Participation of interoceptive afferent impulses in polymodal responses of superior collicular neurons in the cat

Experiments on immobilized, unanesthetized cats showed that interoceptive afferent impulses reaching the brain via the vagus nerves evoke marked responses in, on average, 43% of superior collicular neurons. Both excitatory and inhibitory effects were observed. The latter were found more often during single stimulation of the vagus nerve. In half of the cases the inhibitory responses were characterized by the development of initial inhibition, clearly limited in time to between 180 and 1700 msec. Changes in spike activity of 60% of units were tonic in character. The onset of phasic responses with an initial period of activation was observed in only 9–11% of neurons. The number of these cells and also the total number of responding neurons were greater than when series of stimuli were applied to the vagus nerve. In individual cells during prolonged repetitive stimulation of the nerve gradual weakening of the responses took place. Somatic stimulation evoked mainly the development of phasic responses of excitatory type. Most of the neurons tested were bimodal and often the temporal structure of their responses was determined by the modality of the stimulus applied. The functional role of the changes discovered in spontaneous activity of superior collicular neurons under interoceptive influences and the central mechanisms of realization of such influences on the activity of the neuronal system in this brain structure are discussed.Ivano-Frankovsk Medical Institute, Ministry of Health of the Ukrainian SSR. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 590–596, November–December, 1978.     

Dynamics of single unit responses of the rabbit visual cortex to repetitive photic stimulation

Single unit responses in the visual cortex of the waking rabbit to repetitive photic stimulation at a frequency of once every 2.5 sec were studied. Depending on the total number of spikes in the response, the dynamics of the responses could be divided into two types: "fast" and "slow." From 5 to 15 stimuli were required to establish a stable level of response with changes of the first type, but 50 to 100 stimuli were needed for the response with changes of the second type. About 50% of all neurons did not change the characteristics of response. In the group of neurons with changing responses, partial habituation was found in 55–59% of cells; there were 25% of neurons with sensitization of discharge and 17–20% with a humpbacked type of response dynamics. A "slow" dynamics of unit responses in most cases was accompanied by changes in the duration of inhibitory pauses in the response; negative correlation of these values was observed in 65% of neurons.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 451–459, September–October, 1978.     

Response of rabbit visual cortex neurons to direct stimulation by current of different intensities

Response was investigated in 47 rabbit visual cortex neurons to direct intracortical electrical stimulation consisting of single biphasic pulses of increasing intensities within the 150–2,700 µA range. Minimum level for generating all components of response to electrical stimulation remained similar from one neuron to the next, ranging between 150 and 600 µA. Three different patterns of dependence between numbers of spikes at different stages of response and current amplitude were identified: stable, gradual and selective patterns. Percentages of stable dependences were lower for after-discharges in comparison with initial firing (at 11 and 26% respectively) and the proportion of selective dependences were somewhat higher (at 32 and 21%). The selective dependence observed could imply the existence of optimum current levels at which peak neuronal response occurs. At the same time, duration of inhibitory pauses lengthened uniformly in the response of all test neurons during increasing intensity of the electrical stimuli. Findings obtained during this study may have a practical application in matters connected with visual prosthetics in the blind.M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 239–247, March–April, 1989.     

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.     

Organization of afferent inputs of the parietal association (area 7) and Clare-Bishop areas of the cat neocortex

Unit activity was recorded from two parietal areas of the cat neocortex in semichronic experiments. Cell responses to presentation of adequate stimuli of different modalities and to direct electrical stimulation of various cortical zones were studied. About 4% of neurons of the Clare-Bishop area did not respond to visual stimulation. Cells responding to stimuli of different modalities were found in the Clare-Bishop area. A high percentage of cells in this area responded to direct electrical stimulation of area 17. In the association area (area 7) 27% of neurons tested responded to visual stimuli, but only a very small relative number of cells (compared with responding neurons of the Clare-Bishop area) responded to stimulation of the primary sensory areas. Electrical stimulation of area 7 inhibited evoked and spontaneous unit activity in the Clare-Bishop area. The hypothesis that these areas are the association representation of two different sections of the visual system — retino-geniculocortical and retino-tecto-thalamocortical — is discussed.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 612–620, November–December, 1981.     

Role of interoceptive afferent excitation in sensory integration on neurons of the cat visual cortex

Experiments on cats immobilized with diplacin showed that stimulation of the vagus and splanchnic nerves had a significant effect on spontaneous unit activity in area 17 of the cortex. The unit responses most frequently observed were prolonged tonic changes in the discharge frequency. Complex phasic unit responses with stable inhibitory pauses and periods of activation occur less often. The development of phasic responses could begin either with a period of activation or with initial inhibition of activity. As a result of splanchnic nerve stimulation responses of predominantly excitatory type appeared. These also occurred more often in response to somatic stimulation. The degree of recruiting into the responses and the intensity of the responses themselves increased if a series of stimuli was applied to the nerves. The important role of the lateral hypothalamus and mesencephalic reticular formation in the mechanism of the visceral and somatic events observed on visual cortical neurons was demonstrated.Ivano-Frankovsk Medical Institute. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 361–368, July–August, 1977.     

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.     

Response of neostriatal neurons to direct electrical stimulation of the optic tract and photic stimulation in awake cats

During acute experiments on awake cats the response of 98 neurons belonging to the head and tail of the caudate nucleus to direct electrical stimulation of the optic tract and presentation of photic stimuli was investigated using extracellular recording techniques. Of the test neurons 34.6% responded to stimulation of the optic tract and 36.2% to optic stimulation. Long latency (over 40 msec for the optic tract and over 80 msec for visual stimulation) excitatory responses prevailed in both cases. A small number of cells responded to optic tract stimulation with short latencies of 5–14 msec. Both types of stimulation were presented during investigations of 58 units of which eight were found to respond to both stimuli. The latter varied in their reaction to different stimuli and their response pattern. Findings are discussed in relation to the possible pathways by which visual information reaches the cortical structure under study.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 476–485, July–August, 1986.     

Unit responses in the anterior zone of the suprasylvian gyrus to peripheral stimuli of different modalities

Unit responses in the anterior zone of the suprasylvian gyrus to visual, electrodermal, and acoustic stimulation were investigated in experiments on unanesthetized cats immobilized with tubocurarine. Electrical activity was recorded from 131 units, 121 of which were spontaneously active. In 65.5% of cells responses consisted of a short or long increase or a decrease in intensity of spike activity. Most cells (58.2%) were monosensory. Responses to visual stimulation were given by 72% of neurons, to electrodermal by 61.6%, and to acoustic by 9.3%. The corresponding latent periods were 20–40, 20–30, and 15–20 msec. Responses of the same neurons to different peripheral stimuli were uniform or they differed in their dynamics. Intracellular recording gave responses in the form of EPSPs (amplitude 4–5 mV, duration 60–80 msec) or, rarely, IPSPs (amplitude 2–3 mV, duration 160–200 msec). The functional organization of the associative cortex and mechanisms of analysis of incoming afferent information are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 368–374, July–August, 1972.     

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.     

Polyfunctional character of responses of single neurons of the visual cortex of wakeful rats to light flashes

The activity of single neurons of the visual cortex in the initial state and upon presentation of a certain program of stimuli, which included a series of modality-specific (light flashes, continuous light) and nonspecific (clicks, tone) stimuli used separately and in combination, was recorded extracellularly by glass electrodes in unanesthetized and uncurarized white rats restrained in a stall. The responses of the neurons to flashes and clicks were analyzed by the poststimulus histogram method. The regular shifts of neuronal activity in response to light flashes (with a frequency of one per second) in the form of an increase or decrease of firing rate were noted not only during the first 150–200 msec (short-latent responses — SLR) but also later, after 700–800 msec (long-latent responses — LLR). The LLR differed from the SLR also by greater variability (decrease or increase upon repeating the stimuli) and by pronounced interaction with the modality-nonspecific stimuli, which had a weak effect on the SLR and by themselves very rarely evoked responses of the visual cortex neurons. The neuron could demonstrate several LLR with a different latent period. The independent nature of each LLR was indicated by the relative independence of its dynamics. All these data permit the consideration that one and the same neuron in one cycle of its activity can be included in different functional systems of the brain, which evidently provide direct reception of information arriving over specific sensory conductors and its subsequent processing. Therefore, neurons, which made up more than half of those investigated, can be regarded as polyfunctional.N. I. Grashchekov Laboratory of Problems of Controlling Functions in Man and Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 242–250, May–June, 1970.     

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.     

Excitability cycles and rhythmic responses of visual cortical neurons to diffuse and punctiform light stimuli

The responses of the rabbit's visual cortical neurons to paired and rhythmic punctiform stimulation of their receptive fields were compared with responses to diffuse photic stimuli and the electric stimulation of the optic nerve. Diffuse photic and electric stimuli evoke a short-lasting initial activation of a neuron, followed by an inhibitory phase, during which the response to repetitive stimulation is suppressed. By contrast, localized stimulation of the neuron's receptive field with a spot of light produces an intensive and longer-lasting activation which is not followed by profound inhibition. Fusion of the responses to paired and rhythmic localized stimuli is therefore possible when the intervals between stimuli are brief enough. Rhythmic stimulation is capable of evoking sustained activation of a neuron during the entire duration of light flicker. During stimulation of a single point of the receptive field such prolonged activation can take place only within a limited range of stimulation frequencies (up to 15/sec), while higher frequencies evoke responses to the onset and offset of sequences of light flashes only. If, however, rhythmic stimuli alternate between the various points of a receptive field, prolonged neuronal activation is observed with any frequency of stimulation.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 252–259, May–June, 1971.     

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

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

Electrophysiological analysis of the functional organization of cortico-cerebellar connections

The effect of stimulation of cortical association (orbito-frontal, parietal) and projection (auditory, sensomotor) areas on the activity of Purkinje neurons of the cerebellar cortex was studied in adult cats anesthetized with pentobarbital, with or without chloralose. These responses were compared with those to peripheral stimuli. Definite similarity was found between the responses of Purkinje cells to different cortical (association and projection) stimuli as regards both the types of responses of the neurons and their ability to respond. No similarity was observed in the responses of Purkinje cells to peripheral (visual, auditory, electrodermal) stimulation. Whereas almost identical numbers of neurons (over 50%) were excited in response to the different forms of cortical stimulation, the ability of the neurons to respond to peripheral stimuli differed considerably: 44.6% of neurons responded to electrodermal stimulation, 34.2% to auditory, and 18.8% to visual.Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 483–489, September–October, 1976.     

Electrophysiological investigation of medullary neurons connected with lateral line organs of the catfish (Ictalurus nebulosus)

Unit responses in the acoustic-lateral region of the medulla to electrical and mechanical stimulation of the lateral line organs were investigated in acute experiments on curarized catfish. Of the total number of neurons 70% possessed spontaneous activity. An electrical stimulus evoked a tonic response both in spontaneously active and in "silent" cells. Three main types of firing pattern of the neurons were distinguished: fast-adapting, slow-adapting, and grouped. As regards the relation of the neurons to polarity of the stimulus they were subdivided into two groups. The thresholds of unit responses to electrical stimulation varied considerably: from 2.5·10^–9 to 5·10^–12 A/mm². The effect of intensity of the electrical stimulation on unit responses in the medulla is analyzed. The precise dependence of on- and off-responses of each neuron on stimulus intensity of any polarity was determined. The neurons were shown to be sensitive to both electrical and mechanical stimuli. It is postulated that this phenomenon is due to convergence of impulses from electrical and mechanical receptors of the lateral line on the neurons. The properties of the central neurons are compared with those of the peripheral electroreceptor system in catfish.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 156–163, March–April, 1973.     

Effect of strychninization of the rabbit visual cortex on evoked activity in the lateral geniculate body

Changes in the parameters of responses of "low-frequency" and "high-frequency" neurons evoked in the lateral geniculate body by flashes or electrical stimulation of the optic nerve were investigated in immobilized and anesthetized rabbits after strychninization of the visual cortex. Under these conditions mainly an increase in the mean discharge frequency in the responses and a decrease in their latent periods were found in the "low-frequency" neurons, probable evidence of dominance of corticofugal facilitation. In most "high-frequency" neurons, on the other hand, the mean discharge frequency in the responses decreased and the latent periods were increased, evidence of dominance of corticofugal inhibition. It is suggested that reciprocal corticofugal influences exist on neurons connected with central and peripheral channels of the visual projection pathway.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow, Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 459–466, September–October, 1976.     

Imitation of neurophysiological effects of long-term sensitization with the action of the blockers of protein synthesis in snailsHelix lucorum

The experiments on command neurons of defensive behavior in snailsHelix lucorum have shown that the synaptic components of responses to the testing stimuli are facilitated within 65 to 75 min after the onset of the application of the protein synthesis inhibitors cycloheximide or anisomycin (30 µM during 30 min) to the central nervous system. At the same time, the parameters of the electrical properties of neuronal membrane (membrane potential level and excitability) were not affected by the blockers. The facilitatory effects were not observed when the blockers were applied for a longer period or when their concentration was raised to 300 µM. The blockade of the responses to different sensory stimuli appeared selective. The facilitation of the responses to tactile stimulation of the head, to weak quinine solution, and to carrot juice lasted for about an hour, 2–3 h and about 1.5 h, respectively. The blockers facilitated only the responses to tactile stimulation of the head, but did not change the responses to stimulation of the middle part of the foot or the mantle bolster. Some characteristics of the blocking effects are similar to those of long-term sensitization. The blocking effects observed are suggested to be due to activation of synthesis of short-living proteins functionally related, in particular, to selective regulation of synaptic transmission.Neirofiziologiya/Neurophysiology, Vol. 26, No. 1. pp. 61–67, January–February, 1994.     

Changes in the functional characteristics of Clare-Bishop area cells after partial unilateral isolation of the neocortex in cats

Evoked unit activity was investigated bilaterally in neurons of the Clare-Bishop area in cat brain after unilateral severing of the posterior limb of the internal capsule. Cell responses to photic, acoustic, and somatosensory stimuli, also to electrical stimulation of the association areas of the neocortex were investigated. The most rudimentary type of response to a diffuse light flash, electrical stimulation of the forepaw skin, and acoustic stimulation was restored in a proportion of test cells in the operated hemisphere within one week of operating. Sensitivity to visual stimuli increased considerably in cells of the Clare-Bishop area of the intact hemisphere during the first week after the operation. All test cells responded to presentation of light flashes; 80% had receptive fields located to electrical stimulation of the forepaw skin. Seven days after the operation the number of cells responding to photic stimulation fell to 35% and only 17% of cells responded to somatosensory stimuli. This article discusses features of the neuronal compensatory reorganization of the Clare-Bishop area and its role in the recovery of visual function.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 180–187, March–April, 1986.     

Effect of repetitive stimulation of the locus coeruleus on spinal inhibition evoked in cats by activation of flexor reflex afferents

Repetitive stimulation of the locus coeruleus with a frequency of 40 Hz and strength of 50–150 µA in decerebellated cats anesthetized with chloralose was accompanied by a decrease in the inhibitory action of flexor reflex afferents (FRA) on the extensor monosynaptic reflex. This effect, which appeared after 600 msec, reached a maximum 1500–1700 msec after the beginning of repetitive stimulation. A minimum of 7–10 stimuli was needed to evoke the effect. After the end of stimulation the inhibitory action of FRA was not fully restored until after 2–3 sec. During application of a single stimulus or a short high-frequency series of stimuli of the same strength to the locus coeruleus no such effect was found. An increase in the strength of stimulation in that case was accompanied by activation of adjacent more rapidly conducting structures. The advantage of repetitive stimulation for detecting effects of slowly-conducting brain structures is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 187–195, March–April, 1981.