Effects of lesions in the hippocampus and amygdala on duration and frequency patterns of septum after-discharges.

1) In twenty-two adult cats, septum after-discharges were induced, following placement of lesions in the hippocampus, amygdala and temporal cortex. The duration and frequency patterns of the after-discharge were analyzed. (2) The hippocampus, in contrast to the amygdala, is the main contributor to the duration of the septum after-discharge. Septum discharge durations are shortest following massive hippocampal ablation. Increased seizure duration occurs at a much faster rate with an intact hippocampus and lesioned amygdala. (3) The dorsal hippocampus is the predominant contributor of the faster frequencies in septum after-discharge patterns, whereas the ventral hippocampus and amygdala contribute slower frequencies predominantly. (4) Septum after-discharges were longest following cortical resection alone. This suggested the existence of a cortical inhibitory effect upon limbic system after-discharges.