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

inhibition was proved by means of destruction of conditioned inhibition by reinforcing the action of the inhi y combination by the administration of food and then re-ORie ishing it by dis- continuing the reinforcement. In cont eriments the same destruction and re-establishment wa, a) ed with the tactile conditioned inhibitor. It follows ropes experiments that the sounds acted as true conditioned inhibitors, and, therefore, that the analyser was capable of perform} n inhibitory function while the function of excitation was stil t. In other words, the analysing function of the cortex wa aired. Only several days after the above experiments iea positive conditioned reflexes to sound begin to reappear.

In a second Ghd of testing our suppositions, in particular the supposition treme generalization of sounds, we used long- trace ERG which, as is known, the stimuli are generalized. beyond the limits of a single analyser (Lecture VII). In the case of long-trace reflexes perfectly neutral stimuli assume the character of accessory conditioned stimuli, which act in the same manner as the original trace stimulus, 7.e. the secretion begins after the same latent period. Now it was determined to test whether these condi- tioned accessory reflexes to auditory stimuli in general would still

be present at the time of absence of the specific reflexes to these stimuli. For this purpose the dog had a definite trace reflex estab- lished to a tactile stimulus in which the pause between the end of the conditioned stimulus and the beginning of the unconditioned stimulus was two minutes. Usually the conditioned secretion _ started during the second minute of the pause. Ten days after complete removal of the temporal lobes the trace reflex to the tactile stimulus reappeared. On the twelfth day an auditory stimulus gave 8 drops during 4 minutes, the secretion starting during the third minute after the termination of the stimulus. On the seventeenth day the same auditory stimulus gave 38 drops during 6 minutes, the secretion starting as in the case of the primary trace stimulus during the second minute of the pause. It was only on the thirty-fifth day that the conditioned reflexes to the actual isolated action of the conditioned auditory stimuli first began to appear. This experiment shows once more that the auditory stimuli had assumed an extremely generalized character, so that sound as a general stimulus still continued to act, although individual sounds had Jest their specific conditioned significance. It is, moreover, evide the function of synthesis was not lost, and after these exp nts special testing

The two types of experiment just 16 ed probably belonged to two different post-operative stateg he acoustic analyser, the first an earlier, the second a later &{age.’ This is the more probable since in other dogs which Ae a similar operation (Fig. 12) we also observed a ralization of auditory conditioned simultaneous and short-de stimuli [experiments of Dr. Babkin]. A conditioned Eier reflex had been established to a descending scale (©) neighbouring tones, and this was completely differentiated oar same scale taken in the ascending direction.

On the eighth@ay after removal of the temporal lobes the experiment proceeded am ows : | suite | ce Time '! Conditioned stimulus during Salivary Secretion in drops 30 seconds during 30 seconds LEDS. .; Tapping on a glass bottle 12 apm. Scratching on the table a, Descending scale of tones 2 Reinforced | be eae Descending scale of tones 6 Reinforced 12:25 ©; Tapping on a glass bottle 4 Not reinforced All the stimuli, except the scale of’ tones, used in the above experiment were “ neutral,” i.e. had never been reinforced.

established auditory conditioned stimulus never previously had any conditioned A times as effectively as the descending e of tones. When these extraneous sounds weakened in their\éffect on account of non- reinforcement, the conditioned sti Qi also considerably diminished in its effect (11.49 ; 12.3). Ongaprcins the conditioned stimulus the effect of the other sou so became increased (12.25 p.m.). The sound in its capac yQ a conditioned stimulus had. become extremely generalized, ey analysis had become impaired so as to be practically negfgible. When the power of analysis begins to reappear the impr ent proceeds very often with extreme slowness. First of all raya nes are distinguished from other kinds of sound,

like knocks and noises. The differentiation between different tones remains imperfect for a very long time ; in these experiments of Dr. Babkin, for example, differentiation between single tones only began to return through gradual stages two months after the operation. The absence or the diminished precision of the analysing function of the acoustic nervous apparatus described is obviously identical with what H. Munk terms “ psychic deafness.” It is impossible, however, not to see the fundamental difference between the purely physiological and the psychological interpretation of these facts. According to the definition of Munk “the animal hears but fails to understand,” and experimentation becomes sterile in the interpre- tation of “ understand.” But the physiological point of view opens up a vast field for experimentally investigating the different stages of the re-establishment of functions in the damaged acoustic analyser. Under normal conditions sounds are differentiated according to their strength, duration, continuous or interrupted character, point of origin, and nature— whether tones, knocks, noises, etc. It must be expected—and in this respect it can be stated that we have definite proof—that in returning to normal the damaged acoustic analyser passes through different stages of activity, and only by detailed investigation of these stages can we hope ever to reach a complete understanding of the mechanism of acoustic analysis.

The foregoing does not complete our picture of the disturbances in the functions of the acoustic analyser after the\removal of the temporal lobes. There is another, probably snost important, functional disturbance. It was noticed a lo Gime ago, by many in- vestigators, that after an operation upon ato lobes dogs cease to respond to their names. This was ob also in our experiments, © the special analysis of conditione tory compound stimuli. In order to verify this point a experiments were performed by

i were established to different tones s or with different intervals between them. One definite s ce was used for a positive conditioned redex, others for n e ones (differentiation). These differentia- tions, as menti O the eighth lecture, were much more difficult to establish thay differentiations of single tones. Besides the differen- tiation of e ound auditory stimuli, differentiations of single tones were als NS lished. Both temporal lobes were then extirpated in oka The disturbances which followed the operation were

exactly identical in the five dogs employed for the experiments. While the differentiation of single tones sooner or later became re-established with the same precision as before the operation (a differentiation of intervals of a single tone), there was never the slightest trace of any re-establishment of a differentiation of the successive compound stimuli, though most of the dogs were tested for 2-3 months after the operation, and one dog for nearly three years. In the latter dog [originally observed by Dr. Koudrin] the entire posterior part of the hemispheres was removed as in the two dogs previously described (see Fig. 9, p. 330). The final operation was performed on the 5th May, 1909. The experiments to be described were started towards the end of 1911. Alimentary conditioned reflexes were established to an ascending scale of tones of pneumatic tuning forks—290, 325, 370, and 413 d.v., and to a separate tone of a Stern’s tone-variator—1200 d.v. The reflexes developed fairly quickly and a differentiation between the single tone of 1200 d.v. and a tone of 1066 d.v. was attempted through stages of differentia- tions from 600 and then 900 d.v. The final differentiation was successfully established. A differentiation of the descending scale, on the other hand, completely failed to be established in spite of 150 repetitions of the descending scale contrasted with 400 of the ascending scale. The reaction to calling the dog by name was also absent during the whole period of three years. The following example is taken from a late stage of these experiments Ke arch,

Time Conditioned stimulus during Salivary Sgeetion during 30 seconds : onds following, up to ion aie solitary, case [experiments of Dr. ed alimentary reflex was established to a reflex reached its maximum strength the different component tones were tried separately. They all produced a positive effect weaker than that of the chord but approximately equal in strength among themselves. The effect of intermediate tones was extremely small. After the removal of the anterior portions of the temporal lobes (Fig. 13) the relative effect of the different components underwent a considerable change. The effect of 768 d.v. and of the neighbouring tones disappeared altogether, though the reflex to the chord returned on the fifth day after the operation. The lower component of the chord—85 d.v.—when tested alone began to act with increased vigour, its effect often being equal to that of the whole chord. What can be the explanation of the extremely definite results of these experiments ? The first explanation that suggested itself was that

the reflexes to the higher musical tones had been selectively disrupted as a result of the operation. This, however, was absaqlitely disproved, since when the tone of 768 d.v. was reinforced i dently of the chord it very quickly assumed independe Cand very definite properties as a strong conditioned stimule To our great regret this dog died before we could accompli iferent modifications in the experiments. The absence of the S of the higher tone before it was independently reinforced canfoto® attributed to any difference in strength of the tones in the §ord, since the highest tone was if anything stronger than the tv€o)ldwer ones. The observations are in accord with the theory @,the existence of a special part of the acoustic analyser in wi synthesis and analysis of successive and simultaneous co auditory stimuli is effected (the acoustic area of H. Munk). part of the acoustic analyser would provide a parallel with doubted projection of the retina upon a definite part of the K nalyser. According to this supposition such part

of the acoy rset which is connected with all the parts of the peripheral acoustic apparatus, so that on account of the specially favourable local structural peculiarities a facility is afforded for the formation of various and complicated connections, involving the establishment of reflexes to most complex compound auditory stimuli as well as their ` analysis. A partial destruction of this portion leads to a dropping out from the compounds of some of the individual components, and a complete destruction entirely eliminates the higher synthesis and analysis of compound stimuli. After complete removal of the temporal lobes auditory conditioned . reflexes still continue to exist [Dr. Kalischer,! and our own experiments], and an elementary differentiation can still be effected, while after extirpation of the whole cortex all conditioned reflexes entirely and permanently disappear. Only one conclusion, therefore, can be drawn, namely, that in the cortex, besides the special part of the acoustic analyser, there must exist some extensions of the analyser dispersed more widely over the cortex, and maybe throughout its whole mass. These elements owing to their dispersion are not able to enter into complex interconnections, though they can still perform an elementary synthesis and analysis. It is possible also that the simplification or limitation of activity of different parts of the acoustic analyser increases with their distance from the cortical “ nucleus ”’ of the analyser.

The hypothesis of such a distribution of the cortical pa of the e acoustic, and probably of any other, analyser seems to me,t best with the available facts, and to open also an unlims further investigation. It would fit in with the wi which will be proved later, of any one analyser analysers, far beyond the limits of the hitherto a ed localizations. It would also agree with the existence of cial “ nucleus ” in each analyser in which, on account of the y and the exceptional concentration of the elemental units of geien analyser, the higher synthetic and analytic activity is reņdèed possible. Again, it could also without difficulty explain th ual improvement by practice of the activity of the remnan he analysers, the functions. of which are so limited imme y after the lesion of its nucleus. Ultimately it should a @Xrmine the limits to which such an improvement could exte In the dog last mentioned the elementary — 1Q. Kalischer. “< ktion des Schlafenlappens des Grosshirns.”’

analysis of tones had probably reached the maximal degree possible, the loss of the higher synthesis and analysis remaining permanent even after three years of practice. The hypothesis suggested, of such a wide distribution of analysers in the cortex, naturally sets up further problems for experimentation which should be used to test its validity. In regard to the acoustic analyser, before a partial extirpation there should be developed as great a number as possible of positive elementary and compound stimuli, and various differentiations. The different general pro- perties of the elementary stimuli should be determined for each dog, their threshold strength, the conditions under which positive stimuli acquire an inhibitory character, the mobility of the inhibitory process and the degree of its after-effect, and so on. Only such further ex- periments can demonstrate definitely the changes which occur as the result of an operation, how far these changes affect the general properties of the reflexes and what changes constitute the direct result of damaging different parts of the analyser. During the period of re-establishment of the acoustic function after the operation special attention must be paid, as was previously mentioned, to the determination of the different transition stages. It is obvious that in order to carry out such a plan a healthy and prolonged existence of the animal after the operation must be ensured. Unfortunately this cannot up to the present be satisfactorily a ined.

Pathological disturbances of the cortex, result of surgical interference (continued) : (c) in the visual analyser ; (d) in the tactile cutaneous analyser ; (e) occurriny 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. THE pathological disturbances of the visual analyser, which will be discussed next, have not been studied in our laboratory to the same extent as those of the acoustic analyser, but such experiments as have been performed permit us to trace very similar relations in the activity of the two analysers after extirpation of corresponding parts of the cortex.

It was shown by Goltz with his decorticated animal, that the “ investigatory reflex ” to light can be brought about, in its most rudimentary form of a motor reaction, through sub-cortical areas alone, without any co-operation of the cortex. This, however, is all that could be deduced from Goltz’s experiments. Neither is there any indication in the writings of subsequent authors as to the exis- tence in such animals of any higher visual functions. In decor- ticated dogs [experiments of Dr. Zeliony], even thig ntary reaction was not sharply defined, so that it would se question- able that the entire scope of the visual function nd this very elementary and limited reaction belongs exclusj to the cerebral cortex, exactly as in the case of the analysdr)ot the mouth (e.g. the water-reflex) and the acoustic anal in the experiments previously described. It has been showg that even in the case of the primitive analyser of the mouth Qo conditioned connections could be established in absence ọ e cortex, although a certain rudimentary analysis was still Ropsible (such dogs rejected many non-alimentary or irritatin gtances). In the case of the visual analyser there can be no n at all of any possible establishment of conditioned reflexes(to) visual stimuli exclusively through sub- cortical areas. A

we obtained a definite diminution of the visual field, either in the horizontal or the vertical direction, in one or both eyes, according to the site of the damage in the occipital lobe on one or upon both sides. Thus, objects which happen to fall within the intact parts of the visual field continue to evoke their corresponding reactions, while the same objects but slightly shifted in position fail to evoke any reaction on the part of the animal. Evidently the occipital lobes must contain the nucleus of the visual analyser, upon the integrity of which depends the existence of visual reflexes, involving the more complicated forms of synthesis and the finer shades of physiological analysis. After bilateral extirpation of the entire occipital lobes none of our dogs ever showed any sign of object vision during the whole time of survival after the operation (one animal survived three years). Neither men nor animals nor food were discriminated by these animals by sight. We would frequently lay upon the floor, or suspend on strings at different heights, pieces of food, but there was not a single dog after bilateral extirpation of the occipital lobes, which, however long it had been deprived of food, ever on one single occasion directed its movement by sight. The dogs directed. themselves to the pieces of food obviously only by means of olfactory and tactile stimuli. The definite limitations of the visual field in the horizontal or vertical plane following damage of different regions of the occipital lobes show that the loss of object vision depends upon the absence of the higher synthegis and analysis of visual stimuli rather than upon a accessory visual reactions—convergence and accom moreover, animals with removed occipital lobes N ail to discriminate objects whether large or small, pia ar, in strong, medium or weak light.

Although the main nucleus o Qaa analyser—the organ of the higher analysis and anaes f visual stimuli—is located in the occipital lobes of the on ee these do not constitute the - entire analyser. The aera iat ser is dispersed over a much wider area, and probably over hole mass of the cortex. Even in the older days of the OA of the cortex it was the teaching of several authorities the frontal lobes also had a definite relation to vision. Thi clusion was derived from the impairment of vision which gppeared after extirpation of the frontal lobes—a form

of negativé ence which cannot be accepted as sufficient proof, since t Qis could be interpreted in terms of a protracted indirect EN aftėr-effect of the operation itself. At the present time, however, we are in a position to offer positive evidence for the view that a part of the analyser capable of performing a considerable visual analysis is situated in the anterior part of the cerebral cortex in front of a line beginning from a point above and immediately behind the gyrus sigmoideus, stretching obliquely downwards and laterally to the anterior angle of the gyrus sylviaticus, and then passing along the fissura fossae sylvit to the lower margin of the hemispheres (see Fig. 18, p. 363). We found in our dogs, after extirpation of the entire mass of the cortex behind this line, that stable conditioned reflexes could be established to changes in intensity of illumination, observations which are in complete agreement with the experiments of Kalischer. But, in addition to this, we found that a discrimination of tolerably fine gradations of the intensity of illumination could be definitely established. These observations give a simple and purely scientific interpretation of what has been called by H. Munk “ psychic blindness.” The visual analyser which is considerably damaged after removal of the occipital lobes can now establish conditioned connections only within the scope of a single limited function, namely, reactions to fluctuations in luminosity. On account of this the animal in an illuminated room is still able to avoid dark objects and to walk out through an open door guided by differences in lumi- nosity. In view of these facts it would be more exact to reverse the psychological phrase “ that the dog sees but does not understand,” and to say “ that the dog understands but does not se etiently well.” Such formularization is, of course, impermissib undant, since the whole disturbance primarily consists in ty@Qemitation of the analysing activity. The scientific value of thiNpbjective point of view has been fully confirmed by our furt vestigation.

In one of our dogs which retained the cortex front of the above- mentioned line, it was possible to es conditioned reflexes involving a still higher function of oa analyser than dis- crimination of differences in ot oe 7 This is the dog which was mentioned as having survived eration for three years, and which was described at the C2) he preceding lecture as having Erai lost the pow analysis of compound auditory stimuli. I shall describ, See upon this animal with the use of visual stimuli irhaghoil [experiments by Dr. Koudrin]. The operation on the Lege heres was performed in two stages, with an interval of one ~O in between. The final operation took place on the 5th aO 9. An alimentary conditioned reflex, established

before the operation, to switching on a hundred candle-power lamp in a semi-darkened room, definitely returned on the fifth day after the final operation. On the eleventh day it reached an even greater intensity than in the pre-operative period. Experiments with the visual reflex were then abandoned, the work being continued with auditory stimuli as described in the previous lecture. On the 7th September of the same year we began to establish a conditioned reflex to a moving luminous cross projected upon a screen in a semi- darkened room. The reflex developed quickly, and in the course of a week became of a considerable magnitude. From the 28th Sep- tember the luminous projection of the cross was held stationary. The reflex was still present although somewhat diminished in intensity. The development of a differentiation of the cross from a circle of equal area and equal luminosity was now begun. At the seventh and subsequent applications of the circle there was already a definite indication of a developing differentiation. The experiments were, however, interrupted and were not taken up again until after an intervening period of six months. After this interval the reflex to the cross was found still to be present. Its differentiation from the circle quickly developed and soon became constant. The following examples reveal a definite, though not yet absolute, differentiation.

12.0 noon Cross 6 drops durj seconds Reinforced Experiment of%th April, 1910. A post-mortem ination of the dog three years after the operation Tre e completeness of the removal of the whole There ¢ e no doubt that in this dog the part of the visual analyser was left in the anterior mass of the cortex was capable not wer establishing conditioned reflexes to changes in intensity of illumination, but also to different shapes of illuminated or shaded areas. At the same time, in this dog, as in all others after removal of the occipital lobes, no conditioned reflexes to separate concrete objects could at any time be established. The development of conditioned reflexes to differently shaped areas was successfully achieved so soon as four months after the operation, and could probably have been obtained even sooner. On the other hand, object vision was entirely absent for the whole post-operative period of the dog’s life (3 years), and it is reasonable to suppose that this state of the visual analyser was final and irrevocable, at any rate towards the end of the life of the animal. In this connection it is of interest to inquire how it is that the dog could definitely discrimi- nate areas of different shape during an experiment, and yet could not discriminate objects by their shapes when free. There is, of course, a vast difference between the environing conditions during the experiment and when the animal is set free amid a great number of different objects, each continually changing its aspect either in consequence of its own movement or the movement of the animal in relation to it. The sharpness of contour of the objects similarly never remains constant, depending on changes of illumination and upon the distance from the animal. During the experiment in the stand everything becomes much simpler as compared with the usual environ- ment. Probably, therefore, a very gradual and prolonged practice would have been required for the surviving faculty of siggtnpatng shapes to assume any sort of practical usefulness for t timal. On the basis of our observations the results of age of the visual and acoustic analysers may in the mai considered as comparable.

A limitation of the visual field si Q a small damage of the visual analyser ; in the auditory a , if it is permissible to rely on the experiment upon a singl g, a dropping out of auditory compounds of elementary tones an identical signification, A disappearance of discrimination ofebjects, t.e. disappearance of compounds made up of forms, s , colours (in those exceptional dogs in which colour vision e conjectured), in other words, a disappearance of the high thesis and analysis of visual stimuli, signifies a more extengy KH age of the visual analyser. A com- parable disturbance i e case of the acoustic analyser can be recognized in a ie ac of discrimination of compound stimuli, that is, a loss o ‘Ss er synthesis and analysis of auditory stimuli. In the case of imal disturbance of either of the two analysers—

apart from a total destruction—the only function which survives is the discrimination of intensity of visual or auditory stimuli. Between these extremes there are some intermediate stages, in which, besides differences of intensity, differences in the configuration of luminous areas can be discriminated in the case of the visual analyser, and different types of sound—noises and musical tones— The next question we had to decide was whether the distribution

of the tactile analyser over the cortex is analogous to the distribution of the acoustic and visual analysers ; in other words, whether besides the special nucleus of the highest activity in this analyser there is a wider dissemination of cortical tactile receptive cells with more limited activities. Although we are not in a position to give a final answer to this question we are yet disposed, on the basis of our ex- periments, to consider such a distribution as more than probable. I shall give some of our old and also our recent material relative to this question ; this material, besides its bearing on the distribution of the analyser, also presents some other points of interest. Many years ago it was observed that a removal of the anterior part of the hemispheres led to a disappearance of tactile conditioned reflexes, while reflexes to stimuli belonging to other analysers were retained [experiments of Dr. Tihomirov]. In later experiments [by Dr. Krasnogorsky] it.was definitely established also that ¢he motor area is more or less clearly demarcated from the sp Nucleus of the tactile analyser, and that definite parts of this sp region represent projections of different parts of the skin. On e dogs had, besides different reflexes belonging to other anal , a tactile conditioned reflex to acid, which had ‘been experj ally generalized for the whole surface of the skin. The gyri rius and ectosylvius anterior were now removed on the left rige n Fig. 14). On the fourth day after the operation einen.) exes satu to the analysers other than the tactile wer ent. The generalized conditioned tactile reflex returned on ii ohth day, but only to stimulation on the left side of the a ugh dc soon reached its normal magnitude. On the tenth day Avi reflex returned on the right side of the animal, but onl mulation of the skin of the middle part of the body.

On the limb and hind limb, on the shoulder and pelvic area it wa¢¢frely absent, the line of demarcation between those areas whi ad regained, and those which had lost, the reflex to tactile KMulation being very sharp. The loss of these reflexes persisted up to the 90th day following operation, and after this they gradually became re-established, in order, from the shoulder and pelvis to the corresponding paw. These experiments, besides cor- roborating the localization given by H. Munk, present another interesting detail. During the period while the conditioned stimuli of the above-mentioned places of the skin had lost their positive effect they divulged a definite inhibitory effect, as has already been mentioned in the lecture dealing with sleep (p. 259). The seemingly ineffective stimulation of these different areas of the skin when used together with, or preceding, the stimulation of other cutaneous areas which continued to give a positive effect, or with, or preceding, con- ditioned stimuli belonging to other analysers, invariably diminished

or even abolished such reflexes. Further, a repeat markedly a protracted, stimulation of these a places on the skin resulted in every experi of drowsiness and sleep, even in dogs vt never showed any tendency to E the stand. The sleep developed in these cases exclusively €a\eonnection with the tactile stimulation of these areas ; iek their application the dog These experiments were recently repeated, and with exactly the same results [D senkov]. Ina dog in which the same convolutions were pa destroyed all the reflexes belonging to other analysers were p t, but only so long as the areas of the skin disturbed by the G9 tion were not stimulated. After stimulation of these areas the al invariably became sleepy and all conditioned reflexes dis ared throughout the remainder of the experiment.

It was a problem of considerable interest to determine whether it would be possible by some means to disclose anything in the nature of a positive reaction to these tactile stimuli. We succeeded in demonstrating such an effect by the following modification of the experiments. The isolated stimulation of the refractory places of the skin was abbreviated from its usual duration of 30 seconds to 5 seconds. The abbreviated stimulus was now used several times in each experiment, and at the end of the experiment, in order to test the reflex, reinforcement was again delayed for 30 seconds. Under such conditions it was possible to observe the positive as well as the inhibitory effect of the stimulation. The positive effect appeared quickly, but was very small, and, what is important, disappeared while the conditioned stimulus was still acting, whereas the effect of all other conditioned stimuli increased, as usual, towards the end of their isolated action as the moment of reinforcement approached. The following is taken from an experiment by Dr. Rosenkov :

A metronome, a whistle, the light of an electric lamp, and a tactile cutaneous stimulation served as positive conditioned stimuli. After the cerebral operation the conditioned reflex to stimulation of the fore limb disappeared.. The secretion of saliva was measured as usual by the graduated tube, five divisions of which correspond to one drop. The secretion before the operation in this dog was generally small. No attacks of convulsions had been observed following the operation. The tactile stimulatio he following table was always applied on the fore limb : XS