Conditioned Reflexes

CONDITIONED REFLEXES. Conditioned reflex - now a separate physiological term, denoting a specific nervous phenomenon, the detailed study of which led to the formation of a new department in animal physiology - the physiology of higher nervous activity as the first chapter of the physiology of the higher department of the central nervous system. For a long time, empirical and scientific observations had accumulated that mechanical damage or disease of the brain, and especially of the large hemispheres, caused disturbances in the highest, most complex behavior of animals and humans, commonly called psychic activity. At present, hardly anyone with a medical education doubts that our neuroses and psychoses are connected with the weakening or disappearance of the normal physiological properties of the brain or with its greater or lesser destruction. Then the persistent fundamental question arises: what is the connection between the brain and the higher activity of animals and ourselves, and from what and how to begin the study of this activity? It would seem that since psychic activity is the result of the physiological activity of a certain mass of the brain, physiology should have undertaken its study, just as the activity of all other parts of the organism is now successfully studied. However, this did not happen for a long time. Psychic activity had long ago (not for one millennium) become the object of study of a special science - psychology. Physiology surprisingly recently, only from the 70s of the 19th century, obtained the first exact facts regarding certain (namely motor) physiological functions of the large hemispheres with the help of its usual method of artificial irritation; with the help of another, also usual, method of partial destruction, additional data were obtained regarding the connection of other parts of the hemispheres with the main receptors of the organism: the eye, the ear, and others. This aroused hopes in both physiologists and psychologists regarding the establishment of a close connection between physiology and psychology. - On the one hand, it became common for psychologists to begin textbooks on psychology with a preliminary exposition of the doctrine of the central nervous system and especially of the large hemispheres (organs of sense). On the other hand, physiologists, conducting experiments with the exclusion of different parts of the hemispheres, discussed the results of experiments on animals psychologically by analogy with what would happen in our inner world (e.g. Munk's 'sees but does not understand'). But soon disappointment came in both camps. The physiology of the hemispheres noticeably stopped at these first experiments and did not move significantly further. And among psychologists after this, as before, there were again many decisive people who stood for the complete independence of psychological research from physiological. Along with this, there were other attempts to connect triumphant natural science with psychology through the method of numerical measurement of psychic phenomena. For a time, it was thought to form in physiology a special department of psychophysics, thanks to the happy discovery by Weber and Fechner of a law (called by their name) of a certain numerical connection between the intensity of external irritation and the strength of sensation. But beyond this single law, the new department did not go. - The attempt of Wundt, a former physiologist who then became a psychologist and philosopher, to apply the experiment with numerical measurement to psychic phenomena in the form of so-called experimental psychology was more successful; thus a considerable material has been collected and is being collected. Some, following the example of Fechner, call the mathematical processing of the numerical material of experimental psychophysics. But now it is no wonder to meet among psychologists, and especially among psychiatrists, many bitterly disappointed in the active help of experimental psychology. So what is to be done? However, another path for solving the fundamental question was still felt, imagined and outlined. Is it not possible to find such an elementary psychic phenomenon, which could with full right be considered at the same time as a purely physiological phenomenon, and, starting from it - studying strictly objectively (as in all physiology) the conditions of its occurrence, its various complications and its disappearance - to obtain an objective physiological picture of the entire higher activity of animals, i.e., the normal work of the higher department of the brain, instead of the various experiments of its artificial irritation and destruction previously performed? Fortunately, such a phenomenon had long been before the eyes of many; many had stopped their attention on it and some had even begun to study it (it is especially necessary to mention Thorndike), but for some reason they stopped at the very beginning and did not develop it into the basic, essential method of systematic physiological study of the higher activity of the animal organism. This phenomenon is what is now denoted by the term 'conditioned reflex'; the energetic study of it fully justified the hope just mentioned. Let us, let us make two simple experiments, which will succeed everyone. Let us pour into the mouth of a dog a moderate solution of some acid; it will cause the usual defensive reaction of the animal: with energetic movements of the mouth the solution will be thrown out, outward, and at the same time into the mouth (and then outward) will flow abundant saliva, diluting the introduced acid and washing it away from the mucous membrane of the mouth. - Now another experiment. Several times with any external agent, e.g. a certain sound, let us act on the dog just before introducing the same solution into its mouth. And what happens? Then it will be enough to repeat only this sound - and in the dog the same reaction will be reproduced: the same movements of the mouth and the same flow of saliva. Both of these facts are equally accurate and constant. And both of them must be denoted by the same physiological term 'reflex'. Both of them will disappear if either the motor nerves to the oral musculature and the secretory nerves to the salivary glands, i.e., the efferent pathways, or the afferent pathways from the mucous membrane of the mouth and from the ear, or finally the central stations of transition of the nerve current, i.e., the moving process of nerve irritation, from afferent pathways to efferent pathways are cut; for the first reflex this will be the medulla oblongata, for the second - the large hemispheres. No strict thought will find objections in view of these facts against this physiological conclusion. But at the same time the difference between these reflexes is already visible. Firstly, their central stations are different, as just indicated. Secondly, as is clear from the setting of our experiments, the first reflex was reproduced without any preparation, without any condition, the second was obtained with a special method. What did this mean? In the first - the transition of the nerve current from one pathway to another occurred directly, without special procedure; in the second - for this transition something preliminary was required. The most natural thing to imagine is this. In the first reflex there was direct conduction of the nerve current, in the second it was necessary to form a path for the nerve current in advance; such a concept had long been in nerve physiology and was expressed by the German word Bahnung. Thus, in the central nervous system there are two different central apparatuses: direct conduction of the nerve current and the apparatus of its closure and opening. It would be strange to stop in some bewilderment before such a conclusion. After all, the nervous system on our planet is the incomparably most complex and most delicate instrument of communication, connection of the numerous parts of the organism with each other and of the organism as the most complex system with an infinite number of external influences. If now the closing and opening of an electric current is our ordinary technical device, then can one object to the implementation of the same principle in this amazing instrument? On the basis of the above, the constant connection of an external agent with the response activity of the organism can rightfully be called an unconditioned reflex, and the temporary one - a conditioned reflex. The animal organism as a system exists only in the surrounding nature thanks to the continuous equilibration of this system with the external environment, i.e., thanks to certain reactions of the living system to the external irritations falling on it, which in higher animals is achieved mainly by means of the nervous system in the form of reflexes. The first provision of equilibrium, and therefore also the integrity of the individual organism, as well as of its species, consists of unconditioned reflexes, both the simplest (e.g., cough when foreign bodies enter the respiratory tract) and the most complex, commonly called instincts - food, defensive, sexual, etc. These reflexes are excited both by internal agents arising in the organism itself and by external ones, which determines the perfection of equilibrium. But the equilibrium achieved by these reflexes would be perfect only with the absolute constancy of the external environment. And since the external environment, in its extraordinary diversity, is also in constant fluctuation, unconditioned connections, as constant connections, are not sufficient and it is necessary to supplement them with conditioned reflexes, temporary connections.

For example, it is not enough for an animal to simply take into its mouth the food that is directly before it, as it would often starve and die of starvation. Instead, it must find food based on various random and temporary signs, which are the conditional (signal) stimuli that excite movements of the animal directed toward food, culminating in its introduction into the mouth, i.e., forming a conditional food reflex as a whole. The same applies to everything necessary for the well-being of the organism and the species, both in the positive and negative senses, i.e., to what must be taken from the environment and what must be guarded against. The temporary nervous connection is the most universal physiological phenomenon in the animal world and in ourselves. At the same time, it is also the psychological phenomenon that psychologists call association, whether it be the formation of connections from various actions, impressions, or from letters, words, and thoughts. What basis could there be for distinguishing or separating what the physiologist calls a temporary connection from what the psychologist calls an association? Here there is a complete fusion, a complete absorption of one by the other, an identification. It would seem that this is also recognized by psychologists, since some of them (or at least some) have stated that experiments with C.R. have provided solid support for associative psychology, i.e., psychology that considers association the foundation of mental activity. This is all the more so because with the help of a developed conditional stimulus, a new conditional stimulus can be formed, and in recent years it has been convincingly demonstrated in animals (dogs) that two indifferent stimuli, repeated one after the other, become connected and cause each other. For physiology, C.R. has become the central phenomenon, using which it is possible to study both normal and pathological activity of the cerebral hemispheres more and more fully and precisely. In the present exposition, this study, which has yielded a huge number of facts up to the present moment, of course can be reproduced only in the most basic outlines. The basic condition for the formation of C.R. is generally the coincidence in time, one or more times, of indifferent stimuli with unconditional ones. This formation occurs most readily and with the least difficulty when the first stimuli immediately precede the latter, as shown above in the example of the sound-acid reflex. C.R. are formed on the basis of all unconditional reflexes and from all possible agents of the internal and external environment, both in elementary form and in the most complex complexes, but with one limitation: from everything for whose perception there are receptor elements in the cerebral hemispheres. Before us is the broadest synthesis carried out by this part of the brain! But this is not all. The conditional temporary connection at the same time becomes specialized to the greatest complexity and to the finest degree of division, both of conditional stimuli and of certain activities of the organism, specifically skeletal and verbal motor activities. Before us is the finest analysis as a product of the same cerebral hemispheres! Hence the enormous breadth and depth of the adaptability and equilibrium of the organism with the environment. Synthesis is obviously a phenomenon of nervous closure. What is analysis as a nervous phenomenon? Here there are several separate physiological phenomena. The first basis for analysis is provided by the peripheral endings of all afferent nerve conductors of the organism, each of which is specially constructed for transforming a certain kind of energy (both outside and inside the organism) into a process of nervous excitation, which is then conducted both to special, more limited in number, cells of the lower parts of the central nervous system, and to the most numerous special cells of the cerebral hemispheres. Here, however, the incoming process of nervous excitation usually spreads out, irradiates to different cells over a greater or lesser distance. This is why, when we have developed, let us say, a conditional reflex to one specific tone, not only other tones but also many other sounds evoke the same conditional reaction. In the physiology of higher nervous activity, this is called generalization of conditional reflexes. Consequently, here phenomena of closure and irradiation are simultaneously encountered. But then irradiation gradually becomes more and more limited; the excitatory process concentrates in the smallest nervous point of the hemisphere, probably in a group of corresponding special cells. This limitation occurs most rapidly through the medium of another basic nervous process called inhibition. The process occurs as follows. We first have a generalized conditional reflex to a specific tone. Now we will continue the experiment with it, constantly accompanying it with an unconditional reflex, reinforcing it with this; but alongside it we will apply other, so to speak, self-acting tones, but without reinforcement. In this process, the latter tones gradually lose their effect; and this finally happens even with the closest tone, e.g., a tone of 500 vibrations per second will act, but a tone of 498 vibrations will not, it will be differentiated. These tones that have now lost their effect are inhibited. This is demonstrated as follows. If immediately after applying the inhibited tone one tries the constantly reinforced conditional tone, it either does not act at all or acts much less than usual. Thus, inhibition, which has eliminated extraneous tones, also makes itself known on it. But this is a short-term effect—with a greater interval after the eliminated tones, it is no longer observed. From this it must be concluded that the inhibitory process also irradiates, like the excitatory one. But the more often the unreinforced tones are repeated, the less the irradiation of inhibition becomes, the inhibitory process concentrates more and more both in time and in space. Consequently, analysis begins with the special work of the peripheral apparatuses of afferent conductors and is completed in the cerebral hemispheres through the medium of the inhibitory process. The case of inhibition described above is called differentiated inhibition. Let us cite other cases of inhibition. Usually, in order to have a more or less constant magnitude of C.R., the action of the conditional stimulus is continued for a certain time and then the unconditional stimulus is added to it, reinforcing it. Then the first seconds or minutes of irritation, depending on the duration of the isolated application of the conditional stimulus, have no effect, because as premature signals of the unconditional stimulus they are inhibited. This is an analysis of different moments of a continuing stimulus. This inhibition is called inhibition of the delayed reflex. But the conditional stimulus as a signal is also regulated by inhibition, becoming gradually zero if within a certain period of time it is not reinforced. This is inhibitory extinction. This inhibition lasts for some time and then disappears on its own. Restoration of the extinct stimulus is accelerated by reinforcement. Thus we have positive conditional stimuli, i.e., those causing an excitatory process in the cortex of the hemispheres, and negative ones—those causing an inhibitory process. In the cases cited, we have special inhibition of the cerebral hemispheres, cortical inhibition. It arises under certain conditions where it did not exist before, it is exercised, it fluctuates in magnitude, it disappears under other conditions—and this distinguishes it from the more or less constant and stable inhibition of the lower parts of the central nervous system and therefore was called, in distinction from the latter (external), internal. It would be more correct to call it: developed, conditional inhibition. In the work of the cerebral hemispheres, inhibition participates just as constantly, complexly, and subtly as the excitatory process. Just as incoming irritations from outside become connected there in some cases with specific points in a state of excitation, so the same irritations in other cases, also on the basis of simultaneity, can enter into a temporary connection with an inhibitory state of the cortex, if it is in such a state. This is evident from the fact that such stimuli have an inhibitory effect, cause an inhibitory process in the cortex by themselves, and are conditional negative stimuli. In this case, as in those cited above, we have a transformation under certain conditions of the excitatory process into an inhibitory one. And this can be made to some degree understandable to oneself by recalling that in the peripheral apparatuses of afferent conductors we have a constant transformation of different kinds of energy into an excitatory process. Why should it not happen under certain conditions that the energy of the excitatory process is transformed into the energy of the inhibitory one and vice versa? As we have just seen, both the excitatory and inhibitory processes, having arisen in the hemispheres, first spread out in them, irradiate, and then can concentrate, gathering to the original point. This is one of the basic laws of the entire central nervous system, but here, in the cerebral hemispheres, it appears with mobility and complexity peculiar only to them. Among the conditions determining the onset and course of irradiation and concentration of processes, the strength of both these processes must be considered first.

The material collected to date allows us to conclude that with a weak excitatory process, irradiation occurs; with a medium strength, concentration; and with a very strong process, irradiation again. The same is true for the inhibitory process. Cases of irradiation with very strong processes were less common and therefore less studied, especially during inhibition. Irradiation of the excitatory process at weak intensity, as a temporary phenomenon, makes latent excitation from another existing (but too weak to be detected) stimulus, or from a recently occurring one, or finally from a frequently repeated one that has left behind an increased tone in a specific point, apparent. On the other hand, this irradiation eliminates the inhibitory state of other points of the cortex. This phenomenon is called disinhibition when the irradiation wave of an external weak stimulus transforms the action of a specific, existing, negative, conditioned stimulus into its opposite, positive. At medium intensity of the excitatory process, it concentrates, focusing on a specific limited point and expressing itself in a specific activity. Irradiation with very strong irritation causes the highest tone of the cortex, when against the background of this irritation all other successive stimuli give a maximum effect. Irradiation of the inhibitory process at weak intensity is what is called hypnosis, and in food conditioned reflexes it is characteristically manifested in both components—secretory and motor. When under the specified condition inhibition arises (differentiation and others), which is the most common fact, special states of the cerebral hemispheres occur. First, contrary to the rule of more or less parallel changes in the magnitude of the salivary effect of food conditioned reflexes corresponding to the physical intensity of stimuli, all stimuli are equalized in effect (equalization phase). Then weak stimuli give more saliva than strong ones (paradoxical phase). And finally, a reversal of effects occurs: the positive conditioned stimulus remains completely without effect, while the negative one causes salivation (ultraparadoxical phase). The same is observed in the motor reaction; thus, when food is offered to a dog (i.e., natural conditioned stimuli act), it turns away from it, but when food is removed, it moves away, stretches toward it. Moreover, in hypnosis, one can sometimes directly see in the case of food conditioned reflexes the gradual spread of inhibition along the motor area of the cortex. First, the tongue and masticatory muscles are paralyzed, then inhibition of the neck muscles joins, and finally all trunk muscles. With further spread of inhibition downward in the brain, a cataleptic state can sometimes be observed, and finally complete sleep occurs. The hypnotic state, as an inhibitory one, very easily enters into a temporary conditioned connection based on simultaneity with numerous external agents. With strengthening of the inhibitory process, it concentrates. This serves to demarcate points of the cortex with an excitatory state from points with an inhibitory one. And since in the cortex there is a mass of diverse points, excitatory and inhibitory, relating both to the external world (visual, auditory, etc.) and to the internal (motor, etc.), the cortex represents a grand mosaic with alternating points of different qualities and different degrees of tension of excitatory and inhibitory states. Thus, the awake working state of an animal and human is a mobile and at the same time localized, sometimes more coarse, sometimes finest division of the excitatory and inhibitory states of the cortex, contrasting with the sleeping state, when inhibition at the height of its intensity and extensiveness evenly spreads throughout the mass of the hemispheres and downward to a certain depth. However, even now, individual excitatory points, sentinel and on duty, may remain in the cortex. Consequently, both processes in the awake state are in constant mobile equilibrium, as if in struggle. If suddenly a mass of external or internal irritations is removed from the cortex, inhibition takes a sharp advantage over excitation. Some dogs with peripherally destroyed main external receptors (visual, auditory, and olfactory) sleep 23 hours a day. Along with the law of irradiation and concentration of nervous processes, another basic law constantly operates—the law of mutual induction, consisting in that the effect of a positive conditioned stimulus becomes greater when the latter is applied immediately or soon after concentrated inhibition, just as the effect of inhibition proves more precise and profound after concentrated excitation. Mutual induction is manifested both in the vicinity of the point of excitation or inhibition, simultaneously with their action, and at the point itself after cessation of the processes. It is clear that the law of irradiation and concentration and the law of mutual induction are closely connected with each other, mutually limiting, balancing, and strengthening each other, and thus conditioning the precise ratio of the organism's activities with the conditions of the external environment. Both of these laws are manifested in all parts of the central nervous system, but in the cerebral hemispheres at newly forming points of excitation and inhibition, and in the lower parts of the central nervous system at more or less permanent ones. Negative induction, i.e., the appearance or strengthening of inhibition in the vicinity of the point of excitation, was earlier in the doctrine of conditioned reflexes called external inhibition when a given conditioned reflex decreased or disappeared under the action on the animal of an extraneous, accidental stimulus, which most often elicited an orienting reflex on itself. This was the reason for the cases of inhibition described above (extinction and others) to be combined under the name of internal inhibition as occurring without the intervention of an extraneous stimulus. Besides these two different cases of inhibition in the cerebral hemispheres, there is a third one. When conditioned stimuli are physically excessively strong, the rule of direct connection between the magnitude of the effect of these stimuli and their physical intensity is violated: their effect becomes not greater but less than the effect of stimuli of moderate strength—so-called inhibition beyond the limit. Inhibition beyond the limit appears both with one very strong conditioned stimulus and in the case of summation of not very strong individually stimuli. 44 Inhibition beyond the limit is most naturally classified as a case of refractory inhibition. If to more systematically classify the cases of inhibition, these are either constant, unconditional inhibition (inhibition of negative induction and inhibition beyond the limit) or temporary, conditional inhibition (extinction, differentiation, and inhibition of delay). But there are grounds to consider all these types of inhibition, in their physicochemical basis, as one and the same process, arising only under different conditions. The entire setup and distribution of excitatory and inhibitory states in the cortex of the hemispheres, which occurred in a certain period under the influence of external and internal stimuli, in a uniform, repeating environment, become increasingly fixed, occurring more and more easily and automatically. Thus, a dynamic stereotype (systematicity) is formed in the cortex, the maintenance of which requires less and less nervous effort; the stereotype becomes rigid, often difficult to change, difficult to overcome with a new environment, new stimuli. Every initial setup of the stereotype is, depending on the complexity of the system of stimuli, a significant and often extraordinary effort. The study of conditioned reflexes in a large number of dogs gradually raised the question of different nervous systems in individual animals, and finally grounds emerged to classify nervous systems according to some of their basic features. Such features seemed to be three: the strength of the basic nervous processes (excitatory and inhibitory), their balance with each other, and the mobility of these processes. Actual combinations of these three features appeared in the form of four more or less sharply expressed types of nervous system. By strength, animals were divided into strong and weak; strong ones by balance of processes—into balanced and unbalanced; and balanced strong ones—into mobile and inert. And this approximately coincides with the classical classification of temperaments. Thus, there appear: strong but unbalanced animals with both strong processes, but with predominance of the excitatory process over the inhibitory—excitable unrestrained type, choleric according to Hippocrates. Then strong, perfectly balanced, moreover inert animals—calm slow type, according to Hippocrates, phlegmatics. Then strong, perfectly balanced, moreover labile—very lively mobile type, according to Hippocrates, sanguines. And finally the weak type of animals, most corresponding to Hippocratic melancholics; their predominant and general feature—easy inhibitability both due to internal inhibition, constantly weak and easily irradiating, and especially external under the influence of all kinds of, even insignificant, extraneous stimuli.

In other respects, this is a less uniform type than all others; it is at once animals with both equally weak processes, then predominantly with an extremely weak inhibitory process, then fidgety, constantly looking around, and conversely, constantly stopping, as if freezing animals. The basis of this non-uniformity is, of course, that weak-type animals, just like strong-type animals, differ from each other in other traits besides the strength of the nervous processes. But the predominant and extreme weakness of either the inhibitory process or both processes destroys the vital significance of variations in other traits. Constant and strong inhibitory capacity makes all these animals equally invalids. Thus, the type is an innate constitutional form of the animal's nervous activity - the genotype. But since the animal from birth is subjected to the most diverse influences of the surrounding environment, to which it inevitably must respond with certain activities, which are often finally fixed for life, the final actual nervous activity of the animal is a blend of the traits of the type and changes produced by the external environment - the phenotype, character. All of the above obviously represents indisputable physiological material, i.e., objectively reproduced normal physiological work of the higher department of the central nervous system. But the study of normal work is what should be begun with and is indeed usually begun with in the physiological study of each part of the animal organism. However, this does not prevent some physiologists to this day consider the reported facts as not belonging to physiology. A common case of routine in science! It is not difficult to bring the physiological work of the higher department of the animal's brain described above into a natural and direct connection with the phenomena of our subjective world at many of its points. The conditional connection, as already indicated above, is obviously what we call in ourselves association by simultaneity. Generalization of the conditional connection corresponds to what is called association by similarity. Synthesis and analysis of conditioned reflexes (associations) are in essence the same basic processes of our mental work. When concentrating thought, when absorbed in some affair, we do not see or hear what is happening around us - a clear negative induction. Who would separate in the most complex unconditional reflexes (instincts) the physiological somatic from the psychic, i.e., from the experiences of powerful emotions of hunger, sexual desire, anger, etc.? Our feelings of pleasantness, unpleasantness, ease, difficulty, joy, torment, triumph, despair, etc., are connected either with the transition of the strongest instincts and their irritations into the corresponding effector acts or with their retention, with all variations of either easy or difficult course of the nervous processes occurring in the large hemispheres, as is seen in dogs solving or unable to solve nervous tasks of varying degrees of difficulty. Our contrasting experiences are, of course, phenomena of mutual induction. In irradiated excitation, we say and do what we would not permit in a calm state. Obviously, the wave of excitation turned the inhibition of certain points into a positive process. A strong fall in memory of the present - a common phenomenon in normal old age - is a decrease in the mobility of the specifically excitatory process with age, its inertia. In the developed animal world, at the phase of man, there has occurred an extraordinary addition to the mechanisms of nervous activity. For the animal, reality is signaled almost exclusively only by irritations and their traces in the large hemispheres, directly coming into the special cells of the visual, auditory and other receptors of the organism. This is what we also have in ourselves as impressions, sensations and representations from the surrounding external environment, both as general natural and as our social, excluding the word heard and seen. This is the first signal system of reality, common to us with animals. But the word constituted the second, specifically ours, signal system of reality, being a signal of the first signals. Numerous irritations by the word, on one hand, have removed us from reality, and therefore we must constantly remember this in order not to distort our relations to reality. However, there is no doubt that the basic laws established in the work of the first signal system must also govern the second, because this work is of the same nervous tissue. The brightest proof that the study of conditioned reflexes has put the investigation of the higher department of the brain on the right path and that at last the functions of this department and the phenomena of our subjective world have been united, identified, serve further experiments with conditioned reflexes on animals, in which pathological states of the nervous system of man - neuroses and some individual psychotic symptoms are reproduced, and in many cases a rational, intentional return to normal, healing, i.e., true scientific mastery of the subject, is achieved. The norm of nervous activity is the equilibrium of all the described processes participating in this activity. Violation of this equilibrium is a pathological state, disease, and often in the so-called norm, therefore, to speak more precisely, in the relative norm there is already a known disequilibrium. Hence the probability of nervous disease is clearly connected with the type of nervous system. Of dogs, under the action of difficult experimental conditions, nervous disease develops quickly and easily in animals belonging to the extreme types: excitable and weak. Of course, with extremely strong, exceptional measures, the equilibrium can also be disturbed in strong, balanced types. Difficult conditions that chronically disturb nervous equilibrium are: overstrain of the excitatory process, overstrain of the inhibitory process and the direct collision of both opposite processes, or in other words - overstrain of the mobility of these processes. We have a dog with a system of conditioned reflexes to irritants of different physical intensity, of positive and negative reflexes, applied stereotypically in the same order and with the same intervals. Applying either extremely, exceptionally strong conditional irritants, or very prolonging the duration of inhibitory irritants, or making very fine differentiation, or increasing in the system of reflexes the number of inhibitory irritants, or finally making opposite processes follow directly one after another, or even acting simultaneously with opposite conditional irritants, or at once changing the dynamic stereotype, i.e., turning the established system of conditional irritants into the opposite series of irritants - we see that in all these cases the said extreme types especially quickly come into a chronic pathological state, which in these two types is expressed differently: the neurosis of the excitable type is expressed in that its inhibitory process, which was constantly lagging in strength from the excitatory process even in normal conditions, now very weakens, almost disappears: the developed, though not absolute differentiations are completely disinhibited, extinction is extremely prolonged, the delayed reflex turns into a short-delayed one, etc. The animal becomes generally extremely uncontrolled and nervous during experiments in the stand: either it rages or, which is much rarer, falls into a sleepy state, which did not happen to it before. The neurosis of the weak type bears almost exclusively a depressive character. The conditioned-reflex activity becomes extremely disorderly, or most often completely disappears, the animal in the stand is almost entirely in a hypnotic state, presenting its various phases (no conditioned reflexes, the animal does not even take the food offered to it). Experimental neuroses mostly take a prolonged character, for months and years. In prolonged neuroses, therapeutic methods have been successfully tested. Already for a long time in the study of conditioned reflexes, bromine was used when it came to animals that could not cope with the tasks of inhibition. And it turned out that bromine essentially helped these animals. Long and diverse series of experiments with conditioned reflexes on animals have undoubtedly established that bromine has a special relation not to the excitatory process, reducing it, as was usually accepted, but to the inhibitory process, strengthening it, toning it. It proved to be a powerful regulator and restorer of disturbed nervous activity, but with the indispensable and most essential condition of corresponding and precise dosing of it according to types and states of the nervous system. In the strong type and in a still sufficiently strong state, large doses up to 2-5 g per day must be used on dogs, and in weak types it is necessary to go down to centigrams and even milligrams. Such bromination for a week or two was sometimes already sufficient for the radical cure of a chronic experimental neurosis. In recent time, experiments are being made showing an even more effective therapeutic action, and indeed in especially severe cases, combinations of bromine with caffeine, but again with the finest, now mutual, dosing.

The cure of sick animals was sometimes achieved, although not as quickly and completely, also with one prolonged or short but regular rest from laboratory work in general or from the elimination of only difficult tasks in the system of conditioned reflexes. The described neuroses of dogs are most naturally to be compared with neurasthenia in humans, all the more so that some neuropathologists insist on two forms of neurasthenia: excited and depressive. Then some traumatic neuroses, as well as other reactive pathological conditions, will also fit here. The recognition of two signal systems of reality in humans, one must think, will specifically lead to an understanding of the mechanism of two human neuroses: hysteria and psychasthenia. If people, based on the predominance of one system over another, can be divided into thinkers by preference and artists by preference, then, in pathological cases with general imbalance of the nervous system, it will be understood that the former will turn out to be psychasthenics, and the latter-hysterics. In addition to clarifying the mechanism of neuroses, the physiological study of higher nervous activity gives the key to understanding some aspects and phenomena in the pictures of psychoses. First, let us dwell on some forms of delusion, namely on variations of persecution delusion, on what Pierre Janet calls 'feelings of possession,' and on Kretschmer's 'inversions.' The patient is pursued by exactly what he especially wants to avoid: he wants to have his secret thoughts, but it irresistibly seems to him that they are constantly being revealed, known by others; he wants to be alone, but he is tormented by the inescapable thought that even though he is actually alone in the room, there is still someone there, etc.-feelings of possession, according to Janet. In Kretschmer, two girls, upon reaching sexual maturity and developing an attraction to certain men, however suppressed this attraction for some reasons. As a result, they first developed obsessive-compulsiveness: to their tormenting grief, it seemed to them that sexual excitement was visible on their faces and everyone was paying attention to it-and they greatly valued their sexual purity, inviolability. And then immediately one of them irresistibly began to seem, and even felt, that in her there was and moved, reaching her mouth, a sexual seducer-snake, who seduced Eve in paradise, and the other-that she was pregnant. This latter phenomenon Kretschmer calls inversion. It is obviously identical in mechanism to the feeling of possession. This pathological subjective experience can be understood without strain as a physiological phenomenon of the ultraparadoxical phase. The idea of sexual inviolability as the strongest positive irritation, against the background of an inhibitory, suppressed state in which both girls were, turned into an equally strong opposite, negative idea, reaching even the degree of sensation, in one-into the idea of the presence in her body of a sexual seducer, and in the other-into the idea of her own pregnancy as a result of sexual intercourse. The same is true for the patient with the feeling of possession. The strong positive idea 'I am alone' turns under the same conditions into an equally opposite one-'someone is always around me.' In experiments with conditioned reflexes in various difficult and pathological states of the nervous system, it is often observed that temporary inhibition leads to temporary improvement of these states; and in one dog, a bright catatonic state was noted twice, which led to a marked improvement in a chronic, stubborn nervous disease, almost a return to normal, for several consecutive days. In general, it must be said that in experimental diseases of the nervous system, individual phenomena of hypnosis almost constantly appear, and this gives the right to assume that this is a normal physiological method of fighting against the disease-causing agent. Therefore, the catatonic form or phase of schizophrenia, consisting entirely of hypnotic symptoms, can be understood as a protective physiological inhibition, limiting or completely excluding the work of the diseased brain, which, due to the action of some, as yet unknown, harmful agent, was threatened with the danger of serious disturbance or final destruction. Medicine in the case of almost all diseases well knows that the first therapeutic measure is rest for the affected organ. That such an understanding of the mechanism of catatonia in schizophrenia corresponds to reality is convincingly proved by the fact that only this form of schizophrenia represents a fairly significant percentage of return to normal, despite sometimes the multi-year (20 years) continuation of the catatonic state. From this point of view, all attempts to act on catatonics with exciting methods and means are directly harmful. On the contrary, one can expect a very significant increase in the percentage of recovery if physiological rest through inhibition is combined with special external rest for such patients, and they are not kept among continuous and strong irritations of the surrounding environment, among other sick or more restless patients. In the study of conditioned reflexes, in addition to the general disease of the cortex, extremely interesting cases of experimentally and functionally produced disease of individual very fine points of the cortex were also observed many times. Let there be a dog with a system of diverse reflexes and among them conditioned reflexes to different sounds: tone, noise, metronome beats, bell, etc.-and the patient can be made only one of these conditioned stimuli, while the others will remain healthy. The pathological state of an isolated point of the cortex is produced by the same methods that were described above as disease-causing. The disease manifests itself in various forms, in various degrees. The slightest change of this point is expressed in its chronic hypnotic state: at this point, instead of the normal connection between the magnitude of the effect of irritation and the physical force of irritation, the equilibrating and paradoxical phases appear. And this, based on the above, could be interpreted as a physiological preventive measure in a difficult state of the point. With further development of the pathological state, the stimulus no longer gives a positive effect, but always causes only inhibition. This is in some cases. In others-just the opposite. The positive stimulus becomes unusually stable: it extinguishes more slowly than normal stimuli, is less amenable to successive inhibition from other inhibitory conditioned stimuli, it often sharply stands out in magnitude among all other conditioned stimuli, which was not the case before the disease. This means that the excitatory process of this point has become chronically pathologically inert.-The irritation of the pathological point either remains indifferent to the other conditioned stimuli of the cortex, or one cannot touch it with its irritator without the entire system of reflexes being disturbed in one way or another. There is reason to assume that in the disease of isolated points, when in the diseased point the inhibitory process or the excitatory process predominates, the mechanism of the pathological state consists precisely in the violation of the balance between opposite processes: one or the other process weakens significantly and predominantly. In the case of pathological inertia of the excitatory process, there is the fact that bromine (strengthening the inhibitory process) often successfully eliminates it. It can hardly be considered fantastic the following conclusion. If, as is directly obvious, stereotypy, iteration, and perseveration have their natural basis in the pathological inertia of the excitatory process of different motor cells, then the mechanism of obsessive neurosis and paranoia must be the same. The matter only concerns other cells or their groups, connected with our sensations and ideas. Thus, only one series of sensations and ideas, connected with diseased cells, becomes abnormally stable and does not yield to the inhibiting influence of other numerous sensations and ideas, more corresponding to reality due to the healthy state of their cells.-The next fact, which was observed many times in the study of pathological conditioned reflexes and which has a clear relation to human neuroses and psychoses,-is the circularity in nervous activity. The disturbed nervous activity appeared more or less correctly oscillating. There was a period of extremely weakened activity (conditioned reflexes were chaotic, often disappeared completely or were minimal), and then as if spontaneously, without visible causes, after several weeks or months, a greater or lesser, or even a complete return to normal occurred, which was then again replaced by a period of pathological activity. In circularity, periods of weakened activity alternated with abnormally heightened ones. One cannot but see in these oscillations an analogy with cyclothymia and manic-depressive psychosis. The most natural thing would be to attribute this pathological periodicity to a violation of the normal relations between the excitatory and inhibitory processes, as far as their interaction is concerned. Since the opposite processes did not limit each other at the proper time and to the proper extent, but acted independently of each other and excessively, the result of their work reached an extreme-and only then did the change of one by the other occur.

Thus, another, extremely exaggerated periodicity was obtained: weekly and monthly instead of the short, and therefore very easy, daily periodicity. Finally, one cannot but mention the fact that has been observed so far in an extremely strong form, admittedly, only in one dog. This is the extreme explosiveness of the irritative process. Some individual, or all, conditioned stimuli gave the most rapid and excessive effect (both motor and secretory), but which quickly ceased even during the action of the stimulus; and the dog, when the food reflex was reinforced with food, no longer took it. Obviously, this was a case of strong pathological lability of the irritative process, which corresponds to the irritative weakness of human clinical practice. Cases of a mild form of this phenomenon are not uncommon in dogs under certain conditions. All the described pathological nervous symptoms appear under appropriate conditions in both normal, i.e., surgically untouched dogs, and (especially some of them, e.g., circularity) in castrated animals, i.e., on an organically pathological basis. Numerous experiments have shown that the main feature of the nervous activity of castrates is a very strong and predominant weakening of the inhibitory process, in strong types, however, this equalizes significantly over time. In conclusion, it must be emphasized once again how, when comparing the ultraparadoxical phase with feelings of possession and inversion, and the pathological inertia of the irritative process, with obsessive neurosis and paranoia, physiological phenomena and experiences of the subjective world mutually overlap and merge.

I. Pavlov.