POWER SPECTRUM AND INTRACRANIAL EEG PATTERNS AT SEIZURE ONSET IN PARTIAL EPILEPSY

Intracranial electroencephalographic patterns of seizure onset during preoperative assessment with intracerebral and subdural electrodes hav e been correlated with surgical outcome in 15 patients with partial ep ilepsy assessed for surgery. The presence and topography of electrodec remental events, high frequency activity, irregular sharp waves interm ixed with slow activity, spike-wave activity and rhythmic ictal transf ormation at seizure onset were studied in a total of 78 complex partia l seizures. Raw traces from intracerebral and subdural recordings were assessed visually in conjunction with changes in the following spectr al variables (calculated for consecutive 1.28 sec epochs): amplitude ( sum of amplitude of all components within a frequency band), activity, mobility, and complexity. The time course of these variables during p reictal and ictal periods was displayed and assessed. This technique p roved effective for detecting low-amplitude high-frequency activity an d subtle electrodecremental events. It was concluded that: (a) most pa tients (12/15) showed early electrodecremental events, generalised or local, mainly involving frequencies below 40 Hz; (b) generalised elect rodecremental events at onset did not imply poor outcome; (c) localise d high-frequency activity, between 20 and 80 Hz, was associated with a good outcome.