Sleep Homeostasis Has Circaseptan and Circatrigintan Cycles Over Year‐Long Timescales

Sleep homeostasis, the process by which sleep pressure accumulated during wakefulness is dissipated across non-rapid eye movement (REM) sleep, can be quantified as the nightly rate of decline in slow-wave activity (SWA; 0.5-4 Hz). Disruption of this homeostatic process has been documented in a range of neurological disorders including epilepsy, Alzheimer's disease and REM sleep behaviour disorder, yet its long-term dynamics in healthy individuals remain uncharacterized. The advent of subscalp EEG (sqEEG) platforms now makes continuous, naturalistic sleep recording feasible over months, enabling longitudinal study of sleep homeostasis at an unprecedented scale. Here we report the first such characterization in 20 healthy adults recorded continuously over 12-15 months. SWA slope was predominantly negative across all subjects, confirming intact homeostatic regulation and was stable across sex and age. Continuous wavelet transform analysis revealed significant circaseptan (~7-day) and circatrigintan (~28-day) rhythmicity in the majority of subjects, independent of sex. These findings establish a normative baseline for long-term sleep homeostatic dynamics and suggest that homeostatic sleep pressure dissipation is organized across multiple timescales beyond the single night, with direct relevance for neurological conditions in which this process is disrupted.