Slow Wave Activity During Nocturnal Sleep in Hypersomnolence Disorder

Slow waves during non-rapid eye movement (NREM) sleep are associated with the restorative aspects of sleep. Previous research has suggested reduced normalized slow wave activity (SWA), particularly in the first cycle of NREM sleep, as a feature of hypersomnolence disorder (HD); however, the scarcity of existing research highlights the need for replication studies. Thus, the aim of this investigation was to evaluate normalized SWA in patients with HD, relative to healthy sleeper controls (HSC). Nocturnal polysomnography from 37 unmedicated HD clinical patients were compared against 29 HSC. Six-channel electroencephalographic data from polysomnography was processed according to consensus standards. Normalized SWA (0.5-4.5hz) was calculated from artefact-free NREM epochs for all-night data, as well as sleep cycle 1, 2, and 3. Normalized SWA was compared across groups, with adjusted analyses accounting for age, sex, body mass index, and depressive symptomatology. Post hoc analyses compared HD who met objective criteria for idiopathic hypersomnia (HD/IH+), those who did not (HD/IH-), and HSC. HD demonstrated significantly reduced all-night, normalized SWA in unadjusted analyses across all channels, without significant differences observed in fully adjusted analyses. In cycle 1, HD displayed significantly reduced normalized SWA across all channels in both unadjusted and adjusted analyses. HD/IH+ and HD/IH- were statistically comparable in normalized SWA across all analyses. This study provides further evidence of reduced SWA, particularly during cycle 1 of NREM sleep, as a core feature of HD. Future studies that investigate the causal role of slow waves in the pathophysiology of HD are warranted.