Abstracts

Rationale: Focal cortical dysplasia (FCD) is associated with an increased risk of sleep-related epilepsy. However, the factors influencing the increased seizure-risk during sleep compared to awake states remain unknown. As oscillatory patterns are reported to increase during sleep, we aimed to test the hypothesis that oscillations in a broad range of frequencies (14-250 Hz) in the epileptic focus significantly change during sleep compared to awake states. Additionally, we hypothesized that considering the entire range of frequencies (14-250 Hz, broadband) is more informative regarding differences between sleep and awake states than fast oscillations (80-250 Hz) alone.


Methods: We retrospectively analyzed intracranial EEG recordings (iEEG, 9 patients subdural EEG, 13 patients Stereo-EEG) of 22 consecutive adolescent and adult patients with focal epilepsy due to FCD who underwent iEEG at the Epilepsy Center Freiburg, Germany, between 10/2010 and 10/2022. iEEG electrode positions were identified in post-implantation MRIs. All contacts from the irritative zone and the seizure onset zone were considered part of the epileptic focus. We visually identified one-hour awake and one-hour sleep iEEG recordings. Brain states were identified either with simultaneous scalp EEG (10 patients) or by evaluation of simultaneous video recordings. Fast oscillations in the beta (14-40 Hz), gamma (40-80 Hz), or ripple (80-250 Hz) frequency bands were detected semi-automatically using the Delphos detector (Roehri et al., IEEE 2016). We normalized detection rates of oscillations within the epileptic focus with neocortical detection rates outside the epileptic focus and eloquent brain areas. Using a distance-based multivariate analysis of variance, we compared changes in the detection rate of the broadband oscillations (beta, gamma and ripple) to the detection rate in the ripple frequency band alone.

Results: Per patient, 67.4 ± 28 bipolar iEEG contact pairs were analyzed, with 28.5 ± 15.7 iEEG contact pairs within the epileptic focus. Within the epileptic focus, we observed the following oscillation rates per minute during awake versus sleep recordings: beta - 67.5 ± 75.6 versus 104.2 ± 100, gamma - 156.6 ± 227 versus 329.4 ± 265.6, and ripples - 293.1 ± 383.6 versus 489.2 ± 515.1. Significant differences between awake and sleep states occurred in a broad range of frequencies in 14 patients and in the ripple frequency band alone in 8 patients, demonstrating a significant increase in awake/sleep states detectability when using the broadband (p< 0.05, McNemar’s test). Moreover, no patient showed a significant difference in ripple rates without showing it at the broadband frequency. In contrast, 6 patients showed a significant rate difference for the broadband frequency but not in ripple alone.