High-frequency oscillations during human focal seizures

Area of Science:

• Neuroscience
• Epileptology
• Clinical Neurophysiology

Background:

• High-frequency oscillations (HFOs) are biomarkers of epileptogenicity, previously detected with microelectrodes.
• Limited data exists on HFOs recorded with macroelectrodes in human epilepsy.
• Understanding HFOs' localization and diagnostic value is crucial for pre-surgical evaluation.

Purpose of the Study:

• To investigate the feasibility of recording discrete high-frequency oscillations (HFOs) using depth EEG macroelectrodes in focal epilepsy patients.
• To analyze the localization and timing of HFOs relative to seizure onset and epileptogenic zones.
• To assess the potential of macroelectrode-recorded HFOs as biomarkers for identifying the epileptic focus.

Main Methods:

• Retrospective analysis of 10 epilepsy patients undergoing pre-surgical evaluation with depth macroelectrodes.
• Visual inspection and spectral analysis of electroencephalogram (EEG) data during seizures.
• Identification and characterization of high-frequency band (HF: 100-200 Hz) and very high-frequency band (VHF: 250-500 Hz) oscillations.

Main Results:

• Focal, segmental VHF oscillations (250-500 Hz) were identified near seizure onset in 4/10 mesial temporal lobe epilepsy patients.
• HF or VHF oscillations were detected in seizure-onset zones of 3/4 mesial temporal lobe and 3/3 neocortical epilepsy patients.
• Absent discrete HFOs correlated with poorly localized seizures, while focal HFOs suggested proximity to the epileptogenic focus.

Conclusions:

• Discrete HFOs are recordable with depth EEG macroelectrodes in human focal epilepsy.
• Focal HFOs predominantly occur in primary epileptogenic regions, rarely in secondary spread zones.
• Macrodelectrode-detected HFOs may serve as valuable indicators for localizing the epileptogenic focus in diverse epilepsy types.