Abstract
Postictal inhibition (PI) is a decrease in excitability that follows an epileptic seizure and decreases probability of new seizure occurrence. PI may involve both increased inhibition and persisting elevated excitation.
Our experiments tested whether shorter trains of weak stimuli are able to unmask this residual increase of excitability during the PI. Four epileptic afterdischarges (ADs) were evoked by intense electrical stimulation (20 s, 8 Hz, current intensity at 5x threshold) of the neocortex in two groups (A, B) of Wistar rats.
Before the first AD and during the 10-min interictal period, 8-Hz trains of four weak pulses (half of the intensity used for the AD triggering; 4P) were applied every 20 s in group B and a single pulse with similar parameters in group A. The number of interictal epileptiform events evoked by 4P in the group B was significantly higher than that in the group A (evoked by single pulses) except after the second AD.
Epileptic events were triggered by 4P also immediately after the AD termination. It is apparent that weak stimulation can trigger epileptic phenomena during PI.
Our results indicate that it is no longer possible to perceive PI only as persisting extreme and active inhibition. An appropriate stimulation can reveal more subtle (but important) excitatory events contributing to the functional status during the postictal period.