[Analysis of the multi-unit activity of the cortex and subcortical structures during paroxysmal discharges and grand mal seizures in the photosensitive baboon].

Cortical and subcortical multiunitary activities (MUA) and EEG were simultaneously recorded in baboons rendered photosensitive by a subconvulsant dose of DL-allylglycine. Intermittent light stimulation (ILS) trains induce in those animals fronto-rolandic (FR) paroxysmal discharges (PDs, constituted as spikes and waves) and grand mal seizures. During the induction of FR PDs by ILS trains, the visual structures (occipital cortex, colliculi superioris, pulvinar) show a significant MUA increase which is not related to the PD spike or wave but is correlated to the flashes. The first structure showing bursts of MUA that frequently precede the PD appearance is the FR cortex. When PDs appear, the bursts are related to the spikes of PDs and are followed by an inhibition during the slow wave. The pontine and mesencephalic reticular formations and the facial nuclei are activated in bursts after the FR PDs have reached a certain amplitude. The thalamic nuclei ventralis lateralis, centrum medianum and lateralis posterior are activated only later, when the FR PDs have reached an even greater amplitude. It is suggested that the activation of visual structures is necessary for FR PD appearance. The secondary pontine and mesencephalic activation could reinforce that of the FR cortex and then the thalamus, and could determine the myoclonus observed in unparalyzed animals.