Abstracts

Rationale: Sleep deprivation provokes seizures in susceptible individuals, but the underlying mechanisms are not well understood¹. Slow Wave Sleep (SWS) involves mass synchronized cortical oscillation between depolarised and hyperpolarised states, discernible on electroencephalography (EEG) as high amplitude delta waves (0.5-4Hz). SWS has been shown to promote both synaptic downscaling and memory consolidation², and is a marker of sleep homeostasis: following an extended period awake, percentage of total sleep time (TST) spent in SWS and total EEG delta power both increase. Conversely, sleep pressure and delta power dissipate over the course of recovery sleep³ We aimed to determine whether impairments exist in sleep homeostasis in children with focal epilepsy, and whether these correlate with vulnerability to seizures triggered by sleep deprivation. Methods: Recordings from 17 patients (aged 8-18 years) with focal epilepsy who were sleep deprived during video EEG telemetry were retrospectively analysed. Baseline and sleep restricted nights were scored visually according to standard guidelines⁴. Total delta power in frequency bins 1-4Hz was calculated for each night using fast Fourier transform on 4-second windows (0.25Hz frequency resolution). Delta power in each non-REM cycle was determined, with cycles defined using normalised thresholds based on the subject's mean REM delta power + 2 standard deviations. Results: All patients showed a decrease in delta power with successive NREM cycles over the course of each night. Sleep restriction resulted in an increased proportion of total sleep time (TST) spent in slow wave sleep (SWS); this was correlated with the degree of sleep restriction (Spearman's R=0.515, p<0.05). However, 7 patients showed a paradoxical decrease in total delta power in response to sleep deprivation. This was strongly associated with having a subsequent seizure during the hospital admission (Fisher's exact test, p<0.05). Conclusions: A proportion of children with focal epilepsy show impaired sleep homeostasis, failing to upregulate EEG delta power in response to sleep deprivation. This impairment of presumed synaptic downscaling may contribute directly to increasing the individual's seizure propensity in the face of acute sleep restriction.