Evaluation of High frequency oscillations as markers of epileptogenicity in intracranial EEG and their correlates on surface EEG

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For patients with medically refractory epilepsy, surgical removal of epileptogenic tissue is the most promising treatment. The identification of epileptogenic tissue is complex; even modern imaging techniques and intracranial EEG recordings (iEEG) fail to reliably predict postsurgical outcome. Traditionally, only EEG frequencies below 100Hz are used for clinical purposes, but technical advancements now allow us to record higher frequencies with sampling rates up to 10000Hz. Recent studies have shown that high-frequency oscillations (HFOs) above 100 Hz are closely linked to epileptogenic tissue. They are however generated over small cortical areas and were until now only recorded with iEEG electrodes and not with surface EEG. Additionally, studies of epileptic HFOs may be confounded by physiological HFOs that cannot be easily distinguished from pathological events. This project aims to investigate the following hypotheses about HFOs between 80-500Hz: 1) HFOs are reliable markers of epileptogenicity. 2) Physiological and pathological HFOs have distinguishable electrophysiological patterns independent of frequency 3) HFOs occurring with epileptic spikes can be seen on surface EEG, allowing better delineation of epileptogenic areas with non-invasive EEG.