Recovery cycles of mass evoked potentials of different levels of the visual system following electrical stimulation of the optic nerve

Abstract

Recovery cycles of mass evoked potentials of the optic tract, lateral geniculate body, optic radiation, and primary projection area of the visual cortex were investigated in amytal-anesthetized cats following electrical stimulation of the optic nerve (in some experiments, optic radiation) by paired short stimuli of supraliminal intensity. The recovery of the amplitude and time characteristics of all components of the mass responses to a testing stimulus applied to the nerve at different intervals after an identical conditioning stimulus was studied. The responses of all portions of the visual system (except the retina) were recorded simultaneously, which made it possible to compare the changes of their reactivity arising after the first stimulus under rigorously identical conditions. It was shown that at the upper levels of the visual system the exaltation phase of the recovery cycle and the depression phase following it become increasingly more pronounced and protracted. Depression is especially pronounced in the visual cortex, which maximally affects the recovery of the late components of the mass response. Under the experimental conditions the processes of successive inhibition in the cortex were more pronounced than at the lower levels. There are grounds to assume that the depression of the cortical responses is partially due to pre- and partially postsynaptic inhibition.