Mechanisms of the effect of diazepam on paroxysmal electrical activity of an isolated cortical slab in cats

The effect of diazepam on paroxysmal global electrical activity of a neuronally isolated slab of auditory cortex and on inhibitory responses of its neurons due to intracortical electrical stimulation was investigated in cats. Diazepam (2 mg/kg, intravenously) caused inhibition of paroxysmal electrical activity and increased the number of inhibited neurons in both the acutely isolated slab and three weeks after isolation, compared with the intact cortex. However, the number of disynaptic responses was reduced under these circumstances, especially in the long-isolated slab. It is postulated that diazepam exerts its action through activation of GABA-ergic inhibitory neurons, by synchronizing inhibition and increasing the duration of the IPSPs. The action of diazepam is manifested first, probably, in the initial links of cortical neuron chains.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 3–10, January–February, 1985.     

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.     

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.     

Neuronal responses of a chronically isolated slab of auditory cortex to intracortical stimulation during paroxysmal electrical activity in cats

Responses of 155 neurons 3 weeks after neuronal isolation of a slab of auditory cortex (area AI) to single intracortical stimulating pulses at the level of layer IV were studied in unanesthetized, curarized cats during paroxysmal electrical activity evoked by series of high-frequency (10–20 Hz) electrical stimulation by a current 2–5 times above threshold for the direct cortical response. In response to such stimulation a discharge of paroxysmal electrical activity, lasting from a few seconds to tens of seconds, appeared in the slab. As a rule it consisted of two phases — tonic and clonic. This indicates that cortical neurons can form both phases of paroxysmal cortical activity. Depending on behavior of the neurons during paroxysmal electrical activity and preservation of their ability to respond to intracortical stimulation at this time, all cells tested in the isolated slab were divided into four groups. Their distribution layer by layer and by duration of latent periods was studied. Two-thirds of the neurons tested were shown to generate spike activity during paroxysmal discharges whereas the rest exhibited no such activity. A special role of neurons in layer II in generation of paroxysmal activity in the isolated slab was noted. The view is expressed that at each moment functional neuronal circuits, independent of each other, exist in the slab and also, evidently in the intact cortex, which can interact with one another when conditions change.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 3–11, January–February, 1984.     

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.     

Responses of rabbit visual cortical neurons to intracortical electrical stimulation

Responses of rabbit visual cortical neurons to single and repetitive intracortical electrical stimulation were investigated. The stimulating electrode was located 0.7–1.2 mm away from the recording electrode. Response thresholds to single stimulation were as a rule 150–180 µA, whereas to series of stimuli they were 30–60 µA. The latent period to the first spike averaged 5–15 msec but the probability of the initial discharge was very low, namely 3–6%. With an increase in current intensity the duration of the initial inhibitory pause was increased in half of the neurons responding to it, whereas in the rest it was unchanged. After presentation of series of stimuli spontaneous activity was enhanced for a short time (4–6 sec). In about half of the cells the same kinds of discharge dynamics were observed in response to repetitive stimulation (frequency 0.25 Hz) as in responses to light, but more neurons with sensitization of discharge and fewer "habituating" neurons took part in responses to electrical stimulation. It is postulated that stimulation of a given point of the visual cortex evokes excitation of a local neuron hypercolumn and inhibition of neighboring cell columns.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 412–419, July–August, 1983.     

Effects of food motivation on spike activity of cat somatic cortex neurons

Spike response to unconditioned electrocutaneous stimulation was investigated in cortical neurons of areas 3 and 4 in untrained hungry cats during heightened excitation motivated by food presentation and when at rest. This reinforcement led to changed background activity level, reduced intensity of the initial stages of spike response, and disappearance of late neuronal response. Neuronal response of the same cortical area to a conditioned stimulus (a clicking sound) during reduced food motivation (the animals being sated during the course of the experiment) was also studied under the effects of instrumental feeding reflex. Coordination between the timing of neuronal response and their corresponding movements was discovered from comparing response pattern accompanying the execution of paw-placing (conditioned reflex and intersignal) movements and those recorded at different levels of food-induced excitation, as well as a similarity between these reactions. It was found that the initial stages of neuronal response to a conditioned signal only occurred during contraction of the brachial biceps muscle, while coordination between their timing and that of EMG changes was dependent on the animal's degree of satiation. Findings indicate the possibility of food-induced excitation substantially influencing spike response pattern in somatic cortex neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 725–735, November–December, 1987.     

Neuronal inhibitory responses to intracortical stimulation of an isolated slab of cat auditory cortex

Neuronal responses of an isolated slab of cortex to intracortical stimulation were studied intracellularly. The predominant responses were primary IPSPs. Their latent periods did not exceed 10 msec. Within the volume of cortex studied, neurons inhibited in response to stimulation were most numerous in the upper layers (II, III). Predominance of disynaptic IPSPs is evidence of the important role of cortical interneurons in their genesis. It is concluded from the results that primary IPSPs limit the spread of excitation primarily in the activated area of cortex. Since involvement of neurons of the isolated slab in the inhibition process takes place for only 10 msec after stimulation, neurons giving spike responses to intracortical stimulation with a longer latent period can transmit information into other brain zones. The role of duration of IPSP in the dynamics of interneuronal interaction in the cerebral cortex is discussed.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1. pp. 42–49, January–February, 1984.     

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.     

Connections of neurons of the cat somatosensory cortex with the thalamic relay nuclei

Of 103 neurons in the rostral part of the posterior sigmoid gyrus of the cat cortex 30 responded to stimulation of the ventro-posterolateral and ventrolateral nuclei of the thalamus (VPL and VL), 42 responded to stimulation of VL only, and 31 to stimulation of VPL only. It was shown by intracellular recording that stimulation of VPL induces a spike response with or without subsequent IPSPs in some neurons and an initial IPSP in others. The spike frequency of single neurons reached 60/sec, but the IPSP frequency never exceeded 10–20/sec. Stimulation of VL was accompanied by: a) antidromic spike responses; b) short-latency monosynaptic EPSPs and spikes capable of following a stimulation frequency of 100/sec; c) long-latency polysynaptic EPSPs and spikes appearing in response to stimulation at 4–8/sec; d) short-latency IPSPs; e) long-latency IPSPs increasing in intensity on repetition of infrequent stimuli. It is concluded that the afferent inputs from the relay nuclei to neurons of the somatosensory cortex are heterogeneous. An important role is postulated for recurrent inhibition in the genesis of the long-latency IPSPs arising in response to stimulation of VL, and for direct afferent inhibition during IPSPs evoked by stimulation of VPL. It is shown that the rostral part of the posterior sigmoid gyrus performs the role of somatic projection and motor cortex simultaneously.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 245–255, May–June, 1972.     

Postsynaptic neuronal response of a cat sensorimotor cortex during evoked and self-sustained rhythmic "spike and wave" activity

Intracellular correlates of complex sets of rhythmic cortical "spike and wave" potentials evoked in sensorimotor cortex and of self-sustained rhythmic "spike and wave" activity were examined during acute experiments on cats immobilized by myorelaxants. Rhythmic spike-wave activity was produced by stimulating the thalamic relay (ventroposterolateral) nucleus (VPLN) at the rate of 3 Hz; self-sustained afterdischarges were recorded following 8–14 Hz stimulation of the same nucleus. Components of the spike and wave afterdischarge mainly correspond to the paroxysmal depolarizing shifts of the membrane potential of cortical neurons in length. After cessation of self-sustained spike and wave activity, prolonged hyperpolarization accompanied by inhibition of spike discharges and subsequent reinstatement of background activity was observed in cortical neurons. It is postulated that the negative slow wave of induced spike and wave activity as well as slow negative potentials of direct cortical and primary response reflect IPSP in more deep-lying areas of the cell bodies, while the wave of self-sustained rhythmic activity is due to paroxysmal depolarizing shifts in the membrane potential of cortical neurons.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 298–306, May–June, 1986.     

Electrophysiological investigation of conduction of afferent impulses through the medial geniculate body

Extra- and intracellular reactions of 280 neurons of the pars principalis of the medial geniculate body (MGB) and of 408 auditory cortical neurons in area AI to stimulation of the inferior brachium of the midbrain and geniculocortical fibers were studied in cats immobilized with D-tubocurarine. Single electrical stimulation of the inferior brachium was shown to evoke a long and complex neuronal response in MGB in the form of excitation of some and inhibition of other neurons. The initial component of this response lasted 13 msec. Excitation of 72% of neurons participating in the response took place during the first 3 msec after the beginning of stimulation. In the same period 84% of IPSP arose. The inferior brachium was shown to contain a certain number of descending fibers. Some of them are axons of MGB neurons. Many fibers of the inferior brachium reach the auditory cortex without synaptic relay in MGB. Of all cells of MGB excited by stimulation of the inferior brachium monosynaptically, 76% are thalamocortical relay neurons; the rest are interneurons. Of the relay neurons of MGB 90% are excited monosynaptically, the rest by impulses passing through two or three synaptic relays in MGB. During stimulation of the inferior brachium, responses consisting of EPSP-IPSP and primary IPSP are recorded in many neurons of MGB. About 20% of primary IPSP arise monosynaptically, evidently in response to stimulation of inhibitory fibers of the inferior brachium. Most IPSP arise disynaptically, with the participation of an inhibitory interneuron located at the entrance to MGB. Inhibition observed in this case is direct afferent in nature.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 515–523, November–December, 1979.     

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.     

Analysis of long cortical evoked potentials

Evoked potentials arising in the motor cortex in response to its direct stimulation (dendritic and slow negative potentials), to stimulation of the ventrolateral (primary response) and intralaminar (nonspecific response) thalamic nuclei, and to stimulation of the pyramidal tracts (antidromic response), and also postsynaptic responses of neurons corresponding to them were studied in acute experiments on curarized cats. Evoked potentials arising in response to direct cortical stimulation and also to stimulation of the specific and nonspecific thalamic nuclei and pyramidal tracts were recorded from the same point of the motor cortex, and the corresponding intracellular responses were recorded from the same neuron. Slow negative potentials arising under these conditions of stimulation and the IPSPs corresponding to them were shown to have an identical time course. The results show that slow negative potentials are a reflection of hyperpolarization of pyramidal neurons. It is suggested that the individual components of responses evoked by direct stimulation of the cortex and thalamic nuclei have a common genesis.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 115–121, March–April, 1982.     

Responses of pyramidal tract and corticorubral neurons to stimulation of lateral hypothalamic structures in cats

Responses of pyramidal tract neurons and corticorubral and unidentified neurons in the pericruciate area of the cortex to electrical stimulation in the posterior, tuberal, and anterior zones of the lateral hypothalamus and also to electrodermal stimulation of all four limbs were studied in cats anesthetized with chloralose. The proportion of pyramidal tract, corticorubral, and unidentified neurons which responded to hypothalamic stimulation was 73.3, 55.7, and 79.1% respectively. Data on the possibility of monosynaptic activation of some pyramidal tract neurons and unidentified cells were obtained. The presence of less stable and longer-latency responses of corticorubral neurons indicated the absence of a monosynaptic pathway for realization of ascending hypothalamic influences on neurons of the cortical extrapyramidal system. Some cortical neurons responded to stimulation of more than one zone of the hypothalamus. Pyramidal tract neurons and corticorubral neurons with axon collaterals running into the region of the hypothalamus were discovered for the first time. It was shown that most neurons of the pericruciate area of the cortex to which the ascending influence of the hypothalamus is directed have a large bilateral receptive field and respond to electrodermal stimulation of several limbs.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 298–306, May–June, 1982.     

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.     

Response of cat auditory cortex neurons to tonal stimulation during and after nembutal anesthesia

During acute experiments on 20 cats a comparative study was made of neuronal reaction to a tone, as recorded during the first few hours after administration of Nembutal and after an interval of 10–30 h. No spontaneous activity was seen in 89% of auditory cortex neurons of the anesthetized cats; these produced a sterotyped on- response to the optimal frequency tone. Late neuronal spike discharges at distinct intervals of 100–150 msec appeared in response to the setting up of acoustic stimulation after a brief latent reaction lasting 9–15 msec. It was shown that this stimulation did not produce an off-response in the cortical neurons. When the animals emerged from Nembutal anesthesia, the neurons reacted very differently to the optimal frequency tone. About 76% of the cells produced an on, on-off or off response, while about 21% responded with either tonic spike discharges or total inhibition of these throughout the acoustic stimulation. In unanesthetized cats the vast majority of AI cortical neurons were capable of reacting as long as the stimulus lasted. It is shown how this ability is lost under deep Nembutal anesthetic.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 728–737, November–December, 1985.     

Responses of neurons in cat primary somatosensory cortex to repetitive stimulation of vibrissae

Extra- and intracellular responses of neurons in the primary somatosensory cortex to repetitive mechanical stimulation of the vibrissae at different frequencies were studied in unanesthetized curarized adult cats. Unlike responses to electrical stimulation of the combined afferent input (the infraorbital nerve) spike discharges of neurons in response to vibrissal stimulation can reproduce rather higher frequencies of stimulation and their initial character changes more often in the course of the repetitive series. Most cortical neurons were characterized by limitation of the area of their peripheral receptive fields with an increase in the frequency of adequate repetitive stimulation. A group of cortical neurons was distinguished by its ability to respond to high-frequency stimulation and to generate burst discharges. Comparison of the frequency characteristics of spike responses of these cells and of inhibitory synaptic action in other cortical neurons led to the conclusion that this group of cells thus distinguished may be inhibitory cortical neurons. The role of interaction between excitatory and inhibitory processes arising in cortical neurons during repetitive stimulation of different areas of their receptive fields is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 164–171, March–April, 1982.     

Postsynaptic inhibition in the general cortex of the turtle forebrain

Postsynaptic inhibition in the general cortex of the turtle forebrain was investigated by recording unit activity intracellularly. Depending on the type of IPSPs recorded in response to electrical stimulation of the contralateral optic nerve and cortical surface the neurons were subdivided into three groups: 1) with long direct IPSPs, 2) with long and short direct, and also recurrent IPSPs, 3) with short direct and recurrent IPSPs. It is concluded that inhibitory pathways of the short direct and recurrent IPSPs have a common final component, a stellate interneuron. Compared with the recurrent collaterals of the principal neurons, the direct afferents make contact with more distal portions of the dendrites of this cell. Synapses formed on dendrites of the principal neurons by axons of the stellate cells are nearer to the soma than synapses responsible for generation of the long direct IPSP.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 375–383, July–August, 1973.     

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.