Multisensory convergence on neurons of the motor cortex in unanesthetized cats

Postsynaptic potentials (PSPs) of 83 neurons in the motor cortex of unanesthetized cats in response to electrodermal, photic, and acoustic stimulation were investigated by intra-and quasi-intracellular recording methods. Most cells responded to stimulation of at least one limb. About 60% of neurons of the posterior and over 75% of neurons of the anterior sigmoid gyrus responded to stimulation of two (or more) limbs. In 29 of 39 neurons of the anterior and 12 of 44 of the posterior sigmoid gyrus PSPs with a short (less than 50 msec) and stable latent period were evoked by flashes and clicks. On presentation of two somesthetic stimuli complete blocking (if the interval was less than 30–60 msec) or weakening (interval 30–200 msec) of responses to the second (testing) stimulus was observed. On presentation of paired photic (or acoustic) stimuli or paired stimuli of different modalities at various intervals from 0 to 100 msec, the testing response was often potentiated. The character of the responses and their interaction thus differed from those obtained under chloralose anesthesia [6, 7]. It is postulated that under the action of chloralose a system of neurons with strong excitatory feedback is formed in the motor cortex which may respond to stimuli of different modalities by something resembling the "all or nothing" principle.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 563–573, November–December, 1971.     

Interaction of recovery cycles of evoked potentials in the cerebral cortex of the cat in response to stimulation of the superior colliculi and pulvinar

Similar character of recovery cycles of evoked potentials in the visual cortex to electric stimulation of the superior colliculi (SC) and pulvinar was found in chronic experiments on alert cats irrespective of stimuli presentation order. In the association cortex preceding SC stimulation facilitated the response to test stimulation of pulvinar almost at all delays between the stimuli. If the pulvinar stimulation was applied as a conditioned stimulus, then the response to SC stimulation under intervals of 20-200 ms was depressed. The obtained data point to equivalence of the inputs from SC and pulvinar to the visual cortex, to different informational value of inputs from SC to the association and visual cortex, and to mutual function dependence of the inputs from SC and pulvinar to the association cortex.     

Unit responses of the sensomotor cortex to paired electrical stimuli

Unit responses of the sensomotor cortex to paired electrical stimulation and visual cortex, applied either simultaneously or after various delays (from 0 to 200 msec) depend on the order of application of the stimuli and on the interval between them. If stimulation of the sensomotor cortex was used in a conditioning role the response continued unchanged when the intervals between stimuli were increased to 200 msec. If, however, stimulation of the sensomotor cortex had a testing role interaction was observed between the stimuli so that responses to both first and second stimuli were blocked; this was exhibited most clearly for intervals of 40–80 msec between stimuli. The blocking effect persisted on some neurons with delays of up to 200 msec between stimuli, while the response of others to both the first and the second stimulus was restored.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 628–635, November–December, 1973.     

Mechanisms of interaction between the parietal association and projection areas of the cat neocortex

Changes in evoked potentials in the first visual (VI), first somatic (SI), and parietal areas of the cortex during local cooling of each area were investigated under pentobarbital anesthesia. Two types of interaction were distinguished. Type I interaction was found in all areas in the early stages of local cooling and was reflected in a similar decrease in amplitude of evoked potentials in intact parts of the cortex. In the thalamic association nuclei — the pulvinar and posterolateral nucleus — somatic evoked potentials were unchanged but visual were transformed differently from those in the cortex. Type IIinteraction was found in the later stages of cooling and only between the association area and each of the projection areas. It was reflected in a greater change in amplitude of the evoked potentials and also in their configuration. In response to somatic stimulation in the early stage of type II interaction transformation of evoked potentials in the cortex took place sooner than in the nuclei; in the later stage it took place immediately after transformation of the "subcortical" evoked potentials. In response to photic stimulation transformations of cortical evoked potentials were always preceded by the corresponding transformations in the nuclei. It is suggested that type I interaction is formed by intercortical connections and type II by direct and subcortical relay connections. Differences in the role of the association area in interaction of types I and II when activated by stimuli of different modalities are discussed.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 573–581, November–December, 1978.     

Pattern and correlation of fast and slow spontaneous unit activity in the visual cortex

Spontaneous unit activity in the visual cortex and its changes during stimulation by continuous light or flashes were investigated in waking rabbits. The study of distributions of adjacent intervals showed that the neurons differ in the ratio of burst (fast, with intervals of up to 15–40 msec) and nonburst (slow) activity and in the character of changes from one type of activity to the other. Of the total number of spikes 63% were outside bursts; the ratio of their number to the number of spikes within bursts consisting of two or of three or more spikes was 27:3:1. The relative stability of the burst structure of spontaneous activity and the limited number of spikes in them (on average 2.4) were demonstrated. Bursts of three or more spikes (mean 3.6) were irregular, and in 79% of them a longer interval (18.6±2.4 msec) was observed before the shortest interval (7.9±0.9 msec). Bursts of spikes of most neurons during photic stimulation contain more spikes with shorter intervals; they also began more frequently with the shortest interval, possibly signifying an increase in the steepness and amplitude of the EPSPs lying at their basis. However, in 20% of neurons spontaneous bursts included more spikes and with shorter intervals than bursts evoked by flash stimulation.Research Institute of Psychiatry, Ministry of Health of the RSFSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 4, pp. 311–320, July–August, 1979.     

Transformation of the afferent tactile signal into a motor command in the cat motor cortex

Activity of 112 neurons of the precruciate motor cortex in cats was studied during a forelimb placing reaction to tactile stimulation of its distal parts. The latent period of response of the limb to tactile stimulation was: for flexors of the elbow (biceps brachii) 30–40 msec, for the earliest reponses of cortical motor neurons about 20 msec. The biceps response was observed 5–10 msec after the end of stimulation of the cortex with a series of pulses lasting 25 msec. Two types of excitatory responses of the neurons were identified: responses of sensory type observed to each tactile stimulation of the limb and independent of the presence or absence of motion, and responses of motor type, which developed parallel with the motor response of the limb and were not observed in the absence of motion. The minimal latent period of the responses of motor type was equal to the latent period of the sensory responses to tactile stimulation (20±10 msec). Stimulation of the cortex through the recording microelectrode at the site of derivation of unit activity, which increased during active flexion of the forelimb at the elbow (11 stimuli at intervals of 2.5 msec, current not exceeding 25 µA), in 70% of cases evoked an electrical response in the flexor muscle of the elbow.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 115–123, March–April, 1977.     

Corticofugal influences on segmental responses of lumbar spinal ventral horn interneurons in cats

Experiments on cats using extra- and intracellular recording methods showed that stimulation of the motor cortex of both hemispheres leads to considerable modulation of responses to stimulation of cutaneous and muscular lower limb afferents in spinal ventral horn interneurons in segments L6, 7. Three types of conditioning corticofugal effect were observed: facilitation, inhibition, and facilitation followed by inhibition (biphasic effect), and inhibitory effects predominated. The duration of facilitation of responses did not exceed 30–40 msec. The characteristics of the time course of inhibition varied: in some cases it began with relatively short intervals (8–15 msec), in other cases with an interval of 30–40 msec; its duration was 125–500 msec, or sometimes more. The effect of cortical stimulation on responses to stimulation of various afferent inputs of the same interneuron was shown to differ. The character of the conditioning corticofugal effect correlated with the latent period of segmental responses: facilitation was observed only in responses with a relatively short latent period (under 5 msec); responses with a longer latent period were mainly inhibited. The type of cortical effect also depended on the function performed by the activated afferent input. It is suggested that differential descending control of segmental polysynaptic responses recorded in ventral horn interneurons with wide convergence of afferent influences takes place in the initial stages of the reflex are. The mechanism of this control is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neiorofizologiya, Vol. 14, No. 6, pp. 563–571, November–December, 1982.     

Features of evoked potentials in the cerebellar cortex of rabbits

We investigated evoked responses of the cerebellar cortex of rabbits under Nembutal or chloralose anesthesia to stimulation of the sciatic, brachial, and vagus nerves. The parameters of evoked potentials (E Ps), together with features of their distribution throughout the cerebellar cortex, enabled us to divide them provisionally into three types. Evoked potentials of the first type have a latent period of 5–10 msec and a two-phase or more complex shape. Evoked potentials of the second type have a latent period of 10–23 msec and include from one to four components. Evoked potentials of the third type are discharges with long latent periods (20–50 msec) and consist of a series of slow sinusoidal oscillations. Appearance of an initial electronegative component is characteristic of EPs of the cerebellar cortex of rabbits, especially those of the second and third types. Evoked potentials of the first type are local.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 73–80, July–August, 1969.     

Retrieval of delayed evoked potentials after amygdaloid stimulation

The effect of amygdaloid stimulation on retrieval of delayed evoked potentials recorded in the cortex, mesencephalic reticular formation, lateral geniculate body, and hippocampus was investigated in unanesthetized curarized cats. Delayed evoked potentials were produced to 10–400 combinations of flashes and hypothalamic stimulation and consisted of potentials arising in response to a conditioned stimulus after a delay equal to the interval between it and the unconditioned stimulus. Amygdaloid stimulation facilitated the retrieval of these potentials if they had first been extinguished or had not appeared during initial testing.Institute of Physiology, Academy of Medical Sciences of the USSR, Siberian Branch, Novosibirsk. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 300–304, May–June, 1976.     

Electrophysiological study of connections between the entorhinal cortex and the neocortex

In acute experiments in rabbits immobilized by d-tubocurarine, stimulation of the entorhinal area with rectangular electric impulses led to the appearance of evoked potentials (EP) with a latent period of 6–12 msec in the occipital, temporal, parietal, and cingular areas of the neocortex. The amplitude of the positive response component was 500 µV, and its duration 25–50 msec. The negative component was not always discernible. When rhythmic stimulation was used, these EPs followed stimulation frequencies not exceeding 20 per sec. Stimulation of the medial parts of the entorhinal area with a frequency of one to three per sec was accompanied by recruitment of the EP in the occipital and temporal neocortex areas. Nembutal depressed the amplitude of the neocortex EP appearing in response to stimulation of the entorhinal cortex. With the aid of double stimulation it could be established that, after conditioning stimulation of the entorhinal area, the positive component of the primary response (PR) evoked by stimulation of the contralateral sciatic nerve in the projection zone of the somatosensory cortex is strengthened during the first 50 msec, and subsequently after 80–120 msec. In these cases, the negative component was depressed. These findings are discussed with a view to the influence of limbic structures on the neocortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 73–78, January–February, 1970.     

Evoked potentials of the auditory cortex on paired stimuli

Changes in the responsiveness of the auditory cortex to an acoustic click and to direct stimulation of the medial geniculate body were studied by the method of evoked potentials in an extended experiment on cats with implanted electrodes. It is shown that the minimum interval between two stimuli for which a second click produces an EP in the auditory cortex is from 30 to 50 msec. The relative refractory period consists of two parts. The first (50–100 msec) is characterized by a rapid recovery, and the second (about 500 msec) by a slow recovery. In contrast with a click, direct stimulation of the geniculate body does not produce a refractory condition but one of facilitation. The effects of Nembutal and chloralose anesthesia and the state of alertness on the recovery of auditory cortex responsiveness were investigated. The reason for the absence and the reduction of an EP from the auditory cortex to a testing click during absolute and relative refractory periods is not a passive decrease of excitability of the usual refractory kind, but an active interplay of excitatory and inhibitory processes in the cerebral cortex, geniculate bodies, and reticular formation of the brain stem.A. A. Bogomolets' Institute of Physiology, Academy of Sciences, Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 54–64, July–August, 1969.     

Focal evoked potentials in the rabbit visual cortex: Current source density analysis

Focal evoked potentials arising in the rabbit visual cortex in response to photic stimulation from a point source were analyzed by determination of the current source density. The response to a point stimulus arises in a circumscribed area of cortex, corresponding retinotopically to the stimulated point of the visual field and it consists of two components. The first component is created by a local current sink at a depth of 0.6 to 1.0 mm (the level of layer IV) and has a latent period of 30 msec and a peak time of 50 msec. The second component is created by a more diffuse current sink at a depth of 0.2–0.3 to 1.3–1.5 mm (levels between layers III and VI); the time to the maximum was 90–100 msec. These local sinks are regarded as active, created by depolarizing synapses. Passive current sources are concentrated around zones of active sinks. The two components of the response may reflect two consecutive waves of activation of cortical neurons.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 474–481, September–October, 1981.     

Role of cortical inhibition in heterosensory interaction of neurons of the cat sensorimotor cortex

Background and evoked neuronal activity in the cat sensorimotor cortex was recorded under a-chloralose anesthesia. Pairs of heterogeneous stimuli were applied, spaced at intervals of 0, 100, 200, 300, and 400 msec. A clicking sound, flashing light, and electroshock to the contralateral forepaw were used as stimuli. Partial or complete blockade of response to test stimuli presentations spaced 100–200 msec apart were observed when using stimulation of varying modality. The greatest test response was recorded at interstimulus intervals of 200–300 msec. Intracellular mechanisms of heterosensory interaction were investigated by applying the inhibitory transmitter antagonist picrotoxin microiontophoretically to the test cell to produce local attenuation of inhibitory effects. This substance also reduced the duration of blockage following the conditioning stimulus and the occurrence of peak level test response at a lower interstimulus interval than in the controls. Either a consistent increase in the number of spikes per response at one of the interstimulus intervals or a uniform reinforcement in unit response to several different interstimulus intervals were observed in a proportion of the cells. The contribution of intracortical inhibitory influences to the mechanisms of heterosensory interaction on neurons of the cat sensorimotor cortex is discussed in the light of our findings.A. A. Ukhtomskii Institute of Physiology, A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 147–156, March–April, 1987.     

Effect of local cooling of the cortex on evoked potentials in the reticular formation in response to somatosensory stimulation

Potentials evoked in nuclei of the reticular formation by electrodermal stimulation of the limbs were investigated in acute experiments on unanesthetized, immobilized rats during cooling of the somatosensory cortex in the area of representation of one forelimb. Evoked potentials in the reticular formation were found to depend on the degree of cold inhibition of the cortical primary response to the same stimulation. The peak time of the main negative wave increased from 40–50 to 60–80 msec with a simultaneous decrease in its amplitude or its total disappearance in the case of deep cooling of the cortex. Cooling of the cortex had a similar although weaker effect on the earlier wave of the evoked potential with a peak time of 14 msec, recorded in the ventral reticular nucleus. In parallel recordings of potentials evoked by stimulation of other limbs they remained unchanged at these same points of the reticular formation or were reduced in amplitude while preserving the same temporal parameters. Cooling of the cortex thus selectively delays the development and reduces the amplitude of the response to stimulation of the limb in whose area of representation transformation of the afferent signal into a corticofugal volley is blocked. Consequently the normal development of both late and early components of the potential evoked in the reticular formation by somatic stimulation requires an additional volley, descending from the cortex, and formed as a result of transformation of the same afferent signal in the corresponding point of the somatosensory cortex.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 32–38, January–February, 1981.     

Corticofugal influences on the motoneurons of the trigeminal nucleus

We studied the postsynaptic potentials evoked from 76 trigeminal motoneurons by stimulation of the motor (MI) and somatosensory (SI) cortex in the ipsilateral and contralateral hemispheres of the cat. Stimulation of these cortical regions evoked primarily inhibitory postsynaptic potentials (PSP) in the motoneuron of the masseter muscle, but we also observed excitatory PSP and mixed reactions of the EPSP/IPSP type. The average IPSP latent period for the motoneurons of the masseter on stimulation of the ipsilateral cortex was 6.1±0.3 msec, while that on stimulation of the contralateral cortex was 5.2±0.4 msec; the corresponding figures for the EPSP were 7.6±0.5 and 4.5±0.3 msec respectively. Corticofugal impulses evoked only EPSP and action potentials in the motoneurons of the digastric muscle (m. digastricus). The latent period of the EPSP was 7.6 msec when evoked by afferent impulses from the ipsilateral cortex and 5.4 msec when evoked by pulses from the contralateral cortex. The duration of the PSP ranged from 25 to 30 msec. Postsynaptic potentials developed in the motoneurons studied when the cortex was stimulated with a single stimulus. An increase in the number of stimuli in the series led to a rise in the PSP amplitude and a reduction in the latent periods. When the cortex was stimulated with a series of pulses (lasting 1.0 msec), the IPSP were prolonged by appearance of a late slow component. We have hypothesized that activation of the trigeminal motoneurons by corticofugal impulsation is effected through a polysynaptic pathway; each functional group of motoneurons is activated in the same manner by the ipsilateral and contralateral cortex. The excitation of the digastric motoneurons and inhibition of the masseter motoneurons indicates reciprocal cortical control of their activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 512–519, September–October, 1971.     

Investigation of the stability of the potentials of the dorsal surface evoked by single and paired stimulations of the afferent nerve

In spinal and anesthetized cats in the region of the lumbosacral thickening we have recorded the potentials of the dorsal surface (PDS) in response to single or paired stimulation of the peripheral nerves. The intervals between the stimuli were 400, 100, and 20 msec. The recording was made once every 15 sec. We have constructed the histograms of the changes in the N₁-component recorded on conditioning and single stimulation. After conversion of the histograms for single responses we established agreement of the newly obtained histograms with those constructed for the conditioned responses. The coefficients of variance for both cases proved to be practically identical. In applying single stimulation of different strengths the coefficient of variance increased if the amplitude of the responses fell. The coefficient of variance for the low amplitude responses did not change on conditioning unlike that for the responses evoked by weak single stimulation. It has been shown that the confidence limits of change in the coefficient of variance for a confidence probability of 0.99 and 0.95 obtained in experiments with conditioning practically concur with the intervals for the single stimulation. It is concluded that presynaptic inhibition has no appreciable antifluctuation influences on the N₁-component of the PDS.Dnepropetrovsk State University. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 10–16, January–February, 1970.     

Unit responses of the first and second somatosensory cortical areas to peripheral,thalamic, and cortical stimulation

Unit responses of the first (SI) somatosensory area of the cortex to stimulation of the second somatosensory area (SII), the ventral posterior thalamic nucleus, and the contralateral forelimb, and also unit responses in SII evoked by stimulation of SI, the ventral posterior thalamic nucleus, and the contralateral forelimb were investigated in experiments on cats immobilized with D-tubocurarine or Myo-Relaxin (succinylcholine). The results showed a substantially higher percentage of neurons in SII than in SI which responded to an afferent stimulus by excitation brought about through two or more synaptic relays in the cortex. In response to cortical stimulation antidromic and orthodromic responses appeared in SI and SII neurons, confirming the presence of two-way cortico-cortical connections. In both SI and SII intracellular recording revealed in most cases PSPs of similar character and intensity, evoked by stimulation of the cortex and nucleus in the same neuron. Latent periods of orthodromic spike responses to stimulation of nucleus and cortex in 50.5% of SI neurons and 37.1% of SII neurons differed by less than 1.0 msec. In 19.6% of SI and 41.4% of SII neurons the latent period of response to cortical stimulation was 1.6–4.7 msec shorter than the latent period of the response evoked in the same neuron by stimulation of the nucleus. It is concluded from these results that impulses from SI play an important role in the afferent activation of SII neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 351–357, July–August, 1976.     

Interaction of heterosensory afferent impulses on neurons of thalamic associative nuclei

The character and particular features of interaction between visual, auditory, and electrodermal afferent impulses on neurons of the pulvinar, posterolateral, and mediodorsal thalamic nuclei were studied in acute experiments on cats anesthetized with a mixture of pentobarbital and chloralose. Interaction discovered on cells of both groups of structures was of two types. In the first (the one most frequently found) only inhibition was observed or inhibition followed by facilitation of the response to testing stimulation; in the second type only facilitation or facilitation followed by inhibition of unit activity was found. Overall ability for interaction to take place on neurons of the mediodorsal nucleus was weaker than on cells of the pulvinar-posterolateral complex (P<0.05). Interaction was strongest on trisensory cells; it was also observed on monosensory cells or on cells which did not respond to isolated stimulation.Donetsk Medical Institute. Kemerovo Medical Institute. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 478–485, September–October, 1978.     

Neuronal and synaptic mechanisms of cortical inhibition

The latent periods, amplitude, and duration of IPSPs arising in neurons in different parts of the cat cortex in response to afferent stimuli, stimulation of thalamocortical fibers, and intracortical microstimulation are described. The duration of IPSPs evoked in cortical neurons in response to single afferent stimuli varied from 20 to 250 msec (most common frequency 30–60 msec). During intracortical microstimulation of the auditory cortex, IPSPs with a duration of 5–10 msec also appeared. Barbiturates and chloralose increased the duration of the IPSPs to 300–500 msec. The latent period of 73% of IPSPs arising in auditory cortical neurons in response to stimulation of thalamocortical fibers was 1.2 msec longer than the latent period of monosynaptic EPSPs evoked in the same way. It is concluded from these data that inhibition arising in most neurons of cortical projection areas as a result of the arrival of corresponding afferent impulsation is direct afferent inhibition involving the participation of cortical inhibitory interneurons. A mechanism of recurrent inhibition takes part in the development of inhibition in a certain proportion of neurons. IPSPs arise monosynaptically in 2% of cells. A study of responses of cortical neurons to intracortical microstimulation showed that synaptic delay of IPSPs in these cells is 0.3–0.4 msec. The length of axons of inhibitory neurons in layer IV of the auditory cortex reaches 1.5 mm. The velocity of spread of excitation along these axons is 1.6–2.8 msec (mean 2.2 msec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 394–403, May–June, 1984.     

Neuronal responses of the reticular and anterior ventral thalamic nuclei to stimulation of the thalamic ventrolateral nucleus and motor cortex

Responses of 137 neurons of the rostral pole of the reticular and anterior ventral thalamic nuclei to electrical stimulation of the ventrolateral nucleus and motor cortex were studied in 17 cats immobilized with D-tubocurarine. The number of neurons responding antidromically to stimulation of the ventrolateral nucleus was 10.5% of all cells tested (latent period of response 0.7–3.0 msec), whereas to stimulation of the motor cortex it was 11.0% (latent period of response 0.4–4.0 msec). Neurons with a dividing axon, one branch of which terminated in the thalamic ventrolateral nuclei, the other in the motor cortex, were found. Orthodromic excitation was observed in 78.9% of neurons tested during stimulation of the ventrolateral nucleus and in 52.5% of neurons during stimulation of the motor cortex. Altogether 55.6% of cells responded to stimulation of the ventrolateral nucleus with a discharge of 3 to 20 action potentials with a frequency of 130–350 Hz. Similar discharges in response to stimulation of the motor cortex were observed in 30.5% of neurons tested. An inhibitory response was recorded in only 6.8% of cells. Convergence of influences from the thalamic ventrolateral nucleus and motor cortex was observed in 55.7% of neurons. The corticofugal influence of the motor cortex on responses arising in these cells to testing stimulation of the ventrolateral nucleus could be either inhibitory or facilitatory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 460–468, September–October, 1978.