On-scalp magnetoencephalography based on optically pumped magnetometers to investigate temporal lobe epilepsy

Cryogenic magnetoencephalography (MEG) has a lower yield in temporal lobe epilepsy (TLE) than in extratemporal lobe epilepsy. The advent of optically pumped magnetometers (OPMs) might change this situation thanks to on-scalp MEG. This study aims to investigate the detection/localization accuracy of interictal epileptiform discharges (IEDs) using on-scalp MEG in TLE and the added value of face-OPMs. Eleven patients underwent a 1-h MEG recording with OPMs placed both on the scalp (flexible cap, scalp-OPMs) and on the face (glasseslike structure, face-OPMs). Nine patients underwent cryogenic MEG. IED amplitude and signal-to-noise ratio (SNR) were compared when ≥10 IEDs were detected. A mean of 13 IEDs/patient were detected using on-scalp MEG (mean amplitude = 3.3 pT, mean SNR = 9.4) and localized in the (medial, anterior, basal, lateral, posterior) temporal lobe. Amplitude and SNR were either higher or similar between on-scalp and cryogenic MEG, with neural sources separated by 6-16 mm. In two patients, on-scalp MEG source locations were confirmed by surgical resection cavity or stereoelectroencephalography. Face-OPMs had a clear added value in one patient with anteromedial TLE. On-scalp MEG can detect/localize IEDs in TLE. Face-OPMs may have added value in patients with anterior/medial TLE and increase the spatial coverage of the temporal lobe. This study paves the way for the use of on-scalp MEG in patients with refractory TLE.