Fast oscillations >40 Hz localize the epileptogenic zone: An electrical source imaging study using high-density electroencephalography

Tamir Avigdor; Chifaou Abdallah; Nicolás von Ellenrieder; Tanguy Hedrich; Annalisa Rubino; Giorgio Lo Russo; Boris Bernhardt; Lino Nobili; Christophe Grova; Birgit Frauscher

doi:10.1016/j.clinph.2020.11.031

Fast oscillations >40 Hz localize the epileptogenic zone: An electrical source imaging study using high-density electroencephalography

Clin Neurophysiol. 2021 Feb;132(2):568-580. doi: 10.1016/j.clinph.2020.11.031. Epub 2020 Dec 22.

Authors

Affiliations

¹ Analytical Neurophysiology Lab, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Multimodal Functional Imaging Lab, Biomedical Engineering Department, McGill University, Canada.
² Multimodal Functional Imaging Lab, Biomedical Engineering Department, McGill University, Canada.
³ Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada.
⁴ Claudio Munari Epilepsy Center, Niguarda Hospital, Milan, Italy.
⁵ Department of Neuroscience (DINOGMI), University of Genoa, Italy; IRCCS, Child Neuropsychiatry Unit, Instituto Giannina Gaslini, Genoa, Italy.
⁶ Multimodal Functional Imaging Lab, Biomedical Engineering Department, McGill University, Canada; Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Multimodal Functional Imaging Lab, PERFORM Centre, Department of Physics, Concordia University, Montreal, QC, Canada.
⁷ Analytical Neurophysiology Lab, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Department of Medicine, Queen's University, Kingston, ON, Canada. Electronic address: birgit.frauscher@mcgill.ca.

PMID: 33450578
DOI: 10.1016/j.clinph.2020.11.031

Abstract

Objective: Fast Oscillations (FO) >40 Hz are a promising biomarker of the epileptogenic zone (EZ). Evidence using scalp electroencephalography (EEG) remains scarce. We assessed if electrical source imaging of FO using 256-channel high-density EEG (HD-EEG) is useful for EZ identification.

Methods: We analyzed HD-EEG recordings of 10 focal drug-resistant epilepsy patients with seizure-free postsurgical outcome. We marked FO candidate events at the time of epileptic spikes and verified them by screening for an isolated peak in the time-frequency plot. We performed electrical source imaging of spikes and FO within the Maximum Entropy of the Mean framework. Source localization maps were validated against the surgical cavity.

Results: We identified FO in five out of 10 patients who had a superficial or intermediate deep generator. The maximum of the FO maps was localized inside the cavity in all patients (100%). Analysis with a reduced electrode coverage using the 10-10 and 10-20 system showed a decreased localization accuracy of 60% and 40% respectively.

Conclusions: FO recorded with HD-EEG localize the EZ. HD-EEG is better suited to detect and localize FO than conventional EEG approaches.

Significance: This study acts as proof-of-concept that FO localization using 256-channel HD-EEG is a viable marker of the EZ.

Keywords: Electrical source imaging; Epilepsy; High-density electroencephalography; Maximum entropy of the mean; Non-invasive localization.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adolescent
Adult
Brain Mapping / methods*
Child
Drug Resistant Epilepsy / diagnosis
Drug Resistant Epilepsy / diagnostic imaging
Drug Resistant Epilepsy / physiopathology*
Electroencephalography / methods*
Humans
Magnetic Resonance Imaging / methods