Fast oscillations>40Hz localize the epileptogenic zone: an electrical source imaging study using high-density electroencephalography
Avigdor, T., Abdallah, C., von Ellenrieder, N., Rubino, A., Lo Russo, G., Bernhardt, B., Nobili, L., Grova, C., Frauscher, B.
Clinical Neurophysiology. 132(2): 568-580
Abstract
Objective: Fast Oscillations (FO) >40 Hz are a promising biomarker of the epileptogenic zone (EZ). Evidence using scalp electroencephalography (EEG) remains scarce. We assessed if electrical source imaging of FO using 256-channel high-density EEG (HD-EEG) is useful for EZ identification.
Methods: We analyzed HD-EEG recordings of 10 focal drug-resistant epilepsy patients with seizure-free postsurgical outcome. We marked FO candidate events at the time of epileptic spikes and verified them by screening for an isolated peak in the time-frequency plot. We performed electrical source imaging of spikes and FO within the Maximum Entropy of the Mean framework. Source localization maps were validated against the surgical cavity.
Results: We identified FO in five out of 10 patients who had a superficial or intermediate deep generator. The maximum of the FO maps was localized inside the cavity in all patients (100%). Analysis with a reduced electrode coverage using the 10-10 and 10-20 system showed a decreased localization accuracy of 60% and 40% respectively.
Conclusions: FO recorded with HD-EEG localize the EZ. HD-EEG is better suited to detect and localize FO than conventional EEG approaches.
Significance: This study acts as proof-of-concept that FO localization using 256-channel HD-EEG is a viable marker of the EZ.