The postictal electroencephalogram.

Postictal phenomena, their laterality and duration, were studied among 51 patients with scalp EEG-recorded seizures whose origin, evolution and postictal phase were clearly depicted. Regional delta was the most common postictal change (PIC), appearing in 29 patients (57%). Regional attenuation occurred in 15 cases (29%) while the EEG reverted immediately to its interictal nature in 16 instances (31%). 'Activation' of spikes postictally occurred after 13 of the 51 seizures (25%), always over the lobe of seizure onset. PIC, whatever its nature, appeared principally or exclusively ipsilateral to seizure origin in all 35 patients. Moreover, when such changes were bilaterally distributed, they persisted longer on the side of seizure origin in all but one case when durations were bilaterally equal. A multiple PIC (greater than 1 phenomenon) occurred after 21 seizures (41%) while a single change appeared after 14 attacks (27%). Multiple changes occurred more commonly when the seizures had evolved to independent bilateral seizures or to grand mal (77%) than when they were confined to the hemisphere of origin (14%). Thus multiple changes were more often distributed bilaterally (90%) than were single changes (29%). Conversely, seizures without any propagation (focal only) were those most likely to show no postictal change. Multiple changes lasted longer (mean 406 sec) than single changes (79 sec), but duration of PIC was unaffected by seizure propagation or its nature, except for grand mal. Seizure duration had no effect on PIC duration except for grand mal attacks whose postictal effects were predictably longer.(ABSTRACT TRUNCATED AT 250 WORDS)