Analysis of seizure onset on the basis of wideband EEG recordings

Seventy-five seizure onsets recorded with depth electrodes in the frequency band from 0.1 to 70 Hz were analyzed in 19 patients with intractable temporal lobe epilepsy. It was shown that 89% of low-voltage fast-type seizures contained ail initial slow wave, whereas hypersynchronous-type seizures did not show in initial slow wave. Voltage depth profile analysis illustrated that the peak amplitude of the initial slow-wave onset was in white matter, whereas the peak amplitude of hyper-synchronous onset was in deep temporal areas (hippocampus, entorhinal cortex, or amygdala). The difference in voltage depth profiles suggests that these two types of seizure onsets have different mechanisms of generation. The absence of phase reversal of the initial slow wave in white matter or at the border of deep temporal areas indicates a possible nonneuronal mechanism of generation.