High-frequency oscillations in intraoperative recordings from hybrid arrays with micro-and macrocontacts

High-frequency oscillations (HFOs) are a potential biomarker of the epileptogenic zone (EZ) in patients with focal epilepsy. Previous research has estimated that HFOs arise from regions as small as a single cortical column (1 mm3), making events difficult to detect with the coarse spatial sampling of clinical-standard electrocorticographic (ECoG) arrays. We tested whether high-resolution micro-electrocorticograpic (µECoG) arrays enable improved detection of HFOs compared to clinical-scale ECoG arrays.&#xD;Methods: We designed a hybrid array with both micro- (200 µm diameter, 1 mm spacing) and macrocontacts (2.3 mm diameter, 10 mm spacing). We used the arrays to record neural activity from cortical areas exposed during surgical resections for focal epilepsy (n=3 subjects). We identified HFOs in the ripple (80-250 Hz) and fast ripple (250-600 Hz) bands using a common energy thresholding criterion. We mapped HFO activity and quantified differences in event count, detection rate, amplitude, signal-to-noise ratio, and spatial extent between contact configurations.&#xD;Results: Microcontacts detected 14x as many HFO events as macrocontacts while spanning the same area of cortex. The highest rates of HFO detections occurred on microcontacts positioned within the inter-contact spacing of the macrocontacts. 82% of microcontact HFOs spanned multiple contacts, providing an estimate that events typically involved a 1.25 mm radius of cortex. The remaining 18% occurred on only one 200-µm-diameter contact. In contrast, only 15% of macrocontact HFOs were large enough to span multiple contacts and were estimated to involve a 10.3 mm radius of cortex, a significantly larger region than that of microcontacts (p < 0.0001, Wilcoxon rank sum).&#xD;Significance: High-resolution microcontacts captured 99% of HFOs, including 93% undetected by clinical-scale macrocontacts, revealing that most events arose from a <1 mm radius of cortex and providing further rationale for the development of µECoG arrays for EZ localization in patients with drug-resistant epilepsy.