Influence of food motivation on neuronal response of the cat somatic cortex during instrumental reflex

Spike activity in neurons of areas 3 and 4 was investigated in experiments on cats during the conditioned reflex response of placing the paw on a support both before and after feeding ad libitum. Ingestion of a feed consisting of a rapidly absorbed glucose dairy mix did not prevent the reflex taking place if the animals' favorite food was used as reinforcement. Background activity increased in two-thirds of the neurons after the feed; the tonic constituent of neuronal response declined substantially and repeated contraction of the biceps occurring at the same rate as locomotor movements disappeared. Difference in latency of response produced by the conditioned stimulus in the same neurons before and after feeding measured 50–300 msec during the experiment. Measurements of latency of placing motion remained largely unchanged. Changes in the latency of neuronal spike response were thus found to be interrelated with the intensity of the animal's motivational excitation. It is suggested that fluctuations in degree of food motivation lead to changes in cortico-subcortical relationships responsible for initiation and performance of conditioned movements in these animals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 5, pp. 646–653, September–October, 1987.     

Effects of acetylcholine and cholinergic transmission blockers on neuronal spike activity in the cat motor cortex associated with conditioned reflex

The effects of direct application of acetylcholine (ACh) and m- and n-cholinoreceptor blockers on test cells were investigated in waking cats having developed instrumental lever-pressing conditioned reflex. Changes were recorded in both spontaneous and invoked firing activity in a functionally homogeneous group of motor cortex cells, in which increased discharge rate usually preceded the start of conditioned reflex movements. It was found, however, that ACh increased spontaneous activity considerably in some of the neurons tested and reduced it moderately in others. Atropine sharply reduced background activity in cortical neurons while preserving spike response to presentation of a conditioned stimulus and n-cholino-blockers such as hexonium and (occasionally) tubocurarine inhibited spike response produced by conditioned stimuli; background activity was slightly inhibited by hexonium and reinforced by tubocurarine. It was concluded that ACh put out by cholinergic fibers helps to maintain background firing activity level in cortical neurons under naturally occurring conditions, acting via m-cholinoreceptors, whereas factors influencing generation of spike discharges associated with performance of conditioned reflex movements are mediated by n-cholinoreceptors.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 579–589, September–October, 1989.     

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.     

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.     

Inhibitory effects of external stimulation on neuronal spike response in the cat association cortex during conditioning

The effects of external stimulus presentation on neuronal spike response induced in area 7 by conditioned and unconditioned stimuli were investigated in waking cats. Pointing reaction arising in response to the action of external stimuli led to the phasing out of spike response to unconditioned cutaneous stimulation, as well as depression or complete suppression of response in area 7 neurons to conditioned stimulus presentation, despite occurrence of conditioned reflex motion. External stimuli no longer exerted an inhibitory effect on the neuronal spike response induced by protracted use of conditioned and unconditioned stimuli. The fact that the conditioned lever-pressing reflex could occur either following or without neuronal spike response in area 7 would raise the question of whether neurons belonging to this area always participate directly in the triggering and occurrence of conditioned reflex motion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziogiya, Vol. 22, No. 2, pp. 147–155, March–April, 1990.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Role of the midbrain periaqueductal gray matter in conditioned reflexes

Unit activity in the midbrain periaqueductal gray matter (PGM) during an instrumental placing reflex, its extinction, differentiation, and conditioned inhibition, was studied in chronic experiments on cats. Spike responses 1–2 sec in duration in 69 (36.7%) of 182 neurons preceded by 400–800 msec the beginning of conditioned-reflex and voluntary intertrial movements. These advanced responses appeared 200 msec before the corresponding advance responses of motor cortical neurons. Fifty-eight neurons (30.9%) responded directly to acoustic stimulation with a latent period of 10–50 msec for 2–6 sec, 19 neurons (10.1%) generated double responses, linked with both the acoustic stimulus and subsequent conditioned-reflex movement, and 42 neurons (22.3%) did not respond to acoustic stimulation, although individual neurons of this group changed the level of their spontaneous activity in response to repeated conditioned stimulation, and this change was maintained for some tens of minutes. Extinction, differentiation, and conditioned inhibition all abolished conditioned-reflex movements, but each type of internal inhibition was accompanied by its own characteristic changes in the firing pattern of PGM neurons. Functional independence of neurons of the first and second groups was demonstrated during extinction and recovery of the conditioned-reflex. The results indicate the important role of PGM not only in the mechanism of the conditioned reflex, but also in the development of its internal inhibition.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 403–419, May–June, 1984.     

Neuronal response in the cat parietal association cortex to conditioned and non-conditioned acoustic stimuli

Neuronal response in the cat association cortex (area 5) to conditioned and non-conditioned acoustic stimulation was investigated. Numbers of neurons responding to a conditioned acoustic stimulus according to the traditional reflex pattern were twice as high. Numbers of inhibitory neuronal responses to the stimulus increased when instrumental reflex occurred. Neurons were found which only reacted to a conditioned acoustic stimulus in the absence of conditioned reflex movement occurring with instrumental food reflex. Although findings do not exclude the possibility of this cortical area contributing to the analysis of sensory signals and evaluation of their biological significance, it might be supposed that its main functional property lies in its involvement in the process of initiating behavioral response to a conditioned response.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 637–645, September–October, 1988.     

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.     

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.     

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.     

Effects of serotonin on neuronal response induced in the sensorimotor cortex by tactile and conditioned acoustic stimuli

Neuronal firing response in the sensorimotor cortex to tactile (non-conditioned) and acoustic (conditioned) stimuli was investigated in trained cats before and after iontophoretic application of serotonin and lysergide. Three functionally distinct groups of neurons were identified from the response produced by presenting tactile and acoustic stimuli. Applying serotonin was found to facilitate preliminary and residual spike response induced by tactile stimulation; it also facilitates and modulates response in many cortical neurons to conditioned stimuli. Facilitation takes the form of reduced latency of response and increased numbers of spikes in response to conditioned stimulus presentation, especially at the initial phase of response to sound and immediately after the onset of conditioned reflex motion. Additional neurons formerly unresponsive to acoustic stimuli joined in the reaction under the effects of serotonin. Changed response patterns often evolve following minor fluctuations in background activity level. It is suggested that facilitation of response following iontophoretic serotonin application in the neocortex is associated with activation of excitatory serotonin receptors (S₂). The lysergide-induced increase in background and evoked activity noted during experimentation can apparently be put down to blockade of inhibitory serotonon (S_1B) receptors.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 3, pp. 337–347, May–June, 1990.     

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.     

Neuronal spike response produced in the feline thalamic reticular nucleus by instrumental conditioned reflex

Spike response was investigated in 156 units of the thalamic reticular nucleus (RN) during performance of the instrumental feeding reflex of lever-pressing. This response consisted of lead and lag phases. Latency of the lead phase of response varied between 10 and 100 msec and total duration of response between 50 and 250 msec; minimum latency of the lag phase: 100–300 msec. Initial response to a conditioning clicking sound was found in 27 units, of which 26 showed excitation and the remaining single unit an inhibitory-excitatory pattern. The lag stage of response associated with performance of conditioned lever-pressing was found in 134 neurons, of which 115 showed an excitatory pattern, 19 displayed inhibition and the remaining 22 units failed to respond. The lag phase of response preceded the onset of conditioned reflex movement (CRM) in 30 neurons. A total of 118 neurons responded between the onset of CRM and the point of lever-pressing. It was concluded that the RN plays a part in perception of the conditioned signal as well as producing and controlling performance of CRM.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 8–18, January–February, 1991.