Correlations between the properties of visual cortex neurons in the cat

In acute experiments on immobilized cats 13 functional characteristics of 96 visual cortex neurons were investigated. By means of regression, cluster, and multivariate analyses, these could be divided into two subgroups with varying degrees of correlatedness. Cells of the first subgroup were more frequently characterized by their relatively central location in the visual receptive field, while those of the second subgroup were more often found at the periphery. A significant correlation was found between 11 of the properties investigated. In each subgroup, cells with more centrally localized small receptive fields had, in comparison with neurons of the peripheral visual projection, short latent periods, lower thresholds, phasic response, and brief summation; their responses varied widely in intensity, and they had greater differential sensitivity, and were distinguished by high-frequency discharges. Significant correlation coefficients between the factors studied fluctuated between 0.21 and 0.99; moreover, there were almost twice as many significant relationships in the first subgroup of neurons as in the second. The possible mechanisms of correlations between the properties of the visual cortex neurons are discussed, as well as the reasons why they differ in cells of the two subgroups, the cortex, and the lateral geniculate body.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 587–596, September–October, 1985.     

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.     

Reactions of cat motor cortex neurons to stimulation of the pyramidal tract and ventroposterolateral thalamic nuclei

Responses of neurons of motor cortex evoked by stimulations of pyramidal tract (PT) and ventroposterolateral (VPL) nucleus of thalamus were studied in cats immobilized by Myorelaxin. Antidromic spikes were found in 22.6% and in 9.9% of cortical cells when PT and VPL were stimulated, respectively. Fast- and slow-conducting PT-neurones could be differentiated according to antidromic excitation latencies. PT stimulation evoked EPSPs in 46.3% of studied neurones and VPL stimulation--in 48.2% ones. Monosynaptic EPSPs were identified in responses of fast- and slow-conducting PT-units and of neurones projecting in VPL; mechanisms and functional role of such reactions are discussed. Di- and polysynaptic IPSPs were evoked in 74.5% of units by PT stimulation and in 94.4%--by VPL stimulation. Three groups of IPSPs were classified with durations to 120, 130-280 and more than 300 ms. Duration of PT-evoked IPSPs was higher in cortical neurones from surface layers and VPL-evoked ones--in units localized in deep layers.     

Unit responses of the cat parietal association cortex to stimulation of reticular and anteroventral thalamic nuclei

Responses of 124 neurons in the anterior division of the middle suprasylvian gyrus to stimulation of the reticular (R) and anteroventral (VA) nuclei and the pulvinar (Pulv.) of the thalamus were studied in acute experiments on unanesthetized cats immobilized with D-tubocurarine. Responses of 70 neurons to stimulation of R and Pulv. were investigated. Altogether 51.5% of the cells of this group responded to stimulation of R while 38.6% of neurons responded to stimulation both of R and of Pulv., indicating convergence of afferents from nonspecific and associative nuclei of the thalamus on these neurons. Responses of 54 cells to stimulation of VA and Pulv. were investigated. The tests showed that 72.2% of neurons responded to stimulation of VA and convergence of afferents from VA and Pulv. was found in 29.6% of neurons. As a rule neurons were excited in response to stimulation of R and VA. Inhibition was observed in only one neuron in response to stimulation of R and in six neurons in response to stimulation of VA. The latent period of responses to stimulation of R varied between 2.2 and 37.0 msec, of VA from 6.0 to 35.5 msec, and of Pulv. from 2.1 to 35.0 msec. The length of the latent periods to stimulation of nonspecific and associative nuclei were compared for groups of neurons for which convergence of afferent influences from R and Pulv. or from VA and Pulv. was found. The question of connections of R and VA with the parietal association cortex is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 339–347, July–August, 1973.     

Activity of callosal neurons of the visual cortex in the cat

Activity of 28 identified neurones of the visual cortex was recorded in cats immobilized by d-tubocurarine. Stimulation of the callosal body with a single stimulus or high-frequency train elicited a short-latency antidromic reaction of neurones in the visual cortex whose axons constitute the main part of the large cerebral commissure. Some commissural neurones responded to a single callosal stimulation by two action potentials the first one being antidromic, the second one being of long-latency postsynaptic origin. The second action potential was generated as a result of activation of axonal collaterals of the same neurone or the neighboring callosal neurones. More than a half of callosal neurones responded to a single stimulation of the lateral geniculate body by short-latency antidromic discharges and by long-latency postsynaptic reactions. These data indicate the existence of the systems of two-way neuronal connections, i.e. calloso-geniculate and geniculo-callosal ones.     

Synchronous membrane potential fluctuations in neurons of the cat visual cortex

We have recorded intracellularly from pairs of neurons less than 500 microm distant from one another in V1 of anesthetized cats. Cross-correlation of spontaneous fluctuations in membrane potential revealed significant correlations between the cells in each pair. This synchronization was not dependent on the occurrence of action potentials, indicating that it was not caused by mutual interconnections. The cells were synchronized continuously rather than for brief epochs. Much weaker correlations were found between the EEG and intracellular potentials, suggesting local, rather than global, synchrony. The highest correlation occurred among cells with similar connectivity from the LGN and similar receptive fields. During visual stimulation, correlations increased when both cells responded to the stimulus and decreased when neither cell responded.     

Orientation scanning effect monitored in neurons of the cat visual cortex

Incidence of the phenomenon of dynamic scanning of a portion of the orientation range during the development of neuronal response in cells of the primary visual cortex was monitored in immobilized cats using a technique involving time bins, having smoothed latencies and estimating only the highly significant portions of their response. It was found that this effect persisted in 13 out of 17 test neurons, actually remaining invariable in seven units, and modified in a further six cells owing to a shift in the starting point of the scanning process along the directional range, either extending the latter or producing a change in the direction of scanning. Directional tuning stabilized in 4 cells only following smoothing of latent periods. Findings indicate that dynamic changes in directional tuning are associated with a restructuring of the time course of response in most neurons, indicative of spatio-temporal directional coding.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translating for Neirofiziologiya, Vol. 19, No. 2, pp. 179–185, March–April, 1987.     

The neurons in layer 1 of cat visual cortex.

We have examined the morphology of neurons in layer 1 by injecting them intracellularly with lucifer yellow in lightly fixed brain slices (250 microns thick) taken from the medial bank of area 17 in adult cats. Of 22 neurons with well-filled dendrites, 16 had smooth dendrites, two had sparsely spiny dendrites (less than 200 spines) and, unexpectedly, four had spiny dendrites typical of pyramidal cells. The axon was generally not well filled. Computer reconstructions showed that parts of the dendritic tree had been lost in the sectioning. Nevertheless, measurements of the length of intact dendrites suggested an average diameter of the dendritic tree of 220 microns. The density of the neurons was such that the dendritic trees of about six neurons cover each point in layer 1. Thus, despite the very low density of neurons that characterizes layer 1, there are more than sufficient neurons to sample from the entire representation of the visual field in area 17.     

Tuning for cruciform stimuli in visual cortex neurons of cat

In the primary visual cortex of an immobilized awake cat, nearly one-third of the neurons studied (8 out of 22) were found to respond to flashing cruciform light stimuli 1.5–4 times better than to single stimulations with the strips of preferred orientation. It is suggested that such neurons can detect angles and line intersections.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 362–364, September–October, 1993.     

Response of parietal association cortex neurons to acoustic stimulation before and after auditory cortex blockage in the cat

The effect of auditory cortex blockade on response patterns of parietal association cortex neurons responding to different frequency tones was investigated in the cat. Blockade was produced by two methods: bilateral isolation and application of a 6% Nembutal solution to the auditory cortex surface. Frequency threshold curves were plotted for all test neurons. The majority of test neurons (84%) displayed one or two characteristic frequencies before blockade, as against only 63% of all neurons responding following blockade. Changes also affect the range of frequencies at which the cells could respond. Virtually all test neurons responded to application of a broad spectrum of frequencies under normal conditions. After blockade of the auditory cortex 69% of neurons no longer responded to tones above 8–10 kHz. This would suggest that mainly information on high frequency tones is transmitted via the auditory cortex. The question of where acoustic information for parietal association cortex neurons mostly originates is also discussed; association thalamic nuclei are thought to be the main source.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 354–360, May–June, 1986.     

Relationship between functional characteristics of cat visual cortex neurons,their response to novelty,and short-term memory

In the visual cortex of unanesthetized cats, the number and frequency of discharges in response to a new stimulus differed from the subsequent responses: the first response was more intensive in 34% of the neurons, but in 30% it was inhibited. The phenomenon of short-term memory was detected in 19% of the cells: it was expressed in regeneration of the configuration of response discharges after the cessation of rhythmic stimulation. These peculiarities can be linked with functional organization of the neurons. We divided them into two groups according to their response to photic stimuli. The first group includes short-latent neurons that respond with discharges of the phasic type and that virtually or totally lack spontaneous activity. The second group consists of long-latent neurons with the tonic type of discharges and distinct spontaneous activity. In the overwhelming majority of cases, response to novelty and short-term memory were discovered in neurons of the second group. It is hypothesized that the population of neurons of the first group — having narrower afferent connections — takes part mainly in analysis of properties of a photic stimulus; the population of neurons of the second group participates in information processing at the final and highest level, on which mechanisms of memory and attention are implicated.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 611–617, November–December, 1970.     

Responses of neurons in cat visual cortex with sensitivity to bar and cross-like figure

In the cat primary visual cortex (area 17) the response magnitude and latency were studied in 280 neurons sensitive to bar or cross-like-figure. Under natural conditions half of the studied 195 cells preferred bar (first group) or cross (second group). In the first group responses to both figures were near equal, while in the second one cross evoked much stronger response. Response latencies with the optimal bar in the first group were shorter than in the second group and longer to a cross than to a bar while in the second group they were considerably shorter to a cross than to bar. Under local blockage of GABA-ergic inhibition by microiontophoretic application of bicuculline about one-fourth of 85 neurons generated greater responses and were bar-sensitive irrespective to presence or absence of inhibition. Other neurons were cross-sensitive at least in one of the conditions (with and/or without of inhibition). They responses grew under bicuculline action relatively more than in the first group. Significance of the data obtained for tuning to image features and temporal succession of their detection is discussed.     

Changes in responsiveness of parietal association cortex neurons to stimulation of thalamic association nuclei during development of inhibition

Reactions of neurons of area 7 in the parietal association cortex to paired stimulation of the dorsolateral and posteriolateral thalamic nuclei were investigated using methods of extra- and intracellular recording. It was found that conditioning stimulation of association nuclei caused inhibition or facilitation of the test response; in some cases, the effect was indeterminant. Inhibition frequently led to other types of reactions. Inhibition of response to the test stimulus was pronounced during the initial period of IPSP, but facilitation of the response was possible during the repolarization phase. There was no inhibition of test responses when the chloride component of the IPSP was reversed. It is suggested that inhibition of responses to the test stimulus takes place in the presence of an inward chloride current and that facilitation of responses to such a stimulus may be due to increased effectiveness of late EPSPS.I. I. Mechnikov State University, Odessa. Translated from Neurofiziologiya, Vol. 24, No. 2, pp. 198–207, March–April, 1992.     

Aspects of excitation and inhibition produced in parietal association cortex neurons by stimulating thalamic association nuclei

Neuronal response to single stimuli applied to the thalamic dorsolateral and posterolateral nuclei (DLN and PLN resepctively) was investigated in the parietal association cortex. Primary IPSP following DLN and PLN stimulation was noted in 62.5% and 79.6% of instances respectively. Latencies of EPSP and IPSP when stimulating the two nuclei were longer for the DLN. The amplitude of EPSP evoked by stimulating association nuclei rose and declined smoothly, while that of IPSP showed a fast rise and a more steady decline. The EPSP appearing during the evolution of IPSP were of higher amplitude than control level of resting potential. Both amplitude and duration of IPSP induced in a single unit by stimulating different association nuclei were extremely similar, thus confirming the involvement in this operation of the same inhibitory cortical interneurons. Duration of IPSP was shorter than that of inhibitory background spike activity. It is postulated that the discrepancy in duration can largely be ascribed to properties of the neurons themselves.State University, Odessa. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 529–536, September–October, 1991.     

Bursting activity in visual neurons of the cat cortex during pattern detection

The time course of neuronal response to presentation of a static flashing slit at different angles and both light spots and light strips moving in different directions was investigated in the Clare-Bishop area of the cat cortex. It was found that orientational and directional tuning patterns were mainly determined by the bursting constituent of the response and could be measured according to the number of spikes per burst or the actual number of bursts. A closed-loop model for pattern detection is introduced to shed light on bursting activity.V. Kapsuko State University, Vil'nius. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 335–343, May–June, 1987.     

Dynamics of tuning to orientation of cross-like figures in neurons from the cat visual cortex

Dynamics of tuning to orientation of flashing light bar and to orientation of cross-like figure was studied by a temporal slices method in 87 neurons of the cat primary visual cortex. Tuning was plotted by spikes number in the entire response and in its successive fragments with a step of 20 ms. It was found that successive dynamic shift of preferred orientation of a bar was typical for 87% units, white such shift of preferred orientation of a cross was met in 75% of cases. Comparison of tuning dynamics for bar and cross allowed to separate units into three groups: the first one (58.6% of cases) with larger dynamic shift of a bar preferred orientation then of a cross (74.9 +/- 5.8 degrees [symbol: see text] 29.8 +/- 4.1 degrees, correspondingly, p < 0.00001), the second group (21.5%) with opposite effect (24.2 +/- 5.2 degrees and 69.2 +/- 10.0 degrees, p < 0.0002) and the third group (19.8%) without significant shift of preferred orientation of bar and cross and without difference in their dynamics. Possible mechanisms of the preferred orientation dynamics and its difference for bar and cross are discussed.