Assessing Epileptogenicity Using Phase-Locked High Frequency Oscillations: A Systematic Comparison of Methods

Area of Science:

• Neuroscience
• Epileptology
• Biomedical Engineering

Background:

• High frequency oscillations (HFOs) are established biomarkers for identifying epileptogenic zones in epilepsy surgery.
• Coupling between HFO amplitude and low-frequency phase is a newer biomarker associated with improved surgical outcomes.
• Accurate quantification of this coupling is crucial for effective presurgical evaluation.

Purpose of the Study:

• To compare the predictive value of ictal HFOs and four phase-amplitude coupling quantification methods for surgical outcomes.
• To determine the most effective method for identifying epileptogenic tissue based on phase-amplitude coupling.
• To investigate the importance of analyzing the entire seizure duration versus only the onset.

Main Methods:

• Analysis of 32 seizures from 16 pharmacoresistant epilepsy patients.
• Identification of channels with HFOs and phase-locked HFOs during seizures.
• Comparison of resection ratios (percentage of coupled channels resected) with postsurgical outcomes using four coupling metrics: mean vector length, phase-locked high gamma, phase locking value, and modulation index (MI).

Main Results:

• The modulation index (MI) was the only method showing a significant difference in resection ratios between patients with good and poor surgical outcomes.
• Phase-locked HFOs throughout the entire seizure, not just the onset, are critical for assessing epileptogenicity.
• MI's superiority may be due to its ability to assess discrete coupling events and independence from HFO power.

Conclusions:

• Quantitative analysis of HFO phase-amplitude coupling significantly enhances presurgical epilepsy evaluation.
• The modulation index (MI) is a superior method for quantifying phase-amplitude coupling in this context.
• Algorithm selection is paramount for the clinical application of HFO analysis in epilepsy surgery.