AN EPILEPTOGENIC FOCUS IN FROG TELENCEPHALON . PATHWAYS OF PROPAGATION OF FOCAL ACTIVITY

The routes by which focal epileptic activity spreads from one forebrain hemisphere into the contralateral one were studied in the frog, using artificial penicillin foci and transection of pathways which could be involved in this propagation. The preferential pathways here are the forebrain commissural connections, the latency of the secondary discharge being about 20 msec. After interruption of these connections, a considerably longer, multineuronal pathway through thalamic and lower brain structures can be used. The latency of the secondary discharge in this case is several times longer (more than 100 msec). Thalamus and lower (mesencephalic and rhombencephalic) centers, or sensory impulses transmitted through brain-stem structures, or both, have an important influence on the development of the secondary (mirror) focus and on the seizure susceptibility of the forebrain. In an isolated forebrain with preserved commissural pathways-modified cerveau isolé preparation-the secondary focus and the transition of the focal activity in an electrographic seizure, after metrazol application, are remarkably altered. In about one third of these cerveau isolé preparations, a high-voltage slow-wave activity was observed in the spontaneous EEG resembling the telencephalic sleep of higher vertebrates. © 1968.