T148. Slow wave activity from bilateral subdural electrode contacts during awake, sleep, and postictal states

Introduction Increased slow wave activity is typically associated with decreased levels of awareness. Previous work has shown greater slow wave activity (1–2 Hz) in frontal and parietal areas during seizures that impair awareness than seizures that do not ( Englot, 2010 ). During non-REM sleep, slowing was increased for patients with epilepsy compared to controls, including a local increase at the seizure onset zone (SOZ) ( Boly, 2017 ). Here, we examined slow wave activity for patients with epilepsy in wake, sleep, and post-ictal states. Methods Data were recorded with the Natus Neurolink IP 256 channel EEG amplifier (0.16 Hz High pass filter, 1024 Hz sampling frequency). Inclusion criteria were: (1) bilateral subdural electrode coverage ( > 30 electrode contacts per hemisphere), (2) no known hemispheric abnormalities or diffuse abnormalities affecting the frontal lobes, (3) well-defined SOZs in either the temporal or frontal regions, and (4) at least three recorded clinical seizures with impaired awareness without generalized convulsive activity. Intracranial data from five patients was studied. The patients had 237, 198, 238, 241, and 229 contacts and seizures emerging from regions in the left frontal ( n  = 2), left temporal ( n  = 1), and right temporal ( n  = 1) lobes. 15 min in the wake, non-REM sleep, and postictal states following each of three focal seizures was examined, for a total of 2.25 h of data per patient. Results Power was increased for all frequency band (0.1–50 Hz) in the postictal state (0-3 min following seizure cessation) compared to sleep, while low frequency power during sleep showed a peak at about 0.6 Hz. In the postictal state, power ipsilateral to the SOZ was increased for frequencies 2–50 Hz compared to the contralateral side. However, delta activity (0.5–4 Hz) normalized by beta (12–50 Hz) activity was increased for the contralateral side relative to the ipsilateral side. The average signal correlation for a given distance was increased for low frequency bands relative to high frequency bands but did not differ across patient states. Conclusion Slow wave activity appears to be more uniformly increased during the postictal state as compared to sleep. Relative amounts of low frequency delta activity are decreased ipsilateral to the SOZ. These results suggest that delta activity (0.5–4 Hz) may represent different underlying physiology when comparing wake, sleep, and postictal states.