Centrifugal and centripetal connections of the cat visual cortex

In experiments on curarized cats unit responses in the dorsal lateral geniculate body to stimulation of various zones in area 17 of the visual cortex were analyzed. Of all cells tested 69% were found to respond antidromically and 8% orthodromically; in 7.6% of cells IPSPs occurred either after an initial antidromic spike or without it. The velocities of conduction of excitation along the corticopetal fibers of the optic radiation varied from 28 to 4.3 m/sec, but the three commonest groups of fibers had conduction velocities of 28–19, 14–12, and 10–9.5 m/sec. A difference between latent periods of antidromic responses of the same neurons was found to stimulation of different zones of the visual cortex; this indicates that axons of geniculo-cortical fibers split into several branches which form contacts with several neurons in area 17 of the visual cortex. The degree and possible mechanisms of cortical influences on neurons of the lateral geniculate body are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 243–249, May–June, 1976.     

The intrinsic, association and commissural connections of area 17 on the visual cortex.

An experimental neurohistological study has been made of the intrinsic connections of the cortex of area 17 of the monkey, of the commissural connections of the visual cortex of the cat and monkey and of the association fibres passing into area 17 of the cat. In light microscopic studies the axonal degeneration method of Nauta has been used, and the site and mode of termination of the degenerating fibres has also been determined with the electron microscope...     

Interhemispheric connections of the parietal area of the cat cerebral cortex

The interhemispheric connections of the temporal cortical area in the cat cerebrum have been investigated after electrolytic coagulation of separate fields with subsequent study of the degenerated fibers course after Nauta--Gygax method. The fields 5 and 7 give origin mainly to homotopic fibers, terminating in symmetrical fields of the contralateral hemisphere. These fields also give origin to a small number of heterotopic commissural fibers, that provide bilateral connection of the fields 5 and 7 and do not get beyond the limits of the temporal cortex. The commissural fibers of the temporal cortex get into the contralateral hemisphere through the corpus callosum. In the latter, the commissural fibers of the field 5 are situated more rostral of the fibers running from the field. 7. This corresponds to topographic arrangement of the fields on the cortical surface.     

Stimulus-entrained oscillatory activity propagates as waves from area 18 to 17 in cat visual cortex

Previous studies in cat visual cortex reported that area 18 can actively drive neurons in area 17 through cortico-cortical projections. However, the dynamics of such cortico-cortical interaction remains unclear. Here we used multielectrode arrays to examine the spatiotemporal pattern of neuronal activity in cat visual cortex across the 17/18 border. We found that full-field contrast reversal gratings evoked oscillatory wave activity propagating from area 18 to 17. The wave direction was independent of the grating orientation, and could not be accounted for by the spatial distribution of receptive field latencies, suggesting that the waves are largely mediated by intrinsic connections in the cortex. Different from the evoked waves, spontaneous waves propagated along both directions across the 17/18 border. Together, our results suggest that visual stimulation may enhance the flow of information from area 18 to 17.     

Heterogeneity of neuron populations with complex receptive fields in the cat visual cortex

The selectivity of striate neurons with complex receptive fields to the orientation, direction, and velocity of movement of various stimuli was investigated in unanesthetized and uncurarized cats. On the basis of all characteristics obtained by the study of single-unit responses to a stationary flickering slit, a moving spot of light, and a moving oriented stimulus, four groups of complex neurons were distinguished. The characteristics of group I neurons indicate a mechanism of orientation selectivity in the organization of their receptive fields, group IV neurons have a mechanism of directional selectivity, and neurons of groups II and III possess both mechanisms. The existence of separate neuronal systems coding the orientation and direction of stimulus movement is suggested.V. Kapsukas State University, Vilnius. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 109–116, March–April, 1979.     

Associative connections of the cat parietal cortex

Interneuronal connections of area 7 of the cat parietal cortex with projection areas of the visual, auditory, and somatosensory cortex were analyzed by orthograde degeneration and retrograde transport of horseradish peroxidase methods. By combined investigation the cortico-cortical sources of afferentation of parietal area 7 could be precisely identified and concentration sites of neurons sending their axons into this area identified, and the morphological characteristics of these neurons could also be determined.A. A. Ukhtomskii Physiological Institute, A. A. Zhdanov Leningrad State University. Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 13–17, January–February, 1980.     

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.     

Factors governing the adaptation of cells in area-17 of the cat visual cortex

Neurons in area 17 of the cat visual cortex adapt when stimulated by drifting patterns of optimal orientation, spatial frequency and temporal frequency (Ohzawa et al. 1982; Albrecht et al. 1984; Ohzawa et al. 1985). A component of this adaptation has been attributed to a contrast gain-control mechanism, rather than to neural fatigue, and results in enhanced differential sensitivity around the adapting contrast level (Ohzawa et al. 1982; Albrecht et al. 1984; Ohzawa et al. 1985). Experiments described here suggest that neural response rate, the directional selectivity of the cell, and the temporal frequency of the stimulus, are the principal determinants of adaptation, irrespective of other stimulus parameters such as contrast, velocity, or spatial frequency. The present results can nevertheless accommodate the results of previous studies of adaptation, and additionally provide scope for the resolution of apparent contradictions between results from psychophysical and neurophysiological studies of adaptation.