Changes in cortical delta power during chronic invasive epilepsy monitoring

Cortical delta band (1-4 Hz) activity is considered a biomarker for states of altered consciousness, with increased delta power observed during anesthesia, sleep, coma, and delirium. The current study sought to characterize delta power following electrode implantation with respect to patient demographics and clinical characteristics as well as type and duration of surgery.

Participants were 25 adult neurosurgical patients implanted with intracranial electrodes for clinical monitoring of their epilepsy. Resting state cortical activity was recorded at multiple occasions over the course of the monitoring period. The initial time point was defined as the first recording within 72 h following surgery. Analyses of cortical activity were conducted using a linear mixed effects modeling approach to account for within-participant correlations and between-participant heterogeneity.

Throughout the monitoring period, delta power decreased in frontal, occipital, parietal, and temporal regions, indicating a global phenomenon. By contrast, beta (14-30 Hz) power remained stable. Delta power was higher following surgical cases that required craniotomy compared to stereoelectroencephalography cases. Surgery duration and anesthesia emergence duration were associated with higher delta power. Recordings from depth electrodes showed higher delta power compared to subdural electrodes. No significant effects of patients' age, sex, white blood cell count, antiseizure medication, and opioid medication dosage on postoperative delta power were found.

The results are consistent with a postoperative elevation in delta power that resolves over the course of the monitoring period and indicate an association between increased delta power and craniotomy surgery, as well as longer surgery and emergence durations. The current work provides a comprehensive analysis of surgical, clinical, and physiological factors, suggests risk factors, and lays fundamental groundwork for future studies.