Impedance Changes during Epileptic Seizures

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.

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