The Space–Time Organisation of Sleep Slow Oscillations as Potential Biomarker for Hypersomnolence

Research suggests that the spatial profile of slow wave activity (SWA) could be altered in hypersomnolence. Slow oscillations (SOs; 0.5-1.5 Hz), single waveform events contributing to SWA, can be labelled as Global, Frontal, or Local depending on their presentation on the scalp. We showed that SO space-time types differentiate in their amplitudes, coordination with sleep spindles, and propagation patterns. This study applies our data-driven analysis to the nocturnal sleep of adults with and without hypersomnolence and major depressive disorder (MDD) to explore the potential relevance of SO space-time patterns as hypersomnolence signatures in the sleep EEG. We leverage an existing dataset of nocturnal polysomnography with high-density EEG in 83 adults, organised in four groups depending on the presence/absence of hypersomnolence and on the presence/absence of MDD. Group comparisons were conducted considering either two groups (hypersomnolence status) or the four groups separately. Data shows enhanced Frontal SO activity compared with Global activity in hypersomnolence, with or without MDD, and a loss of Global SO amplitude at central regions in hypersomnolence without MDD compared to controls. As Global SOs travel fronto-parietally, we interpret these results as likely driven by a loss of coordination of Global SO activity in hypersomnolence without MDD, resulting in an overabundance of Frontal SOs. This study suggests that characteristics of Frontal SO and Global SOs may have the potential to differentiate individuals with hypersomnolence without MDD, and that the space-time organisation of SOs could be a mechanistically relevant indicator of changes in sleep brain dynamics related to hypersomnolence.