Neocortex neuron reactions caused by stimulation of the substantia innominata in cats

We investigated neuronal impulse activity in the sensorimotor cortex after substantia innominata (SI) stimulation in cats during the execution of an instrumental conditioned response consisting of placement of a paw on a pedal coupled with alimentary reinforcement. Stimulation of the SI was initiated 1 or 3 sec prior to conditioned stimulation. Background activity of the neurons was inhibited during stimulation of the SI. Preliminary stimulation of the SI one second in advance caused an increase of reactions linked to a subsequent conditioned stimulus and a conditioned-response movement in 32% of the neurons; a 3-sec lead caused increases of such reactions in 33% of neurons. In some cells which originally did not react to the conditioned excitation, a clear reaction did manifest after stimulation. Moreover, stimulation of the SI with a 1-sec lead caused inhibition of impulse reactions in 6% of the cells; with a 3-sec lead, it caused inhibition of impulse reactions in 33% of the cells. The spread of latencies of conditioned-response actions decreased 2- to 3-fold in this case. We discuss the possibility that acetylcholine, which is released by the terminals of cholinergic neurons of the SI, has a facilitating influence on the impulse activity of neocortical neruons.Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 1, pp. 11–20, January–February, 1992.     

Effect of response inhibition in cat motor cortex neurons during the expectation of conditioning stimulus

The spike responses of the motor cortex neurons (area 4) associated with forelimb movement were studied in awake cats earlier trained to perform placing motor reactions. Responses produced by the same neurons were compared in two situations: 1) when a sound-click conditioning stimulus (CS) was applied in isolation; 2) when a CS followed a preliminary warning stimulus (WS), a light flash, with a 100–1000 msec delay. During the reflex initiation by combined action of the WS and CS, response components that occurred prior to the placing movement (PM) performance under isolated CS action weakened and arrived 50–150 msec later; yet, response components that appeared in the same situation simultaneously with PM onset or later remained unchanged. PM latent periods were not changed when WS was applied. The temporal interval between WS and CS was characterized by depression of neuronal activity; depression duration was determined by the interstimulus delay. It is conceivable that the described transformations in spike responses of cortical neurons occurred due to changes in the sensory direction of the animal's attention; this direction, in all cases, is a crucial factor in the formation of neuronal activity in the cortex.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 21–27, January–February, 1993.t     

Effect of catecholaminergic transmission deficiency upon neuronal responses of the ventrolateral thalamic nucleus evoked by stimulation of cerebellar and pallidal inputs

During chronic experiments on cats, we investigated neuronal responses of the ventrolateral thalamic nucleus (VL) to stimulation of afferent inputs before and after injection of haloperidol and droperidol in cataleptic doses. In contrast to reactions in intact animals, the initial excitatory response of the VL neurons to stimulation of the cerebellar input after injection of neuroleptics was characterized by irregularity of manifestation and variability of the latent period; responses were in the form of burst discharges. Upon stimulation of pallidal afferents there was a consistent increase in the number of initial inhibitory responses consisting of two periods of suppression of background activity separated by an excitatory phase, at the same time that monophase inhibitory responses (68%) predominated in intact animals. Under neuroleptics, responses exhibiting a rhythmic alternation of periods of excitation and inhibition of impulse activity with a frequency of 3–5/sec appeared. It is proposed that these features of VL neuronal responses are a consequence of a hyperpolarized state of neurons caused by argumentation of external inhibitory influences in connection with blocking of the dopamine D2-receptors of the nigrostriatal system or due to a weakening of depolarizing influences during disruption of central -adrenergic transmission.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 222–231, March–April, 1991.     

Unit responses of the cat caudate nucleus to cortical stimulation before and after destruction of nonspecific thalamic nuclei

Responses of caudate neurons to stimulation of the anterior sigmoid and various parts of the suprasylvian gyrus were studied in acute experiments on cats. The experiments consisted of two series: on animals with an intact thalamus and on animals after preliminary destruction of the nonspecific thalamic nuclei. Stimulation of all cortical areas tested in intact animals evoked complex multicomponent responses in caudate neurons with (or without) initial excitation, followed by a phase of inhibition and late activation. The latent periods of the initial responses to stimulation of all parts of the cortex were long and averaged 14.5–25.5 msec. Quantitative and qualitative differences were established in responses of the caudate neurons to stimulation of different parts of the cortex. Considerable convergence of cortical influences on neurons of the caudate nucleus was found. After destruction of the nonspecific thalamic nuclei all components of the complex response of the caudate neurons to cortical stimulation were preserved, and only the time course of late activation was modified.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 464–471, September–October, 1980.     

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.     

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.     

Investigation of heterosynaptic interactions in hippocampal areas CA1, and CA3 in vitro

Heterosynaptic interactions between synapses located at a considerable distance from the cell body (perforant path) and lying close to the body of the neuron (synapses of Schaffer's collaterals and axons of the dentate fascia) on guinea pig hippocampal neurons were investigatedin vitro. It was shown by the paired stimulus method that, using stimulation of subthreshold intensity for action potential generation, spatiotemporal summation takes place in both pairs of synaptic systems. If above-threshold stimulation was used, afferents lying close to the cell body suppressed responses evoked by stimulation of distant afferents for a longer time (up to 20 msec in area CA₁ and up to 300 msec in area CA₃) than during the opposite combination of stimuli (up to 3–8 msec). After tetanization of the dentate fascia depression of responses of area CA₃ neurons to stimulation of the perforant path was observed for 2–30 min. In the remaining cases, no significant prolonged heterosynaptic posttetanic changes were observed. The possible mechanisms of these interactions are discussed.Institute of Biophysics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 524–532, November–December, 1979.     

Effect of local surface cooling of the rat cortex on the impulse activity of neurons assumed to be the sources of corticofugal influences

In an experiment on albino rats with electrodermal stimulation of the forepaw evoked potentials (EP) in the neostriatum (NS), the cortical primary response (PR), and impulse reactions of neurons (mainly of layers V and VI of the cortex) were recorded. The zone of leading-off of the potentials in the cortex was subjected to local surface cooling, which led to an increase in the PR amplitude. This facilitation was accompanied by a change in the time parameters of the impulse reactions of the cortical neurons: the latency and duration increased, and a rhythmic organization of activity appeared or intensified (if it was already present). The increase in the PR amplitude and number of spikes in the response of the cortical neurons to stimulus presentation was far less intensive than the sharp increase in EP amplitude in the NS, and did not correspond to it fully in time. The data suggest that the activating influence of the corticofugal signal on EP in the NS is determined not so much by the intensity of the descending signal as by its temporal organization.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 181–189, March–April, 1991.     

Involvement of glutamatergic intracortical connections in conditioned reflex activity

The influence of iontophoretic application of glutamate and its blockers on the impulse activity of neurons of the sensorimotor cortex, associated with conditioned reflex activity, was investigated in chronic experiments on trained cats. It was established that in many neurons glutamate promoted an intensification of the impulse reactions to the conditioned stimulus. This intensification arose directly during the application of glutamate, several seconds after it was begun, and was maintained for 5–10 min after iontophoresis ceased. Similar inhibiting effects on neuronal reactions were demonstrated for 2-amino-5-phosphonovaleric acid, kinurenate, and ketamine. It was concluded that under natural conditions of functioning or the performance of acquired reactions, facilitation of intracortical interneuronal glutamatergic connections, providing for increased readiness of the neocortex for subsequent reactions, is systematically maintained in the cerebral cortex through the NMDA receptors. During the reactions the glutamatergic connections are intensively activated and participate negligibly in the organization of the background activity of the neurons.A. A. Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 6, pp. 701–712, November–December, 1992.     

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.     

Convergence of signals of various sensory modalities on the neurons of the sensorimotor zone of the rabbit cerebral cortex

The responses of the neurons to electrocutaneous stimulation, light flashes, and clicks in the cortical region of the motor representation of the rabbit forelimb were investigated by means of intra- and quasiintracellular recordings. In unanesthetized animals, in only eight out of 65 neurons did postsynaptic potentials (PSP) with a short (10–30 msec) latent period arise in response to light and sound. In 15 neurons, long latency (50–150 msec) responses to one or both of these stimuli were recorded. In most of the cells, short latency stable responses to stimulation of the contralateral forelimb and unstable long latency responses to light and/or sound, frequently of the nature of an increase in the background "synaptic noise," were observed. Under deep chloralose narcosis, the type of convergence was sharply changed: in most of the neurons, short latency responses to all the stimuli used appeared. However, the picture of convergence differed from that described earlier [5,6] for the motor cortex of the cat under chloralose narcosis. The responses to various stimuli were less similar to one another; the somesthetic modality substantially "predominated" (judging by the stability and nature of the interaction of the response).Brain Institute, Academy of Medical Sciences of the USSR. Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 474–483, September–October, 1971.     

Monosynaptic inhibitory postsynaptic potentials of cortical neurons

Monopolar intracortical stimulation of the auditory cortex was carried out in cats immobilized with D-tubocurarine. A macroelectrode (tip diameter 100 µ) or a microelectrode (tip diameter 10–15 µ) was used for stimulation. In both cases, besides excitatory responses, primary IPSPs with latent periods of 0.4–1.2 and 1.4–6.0 msec were recorded in cortical neurons close to the point of stimulation. The first group of IPSPs are considered to be generated in response to direct stimulation of bodies or axons of inhibitory cortical neurons, i.e., monosynaptically. The amplitude of these IPSPs varied in different neurons from 3 to 15 mV, and their duration from 4 to 150 msec. Additional later inhibitory responses were superposed on many of them. Of the IPSPs generated in auditory cortical neurons in response to stimulation of geniculocortical fibers 1.5% had a latency of 0.8–1.3 msec. They also are assumed to be monosynaptic. It is concluded that the duration of synaptic delay of IPSPs in cortical neurons and spinal motoneurons is the same, namely 0.3–0.4 msec. Axons of auditory cortical inhibitory neurons may be 1.5 mm long. The velocity of impulse conduction along these axons is 1.6–2.8 m/sec. The genesis of some special features of IPSPs of cortical neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 5, pp. 458–467, September–October, 1975.     

Inhibition in the neurons of the somatosensory cortex and the possibility of intracortical propagation of excitation

Extra- and intracellular leads were used to study the reactions of neurons in the pyramidal tract (PT) of the cat brain to antidromic and afferent effects. It was shown that afferent activation of PT neurons proceeds heterogeneously. Three types of PT neurons were identified, successively involved in the impulse response to afferent stimulation. By means of paired stimuli we determined the heterogeneous changes in sensitivity of late reacting PT neurons. It was found that, under certain conditions, the different IPSP evoked by afferent stimulation or PT stimulation do not prevent the appearance of impulse responses to secondary synaptic activation. A conclusion was drawn from these experiments on the localization of the excitatory intracortical terminals on the somas of the PT neurons and on the limited effect of inhibitory processes upon intracortical propagation of the afferent signal reaching the cortex. A functional scheme of intracortical PT neuron links is presented.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 465–473, September–October, 1971.     

Unit responses in the cat auditory cortex to electrical stimulation of nerve fibers innervating receptor cells in different parts of the organ of corti

Responses of 200 primary auditory cortical neurons to electrical stimulation of nerve fibers in different receptor zones of the cochlea were studied in cats anesthetized with pentobarbital. Under the influence of paired stimulation, after the response to the conditioning stimulus a state of prolonged (from 4 to 200 msec) refractiveness to the second stimulus developed in all the neurons tested. This long-lasting inhibition of unit activity was due to inhibition developing in the thalamus and the auditory cortex itself. The intensity and duration of excitation and inhibition in the cortical projection focus were maximal when the center of the receptive field was stimulated and decreased when the stimulus shifted from the center to the periphery. The region of the receptor surface of the cochlea to stimulation of which the auditory cortical neurons respond by an action potential is much narrower than the region whose electrical stimulation depresses the discharge of these neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 418–425, July–August, 1982.     

Functional classification of neurons of the cat inferior colliculus on the basis of temporal characteristics

We investigated the impulse activity of 103 neurons in cats anesthetized with a mixture of chloralose and urethane. The following response characteristics were studied in detail: 1) the latent period of the first impulse as a function of tone intensity; 2) threshold as a function of duration; 3) the frequency-threshold curves under the action of short (1–2 msec) and long (100–200 msec) tones; 4) the discharge "pattern" and the number of impulses under the action of signals with different durations and intensities. We demonstrated that the temporal characteristics of different neurons exhibit substantial differences. The high positive correlation among the temporal characteristics investigated enabled us to distinguish three groups of neurons. The first group was characterized by the following properties: a) short latent periods with a threshold tone intensity; 2) a short summation time (or none at all); 3) similarity of the frequency-threshold curves for short and long signals; 4) an initial on-discharge of 1–3 impulses. The second group was characterized by: 1) long latent periods with a threshold tone intensity; 2) pronounced temporal summation; 3) steeper frequency-threshold curves when the tone duration was increased; 4) prolonged discharge.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 137–146, September–October, 1969.     

Neuronal activity of the lateral vestibular nucleus of the guinea pig evoked by tilting the animal about the longitudinal axis during locomotion

In experiments on decerebrate guinea pigs, the impulse activity of neurons of the lateral vestibular nucleus evoked by tilting the animal about the longitudinal axis was investigated under conditions of spontaneous and mesencephalon stimulation-evoked locomotor activity. In most investigated neurons, locomotor activity led to changes in their responses to adequate vestibular stimulation. The dominant reaction was intensification of such responses, which was observed in almost all vestibulospinal neurons and in 2/3 of cells not having descending projections. Responses were suppressed only in 1/4 of the neurons not projecting to the spinal cord. The changes in the evoked responses had an amplitude character; the lag of the changes in the discharge frequency relative to the acceleration that caused them was constant. It is suggested that intensification of dynamic reactions of vestibular neurons during locomotion provides maintenance of the animal's equilibrium during movements in space by various gaits and along different trajectories.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 541–549, September–October, 1991.     

Neuronal correlates of the activation of the brain-reinforcing system in dogs

In analysis of neuronal activity of g. proreus of dogs brain in response to positive and differentiation conditioned cutaneous stimuli, in 44% of 78 studied neurons "late responses" appeared in the form of impulse activity intensification elicited by a positive conditioned stimulus after the end of eating and by a differentiation one--during conditioned signal action; it persisted in different neurones for 30--60 s. By means of various functional tests it has been shown that these reactions are a neurophysiological correlate of animals emotional state gradient.     

Interaction between central and peripheral temperature signals on temperature-sensitive hypothalamic neurons

Changes in the mean firing rate of posterior hypothalamic neurons were studied in experiments on unanesthetized cats in response to elevation of the brain temperature by 0.7–1.5°C and the skin temperature by 3–5°C separately or simultaneously. Altogether 85 neurons were studied in 14 animals: 11 responded to only one form of temperature stimulation, whereas in 16 neurons changes in the firing pattern (in most cases in the same direction) were observed in response to both forms of temperature stimulation. Different types of responses of these neurons were established. Sensitivity to the central temperature stimulus was increased in some neurons of this group when skin temperature stimulation was intensified.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 613–619, November–December, 1976.     

Habituation of postsynaptic unit responses of the cat motor cortex to stimuli of different modalities

Habituation (extinction) of postsynaptic unit responses of the cat motor cortex to repetitive electrodermal, photic, acoustic, and combined bimodal stimulation was investigated by intracellular recording. Habituation was shown by a decrease in the number of spikes per grouped discharge and a decrease in the amplitude and duration of the EPSPs, and sometimes IPSPs, on repetition of the stimulus. The way in which the course of habituation depends on the modality and duration of stimulation (at a constant frequency of 1/sec) is examined. Habituation of postsynaptic responses to sensory stimuli is observed with neurons of different functional groups, namely identified neurons of pyramidal tract and unidentified neurons, some of which were evidently pyramidal neurons and interneurons. The hypothesis is put forward that the habituation of PSPs of the cortical neurons is based on processes taking place mainly at the subcortical level.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 545–553, September–October, 1972.     

Neuron activity in the motor cortex of a cat with inhibition of a conditioned postural change reflex

A study was made of the neuron spike reactions in the primary motor cortex of the cat in the projection zone of the contralateral forelimb with external and internal inhibition of the conditioned reflex for posture change that consisted of shifting the body weight to the forelimb being studied. Spike responses of the neurons to extraneous stimuli and the conditioned signal were determined to a significant degree by the condition of the animal and its habituation to the signal used. In trained animals, the duration of responses to extraneous stimulation was shorter than in the nontrained. With external and internal inhibition, we observed simultaneous disappearance of conditioned reflex movements and the trace spike discharges connected with them. Frequently extraneous stimulations could suppress trace discharges even when learned movement was present. Extraneous stimulations of a different modality inhibited the reflex to different degrees. The change in neuron spike reaction connected with a conditioned reflex change in posture was similar to well-learned local reflex phenomena.A. A. Bogomol'ets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 489–500, July–August, 1985.