Responses of medial geniculate body neurons to auditory cortical stimulation

Extracellular and intracellular unit responses of thepars principalis of the medial geniculate body to stimulation of the first (AI), second (AII), and third (AIII) auditory cortical areas were studied in cats immobilized with D-tubocurarine. In response to auditory cortical stimulation both antidromic (45–50%) and orthodromic (50–55%) responses occurred in the geniculate neurons. The latent period of the antidromic responses was 0.3–2.5 msec and of the orthodromic 2.0–18.0 msec. Late responses had a latent period of 30–200 msec. Of all neurons responding antidromically to stimulation of AII, 63% responded antidromically to stimulation of AI also, confirming the hypothesis that many of the same neurons of the medial geniculate body have projections into both auditory areas. Orthodromic responses of geniculate neurons consisted either of 1 or 2 spikes or of volleys of 8–12 spikes with a frequency of 300–600/sec. It is suggested that the volleys of spikes were discharges of inhibitory neurons. Intracellular responses were recorded in the form of antidromic spikes, EPSPs, EPSP-spike, EPSP-spike-IPSP, EPSP-IPSP, and primary IPSP. Over 50% of primary IPSP had a latent period of 2.0–4.0 msec. It is suggested that they arose through the participation of inhibitory interneurons located in the medial geniculate body.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 5–12, January–February, 1976.     

Unit responses in the auditory cortex to stimulation of geniculocortical fibers

Extracellular and intracellular single unit responses of neurons of the auditory cortex to electrical stimulation of geniculocortical fibers (GCF) were recorded in experiments on cats immobilized with tubocurarine. The latent period of responses of 15% of neurons to GCF stimulation was 0.3–1.5 msec. It is postulated that they were excited anti-dromically. The latent period of spikes generated by neurons responding to GCF stimulation orthodromically varied from 1.6 to 12 msec. In 28.6% of neurons the latent period was 1.6–2.5 msec. It is postulated that these neurons were excited monosynaptically. Intracellular recording revealed primary IPSPs in response to GCF stimulation in 63.3% of neurons, a brief EPSP followed by a prolonged IPSP in 17.7%, an EPSP-spike-IPSP complex in 12.3%, and subthreshold EPSPs in 7% of neurons. The latent period of the primary IPSPs varied from 1.8 to 11 msec, being 1.8–3.7 in 72%, 3.8–5.7 in 20.0%, and 5.8–11 msec in 8.0% of neurons. The latent period of responses beginning with an EPSP was 1–4 msec (mean 1.8 msec). Orthodromic responses arising 3–10 msec after the antidromic response, and consisting of 3–5 spikes, were recorded in some antidromically excited neurons. Hypotheses regarding the functional organization of the auditory cortex and mechanisms of inhibition in its neurons are put forward on the basis of the results obtained.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 227–235, May–June, 1972.     

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.     

Responses of parietal associative neurons to stimulation of primary sensory areas

Responses of 251 neurons in the anterior part of the middle suprasylvian gyrus to stimulation of primary sensory (auditory, visual, somatosensory) areas and also to acoustic, visual, and somatosensory stimuli were studied in acute experiments on cats anesthetized with chloralose (40 mg/kg) and pentobarbital (20 mg/kg). Three groups of neurons were distinguished by their responses to stimulation of the primary sensory areas: those responding by an increased firing rate (117) or by inhibition (35) and those not responding (99). Responses of 193 neurons to stimulation of the peripheral afferent systems were analyzed. Neurons of the parietal associative cortex responded more frequently to cortical stimulation than to peripheral. By the duration of the latent period of their response to cortical stimulation the neurons were divided into three groups: those with short (less than 20 msec), medium (20–30 msec), and long latent periods (over 30 msec). The first group was the largest.Kemerovo State Medical Institute. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 524–530, September–October, 1972.     

Responses of cat cerebellar cortical neurons to stimulation of the caudate nucleus,globus pallidus,and substantia nigra

Stimulation of the head of the caudate nucleus in cats anesthetized with chloralose and pentobarbital evoked spike responses of the Purkinje cells and other cerebellar cortical neurons in the paramedian lobes, lobulus simplex, and the tuber of the vermis. Phasic responses in the form of simple discharges (on account of activation of the neurons through mossy fibers) appeared mainly after a latent period of 5–12 and 14–20 msec; the latent period of responses consisting of complex discharges (on account of activation of Purkinje cells through climbing fibers) was 5–6, 9–22 msec, or more. Depending on the latent period, the spike responses differed in their rhythm of generation. In response to stimulation of the caudate nucleus with a frequency of 4–6/sec recruiting responses were found. An inhibitory pause was an invariable component of the tonic responses. During stimulation of the globus pallidus responses of the same types (phasic and tonic) appeared as during stimulation of the caudate nucleus, but they differed in the distribution of the neurons by latent period of spike responses. The minimal latent period was 4 msec. Recruiting also was observed during repetitive stimulation of the globus pallidus. During stimulation of the substantia nigra Pukinje cells activated by climbing fibers responded. Evoked complex discharges appeared after a stable latent period of 8.5±0.3 msec. Arguments are put forward regarding the role of the substantia nigra, the globus pallidus, nuclei of the inferior olive, and also the thalamic nuclei in the mechanism of caudato-cerebellar oligosynaptic and polysynaptic connections.N. I. Pirogov Medical Institute, Vinnitsa. Translated from Neirofiziologiya, Vol. 10, No. 4, pp. 375–384, July–August, 1978.     

Unit responses in the cat auditory cortex to medial geniculate body stimulation

Responses of 98 auditory cortical neurons to electrical stimulation of the medial geniculate body (MGB) were recorded (45 extracellulary, 53 intracellularly) in experiments on cats immobilized with tubocurarine. Responses of the same neurons to clicks were recorded for comparison. Of the total number of neurons, 75 (76%) responded both to MGB stimulation and to clicks, and 23 (24%) to MGB stimulation only. The latent period of extracellularly recorded action potentials of auditory cortical neurons in response to clicks varied from 7 to 28 msec (late responses were disregarded), and that to MGB stimulation varied from 1.5 to 12.5 msec. For EPSPs these values were 8–13 and 1–4 msec respectively. The latent period of IPSPs arising in response to MGB stimulation varied from 2.2 to 6.5 msec; for 34% of neurons it did not exceed 3 msec. The difference between the latent periods of responses to clicks and to MGB stimulation varied for different neurons from 6 to 21 msec. Responses of 11% of neurons to MGB stimulation, recorded intracellularly, consisted of sub-threshold EPSPs, while responses of 23% of neurons began with an EPSP which was either followed by an action potential and subsequent IPSP or was at once cut off by an IPSP; 66% of neurons responded with primary IPSPs. Neurons responding to MGB stimulation by primary IPSPs are distributed irregularly in the depth of the cortex: there are very few in layers III and IV and many more at a depth of 1.6–2 mm. Conversely, excited neurons are predominant in layer III and IV, and they are few in number at a depth of 1.6–2 mm. It is concluded that the afferent volley reaching the auditory cortex induces excitation of some neurons therein and, at the same time, by the principle of reciprocity, induces inhibition of others. This afferent inhibition takes place with the participation of inhibitory interneurons, and in some cells the inhibition is recurrent. The existence of reciprocal relationships between neurons in different layers of the auditory cortex is postulated.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 23–31, January–February, 1972.     

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 in an isolated slab of the cat auditory cortex to intracortical stimulation

Neuronal responses in an isolated slab (area AI) to intracortical pulsed electrical stimulation at the level of layer IV were investigated extracellularly in acute experiments on cats immobilized with D-tubocurarine. Responding neurons were found in all layers of the slab. The character of their distribution by depth in the slab depended on the distance between recording and stimulating electrodes. The latent period of responses of different neurons ranged from 0.8 to 25 msec. With interelectrode distances of 0.5–2 mm most neurons responded mono- and disynaptically. However, responses of many neurons had a latent period of over 4 msec, i.e., they were polysynaptic. This indicates the complex character of interneuronal interactions, even in a limited area of the cortex. After intracortical stimulation no after-discharges with a latent period of over 40 msec could be recorded in the isolated slab of auditory cortex.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 85–93, January–February, 1982.     

Unit responses of the first and second somatosensory areas to stimulation of the ventroposterior thalamic nucleus

Single unit responses of the first (SI) and second (SII) somatosensory areas to stimulation of the ventroposterior thalamic nucleus (VP) were investigated in cats immobilized with D-tubocurarine. In response to VP stimulation 12.0% of reacting SI neurons and 9.5% of SII neurons generated an antidromic spike. In most antidromic responses of both SI and SII neurons the latent period did not exceed 1.0 msec. The minimal latent period of spike potentials during orthodromic excitation was 1.5 msec in SI and 1.7 msec in SII. Neurons with an orthodromic spike latency of not more than 3.0 msec were more numerous in SI than those with a latency of 3.1–4.5 msec. The ratio between the numbers of neurons of these two groups in SII was the opposite. In SII there were many more neurons with a latency of 5.6–8.0 msec than in SI. EPSPs appeared after a latent period of 1.1–9.0 msec in SI and of 1.4–6.6 msec in SII. The latent period of IPSPs was 1.5–6.8 msec in SI and 2.2–9.4 msec in SII. The relative importance of different pathways for excitatory and inhibitory influences of VP on SI and SII neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 115–121, March–April, 1976.     

Unit responses of the ventral posterior and ventral lateral thalamic nuclei to electrical stimulation of the thalamic reticular nucleus

A microelectrode investigation was made of responses of 72 physiologically identified neurons of the ventral posterior (VP) and 116 neurons of the ventral lateral (VL) thalamic nuclei to electrical stimulation of the reticular (R) thalamic nucleus. Mainly those neurons of VP and VL (73.7 and 86.2% respectively) which responded to stimulation of the first motor area and nucleus interpositus of the cerebellum responded to stimulation of R; 19.8% of VL neurons tested responded to stimulation of R by an antidromic action potential with latent period of 0.5–2.0 msec and 46.6% of neurons responded by orthodromic excitation; 23% of orthodromic responses had a latent period of 0.9–3.5 msec and 77% a latent period of 4.0–21.0 msec; 19.8% of VL neurons tested were inhibited. Among IPSPs recorded only one was monosynaptic (1.0 msec) and the rest polysynaptic. It is postulated that both R neurons are excitatory and that the inhibition which develops in VL neurons during stimulation of R are connected mainly with activation of inhibitory interneurons outside the reticular nucleus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 477–485, September–October, 1977.     

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.     

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.     

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.     

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.     

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.     

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.     

Analysis of evoked discharges in hypothalamic neurons to somatosensory,acoustic, and photic stimulation

Single unit activity in the supramammillary, mammillary, and anterior hypothalamic areas in response to acoustic, photic, and sciatic nerve stimulation was recorded in cats anesthetized with chloralose and immobilized with succinylcholine. In response to sensory stimulation the spontaneous firing rate was increased or decreased, and silent neurons were activated. Evoked potentials of the silent neurons had the shortest latent period to acoustic and somatosensory stimulation (15 msec), and rather longer to photic stimulation (30 msec); in some cases their latent period was 200 msec. Histograms of interspike interval distribution showed a maximum for intervals of up to 50 msec. Histograms of spike distribution relative to the beginning of stimulation showed maximal density between 100 and 200 msec. A high degree of convergence of excitation was found on units of the anterior as well as the posterior hypothalamus. Unit responses in the hypothalamus to sensory stimuli of all three modalities are regarded as being of secondary, nonspecific type.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 592–598, November–December, 1971.     

Responses of caudate neurons to acoustic stimulation in cats

Responses of 141 neurons of the caudate nucleus to acoustic stimuli — tones (500 and 2000 Hz) and clicks of different frequency (0.2 and 0.8/sec) and intensity (75, 80, 95 dB) — were recorded extracellularly in chronic experiments on cats. The responses recorded showed great variability with respect to character (phasic, tonic), structure (one or two phases of excitation), latent periods (from 7.5 to 300.0 msec), and burst discharge frequency (from 90 to 800 spikes/sec). Analysis of averaged poststimulus histograms and graphs of the dynamics of the responses showed that responses of 74% of neurons were much better expressed if less frequent stimuli were used: The regularity of the responses and the number of spikes in each response increased. Responses of neurons also increased and acquired a more distinct temporal structure if the intensity of the clicks increased. The character of responses to clicks and tones differed qualitatively in 17% of neurons studied: Phasic excitation arose in response to clicks, tonic changes in spike activity to tones. The particular features of responses of caudate neurons to acoustic stimulation with different parameters are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 588–595, November–December, 1980.     

Responses of neurons of reticular and ventral anterior nuclei of the cat thalamus to afferent stimuli of different modalities

Responses of 146 spontaneously active neurons of the reticular nucleus (R) and of 98 neurons of the ventral anterior (VA) nucleus of the thalamus to electrical stimulation of the skin of the footpads, to flashes, and to clicks were studied in experiments on cats immobilized with D-tubocurarine or myorelaxin. Stimulation of the contralateral forelimb was the most effective: 24.9% of R neurons and 31.3% of VA neurons responded to this stimulation. A response to clicks was observed in only 4.4% of R neurons and 2.4% of VA neurons. Nearly all responding neurons did so by phasic (one spike or a group of spikes) or tonic excitation. Depression of spontaneous activity was observed only in response to electrical stimulation of the skin. Depending on the site of stimulation, it was observed in 2.6–4.3% of R neurons and 1.7–2.1% of VA neurons tested. The latent period of the phasic responses of most neurons was 6–64 msec to electrical stimulation of the contralateral forelimb, 11–43 msec in response to stimulation of the hindlimb on the same side, 10–60 msec to photic and 8–60 msec to acoustic stimulation. Depending on the character of stimulation, 75.1–95.6% of R neurons and 68.7–97.6% of VA cells did not respond at all to the stimuli used. Of the total number of cells tested against the whole range of stimuli, 25% of R neurons and 47% of VA neurons responded to stimulation of different limbs, whereas 16% of R neurons and 22% of VA cells responded to stimuli of different sensory modalities. The functional role of the convergence revealed in these experiments is to inhibit (or, less frequently, to facilitate) the response of a neuron to a testing stimulus during the 40–70 msec after conditioning stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 563–571, November–December, 1975.     

Functional properties distinguishing individual auditory cortical neurons

Responses of 246 auditory cortical neurons to paired and repetitive stimulation of geniculo-cortical fibers were studied in experiments on cats immobilized with tubocurarine. The refractory period (RP) varied from 1 to 200 msec in different neurons. For neurons excited antidromically it varied from 1 to 3 msec. Among neurons excited monosynaptically there were some with a short (1.3–6 msec), medium, (8–16 msec) or long (30–100 msec) refractory period. Most neurons excited polysynaptically had a RP of mean length. RPs 30–200 msec in length were due to inhibition arising in the neuron after conditioning stimulation. In some neurons, after a short (1.5–2.0 msec) initial period of refractoriness there was a temporary (for 2–3 msec) recovery of responsiveness, followed by another period of ineffectiveness of the testing stimulus lasting 30–100 msec. Barbiturates selectively inhibited long-latency unit responses in the auditory cortex and during their action the number of responding neurons with a mean RP decreased sharply. The results demonstrate functional heterogeneity of auditory cortical neurons responding to an incoming volley of afferent impulses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 236–245, May–June, 1973.