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

## TL;DR

This study shows that high-frequency brain waves in EEG can help identify the side of the brain causing seizures, even with standard equipment.

## Contribution

Demonstrates reliable HFO detection at 512 Hz and lateralization of the epileptogenic hemisphere in clinical settings.

## Key findings

- HFO rates were significantly higher in the epileptogenic hemisphere than the contralateral hemisphere.
- Younger patients had higher median HFO rates, showing an age-dependent decline.
- Pre-ictal HFO rates increased and decreased post-ictally, suggesting seizure-related dynamics.

## Abstract

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 (≥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.

•Scalp EEG at 512 Hz can reliably detect high-frequency oscillations (HFOs).•HFO rates were significantly higher in the epileptogenic hemisphere than the contralateral hemisphere.•Younger patients had higher median HFO rates, showing an age-dependent decline.

Scalp EEG at 512 Hz can reliably detect high-frequency oscillations (HFOs).

HFO rates were significantly higher in the epileptogenic hemisphere than the contralateral hemisphere.

Younger patients had higher median HFO rates, showing an age-dependent decline.