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 average or bipolar montage. We studied how montage choice affects event identification. Methods: Two reviewers independently marked IEDs and HFOs across three montages (average, horizontal- and vertical-bipolar) 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: Bipolar montages yielded more channels-with-events, higher counts, and greater maximum-amplitude of IEDs and ripples compared to average montages. Average and horizontal-bipolar montages yielded more IED_instances than vertical-bipolar montages. Average 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 bipolar montage detects more events with greater amplitude, while the average montage uncovers a wider variety of unique events. Combining montages provides complementary information. Significance: This study quantitatively revealed how different montages capture epileptiform events.