Temporal stability of intracranial electroencephalographic abnormality maps for localizing epileptogenic tissue

Objective: Identifying abnormalities on interictal intracranial electroencephalogram (iEEG), by comparing patient data to a normative map, has shown promise for the localization of epileptogenic tissue and prediction of outcome. The approach typically uses short interictal segments of approximately 1 min. However, the temporal stability of findings has not been established. Methods: Here, we generated a normative map of iEEG in nonpathological brain tissue from 249 patients. We computed regional band power abnormalities in a separate cohort of 39 patients for the duration of their monitoring period (.92–8.62 days of iEEG data, mean = 4.58 days per patient, >4800 hours recording). To assess the localizing value of band power abnormality, we computed (Formula presented.) —a measure of how different the surgically resected and spared tissue was in terms of band power abnormalities—over time. Results: In each patient, the (Formula presented.) value was relatively consistent over time. The median (Formula presented.) of the entire recording period separated seizure-free (International League Against Epilepsy [ILAE] = 1) and not-seizure-free (ILAE (Formula presented.) 1) patients well (area under the curve [AUC] =.69). This effect was similar interictally (AUC =.69) and peri-ictally (AUC =.71). Significance: Our results suggest that band power abnormality D_RS, as a predictor of outcomes from epilepsy surgery, is a relatively robust metric over time. These findings add further support for abnormality mapping of neurophysiology data during presurgical evaluation.