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.     

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.     

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.     

Involvement of visual specific and association cortex input in the shaping of neostriatal neuron response to visual stimulation in unanesthetized cats

During chronic experiments on unanesthetized cats neuronal response in the caudate nucleus to the presentation of local photic stimuli and electrical stimulation of the specific (field 17) and the association (Clare-Bishop) areas were compared. Stimulation of the Clare-Bishop area proved more effective than stimulating field 17 for neurons of the caudate nucleus; a response was produced in 47% of test neurons in comparison with 8% of units only in the specific area. Lower average values were observed for latency of neuronal response to stimulation of the Clare-Bishop area. An insignificant number of caudate nucleus neurons were activated as a result of stimulation of both cortical areas. A comparison between the response of one set of neurons to electrical cortical and visual stimulation showed that cells responding to visual stimulation were more highly activated by stimulating the Clare-Bishop area than by stimulation of field 17. This type of neuron predominated in the caudate nucleus. A discussion follows of the possible involvement of the Clare-Bishop area in shaping neuronal response to visual stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 619–627, September–October, 1985.     

Two patterns of bulbar neuronal response to microstimulation of locomotor and inhibitory brain stem sites

Synaptic responses (postsynaptic potentials and action potentials) were evoked in mesencephalic decerebellated cats by stimulating pontine bulbar locomotor and inhibitory sites (LS and IS, respectively) with a current of not more than 20 µA in "medial" and "lateral" neurons of the medulla. Some neurons even produced a response to presentation of single (actually low — 2–5 Hz — frequency) stimuli. The remaining cells responded to stimulation at a steady rate of 30–60 Hz only. Both groups of medial neurons were more receptive to input from LS. Lateral neurons responding to even single stimuli reacted more commonly to input from LS and those responding to steady stimulation only to input from IS. Many neurons with background activity (whether lateral or medial) produced no stimulus-bound response, but rhythmic stimulation either intensified or inhibited such activity. This response occurs most commonly with LS stimulation. Partial redistribution of target neurons in step with increasing rate of presynaptic input may play a major part in control of motor activity.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 257–266, March–April, 1990.     

Dynamics of functional reciprocal connections between cerebral motor cortex neurons under stimulation in cats

Activity was recorded from neurons belonging to the representation of the forelimb in the motor cortex (sulcus cruciatus, L 7–9 mm) using multiple multi-channel/barrel electrodes during acute experiments on cats. Cross-correlation analysis of impulse trains was adopted to investigate dynamics of interneuronal connections during passive flexion and electrical stimulation of the limb contralateral to the recording site. It was found that neither passive bending nor electrical stimulation of the limb leads to a significant increase in the total number of direct relationships between cortical neurons. At the same time, passive flexion does produce a considerable decrease in the number of instances of both inputs operating in neighboring neurons (50–100 µm apart) and an increase in cells located further (between 100 and 400 µm) apart. Some increase in the number of direct inhibitory interactions between neighboring neurons was observed during electrical stimulation.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Nentskii Institute of Experimental Biology, Warsaw, Poland. Center of Experimental and Clinical Medicine, Warsaw, Poland. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 73–80, January–February, 1991.     

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.     

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.     

Functional characteristics of visual cortical neurons of the cat

The characteristics of neurons in Area 17 of the visual cortex in cats were investigated by extracellular recording of their activity. Unit responses to flashes modulated by intensity and duration (100 µsec-1 sec) were recorded. Of 80 neurons tested, 67.6% were spontaneously active and 32.4% were silent. The threshold responses of the neurons to flashes varied by 7 logarithmic units. The distribution curve of the cells by response thresholds had one maximum corresponding to an energy of the order of 1–10 lm·sec. The time during which the cells could summate excitation did not exceed a mean value of 34 msec. Depending on the latent periods of the visual cortical neurons they can be divided into three groups. The first group includes neurons responding 20–40 msec after stimulation, the second and third neurons responding after 100–120 and 160–180 msec, respectively. Photic stimulation considerably altered the ratio between the numbers of cells generating spikes with high and low frequency. No correlation was found between the sensitivity of the visual cortical cells to light, the latent period of their response, and the critical time of summation. This shows that the cortex contains many duplicate units which are grouped together on the basis of only one of the functional characteristics of their spike response.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 2, pp. 173–179, March–April, 1970.     

Electrophysiological investigation of effect of pulvinar stimulation of caudate nucleus neurons that react to visual stimulation

Responses of caudate neurons to electrical stimulation of the afferent input from thepulvinar thalamic nucleus and to visual stimuli of various orientations were studied extracellularly in awake chronic cats. Activation responses dominated among reactions of these neurons. The response latencies have ranged from 4 to 85 msec for units with primary activation and from 20 to 150 msec for inhibited ones. The values are indicative of both rapidly and slowly conducting afferent pathways. A possibility of monosynaptic transmission in thepulvinarcaudate projections is also revealed.Pulvinar stimulation is found to be efficient for a significant (more than 50 percent) number of caudate neurons responding to visual stimuli, including orientation-selective cells. The mode of influences from other structures of the visual system (optic tract, area 17, the Clare-Bishop area) on caudate neurons responding topulvinar stimulation is described. The data are discussed with respect to the possible role of cortical and subcortical projections of the visual system in the creation of sensory specific responses of the caudate nucleus.A. A. Bogomolets Physiology Institute, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 520–529, September–October, 1991.     

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.     

Frequency characteristics of skate electroreceptive central neurons responding to electrical and magnetic stimulation

Responses of single neurons in the lateral lobes of the medulla to stimulation of the electroreceptive system by homogeneous sinusoidal electrical and magnetic fields were investigated in acute experiments on the skateRaja radiata. Thresholds of neuronal responses to electrical stimulation varied from 0.03 to 10 µV/cm. The optimal frequency ranges for electrical and magnetic reception were in the regions of 0.05–5 and 2–3 Hz respectively. The possible mechanisms and functional significance of frequency characteristics of central neurons are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. All-Union Cardiologic Scientific Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 464–470, July–August, 1984.     

Electrophysiological investigation of central neurons of the electroreceptor system of the skate

Bioelectrical responses of acoustico-lateral neurons to electrical stimulation of the ampullae of Lorenzini were investigated in acute experiments on the anesthetized Black Sea skateTrigon pastinaca. Three types of responses were found: a primary composite response, prolonged activity, and single unit activity. Excitation of the neurons corresponded to a more marked negative phase, and inhibition to a more marked positive phase of the primary response. The thresholds of the unit responses to adequate electrical stimulation were 10^–9–10^–10 A/mm² and the minimal latent period 20 msec. The spontaneous activity of some neurons clearly depended on the animal's respiration. The character of the response depended on stimulus polarity, as reflected in the appearance of on- and off-responses. A tonic type of response with features of adaptation was predominant. The dependence of some response parameters (latent period of on- and off-responses, firing rate, duration of the contrast interval, response thresholds) on those of the stimulus is analyzed. The mechanisms of these bioelectrical responses are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.1, pp.59–67, January–February, 1974.     

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.     

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.     

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.     

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.     

Phase relationships of cortical potentials in rabbits in different functional states

Phase shifts in EEG potentials were investigated in the rabbit cortex during photic stimulation and in controls. Degree of phase shift in the predominating theta waves was found to increase gradually with increasing distance between recording electrodes both with and without photic stimulation, pointing to the existence of a phase gradient — the conditions appropriate to the greater proportion of motor reactions. Photic stimulation induces an increase in numbers of non-phasic EEG waves recorded from close-lying sites as well as reduced scatter in levels of phase shift between EEG of the sensorimotor and visual cortex, thus rendering phase shifts more stable. Irradiation of excitation from the visual to the motor analyzer in response to photic stimulation occurs against a background of high correlation coefficient and coherent function levels and with a phase shift from 0 to 10–11°.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR. Moscow. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 507–513, July–August, 1989.     

Neuronal response in nucleus reticularis thalami and neighboring thalamic structures to natural stimulation during chronic experiments on cats

Spike response was investigated in 104 neurons of the nucleus reticularis thalami (R) and adjoining thalamic nuclei to acoustic, tactile, and visual stimuli during chronic experiments on cats. Of the test neurons, 29% responded to acoustic stimulation and 11% showed no preference in relation to different acoustic stimuli. Minimum latencies of response to sounds measured 12–37 msec in excitatory and 18–27 msec in inhibitory cells. Duration of excitation produced by acoustic stimuli reached 50–250 msec; inhibition lasted 27–190 msec. Most cells belonging to this nucleus were excited by different stimuli; the proportion of inhibitory neurons did not exceed 4–10%.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 451–461, July–August, 1989.     

Posttetanic changes in hippocampal minimal evoked potentials

Changes in the EEG induced by a single spike were recorded in the hippocampus of an unanesthetized rabbit. Summation of focal electrical activity synchronous with spontaneous single unit discharges at the symmetrical point of contralateral hemisphere revealed no stable potentials which could reflect these changes. In two cases discharges identified as activity of Shaffer's collaterals were recorded in area CA₁. Summation of post-spike changes in evoked activity recorded by the same microelectrode showed stable negative waves with an amplitute of 40–60 µV, which could have been evoked by single spikes. The curve of amplitude of the averaged evoked potentials versus near-threshold current strength stimulating the intrahippocampal pathways was not smooth in most experiments but stepwise in character. It is suggested that the minimal evoked potential corresponding to the first step (amplitude 40–80 µV) reflects a response to stimulation of one fiber. After above-threshold tetanization prolonged posttetanic potentiation of the minimal evoked potentials did not arise in CA₁ in response to stimulation of Shaffer's collaterals. Minimal evoked potentials recorded in area CA₃ in response to stimulation of the dentate fascia showed clear potentiation. The results are in agreement with the hypothesis of the synaptic localization of the mechanisms responsible for prolonged posttetanic potentiation.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 124–134, March–April, 1977.