Analysis of unit activity in the cat lateral geniculate body

Spontaneous and evoked single unit activity of lateral geniculate body neurons was recorded extracellularly in acute experiments on cats. Eight groups of neurons differing in the durations of the minimal and mean interspike intervals of spontaneous unit activity, and in the latent period and duration of the first volley of spikes of evoked activity, were distinguished by analysis of the data. On the basis of this classification a scheme for interaction between neurons of the lateral geniculate body is suggested.Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 30–37, January–February, 1978.     

Corticofugal control of unit responses of the cat lateral geniculate body

Acute experiments on anesthetized cats showed that blocking the projection connections of the cortex unilaterally increased the number of lateral geniculate neurons which generated long-latency phasic responses and the number of spikes in the responses of single neurons. Unit responses were monophasic more frequently in the lateral geniculate body on the side of the operation than in the same structure on the opposite side. On the basis of these results a hypothesis is developed to explain the mechanisms of monomodal descending cortical effects in microsystems of neurons of the lateral geniculate body.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 367–374, July–August, 1973.     

Computation of responses to color and brightness differences of neurons in the rabbit lateral geniculate nucleus

Changes in activity of 51 neurons in the rabbit lateral geniculate nucleus evoked by the replacement of eight color and eight achromatic stimuli in pairs were analyzed. It was found that neurons displayed the earliest phasic (within 50-90 ms after the replacement) and tonic response components. The earliest component strongly correlated with differences between stimuli, whereas the tonic component depended on stimuli intensity. Analysis of phasic component revealed two neuronal populations: the first group of cells was specialized for stimuli differentiation only by their intensities, and, and the second group could measure differences in colors and intensities. Neuronal perceptual spaces were reconstructed using the average of the earliest response component as a measure of differences between stimuli. Spaces of 44 neurons (86%) were two-dimensional with brightness and darkness axes. Such neurons had the same structures of space for color and achromatic stimuli. Spaces of 7 neurons (14%) were four-dimensional with two chromatic and two achromatic axes. The structures of perceptual space reconstructed from neurons in the lateral geniculate nucleus were identical to the spaces calculated from the neurons in the primary visual cortex. The structure of the perceptual space reconstructed from neuronal spikes was also similar to space calculated from the N85 visual evoked potential component recorded under similar conditions and to another space reconstructed on the basis of rabbit's instrumental learning. This fact confirmed the general principle of vector coding in the visual system. The tonic component of the most of neurons in the lateral geniculate nucleus showed a linear correlation with changes in intensities, thereby these neurons could be characterized as pre-detectors for cortical selective detectors.     

Cortical control of the afferent flow in the cat lateral geniculate body

Single unit responses in the dorsal lateral geniculate body to stimulation of the optic chiasma (testing) and area 17 (conditioning) of the visual cortex were studied in unanesthetized cats immobilized with tubocurarine. Two types of unit responses were found: P-responses (considered to be of relay, or principal, cells) and I-responses (considered to be of interneurons), whose parameters differed distinctly. Interaction between stimulation of the visual cortex and optic chiasma consisted of depression of the ability of the P cells of the nucleus to respond to testing stimulation. It is suggested that cortical influences on stimulus conduction by P cells of the nucleus is based on postsynaptic inhibition with the participation of interneurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 563–570, November–December, 1981.     

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.     

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.     

Electrophysiologic relations in the lateral geniculate body

Responses were evoked in the lateral geniculate body (L.G.B.) of "encéphale isolé" cats by single-shock stimulation of either the geniculate body or the optic tract of the other side. Responses to optic tract stimulation were modified following excitability changes in the contralateral L.G.B. due to topical application of strychnine and KCl. Laminar stimulation and recording in different layers (A, A1, and B) suggested the existence of a certain homotopic organization of L.G.B. interconnections. The activity evoked in the L.G.B. was found to be abolished by electrocoagulation of the posterior commissure and intermediate gray matter. These results point to the presence of a transthalamic pathway which might mediate L.G.B. activity to the contralateral visual cortex.