Simultaneous MEG and EEG to detect ripples in people with focal epilepsy

Publication date: Available online 23 February 2019

Source: Clinical Neurophysiology

Author(s): Nicole van Klink, Anne Mooij, Geertjan Huiskamp, Cyrille Ferrier, Kees Braun, Arjan Hillebrand, Maeike Zijlmans

Abstract

Objective

We studied ripples (80-250Hz) simultaneously recorded in electroencephalography (EEG) and magnetoencephalography (MEG) to evaluate the differences.

Methods

Simultaneous EEG and MEG were recorded in 30 patients with drug resistant focal epilepsy. Ripples were automatically detected and visually checked in virtual channels throughout the cortex. The number and location of ripples in EEG and MEG were compared to each other and to a region of interest (ROI) defined by clinically available information.

Results

Eleven patients showed ripples in both MEG and EEG, 11 only in EEG and one only in MEG. Twenty-four percent of the ripples occurred simultaneously in EEG and MEG, 71% only in EEG, and 5% only in MEG. Three patients without spikes in EEG showed EEG ripples. Ripple localization was concordant with the ROI in 80% of patients with MEG ripples, as opposed to 62% full or partial concordance for EEG ripples. With the optimal threshold for localizing the ROI, sensitivity and specificity were more than 80%.

Conclusions

Ripples in MEG are less frequent but more specific and sensitive for the region of interest than ripples in EEG. Ripples in EEG can exist without spikes in the EEG.

Significance

Ripples in MEG and EEG provide complementary information.

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