Ictal wideband ECoG: direct comparison between ictal slow shifts and high frequency oscillations.

OBJECTIVE

With advanced electroencephalography (EEG) technology, 'wideband EEG' ranging from slow shift to high frequency oscillation (HFO) is clinically available to study human epileptogenesis. The purpose of our study is to clarify the relationship between slow shift, HFO and conventional electrocorticographic (ECoG) change.

METHODS

A patient with right temporal lobe epilepsy who underwent presurgical evaluation with subdural electrodes was studied. Slow shift and HFO were evaluated in 16 habitual seizures with wideband EEG technique (bandpass filter of 0.016-600 Hz).

RESULTS

Upon seizure occurrence in wideband ECoG, negative slow shifts coexisted with HFO (100-300 Hz) in the ictal onset zone in all investigated seizures. The former always preceded HFO and conventional initial EEG changes by mean value of 1.6 and 20.4s, respectively. The slow shifts and HFOs were observed only in the restricted ictal onset zone.

CONCLUSIONS

In this particular patient, wideband EEG could delineate both ictal slow shift and HFO to define ictal onset zone, and the earliest occurrence of slow shifts may suggest an early role of glia in slow EEG shift generation than neurons.

SIGNIFICANCE

The time difference of the onset between ictal HFO and slow shift may help to understand epileptogenesis.