Lateral geniculate cell responses to electrical stimulation of the retina

Electrical stimulation of the retina evokes at the optic tract level rhythmic bursts of activity whose temporal structure is predictable from the polarity of the stimulation and the receptive field type. The reaction of lateral geniculate units to this input was studied in fast and slow relay cells as well as in interneurons. The results revealed that fast relaty cells presented a response whose temporal structure remained essentially unmodified in comparison to that observed at the optic tract level: that both anodal and cathodal polarities produced rythmic pattern of excitation the latency of which depended upon receptive field type and polarity applied. In slow relay cells and interneurons responses with equal latencies could be evoked for both polarities. Following cortical depression with 3 M KCl the latency of first bursts was unaffected in relay cells, while about one third of interneurons showed a temporal pattern which was similar to that recorded at the optic tract level after the treatment. This suggests that both ON and OFF retinal networks converge upon one geniculate slow P cell and interneuron, whereas fast relay cells are mostly driven by one of the two systems. Furthermore this convergence may be achieved through visual cortex in some units.