High-frequency oscillations in scalp EEG lateralize to the epileptogenic hemisphere in children and adults

High-frequency oscillations (HFO) in scalp electroencephalography (EEG) are promising biomarkers for localizing epileptogenic zones. Prior studies mainly used high sampling frequencies ( $>$ 1000 Hz), whereas clinical monitoring often employs lower rates ( $<$ 512 Hz). We assessed scalp EEG HFO detection feasibility at 512 Hz, examining whether HFO rates lateralize the epileptogenic hemisphere (EH) and localize seizure onset zone (SOZ).

We retrospectively analyzed EEG from 32 patients during sleep, and seizures in 10 patients. A semi-automated algorithm combining band-pass filtering, sliding-window thresholding, and time-frequency validation was applied. HFO rates were compared between EH versus contralateral hemisphere (CH), and SOZ versus non-SOZ channels.

HFOs were detected in 27 patients, with higher rates in EH than CH (p = 0.0002). The asymmetry index lateralized EH in 22 patients (p = 0.0003). SOZ channels had higher HFO rates in 11 of 18 patients, though not significantly (p = 0.32). Pre-ictal HFO rates increased (p = 0.02), were higher in EH (p = 0.05), and decreased post-ictally (p = 0.004). Age-dependent decline was observed, with younger patients exhibiting higher median HFO rates than adults ( $\ge$ 18 years).

Scalp EEG at 512 Hz reliably detects HFOs and lateralizes the EH, though SOZ localization remains limited.

: Routine 512 Hz EEG can analyze HFOs, potentially enhancing presurgical evaluation.