Spatial distribution and interaction of responses in receptive fields of cat lateral geniculate neurons

Responses of lateral geniculate neurons to local photic stimulation and to adaptation of the central, antagonistic, and disinhibiting zones of their receptive fields were compared in unanesthetized cats immobilized with D-tubocurarine. Under most conditions of local adaptation, activation of on- and off-responses of neurons occurred after stimulation of the peripheral zones and inhibition of responses after stimulation of the central zone of the receptive field. As a result most neurons acquired the ability to generate a considerable on- and off-signal in response to stimulation. Comparison of this fact with the properties of on-off neurons [7] supports the view that under light-adaptation conditions the processing of large volumes of visual information and the more sophisticated performance of visual functions are connected with activation of responses from peripheral zones of circular receptive fields. It is concluded that local adaptation to light can extend the functional capacity of circular receptive fields.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 15, No. 5, pp. 451–456, September–October, 1983.     

Role of lateral geniculate neurons in color discrimination in cats

Responses of 43 lateral geniculate neurons to stimulation by flashes of different wavelengths were studied in cats. The neurons were divided into two groups. The first group (44%) gave high-frequency spike discharges which were unaltered by a change in stimulus wavelength. The second group (51%) responded differently to different colors. Statistically significant differences were found in their responses to flashes of different wavelengths. A possible inhibitory influence of the first group of neurons on the second group was demonstrated and its possible significance for color vision is discussed.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 195–200, May–June, 1979.     

Statistical features of impulse trains in cat's lateral geniculate neurons

The spontaneous discharges which recorded extracellularly from cells in the lateral geniculate nucleus (LGN) of a cat were classified into the following 3 main groups depending upon the shapes of their interval histograms and autocorrelation functions: the gamma type whose interval histogram is fitted by a gamma distribution function and whose autocorrelation function has some periodic property which damps down within about several 10 ms, the burst type whose interval histogram has a peak in the first bin (less than 8 ms) and whose autocorrelation function has a large positive peak within several msec, and the multimodal type whose interval histogram has a complex shape with three or more peaks and whose autocorrelation function has a periodic property. Each type of spontaneous discharge seems to be inherent at scotopic and mesopic backgrounds, and the cells whose spontaneous discharges are the gamma type, the burst type, and the multimodal type are called here a gamma cell, burst cell, and the multimodal cell, respectively. Gamma cells are subdivided into X- and Y-cells (gamma-X and gamma-Y cells), but burst cells are all Y-cells and multimodal cells observed up to now are all X-cells. It is clear that these various types of cells are distributed significantly differently in each lamina. All the cells that we found up to now in lamina A were either burst cells or multimodal cells, but every type of cell was found in lamina A1. The majority of cells in lamina C were the gamma type. In most cases, the peak values of the PST histograms of gamma-Y cells (especially, on-center cells) are larger than those of burst cells. These results suggest that Y-cells projecting to area 17 from laminae A and A1 are the burst type, and Y-cells projecting to area 18 from laminae C and A1 are the gamma-Y type.     

Functional heterogeneity of lateral geniculate body neurons in the rabbit]

Background and evoked activity of LGB units was studied on immobilized and anaesthetized rabbits. Two groups of projection units were revealed, differing by the level of background activity, latencies and mean frequency of discharges in responses to single photic flashes and to electrical stimulation of the optic nerve. It is assumed that these groups of units belong to the slowly and rapidly conducting paths of sensory information transmission in the visual projection system.     

Plastic response changes in neurons from lateral geniculate body in rats submitted to conditional reflectory stimulation]

In alert curarized rats the influence of an electric stimulation of the tail skin on the flash-evoked activity of single units of the dorsal part of the lateral geniculate body (CGLd) was investigated. The light flashes were applied 400 msec prior to the electric shocks. 50% of the units showed a change of the response pattern to flash. In the majority of cases the response shifts consisted in a facilitation, which developed gradually and persisted in most of the units examined, even when the electrical stimulus was no longer given in combination with the light. The results are discussed taking into consideration the possibility of an altered emotional or motivational status of the animal, which could play a role in the development of plasticity at the unitary level.     

Cytoplasmic organelles in neurons of the dorsal lateral geniculate nucleus of aged rats

The ultrastructural characteristics of the neurons containing complex convolutions have been studied in the dorsal lateral geniculate nucleus of the 31-month-old rat. Neurons were seen to contain oval or round dense bodies which were surrounded by a nuclear membrane and granular endoplasmic reticulum. Their perikarya showed rarely clusters of pleomorphic and small clear vesicles intermingled with a few larger vesicles of dense material. Dendrites occasionally exhibited intermediate forms between laminated bodies and complex convolutions. The significance of these features has been discussed.     

Receptive field types in the lateral geniculate body and their frequency characteristics]

Time amplitude -- frequency characteristics of the I and II types of receptive fields (RF) of lateral geniculate and their dependence on the contrast and spatial parameters of the light stimulus were studied. It is shown that the frequency characteristics of the RF I type depends on the contrast and area of the light stimulus, the higher being the contrast at a small area the smaller are the low frequencies. However at a large area of the stimulus the inhibition of low frequencies is greater at a small contrast. The transmitting band of frequency characteristics of RF II type does not depend on the contrast at a small area of the stimulus, at a large area a fall of low frequencies takes place at high contrasts of the stimulus. Such different behaviour of the receptive fields is explained by the models, which take into account RF spatial characteristics.     

Sensitivity of the cat lateral geniculate body neurons to orientation of the brightness gradient vector

A new property of visual neurons: their sensitivity to orientation and the vector brightness gradient, was revealed and described. Receptive fields of the lateral geniculate body neurons in the cat have preferred orientation maximum reaction (average mean of orientation sensitivity coefficient--0.55 +/- 0.20). The preferred orientation mainly has a radial or tangential trend in the visual field. Temporal characteristics of the neuronal responses were analysed. A role of inhibition processes in the orientation sensitivity is discussed.