The optimal montage to mark interictal epileptiform discharges and high-frequency oscillations in intraoperative electrocorticography.

Objective: In intraoperative electrocorticography (ioECoG), interictal epileptiform discharges (IEDs) and high-frequency oscillations (HFOs; ripples 80-250 Hz, fast ripples (FRs) 250-500 Hz) can be identified in or montage. We studied how montage choice affects event identification.

Methods: Two reviewers independently marked IEDs and HFOs across three montages ( horizontal- and vertical-) from 13 patients who were seizure-free after ioECoG-guided surgery. We analyzed the number of channels-with-events, total events count, events morphology (maximum-amplitude, duration, frequency), number of instances with overlapping events across multiple channels (event_instance), concordance of event_instances over montages, and percentage of channels-with-events in the resected-area.

Results: montages yielded more channels-with-events, higher counts, and greater maximum-amplitude of IEDs and ripples compared to montages. and horizontal montages yielded more IED_instances than vertical montages. montages detected the highest percentage of event_instances occurring only in this montage. Event duration, frequency, and percentage of channels-with-events in the resected-area did not differ across montages.

Conclusions: All three ioECoG montages are clinically useful to find epileptic events. The montage detects more events with greater amplitude, while the montage uncovers a wider variety of unique events. Combining montages provides complementary information.

Significance: This study quantitatively revealed how different montages capture epileptiform events.