Modification of seizure activity by electrical stimulation: cortical areas.

1. Three different cortical areas were found with respect to the development, by repeated electrical stimulation, of electrographic and motor seizures in rats. Paleocortical areas responded similarly to subcorticallimbic structures. Initial after-discharges (ADs) were accompanied by little or no behavioral response. With spaced reptition ADs became longer, propagated more strongly, and were eventually accompanied by a convulsive response in which the dominant components were forelimb clonus and rearing. Anterior neocortical placements, on the other hand, yielded convulsive responses from the first AD. These convulsive responses became stronger with repeated stimulation until a mild form of extension was triggered. ADs remained relatively short. Posterior neocortical areas showed electrographic developments very similar to those found in anterior neocortical areas but convulsive responses never developed. 2. All areas tested showed similar reductions in AD thresholds when repeatedly stimulated. Initial thresholds were lower in paleocortical than in neocortical areas. 3. Motor seizures developed more rapidly with stimulation of contralateral homologous sites after seizures had been developed in the primary (initially stimulated) focus. AD thresholds, on the other hand, were not significantly affected in contralateral sites after being lowered in primary sites.