Lateralization of event-related potentials during discontinuation of antiepileptic medication.

The effect of short-term withdrawal of antiepileptic drugs (AEDs) on auditory event-related potentials (ERPs) was studied in 16 patients undergoing preoperative evaluation for epilepsy surgery. ERPs were performed for all patients during treatment with full medication and after a 1-week period during ongoing tapering of AEDs. To clarify whether AED discontinuation would provide evidence of lateralizing for ERPs, we also studied the subgroup of 9 patients who had already undergone temporal lobectomies (TLE group). In the TLE group, if habitual seizures occurred < 30 h before the ERP recording session, auditory N1 and P3 amplitudes across sphenoidal electrodes were markedly decreased on the side ipsilateral to the epileptic focus. If seizures did not occur, asymmetries in amplitudes were equivocal and not of lateralizing value. In the whole group, midline N1 latencies for standard responses decreased significantly during AED discontinuation. At baseline, long-term habituation of the N1 component for standard responses was attenuated as compared with that of controls. During AED discontinuation, however, enhanced habituation of N1 was observed in TLE patients who did not exhibit seizures before ERP recording.