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.     

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.     

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.     

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.     

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.     

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.     

Effects of sombrevine on orientational tuning of visual cortex neurons in the cat

Changed orientational tuning (OT) in 58 visual cortex units was investigated during acute experiments on immobilized cats under light short-lasting sombrevine-induced anesthesia. A 47.6±5.6° alteration in the preferred orientation of 60% of cells occurred following sombrevine injection but no change occurred at any stage of anesthesia in the remainder. The latter group showed a preference for horizontal and vertical orientations, less pronounced in the former category. "Stable" neurons also displayed less acute tuning and more selective detection in comparison with "unstable" units. Breadth of orientational tuning consistently changed by an average of 65.2±6.7° in 55% of neurons, while tuning deteriorated in 31% and sharpened in 24% of cells. No regular change in tuning band occurred in the remainder. Background firing rate and evoked spike activity declined by 58% and 35%, respectively under anesthesia in 2/3 of the cells tested. Tuning bandwidth of unit firing rate had generally recovered within 20–40 min after administering the anesthetic (i.e., as the anesthesia wore off).Higher Nervous Activity and Neurophysiology Research Institute. Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 812–820, November–December, 1989.     

Directional tuning of visual cortex neurons in the cat before and after nembutal injection

Directional tuning was investigated in 40 neurons of the primary visual cortex (area 17) before and after Nembutal injection during acute experiments on immobilized cats. Preferred orientation (PO) in 50% of neurons was found to be stable after the drug, while the remainder showed a consistent shift in PO (averaging 53.6±8.0°) for a number of hours. Neurons with consistent PO more frequently showed a preference for horizontal and vertical stimulus orientation; cells with unstable tuning had a wider PO distribution. More refined directional detection (i.e., finer tuning) was noted in "stable" rather than in "unstable" neurons both before and after administering the drug. Under narcosis, directional tuning altered in 50% of cells — an effect more marked in "unstable" than in "stable" cells (68% as against 38%). Mean background discharge rate also fell by an average of 5.5-fold and induced firing rate declined 1.5-fold during narcosis, moreover.Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 669–676, November–December, 1991.     

Local synchronized activity of neurons of different classes in cat primary visual cortex

The goal of the present study was to investigate the local synchronized neuronal activity in the cat visual cortex and the role of different classes of neurons in neural synchrony. Four classes of neurons were identified on the basis of electrophysiological properties of extracellularly recorded cells: RS, FS, IB, and FRB. It was revealed that neurons with short spikes and FRB type of activity were first engaged in synchronization. The model study revealed that neurons with the short action potential had more stable synchronized activity.     

Comparative electron microscopic study of the visual cortex neurons of the cat in postnatal ontogeny

The maturation of layers II-VI of neurons and perineuronal neuropil of the cat visual cortex (field 17) was studied from postnatal day 1 to day 21. The differentiation of large, small (associate) pyramid and stellate neurons was described. During the first postnatal week, the somata of layers II-VI of neurons undergo significant changes, the perikaryal cytoplasm increases in volume. Cell bodies of large pyramidal neurons mature by day 15. During the second postnatal week and almost till day 15, the rough endoplasmic reticulum of small pyramidal and stellate neurons undergoes proliferation; dendritic processes are branching. In stellate neurons the amount of cytoplasmic organelles increases dramatically only after the second postnatal week, and this is presumably induced by the opening of eyes on day 12. The second postnatal week is the period of greatest growth of dendritic, axonal and glial processes in perineural neuropil of layers V-VI. In the perineuronal neuropil of large pyramidal neurons (layers V-VI) there appear symmetric synapses with pyramidal cells, dendritic processes and dendritic spines. This occurs just at the time when kittens first open the eyes. From this time and during postnatal days 15-21, asymmetric synapses appear in the perineuronal neuropil of large pyramidal neurons. In the perineuronal neuropil of small pyramidal and stellate neurons. (layers II-IV), synapses reveal the mature appearance by day 15. After the opening of the eyes and up to postnatal day 21, dendritic growth and spine production occur in the perineuronal neuropil of small pyramidal and stellate neurons.     

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.     

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 the dendritic organization of the neurons of the isolated visual cortex of the cat]

The cortex of one hemisphere in cats was isolated according to M.M. Khananashwili method by means of surgical section of its projection fibres which connect it with subcortical structures. In five cats of means of Nissl's method the neuronal status of different cortical layers in the field 17 was studied during long postoperative terms (from 9 months up to 2 years). In 9 cats the neurons of the same field were impregnated after Golgi-Bubenett method and studied during the same postoperative terms. Cytological investigation in the majority of neurons did not reveal any pathologic changes during different postoperative terms up to one year. In two years, slight neuronal changes were noted presented in poor staining and vacuolization of cytoplasm. As a result of deafferentation performed shortening and thickness of dendritic branching was noted, as well as decrease in the number of thorns of large pyramids in layers III, IV, and V of the isolated cortex. Dendrites and thorns in small and medium-sized pyramids in layers II, III, IV, V, and VI were preserved to a great extent. It is possible to conclude, on the fact of thorns preserving in the major number of the neurons, that the neocortex possesses an enormous intracortical connective system that is responsible for the high degree of functional neuronal activity in the isolated cortex.