Changes in the excitability of rat cerebral cortex after a self-sustained after-discharge.

Changes in the duration of the cortical self-sustained after-discharge (SSAD) were studied in relation to the preceding SSAD in adult rats. An "excitability cycle" could be constructed by means of different intervals between the end of the first SSAD and the beginning of subsequent electrical stimulation of the sensorimotor cortex. During short intervals (30, 60 and 120 sec) the second SSAD was significantly shorter than the first. No significant differences were found with intervals of 3 and 5 min; all longer intervals, except 120 min, resulted in significant prolongation of the second SSAD. The possibility of elicitation of the second SSAD also increased with increasing intervals, demonstrating thus the presence of a "refractory period." The results with manifold stimulation demonstrated the rather complicated nature of the changes of excitability during post-ictal periods.