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.     

Varying response of caudate neurons to visual stimuli in awake cats

Activity in 62 caudate nucleus neurons produced during presentation of visual stimuli was recorded during experiments on awake cats. Response of a sensory pattern, associated with a photic stimulus falling within a certain section of the visual field was observed in 52% of the neurons tested as against only 11% manifesting motor response related to eye movement guided towards a target. About a quarter of the cells responded to biologically significant stimuli, producing a nonspecific response, i.e., not specifically related to the nature of the visual stimuli presented. Several different response patterns could be recorded from a single unit. A hypothesis that more than one parallel pathway for afferent visual inferences on the caudate nucleus may exist is presented on the basis of findings from this research.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 3, May–June, pp. 372–378, 1989.     

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.     

Effect of reticular formation on hippocampal neurons (field CA1)

The reaction of field CA₁ hippocampal neurons to stimulation of the reticular formation (RF) with impulses of different frequencies was investigated in experiments on unanesthetized rabbits. The effect of electrical and sensory stimuli was compared and the effect of reticular stimulation on the sensory responses was determined. With an increase in the frequency of RF stimulation, the number of neurons of field CA₁ responding with inhibition of the activity increases. Multimodal neurons of the hippocampus depend on the reticular input to a greater degree than unimodal neurons. Neurons whose activity does not change in response to the effect of sensory stimuli also do not respond to stimulation of the RF. Neurons responding with inhibitory reactions to sensory stimulation show a higher correlation with the effects of RF stimulation than neurons with activation reactions and, especially those with "complex" responses to the effect of sensory stimuli. In a considerable number of hippocampal neurons the responses to sensory stimuli change in the course of 10–15 min after stimulation of the RF. The role of the RF in the organization of the reactions of hippocampal neurons is discussed.Division of Memory Problems, Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oke. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 227–235, May–June, 1971.     

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.     

Effect of stimulus intensity on unit responses in the cat frontal cortex

Unit activity of the frontal cortex during changes in stimulus intensity in the near-threshold range (15–16 dB above the threshold for the combined evoked potential) was investigated by an extracellular recording method in acute experiments on cats anesthetized with chloralose (70 mg/kg). Comparative analysis of unit responses in specific (SI) and nonspecific projection areas revealed basically similar changes in pattern during an increase in stimulus intensity: A decrease in the latent period, an increase in the total frequency and the phasic character of the discharge, and an increase in the probability of response. However, a relatively stable latent period and probability of response were observed in specific projection neurons for a stimulus intensity of 3–5 threshold units, whereas for the nonspecific projection neurons it was observed for a stimulus intensity of 10–15 threshold units. All sensory projections in the frontal cortex are formed by two inputs: short-latency low-threshold and long-latency high-threshold. Analysis of modality-dependent differences in the threshold of sensitivity and the latent period of response of the polysensory neurons suggests that stimuli of different modalities converge directly on cortical neurons.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 606–612, November–December, 1976.     

Responses of the neurons of the cortical secondary auditory area to acoustic and non-acoustic stimuli in cats

The responses of the cortical secondary auditory area (AII) to the non-acoustic stimuli (electrical stimulation of the skin in the vibrissae area and light flash) and their combination with acoustic stimulation (sound click or tone) were studied in experiments on cats anesthetized by kalipsol using extra- and intracellular recording. Of the total number of neurons, 69% of the units generating spike responses to the acoustic stimulation responded to the non-acoustic stimulation too. The responses to the modal-nonspecific stimulation, as a rule, were weak and variable; they were mostly represented by a tonic change in the neuronal discharge frequency. The nonspecific stimulation evoked primary excitatory and inhibitory postsynaptic potentials in 77% and 20% of the examined neurons, respectively. We found that synaptic effects of the nonspecific and specific stimulations interact with each other, ensuring considerable modulation of the latter (mostly a significant facilitation resulting from the EPSP summation and suppression of an inhibitory component of the response to acoustic stimulation). Possible participation of the midbrain reticular formation in the transmission of the modal-nonspecific influences to the cortical neurons is considered; stimulation of this structure evoked responses similar to those evoked by the modal-nonspecific sensory stimuli.Neirofiziologiya/Neurophhysiology, Vol. 26, No. 5, pp. 356–364, September–October, 1994.     

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.     

Unit responses in the anterior and posterior hypothalamus to stimulation of the splanchnic and sciatic nerves and to photic stimulation

By extracellular recording of spike discharges the sensory properties of neurons of the anterior and posterior regions of the cat hypothalamus were studied during stimulation of the splanchnic and sciatic nerves and during photic stimulation. Hypothalamic neurons were shown to be characterized by wide convergence of heterosensory excitation: 68% of spontaneously active hypothalamic neurons responded to somatovisceral and photic stimulation. Some posterior hypothalamic neurons responded to somatovisceral stimulation but not to photic stimulation. Neurons responding only to photic stimulation were found in the anterior hypothalamus; no neurons responding only to visceral stimulation were found in the hypothalamus. Total convergence of somatic and visceral afferentation of neurons of the posterior and anterior hypothalamus was observed. Mostly responses of phasic type were obtained to stimulation of all modalities. The study of the quantitative ratio between responses of excitatory and inhibitory types showed that the former predominate. The principles governing the functional organization of hypothalamic afferent systems are discussed.Academician L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 276–282, May–June, 1976.     

Synaptic events during specific and nonspecific inhibition of visual cortical neurons

Intracellular and quasi-intracellular recordings were made of changes in membrane potential in visual cortical neurons of the waking rabbit during specific (to flashes) and nonspecific (to nonvisual stimuli) inhibition. As a rule, specific inhibition was accompanied by some degree of hyperpolarization of the cell membrane while nonspecific was unaccompanied by any appreciable degree of membrane hyperpolarization. It is postulated that this difference is caused by differences in the arrangement of the inhibitory synapses on the body and dendrites of the neurons. Long-latency prolonged IPSPs arising in response to photic stimulation can be suppressed by the action of various nonvisual stimuli and by stimulation of the mesencephalic reticular formation. A decrease in amplitude of the IPSPs may lead to filling of the inhibitory pauses with spikes. These phenomena are evidently based either on inhibition of inhibitory neurons or on a disturbance of the synchronization of their discharges, leading to weakening of the integral IPSPs.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 349–357, July–August, 1972.     

Spatial organization of detector neurons in the caudo-medial part of the frog tectum opticum

Investigation of the spatial organization of detector neurons of the frog tectum opticum showed that these neurons are mainly in the nuclear layers. When responding to a photic stimulus they form a mosaic of groups of synergically excited cells separated by inhibited or nonresponding neurons. Inhibited neurons are much more numerous than excited. Different photic stimuli (shaped or diffuse) evoke the appearance of mosaics of different structure; mosaics connected with different forms of detection are to a considerable degree stratified.Rostov State University. Research Institute of Neurocybernetics, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 468–475, September–October, 1973.     

Response of caudate nucleus neurons to a photic stimulus at various locations on the visual field in the awake cat

The response of caudate nucleus neurons to presentation of photic stimuli located at varying distances from the fovea centralis was investigated in awake cats. Stimulation of different sites on the visual field below the fovea produced dissimilar reactions in 25 of the 35 (or 71%) of these neurons responding to photic stimulation. This divergence of response indicates that in 6 of these cells (or 17%) the receptive fields in the test area of the visual field bordered on the central area of the latter and 6 neurons (17%) showed reduced sensitivity to the effects of stimuli nearer to the periphery than to the center of the visual field, while 13 units (37%) were receiving qualitatively different information from various sites on the field of vision. On the basis of our findings we deduced that caudate nucleus neurons are involved in the analysis of visual sensory signals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 241–250, March–April, 1986.     

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.     

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.     

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.     

Responses of secondary sensomotor cortical neurons to electrodermal and acoustic stimulation in waking cats

Unit responses in the second somatosensory cortical projection area (SII) to clicks and electric shocks applied to the contralateral limb were investigated in chronic experiments on cats. In response to specific stimulation for the cortical region studied the discharge frequency of 75% of neurons increased, spontaneous activity of 18% was reduced in frequency or the discharges ceased altogether, and 25% of cells did not respond. In response to "nonspecific" stimulation (clicks) 30% of neurons were activated; the discharge of 25% of cells was inhibited and 45% did not respond. The results of investigation of intersensory convergence of stimuli from different sensory systems showed that a high proportion (55%) of SII neurons give bimodal responses. Another 18% of neurons give a specific response to both adequate and inadequate stimulation. It is suggested that the presence of polysensory convergence of SII neurons and of short pathways for the conduction of sensory information, and also the ability of neurons to acquire polysensory properties during stimulus presentation are evidence of the important role of this cortical region in conditioning.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 453–459, September–October, 1977.     

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.     

Correlations of neuronal spike discharges of VL neurons during spontaneous firing and during the activity evoked by peripheral stimulation

The temporal relations between simultaneously recorded neurons of the nucleus ventralis lateralis (VL) of cat thalamus were studied. The interaction and the functional connections between individual VL neurons are described. This was achieved with an application of cross correlation techniques. The response patterns of different individual neurons to somatic sensory and photic stimuli were also analyzed. For the purpose of classifying neurons as thalamocortical relay cells (T-C) and non relay cells (N-C) which do not project to the motor sensory cortex antidromic cortical stimulation was used. This stimulation was also used as conditioning one when proceeded peripheral stimuli. To analyze the nonspecific specific interactions upon single neurons conditioning photic stimuli were applied. The results show that T-C neurons are antidromically excited from a wide cortical areas and that the functional interaction between T-C neurons is mediated by a shared input from common sources. It is further postulated that N-C cells interposed between relay neurons subserve the functions of gating units modifying the neuronal network of lateral ventral nucleus of the thalamus.     

Participation of midbrain periaqueductal gray matter in defense conditioning in rats

Responses of neurons of the periaqueductal gray matter (PAG) were studied in chronic experiments on cats during formation and extinction of a defensive conditioned reflex to sound and its differential inhibition. In response to conditioned stimulation these neurons developed phasic-tonic spike responses up to 3 sec in duration. During combination of stimuli these responses were formed long before the conditioned reflex and disappeared long after the latter was extinguished. In the case of an established conditioned reflex, the onset of spike responses occurred 100–200 msec before the appearance of motor responses. An increase in spike activity of tonic character in neurons of PAG preceded voluntary movements by 100–500 msec. The responses of these neurons to presentation of a differential stimulus consisted of groups of spikes 150–200 msec in duration. They were formed with difficulty, and their manifestation was made even more difficult by an interruption during the experiment and by preceding positive stimuli. On the basis of the results a conditioned reflex can be regarded as the result of a multilevel hierarchic process of readjustment of unit activity, which begins in the nonspecific structures of the midbrain.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 15, No. 3, pp. 278–287, May–June, 1983.     

Conditions of appearance of off responses of sensomotor cortical neurons to photic stimulation in cats

In acute experiments on cats under chloralose anesthesia (70 mg/kg) unit activity was recorded extra- and intracellularly in the sensomotor cortex (areas 4 and 6) during prolonged (up to 1000 msec) photic stimulation. Responses of on-off type were generated by 100% of neurons tested to photic stimuli whose duration corresponded to the recovery cycle of functional changes after a single flash, determined by the paired stimulation method. Cutaneous stimulation affected the appearance of the photic off response if it led to a spike discharge of the neuron before the off response. It is suggested that IPSPs of cortical neurons largely determine both the duration of the cycle of functional recovery after a single flash and also differences in the pattern of generation of the off response and its interaction with responses to cutaneous stimulation.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 355–360, July–August, 1977.