Electrophysiological correlates of optokinetic and reversed postoptokinetic nystagmus in the rabbit.

Six rabbits with implanted electrodes in visual cortex, lateral geniculate body, superior colliculus and the mesodiencephalic nystagmogenic centres were exposed to 90 min optokinetic stimulation, followed by 30 to 60 min observation of reversed postoptokinetic nystagmus (RPN) in darkness. The oculographically recorded nystagmus was used to trigger a LINC 8 computer programmed for perisaccadic EEG averaging and for examination of excitability of visual centres by flashes applied at different intervals after the saccade onset. Whereas optokinetic nystagmus (OKN) was accompanied by marked electrical potentials appearing at all recording sites during and for about 100 msec after the saccade, these potentials were considerably attenuated or absent during RPN. Visual evoked responses to flashes applied during the OKN saccades were considerably smaller than responses to flashes delayed by 130-200 msec. No saccadic suppression was observed when the same visual stimuli were applied during RPN saccades in darkness. It is concluded that eye movements generated in the absence of external stimuli during RPN elicit only weak corollary discharge.