Mapping intraoperative interictal epileptiform discharges using high-resolution, thin-film cortical arrays

Interictal epileptiform discharges (IEDs) are transients observed on the electroencephalogram (EEG) of patients with epilepsy. IEDs have traditionally been recorded from scalp or intracranial EEG macrocontacts, which coarsely sample neural activity. Here, we investigated the use of flexible, high-resolution microelectrocorticographic (μECoG) arrays for measuring IEDs with greater spatiotemporal precision to test whether there exist microscale patterns of IED activity that may be missed on standard intracranial EEG.

We used liquid crystal polymer thin-film μECoG arrays with both high resolution (.76-1.72-mm spacing, 200-μm diameter) and large cortical coverage (144-1596 mm²) to record from seven patients undergoing surgical treatment of epilepsy. We identified IEDs by a combination of expert review and automated detection. We quantified the spatial extent of IEDs, mapped patterns of repeated IED activity, and quantified IED propagation direction using multilinear fit models. We also compared IED detection rates and propagation measurements between μECoG arrays and simulated macroarrays (10-mm spacing, 2.3-mm diameter).

We demonstrated successful use of μECoG arrays to map intraoperative microscale patterns of IEDs. The majority of patients (5/7) exhibited elevated IED activity that was highly localized (subcentimeter localization). Across all patients, 40% of detected IEDs were observed within a 4-mm radius of cortex. μECoG arrays also mapped the direction of IED propagation. An average of 39% (range = 4.2%-96.5%, SD = ±36.8%) of the IED events captured by the μECoG arrays were not detectable by simulated macrocontacts.

These intraoperative data demonstrate that μECoG arrays can map the microscale spatiotemporal activity of IEDs. These patterns of IEDs may be poorly captured by standard, macroscale recording devices. Our findings support the use of high-resolution, large area coverage μECoG arrays for the presurgical and intraoperative mapping of epileptic cortex.