Abstract
High-frequency oscillations (HFOs) have been proposed as a promising biomarker of the epileptogenic zone (EZ). But accurate delineation of EZ based on HFOs is still challenging. Our study compared HFOs from EZ and non-EZ on the basis of their associations with interictal slow waves, aiming at exploring a new way to localize EZ. Nineteen medically intractable epilepsy patients with good surgical outcome were included. Five minute interictal intracranial electroencephalography (EEG) epochs of slow-wave sleep were randomly selected; then ripples (80–200 Hz), fast ripples (FRs; 200–500 Hz), and slow waves (0.1–4 Hz) were automatically analyzed. The EZ and non-EZ were identified by resection range during the surgeries. We found that both ripples and FRs superimposed more frequently on slow waves in EZ than in non-EZ (P < 0.01). Although ripples preferred to occur on the down state of slow waves in both two groups, ripples in EZ tended to be closer to the down-state peak of slow wave than in non-EZ (-174 vs. -231 ms, P = 0.008). As for FR, no statistical difference was found between the two groups (P = 0.430). Additionally, slow wave-containing ripples in EZ had a steeper slope (1.7 vs. 1.5 μV/ms, P < 0.001) and wider distribution ratio (32.3 vs. 30.1%, P < 0.001) than those in the non-EZ. But for slow wave-containing FR, only a steeper slope (1.7 vs. 1.4 μV/ms, P < 0.001) was observed. Our study innovatively compared the different features of association between HFOs and slow wave in EZ and non-EZ from refractory focal epilepsy with good surgical outcome, proposing a new method to localize EZ and facilitating the surgical plan.
Highlights
MATERIALS AND METHODSHigh-frequency oscillations (HFOs) have been proposed as a promising biomarker of the epileptogenic zone (EZ) (Bragin et al, 1999; Jirsch et al, 2006; Thomschewski et al, 2019; Frauscher, 2020)
We observed that HFOs in the EZ tended to occur before the peak of the deactivated down state of the slow wave, which was concordant with the previous reports (Frauscher et al, 2015; von Ellenrieder et al, 2016; Song et al, 2017; Samiee et al, 2018)
It is proved that some fast ripples (FRs) in nonEZ and EZ might be related by epileptic network; it is reasonable that they had similar characteristics when they were closed in distance
Summary
High-frequency oscillations (HFOs) have been proposed as a promising biomarker of the epileptogenic zone (EZ) (Bragin et al, 1999; Jirsch et al, 2006; Thomschewski et al, 2019; Frauscher, 2020). The normal brain functional activity such as learning, memory, and emotional activities can induce physiological HFOs (Blanco et al, 2011; Buzsáki and Silva, 2012). This characteristic further improves the difficulty to accurately localize EZ on the basis of HFOs in clinical practice
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