applied and the animal immediately approac Ome plate and quietly takes the food. On dispersing the hyj oats all the conditioned stimuli again give their normal N Obviously in the special phase of hypnosis of the anima Le> d and usual stimuli now produce the effect of very strong cs Sg ean an inhibitory reflex. In a similar manner, in our ex ingly inhibitable dog “‘ Brains ” as soon as the pitch of the S pility of the cortex was raised by the special method K on page 381, there was observed a considerable

weakening of the otherwise, almost continuous reflex of passive self-preservation. In all the cases which have just been described what is most striking is the extremely characteristic passive self-protective postures of the animal. When I recall a large number of experiments performed one after another and year after year it is hardly possible not to conclude that at least in most cases what is known in psychology under the names of “ fear,” “ cowardice ” or “ caution” has a physiological substrate in a state of inhibition of the nervous system, which varies in intensity and so produces different intensities of the reflex of passive self-protection. Developing these conceptions further we are bound to regard the obsession of fear, and different phobias as natural symptoms of inhibition in a pathological and weakened nervous system. There are, of course, certain forms of fear and cowardice, as for instance flight and panic, and certain postures of servility, which apparently do not conform with the idea of an underlying inhibitory process, having a much more active aspect. These types must, of course, be subjected to experimental analysis, but it is perhaps not impermissible to regard them provisionally as developing in co-operation with, and as a result of, inhibition of the cortex. We have even now a few observations which conform with this point of view.

I would like to turn briefly to the experiments described at the end of the preceding lecture. If on repeatin S in different variations the preliminary results should fin 1 confirmation, these results will throw some light upon o he darkest points of our subjective self—namely, upon t lations between the conscious and the unconscious. The ments if confirmed will have demonstrated that such angi tant cortical function as synthesis (“‘ association ”) may gta areas which are in a state of ae ition on account of the existence at that moment of a predomipant‘tocus of strong excitation. Though the actual synthesizing acja may not enter our field of conscious- ness the synthesis ma heless take place, and under favourable conditions it may e N e field of consciousness as a link already formed, seemin ginate spontaneously.

In concludin&this series of lectures I want to repeat that all the SENN se of other workers as well as our own, which have _ only of a preliminary inquiry, which has however, I fully believe, entirely justified its inception. We have indisputably the right to claim that our investigation of this extraordinarily complex field has followed the right direction, and that, although not a near, nevertheless a complete, success awaits it. So far as we ourselves are concerned we can only say that at present we are confronted with many more problems than ever before. At first, not to lose sight of the main issue, we were compelled to simplify, and, so to speak, schematize the subject. At present, after having acquired some knowledge of its general principles, we feel surrounded, nay crushed, by the mass of details, all calling for elucidation.

THE following bibliography comprises all the published researches upon the physiology of conditioned reflexes performed in my own laboratories in Petrograd. The first paper giving.a more or less systematic description of “natural” conditioned reflexes—then called “‘ psychic reflexes ’—was published by Dr. Wolfson in the form of a thesis entitled Observations upon Salivary Secretion (Petrograd, 1899). The term “ conditioned reflex ” was first used in print by Dr. Tolochinov, who completed his experiments in 1901 and communicated the results at the Congress of Natural Sciences in Helsingfors in 1903.

The bibliography is divided into twenty-three sections. This division has been made for the convenience of those who wish to obtain a preliminary acquaintance with one or another aspect of the subject. The titles of papers quoted in more than one section are given in full in that section to which their main part belongs. Since the papers referred to in one section treat also of other aspects, a detailed knowledge can be achieved only Ry reading the main bulk of the literature. In each section t Wane is set down in chronological order. Many of the capri quoted in

these lectures were taken from researches w ave only recently been completed and are not yet publish which are still in pro- gress. These could not, therefore, be j ed in the bibliography. (1) Pavlov, I.P. wenty years of objective study of the higher nervous activi animals.” Article, No. 12. Š (4) Podkopaev, N. A. “ The technical methods employed in the study of conditioned reflexes.” Petrograd, 1926. (2) Vassiliev, P. N. “ The action of extraneous stimuli upon established conditioned reflexes.” Proc. Russian Med. Soc. in Petrograd, vol. 73, 1906.

(3) Mishtovt, G. V. “ Development of inhibition of an artificial condi- tioned reflex (auditory) by means of different stimuli.” Thesis, Petrograd, 1907 ; Preliminary communication in the Proc. Russian Med. Soc. in Petrograd, vol. 74, 1907. (6) Nikiforovsky, P. M. . “ An interesting form of dis-inhibition of conditioned reflexes.” Proc. Russian Med. Soc. in Petrograd, vol. 76, 1909. (7) Bilina, A. S. “The simple inhibition of conditioned reflexes.” Thesis, Petrograd, 1910.

(8) Egorov, J. E. “ The influence of different alimentary conditioned reflexes one upon another.” Thesis, Petrograd, 1911. (9) Savich, A. A. “ Further contributions to eae study of the influence of conditioned reflexes one upon another.” Thesis, Petro , 1913. (10) Rosova, L. V. ‘‘ Interaction between different forms%Qh external inhibition of conditioned reflexes.” Thesis, Petro 1914. (11) Foursikov, D.S. “ Effect of external inhibition up development of differentiation and of a conditioned inhibi Y Russian J ournal of Physiology, vol. iv. 1922.

(12) Foursikov, D. S. “‘ Effect of the are y reaction upon the development of a conditioned inhipit nd of differentiation.” Russian Journal of Physiology, vo 1922. IV. INTERN Cs ae Q Pion (1) Tolochinov, I. E. “Co ions à l’étude de la physiologie et de la psychologie des gfindee salivaires.”” Forhindlingar vid Nordiska Naturforskare och Békaremotet. Helsingfors, 1903. (2) Boldirev; P. N.* jhe development of artificial conditioned reflexes and their erties.” Proc. Russian Med. Soc. in Petrograd,

(11) Potehin, S. I. *“ Contributions to the physiology of internal inhi- bition of conditioned reflexes.” Thesis, Petrograd, 1911; Pre- liminary communication, Proc. Russian Med. Soc. in Petrograd, vol. 78, 1911. (15) Ten-Cate, J. J. “Contributions to the study of irradiation and concentration of extinctive inhibition.” Bulletin of the Institute of Lesgaft, vol. 3, 1921. (17) Frolov, @. P., and Vindelband, O. A. “A wage of extinction of an artificial conditioned reflex.” Com 38th meeting

Commun. at aGefeeting of Petrograd Physiol. Soc., 1924. (23) Popov, N. tinction of the investigatory reflex in the dog.” Russian Physiol., vol. iii. 1923. cial conditioned reflex.” Archive of Biological Sciences, v. Nos. 4 and 5, 1926. (24) F ot eye and Windelband, O. A. “ A special case of extinction (1) Zeliony; G. P. ‘‘ Contribution to the problem of the reaction of dogs to auditory stimuli.” Thesis, Petrograd, 1907 ; Prelim..Commun. Russian Med. Soc. in Petrograd, vol. 73, 1906.