Analysis of spike discharge of a neuron population in the cat motor cortex during a conditioned change of posture reflex

Spike responses of area 4 neurons in the projection area of the contralateral forelimb to acoustic stimulation (1 sec), which became the conditioned stimulus after training, and to dropping of the platform beneath the test limb, which served as reinforcing stimulus, were studied in trained and untrained cats. Responses only of those neurons which were activated during a passive movement caused by dropping of the platform were studied. In trained animals the number of these neurons which responded to the conditioned stimulus if a reflex occurred was 100%, and in the absence of conditioned-reflex movements to the conditioned stimulus it was 70%, much greater than the number of neurons responding to the same acoustic stimulus in untrained animals (45%). On peristimulus histograms of responses of the test neuron population in untrained and trained animals to acoustic stimulation (in the absence of movements) only the initial spike response with a latent period of under 50 msec and a duration of up to 100 msec could be clearly distinguished. In the presence of reflex movement multicomponent spike responses were observed: an initial spike response and early and late after-responses linked with performance of conditioned-reflex limb flexion. Early after-responses 100–200 msec in duration, appearing after a latent period of 100–150 msec, were linked to the time of application of the conditioned stimulus, whereas the appearance and duration of late after-responses were determined by the time of onset of conditioned-reflex movement. The magnitude of the neuronal response to reinforcement in trained animals does not depend on the appearance of the conditioned movement.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 93–102, January–February, 1985.     

Unitary activity in the cat motor cortex during a conditioned postural adjustment reflex

Unitary activity in the motor cortex (area 4) during a conditioned postural adjustment reflex was investigated in cats. Responses of the overwhelming majority of neurons connected with conditioned-reflex placing movements were activational in type. They consisted of several components and preceded the movements themselves by 50–600 msec. During realization of incorrect responses to presentation of a differential stimulus and of "spontaneous" interstimulus movements, the unitary responses were similar in direction but differed in their lower intensity and, in most cases, they appeared simultaneously with these movements. In the course of extinction both the conditioned-reflex movements and the corresponding unitary responses disappeared simultaneously. The technique of formation of a conditioned postural adjustment reflex suggested in this paper can be used to from natural, well-coordinated forelimb movements in animals in response to conditioned stimulation which are necessary initial components of more complex behavioral motor responses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 745–753, November–December, 1984.     

Unit responses of the secondary somatosensory cortex during defensive conditioning in cats

Unit responses in the secondary somatosensory cortex during the formation and extinction of a defensive conditioned reflex to acoustic stimulation were investigated in chronic experiments on cats. In 21 of 28 neurons tested during defensive conditioning the firing pattern changed in accordance with the character of responses to electric shock reinforcement. Two types of conditioned-reflex unit responses were distinguished: excitatory and inhibitory. Most neurons responding to the conditioned stimulus by activation did so during the first 50 msec, which was 80–100 msec before the conditioned motor response. Considerable variability of the unit responses was observed during conditioning. By the time of stabilization of the conditioned-reflex connections the unit response to the conditioned stimulus was stable in form. The pattern of extinction of the conditioned unit activity was expressed as a decrease in the discharge frequency in responses of excitatory type and disinhibition of activity in the case of inhibitory responses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev, Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 232–238, May–June, 1977.     

Neuronal responses in area 7 of the cat cortex during defensive conditioning

Responses of neurons in area 7 of the parietal association cortex during and after formation of a defensive conditioned reflex to sound were recorded in waking cats. Changes in spike responses of the neurons as a result of the onset of conditioned reflex limb movements were observed in 68% of neurons. Spike responses of neurons formed as a result of learning appeared only if conditioned-reflex limb movements appeared, and they were not observed if, for some reason or other, movements were absent after presentation of the positive conditioned stimulus or on extinction of the reflex. Responses of 46% neurons to conditioned stimulation preceded the conditioned-reflex motor responses by 50–450 msec. The remaining responding neurons were recruited into the response after the beginning of movement. Characteristic spike responses of neurons to the conditioned stimulus appeared 500–900 msec before the beginning of movement and, in the case of appearance of special, "prolonged" motor responses of limb withdrawal, evoked by subsequent reinforcing stimulation.     

Participation of midbrain periaqueductal gray matter in defense conditioning in rats

Responses of neurons of the periaqueductal gray matter (PAG) were studied in chronic experiments on cats during formation and extinction of a defensive conditioned reflex to sound and its differential inhibition. In response to conditioned stimulation these neurons developed phasic-tonic spike responses up to 3 sec in duration. During combination of stimuli these responses were formed long before the conditioned reflex and disappeared long after the latter was extinguished. In the case of an established conditioned reflex, the onset of spike responses occurred 100–200 msec before the appearance of motor responses. An increase in spike activity of tonic character in neurons of PAG preceded voluntary movements by 100–500 msec. The responses of these neurons to presentation of a differential stimulus consisted of groups of spikes 150–200 msec in duration. They were formed with difficulty, and their manifestation was made even more difficult by an interruption during the experiment and by preceding positive stimuli. On the basis of the results a conditioned reflex can be regarded as the result of a multilevel hierarchic process of readjustment of unit activity, which begins in the nonspecific structures of the midbrain.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 15, No. 3, pp. 278–287, May–June, 1983.     

Response of recticular and dorsal thalamic nuclei neurons during extinction of conditioned implementation in the cat

Unit activity in 66 neurons of the reticular (R) nucleus and 31 neurons of the ventropostrolateral nuclei of the thalamus, and 14 neurons of the posterolateral nuclear complex, the pulvinar, were studied during extinction of the conditioned food implementation reflex. The number of R neurons that had responded to initial excitation in the first 300 msec after the conditional stimulus (CS) decreased with the extinction. Simultaneous disappearance of conditioned-reflex placement movements and late excitatory and inhibitory responses of R and dorsal thalamic nuclei neurons with latent periods exceeding 300 msec was also observed. Extinction of the conditioned reflex (CR) led to a significant lowering of background activity in two-thirds of investigated R and other thalamic nuclear neurons. This suggests that efferent effects from the reticular nucleus are decreased during Cr extinction.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 3–8, January–February, 1991.     

Dynamics of single unit activity in the association cortex of waking cats during defensive conditioning

Responses of neurons in association area 5 during defensive conditioning to acoustic stimulation were studied in chronic experiments on cats. As a rule the neurons responded by excitation to presentation of conditioned and unconditioned stimuli. During the conditioned reflex unit responses usually appeared in the first 50 msec after the beginning of acoustic stimulation, i.e., they were connected with the action of the conditioned stimulus and not with manifestations of conditioned-reflex motion. The most significant changes in responses of cortical association units were observed in the initial period of conditioning. During stabilization of the conditioned reflex, responses of some neurons became stabilized, whereas in other neurons the spontaneous activity and intensity of responses increased, and in a third group the response to one of the stimuli disappeared. This last result indicates a switch during conditioning from polysensory unit responses to monosensory specialized responses. Extinctive inhibition was found to consist of a gradual decrease in the level of the spike discharge and its approximation to spontaneous activity, i.e., to be passive in character.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 563–572, November–December, 1978.     

Dynamics of cortical unit responses during defensive conditioning to sound

Several phases were distinguished in single-unit responses in areas 3 and 4 during defensive conditioning to acoustic stimulation: an initial response, short inhibition of the spike discharge, early and late after-discharges, and changes arising after the end of acoustic stimulation. The initial spike response appeared or intensified (if present already) in the first period of defensive conditioning parallel with an increase in spontaneous unit activity. After-discharges appeared later. The conditioned-reflex movement usually began 100–400 msec after stimulation began. This latent period of the first movement was the same whether for a real conditioned reflex or an after-discharge. Comparison of the latent periods of conditioned movements with the phases of the unit responses showed that the conditioned responses of the cortical neuron were primarily modified after-discharges of neurons evoked by a conditioned stimulus. Differential unit responses to acoustic stimulation, also based on after-discharges, were formed just as actively as positive. The basic role of reinforcement during conditioning is not to increase the excitability of the neurons, which is important in connection with their acquisition of polysensory properties, but to modify the after-discharges of the neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 4, pp. 339–347, July–August, 1978.     

Responses of somatic cortical neurons during the conditioned placing reflex in cats

Unit activity was studied in areas 3 and 4 during the conditioned placing reflex in cats. Responses of somatic cortical neurons in this case were shown to develop comparatively late — 80–100 or, more often, 200–450 msec after the conditioned stimulus. In the motor cortex responses preceded movement by 50–550 msec, whereas in the somatosensory cortex they usually began simultaneously with or after the beginning of the movement. Judging from responses of somatic cortical neurons, the placing reflex is realized by the same neuronal mechanism as the corresponding voluntary movement. The differential stimulus and positive conditioned stimulus, after extinction of the conditioned placing reflex, evoked short-latency spike responses lasting 250–350 msec in the same neurons as took part in the reflex itself. In these types of internal inhibition, responses of the neurons were thus initially excitatory in character. Participation of the neurons in the conditioned placing reflex and its extinction, disinhibition, and differentiation, is the result of a change in the time course of excitatory processes and is evidently connected with differential changes in the efficiency of the various synaptic inputs of the neuron.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 392–401, July–August, 1982.     

Responses of limbic cortical neurons during instrumental conditioned reflexes in cats

Unit activity in cortical areas 24 and 32 was studied during conditioned placing reflex formation in cats. Neuronal responses in the limbic cortex of trained animals correlated with acoustic stimulation, the motor response, and also with the presentation of food reinforcement. In untrained animals 16% of neurons responded to acoustic stimulation. After training the number of neurons responding to sound in area 32 increased to 51.3%. Of the total number of neurons, 34.6% responded by initial excitation and 26.7% by inhibition of spike activity. The latent period of these responses was about 50 msec and their duration up to 200 msec. Similar but weaker responses were observed in area 24. Short-latency activation responses to conditioned and differential stimulation were similar in character. It is suggested that after training processes taking place in the limbic cortex may contribute to better perception of both conditioned and differential acoustic stimuli, irrespective of their functional significance.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 201–208, March–April, 1984.     

Involvement of mesencephalic reticular formation neurons in cat conditioned reflexes

Traditional defensive and operant food reflexes were used to investigate neuronal responses of the mesencephalic reticular formation. It was found that these neurons may be divided into different groups according to function, depending on how they respond to positive conditioning stimuli. Of the two main groups of neurons with sustained tonic reactions one is activated in response to positive acoustic conditioning stimulation; it no longer reacts to the same stimulus after extinction of the reflex, while the other only becomes involved in response to positive stimulation accompanying the initiation of movement. Neurons belonging to the second group begin to respond directly to acoustic stimulation after extinction of the conditioned reflex. Neurons of the mesencephalic reticular formation can thus exercise additional tonic ascending effects both in the production and inner inhibition of the conditioned reflex. The group of neurons with a phasic reaction, i.e., a double response (a direct response to sound and another produced by movement) displayed a drop in spontaneous activity during the shaping of inhibition of differentiation and of extinction in particular. It was found that the initial changes in the spike response of reticular formation neurons during conditioning and pseudo-conditioning are similar. There are thus grounds for stating that neurons of the mesencephalic reticular formation participate in the shaping, production, and inner inhibition of traditional and operant conditioned reflexes in a differentiated capacity rather than as a population reacting identically.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 161–171, March–April, 1986.     

Inhibitory influence of supplementary extraneous stimulation upon neuronal responses in the sensorimotor cortex of the cat during a conditioned reflex

Using alert rabbits trained to perform placing movements in response to a sound click, we investigated impulse responses (IR) of neurons of the somatosensory cortex preceding realization of the reflex by 50–150 msec. When a brief extraneous stimulation (light flashes, audible tone, electrical stimulation of a limb) was applied after initiation of the reflex, learned movements with the earlier behavioral parameters (latent periods and duration) were maintained. However, the IR of neurons to the presentation of a conditioned stimulus (CS) was of lesser intensity and arose 50–250 msec later. A constant extraneous stimulation (an audible tone, a forced stream of air upon the muzzle) or a decrease in the intensity of the CS administered to the threshold of hearing resulted in similar changes in the neuronal responses upon the application of the CS, but the parameters of the learned movements were maintained. We suggest that the cause of these changes in neuronal responses is increased exteroceptive attention to extraneous stimulation to additional extraneous stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 174–181, March–April, 1991.     

Responses of motor cortex neurons of the cat to auditory stimulation and their role in the instrumental food reflex

The responses of motor cortex neurons in the cat to the presentation of a single auditory click and a series of 10 clicks presented with 1,000/sec frequency were studied under conditions of chronic experiments before and after the development of an instrumental food reflex. After reflex development a single presentation of a positive conditioned stimulus (single click) markedly influenced for 7 sec the appearance of instrumental movements. At the same time, the immediate responses of motor cortex neurons to presentation of the conditioned auditory stimulus had no impact on the appearance in the motor cortex of discharges leading to the realization of instrumental movements. Consequently, motor cortex neurons do not require activation from afferent sensory inputs for the generation of such discharges. The immediate neuronal responses to conditioned stimulation did not inhibit the realization of the instrumental reflex. It is proposed that they are associated with the realization of motor function in the unconditioned defensive response evoked by the presentation of an auditory stimulus. The presence or absence of responses to auditory conditioned stimulation was dependent upon the signal meaning of the stimulus, its physical parameters, and the degree of excitability of the animal.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 539–550, July–August, 1985.     

Changes in neuronal responses of area 7 of cat cerebral cortex to unconditioned and conditioned stimulation under the effects of external stimuli

The effects of external stimuli (ES) and feeding motivations on area-7 neuronal impulse responses (IR) elicited by unconditioned and conditioned stimulation in alert cats were investigated. In untrained cats, preliminary (by 1 sec) action of ES resulted in the disappearance of impulse responses to electrical stimulation of the forepaw (EFS) in the first (no more than five-eight) executions; the responses gradually reappeared and in subsequent executions reestablished their former magnitude. The emergence of feeding motivation excitation in the cats, elicited by food presentation, also promoted disappearance of the initial responses to EFS; these were reestablished only after the cats were quieted. In conditioned-reflex cats, the action of the ES, which had been suppressed after onset of the reflex, as well as lowering of initial feeding motivation level (caused by natural satiation of the cats or by change in quality of the reinforcing food item), led to increase in latent periods (by 50–250 msec) and prolongation of neuronal responses to the conditioning stimulus (CS); but these parameters were unchanged during performance of trained movements. Neuronal response lag time to the action of the CS was defined by ES delivery time and by level of feeding excitation in the cats. The reason for the variation of neuronal responses to unconditioned and conditioned stimulation in the parietal cortex is assumed to be associated with variation in exteroreceptive attention level of cats under the effects of stimuli and altered metabolism.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 564–574, September–October, 1991.     

Neuronal responses in the cat substantia innominata during instrumental conditioned reflex

Neuronal spike activity in the substantia innominata was investigated when establishing the instrumental conditioned reflex of lever-pressing with food reinforcement during chronic experiments on cats. Spike activity changed in 44.3% of neurons during this process; 24.3% responded directly to conditioned acoustic stimulation. Reactions associated with conditioned reflex movement were less pronounced. Response of peak intensity and duration was observed during food reinforcement, when the reaction occasionally occurred 500 msec in advance of the reinforcement provided. Involvement of cholinergic substantia innominata neurons in reinforcement is thought to be responsible for the persistence of residual effects in neocortical neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 796–804, November–December, 1989.     

Neuronal responses in the limbic cortex of awake cats during defensive conditioning

Spike activity was investigated in limbic cortex neurons during defensive conditioning to acoustic stimulation in chronic experiments on cats. A relationship was found between the numbers of neurons responding, their contribution to formation of a temporal connection, and the duration of the acoustic stimulus. Phasic responses of 50–500 msec duration with latencies of 15–50 msec were observed for the most part. Intensive spike response with a minimum latency of 15 msec and a duration of between 200 msec and 2.5 sec evolved in most cells (95.1% in field 24 and 83% in field 32) in response to electrical stimulation. Response to acoustic stimulation rose during defensive conditioning in 33.3% cells and declined and finally disappeared in 13.3%, but response at the site where reinforcement was abolished was reproduced in all these cells. It was thus found that the numbers of limbic cortex neurons responding to sound not only fails to increase but actually decreases after training. The limbic cortex is thought to play its most active part in conditioning response to a recognized signal during the period preceding the awaited painful reinforcement.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 660–669, September–October, 1986.     

Neuronal response in the cat parietal association cerebral cortex (area 5) during performance of conditioned reflex motion

Responses in 160 neurons of the cat parietal cortex were investigated during the performance of instrumental food reflex (lever pressing) during experiments involving presentation of a conditioned acoustic stimulus. Discharge rate changed in 49% of neurons during the period preceding the conditioned reflex movement. Three basic types of cell with an excitatory response pattern were discovered apart from a small group showing suppression of activity, each differently involved in the process of conditioned reflex movement performance. Excitation arose in neurons of the first type 200±52.9 msec (average) before the onset of the conditioned reflex movement, reaching its peak discharge rate as the animal placed its paw on the lever. The former parameter was 605±54.2 msec for the second type of neuron, with firing rate peaking between the start of electromyographic response and the completion of lever pressing. The same parameter measured 1,000–2,000 msec in the third type and activation took the form of a diffuse increase in discharge rate without a clear-cut peak occurring during performance of the instrumental reflex. Findings would suggest the involvement of the parietal cortex neuronal system in the triggering as well as the follow-through of conditioned reflex motion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 223–231, March–April, 1987.     

Characteristics of unit responses of the cat cerebellar cortex to acoustic stimuli

Investigation of unit responses of the cerebellar cortex (lobules VI–VII of the vermis) to acoustic stimulation showed that the great majority of neurons responded by a discharge of one spike or a group of spikes with a latent period of 10–40 msec and with a low fluctuation value. Neurons identified as Purkinje cells responded to sound either by inhibition of spontaneous activity or by a "climbing fiber response" with a latent period of 40–60 msec and with a high fluctuation value. In 4 of 80 neurons a prolonged (lasting about 1 sec or more), variable response with a latent period of 225–580 msec was observed. The minimal thresholds of unit responses to acoustic stimuli were distributed within the range from –7 to 77 dB, with a mode from 20 to 50 dB. All the characteristics of the cerebellar unit responses studied were independent of the intensity, duration, and frequency of the sound, like neurons of short-latency type in the inferior colliculi. In certain properties — firing pattern, latent period, and threshold of response — the cerebellar neurons resemble neurons of higher levels of the auditory system: the medial geniculate body and auditory cortex.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 3–12, January–February, 1973.     

Dynamics of auditory cortical unit responses of the waking cat during defensive conditioning to acoustic stimulation

In chronic experiments on cats unit responses of the primary auditory cortex (area 50) were studied by microelectrode recording during defensive conditioning to sound. During formation of the reflex biphasic responses with relatively short-latency (50–100 msec) and longer-latency (400–500 and 800–900 msec) activation predominated. Neighboring neurons, whose activity was recorded by the same microelectrode, also were involved more intensively in activity. Application of a differential stimulus in 70% of cases produced definite changes in unit activity, among which responses of activation type predominated. Analysis of the course of spike responses of the same neuron during the period of action of a large number of combinations and its comparison with the formation of the conditioned-reflex motor response revealed no direct correlation between these events.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 99–108, March–April, 1979.     

Conduction of excitation in the cat visual system

Unit responses in area 17 of the visual cortex to stimulation of the lateral geniculate body and optic tract were studied in experiments on unanesthetized cats immobilized with D-tubocurarine. Of the neurons tested, 53.6% responded to stimulation of the lateral geniculate body. In 92% of these cells the responses were orthodromic with latent periods of between 2 and 12.5 msec. Most cells responded with latent periods of 2.0–2.5, 3.0–3.5, and 4.0–4.5 msec, corresponding to latent periods of the components of the electropositive wave of the primary response. Antidromic responses to stimulation of the lateral geniculate body were given by 8% of neurons. The difference between the latent periods of responses of the same visual cortical neurons to stimulation of the optic tract and lateral geniculate body was 0.1–1.8 msec, but for most neurons (55.8%) it was 0.5–1 msec. The histograms of response latencies of visual cortical neurons to stimulation of the above-mentioned formations were found to be similar. It is concluded that the optic radiation contains three principal groups of fibers with conduction velocities of 28.5–16.6, 11.7–8.9, and 7.4–6.0 m/sec, respectively.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 589–596, November–December, 1975.