Mechanisms of interaction of asymmetrical bilateral epileptogenic foci in neocortex

The mechanisms of interaction of bilateral asymmetrical foci on cat neocortex were studied with varying concentrations of the epileptogenic agent and with callosal splitting and cortical-callosal isolation. When epilepsy was severe, a facilitatory interaction occurred. This was the result of two opposing mechanisms simultaneously operating, namely a transcallosal inhibitory mechanism and a predominant facilitatory subcortical mechanism. When epilepsy was less intense, subcortical structures were not involved and only the inhibitory transcallosal mechanism was at work, leading to an inhibitory interaction. The conclusion is put forward that two asymmetrical cortical foci do not necessarily interact in only one simple way. Their type of interaction (facilitatory or inhibitory) depends on the pathways involved in the interaction and this, in turn, depends on the severity of epilepsy.