Original Research ARTICLE
Assessing epileptogenicity using phase-locked high frequency oscillations: a systematic comparison of methods
- 1Department of Neurology, University Hospital Bern, Switzerland
- 2Department of Neurology, Bern University Hospital, Switzerland
- 3Support Center for Advanced Neuroimaging (SCAN), Bern University Hospital, Switzerland
High frequency oscillations (HFOs) are traditional biomarkers to identify the epileptogenic tissue during presurgical evaluation in pharmacoresistant epileptic patients. Recently, the resection of brain tissue exhibiting coupling between the amplitude of HFOs and the phase of low frequencies demonstrated a more favorable surgical outcome. Here we compare the predictive value of ictal HFOs and four methods for quantifying the ictal phase-amplitude coupling, namely mean vector length, phase-locked high gamma, phase locking value, and modulation index (MI). We analyzed 32 seizures from 16 patients to identify the channels that exhibit HFOs and phase-locked HFOs during seizures. We compared the resection ratio, defined as the percentage of channels exhibiting coupling located in the resected tissue, with the postsurgical outcome. We found that the MI is the only method to show a significant difference between the resection ratios of patients with good and poor outcomes. We further show that the whole seizure, not only the onset, is critical to assess epileptogenicity using the phase-locked HFOs. We postulate that the superiority of MI stems from its capacity to assess coupling of discrete HFO events and its independence from the HFO power. These results confirm that quantitative analysis of HFOs can boost presurgical evaluation and indicate the paramount importance of algorithm selection for clinical applications.
Keywords: epileptogenic zone, presurgical evaluation, Electroencephalography, High frequency oscillations (HFOs), cross-frequency coupling (CFC)
Received: 24 Apr 2019;
Accepted: 10 Oct 2019.
Copyright: © 2019 Bandarabadi, Gast, Rummel, Bassetti, Adamantidis, Schindler and Zubler. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Mojtaba Bandarabadi, Department of Neurology, University Hospital Bern, Bern, 3010, Bern, Switzerland, firstname.lastname@example.org