The role of the corpus callosum in the interhemispheric transmission of epileptic electrical activity.

In acute experiments on 49 curarized adult rats without general anaesthesia, we studied the transmission of discharges of cortical penicillin foci between the two hemispheres after transecting the corpus callosum. Projected discharges of the cortical penicillin focus appeared in the contralateral hemisphere later than in the controls and had a very different shape. The interhemispheric response of the experimental rats consisted of a small positive and a small negative deflection with long latent periods. Focal discharges could be triggered by electrical stimulat;on of the contralateral hemisphere only irregularly and for short periods of time. In rats with a transected corpus callosum, two symmetrical cortical foci at first behaved independently of each other; their synchronization then slowly improved, but never attained 100 per cent. The corpus callosum is the preferential pathway for interhemispheric transmission of focal activity. Transection of this pathway makes the transmission conditions much worse, but further connections, with a longer conduction time and lower efficacy, gradually come into action.