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SUMMARY Impedance measurements and EEG recordings were made in ventral and dorsal hippocampus, amygdala and from the cortex during epileptic seizures induced in cats by injecting tungstic acid gel into the dorsal hippocampus or basolateral amygdala. Consistent changes in impedance occurred during seizures with an increase in the resistive component and a decrease in the capacitive component. Impedance changes provided focal correlates of the presence of epileptic activity. In regions of the brain where discharges did not spread, or spread only weakly, there were no significant impedance changes, but in regions powerfully involved in the seizures, significant shifts in impedance amounting to 10–12% of baseline were found. A regional specificity is indicated by large and consistent impedance changes in hippocampus on the one hand, particularly in the ventral hippocampus, and on the other by very small changes observed in the amygdala. Impedance changes begin after the onset of the seizure and return toward a baseline after termination of the seizure. This is interpreted to indicate that the observed changes in impedance are a consequence of the ictal events. RÉASUMÉA Les variations de l'impeAdance et l'eAlectroenceAphalogramme de l'hippocampe ventral et dorsal, de l'amygdale et du cortex furent enregistreAs sur des chats pendant des crises eApileptiques provoqueAes par injection de gel d'acide tungstique dans l'hippocampe dorsal ou dans la region basolateArale de l'amygdale. Des variations significatives de l'impeAdance ont eAteA observeAes pendant ces crises avec des augmentations de la composante reAsistive et des diminutions de la composante capacitive. Ces changements repreAsentent des manifestations localiseAes de la preAsence d'une activiteA eApileptique. Les reAgions du cerveau peu ou non atteintes par ces deAcharges n'ont montreA aucun changement significatif, par contre des variations de l'ordre de 10—12% furent rencontreAes dans les reAgions ouG la propagation des deAcharges eAtait importante. Une speAcificiteA reAgionale est indiqueAe par de larges variations de l'impeAdance dans l'hippocampe, particulieGrement dans l'hippocampe ventral, et par de petites variations dans l'amygdale. L'impeAdance commence aG varier apreGs le deAbut de la crise et tente de revenir aG son niveau initial apreGs la fin de la crise. Ce dernier point indique que les variations observeAes sont une conseAquence des eAveAnements critiques.

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Microinjections of 2-10 micrograms of carbachol into the mesencephalic reticular formation (MRF) and pontine reticular formation (PRF) of rats consistently induced local electroencephalographic seizures. These seizures had organized, rhythmical patterns and were long lasting. They spread powerfully and bilaterally between the MRF and PRF and also to the hippocampus and cortex. The electroencephalographic seizures were accompanied by severe, long-lasting convulsions. These convulsions were clonic and bilateral, started in the head area and progressed rostro-caudally to become generalized to the entire body. Other nonconvulsive behaviors were activated by the seizures. Immobility and catalepsy were the most frequent nonconvulsive correlates of the brainstem carbachol seizures.