Interictal high-frequency oscillations generated by seizure onset and eloquent areas may be differentially coupled with different slow waves

Objective: High-frequency oscillations (HFOs) can be spontaneously generated by seizure-onset and functionally-important areas. We determined if consideration of the spectral frequency bands of coupled slow-waves could distinguish between epileptogenic and physiological HFOs. Methods: We studied a consecutive series of 13 children with focal epilepsy who underwent extraoperative electrocorticography. We measured the occurrence rate of HFOs during slow-wave sleep at each electrode site. We subsequently determined the performance of HFO rate for localization of seizureonset sites and undesirable detection of nonepileptic sensorimotor-visual sites defined by neurostimulation. We likewise determined the predictive performance of modulation index: M-I(XHz)&(YHz), reflecting the strength of coupling between amplitude of HFOsXHz and phase of slow-wave(YHz). The predictive accuracy was quantified using the area under the curve (AUC) on receiver-operating characteristics analysis. Results: Increase in HFO rate localized seizure-onset sites (AUC >= 0.72; p < 0.001), but also undesirably detected nonepileptic sensorimotor-visual sites (AUC >= 0.58; p < 0.001). Increase in MI(HFOs)&(3-4Hz) also detected both seizure-onset (AUC >= 0.74; p < 0.001) and nonepileptic sensorimotor-visual sites (AUC >= 0.59; p < 0.001). Increase in subtraction-M-IHFOs [defined as subtraction of MI(HFOs)&(0.5-1Hz) from MI(HFOs)&(3-4Hz)] localized seizure-onset sites (AUC >= 0.71; p < 0.001), but rather avoided detection of nonepileptic sensorimotor-visual sites (AUC <= 0.42; p < 0.001). Conclusion: Our data suggest that epileptogenic HFOs may be coupled with slow-wave(3-4Hz) more preferentially than slow-wave(0.5-1Hz), whereas physiologic HFOs with slow-wave(0.5-1Hz) more preferentially than slow-wave(3-4Hz) during slow-wave sleep. Significance: Further studies in larger samples are warranted to determine if consideration of the spectral frequency bands of slow-waves coupled with HFOs can positively contribute to presurgical evaluation of patients with focal epilepsy. (C) 2016 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.