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R V Novikova

Publications and source records attributed to R V Novikova.

30 records · Page 2Linked to original sources
PubMed1985

[Interrelation among properties of visual cortex neurons in the cat].

In acute experiments on immobilized cats 13 functional characteristics of 96 visual cortex neurons were investigated. Regressional and cluster analyses were used to divide these neurons into two subgroups with different density and degree of connections between characteristics. The receptive fields of cells of the first subgroup were localized relatively centrally in the visual field, those of the second subgroup were localized more often on the periphery. A valuable correlation was found in the half of the studied characteristics. In each subgroup the more centrally localized cells with small receptive fields had relatively shorter latencies, lower thresholds, shorter temporal summation, wider intensity range and greater differential sensitivity; their responses were phasic, with high-frequency discharges. The density of valuable correlation of the characteristics varied from 0.21 to 0.99. The amount of these correlations in the first subgroup was two times higher than in the second one. The possible mechanisms of the correlation between the properties of the visual cortex neurons are discussed, as well as their differences in two subgroups and in the cortex and LGB.

Animals↗
PubMed1983

[Orientational tuning of visual cortex neurons to different stimulus intensities in the cat].

The orientation tuning of field 17 neurons of the visual cortex was studied in immobilized and unanesthetized cats under different intensities of test light slits and constant light background. Orientation tuning of five neurons was invariant to stimulus intensity: their preferential orientation did not change. Thirteen cells were variable as during the change of the contrast they showed a statistically significant displacement of orientation tuning from 22 degrees to 90 degrees. Changes in other neurons were not significant. Invariant neurons differed from variable ones in several characteristics. The mechanisms of orientation tuning changes during contrast variations are discussed.

Adaptation, Physiological↗
PubMed1983

[Double orientation tuning of visual cortex neurons in the cat].

Orientation tuning of 148 visual cortex neurons was investigated in immobilized unanaesthetized cats. The light slit of the optimal size flashing in the receptive field was used as a stimulus. It was found that 88 neurons (59%) had double orientation tuning: preferred and additional. Additional orientation was either orthogonal or at a sharp angle to the preferred orientation. In 64% neurons double orientation was found only after a change of the contrast between stimulus and background. This kind of tuning in many neurons appeared only at definite moments after the beginning of the stimulus. Model analysis showed that double orientation tuning might be a consequence of the specific structure of neuronal receptive fields. The functional meaning of double orientation tuning and its role in the detection of visual images signs are discussed.

Animals↗
PubMed1983

[Study of the functional characteristics of visual cortex neurons in the cat upon local photic stimulation of their receptive fields].

Functional characteristics of 103 neurons in field 17 of the visual cortex were studied in immobilized and unanesthetized cats. Unit responses to modification of local light stimuli wer recorded under conditions of light adaptation. Mean photic threshold of investigated neurons was -32 dB, mean critical temporal summation 57 ms, duration of reactivity recovery 190 ms and sharpness of orientation tuning 37 degrees. As compared to dark adaptation, under light adaptation reduction of light sensitivity, sharpening of orientation tuning as well as a lengthening of temporal summation and a shortening in time of reactivity recovery were observed. A number of neuronal characteristics depended on excentricity of their receptive fields: cells with centrally localized receptive fields had a lower threshold, a short summation and rapid recovery of reactivity; their activity was of higher frequency, and they generated brief transient responses more often than cells with receptive fields in the periphery of a visual field. Mechanisms responsible for change of neuronal properties in the central and peripheral visual channels under light and dark adaptation are discussed. Several inhibitory subsystems are suggested by means of which neuronal activity of the visual cortex is regulated.

Adaptation, Physiological↗
PubMed1981

[Temporal signal summcation by at visual cortex neurons].

The summation temporal of signals in neurons of field 17 of the visual cortex was studied in immobilized and unanaesthetized cats. The unit responses to optimal local light stimuli were recorded under conditions of light adaptation. Critical duration of the summation temporal in different units was 5-100 ms, with mean value equal to 31.45 +/- 5.67 ms. Neurons in the central part of the field differed from the peripheral ones by a shorter critical summation temporal, a lower background discharge frequency and a smaller duration of the first burst in the response. In neurons with simple receptive fields the summation temporal was considerably shorter than in complex neurons. The obtained results are compared with data from literature on neurons of cat retina and lateral geniculate nucleus and discussed with respect to division of ascending afferent visual projections into X and Y (1a and 1b) groups.

Adaptation, Physiological↗
PubMedDate not supplied

The disinhibitory zone of the striate neuron receptive field and its sensitivity to cross-like figures.

Acute experiments on immobilized anesthetized cats were used to confirm the suggestion that the sensitivity of many neurons on the primary visual cortex to cross-shaped, angular, and Y-shaped figures may be determined by the presence within their receptive fields of disinhibitory zones, which block end-stopping inhibition. A total of 55 neurons (84 functions, i.e.. on and off responses) were used for studies of sensitivity to crosses, and responses to single bars of different lengths were compared before and after stimulation of an additional lateral zone of the field (the presumptive disinhibitory zone), which was located in terms of responses to crosses. Seventeen of the 55 cells in which increases in the length of a single bar decreased responses, i.e., which demonstrated end-stopping inhibition, showed significant increases in responses (by an average factor of 2.06 +/- 0.16) during simultaneous stimulation of the lateral zone of the receptive field, which we interpreted as a disinhibitory effect on end-stopping inhibition. These data provide the first direct evidence for the role of end-stopping inhibition and its blockade by the disinhibitory zone of the receptive field in determining the sensitivity of some neurons in the primary visual cortex of the cat to cross-shaped figures.

Animals↗
PubMedDate not supplied

[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.

Action Potentials↗
PubMedDate not supplied

[Neurophysiological and simulation study of the striate receptive fields maps: the role of intracortical interaction].

In 27 acute experiments with anesthetized and immobilized adult cats 101 maps of receptive field (RF) in 67 striate neurons were studied by means of mapping with single flashed stimuli presented in different parts of the visual field and under conditions of additional activation of the RF excitatory center by the local oscillating or flashing grid. Under conditions of both classical and combined modes of mapping, the RFs of the classical shape with a single excitatory zone (63.4 and 29.3% of cases, respectively) and RFs with multiple (2-5) excitatory and/or inhibitory zones (36.6 and 70.7%, respectively) were found. We were the first to describe, also, some RFs of horseshoe-like, cross-like and T-like shapes. Simulation of non-classical RFs revealed possible contributions of cooperative excitatory and inhibitory intracortical interactions to the effects under study. The functional role of RFs of different types in the feature detection is discussed.

Animals↗
PubMedDate not supplied

[The sensitivity of the cat visual cortex neurons to cruciform figures during stimulation of the central and peripheral receptive fields].

The role of the central and peripheral zones of the receptive field (RF) in sensitivity to cruciform figures was studied in 29 neurons of the cat primary visual cortex. Separated or combined stimulation of these zones revealed summation, reciprocity response interaction, or the absence of their interaction by the sensitivity index (ratio between response magnitudes to a cruciform figure and a bar). Stimulation of only central or only peripheral zone of the RF in nearly equal number of cases increased or decreased the sensitivity index in comparison with full cruciform figure. The neurons were found which did not change their sensitivity to cruciform figure under conditions of its partial masking. Mechanisms and functional significance of the interaction between the central and peripheral zones of RF for selection of line crossing in the striate cortex are discussed.

Animals↗