Age and sex-related changes in the human REM sleep microstructure

Rapid Eye Movement (REM) sleep alternates between two states - phasic and tonic - defined by the presence or absence of transient neurophysiological events such as rapid eye movements. These states exhibit distinct neural activity and putative underlying function, yet their evolution along with aging remains unknown. Retrospective polysomnographic data from 627 healthy participants (290 females and 337 males), aged 18 to 80 years and drawn from five databases, were analyzed to characterize age- and sex-related changes in the REM sleep microstructure. REM sleep macrostructure declined with age, paralleled by a reduction in phasic REM duration. In addition, the proportion of phasic REM sleep as well as the number and density of eye movements decreased with advancing age. We found sex-related differences in these trajectories, with a steeper decline in phasic REM percentage and REM density in women. Spectral analyses mainly confirmed previously reported differences in power between phasic and tonic states and further revealed differential age-related changes, i.e., while spectral power in tonic REM increased in higher frequency bands, phasic REM exhibited a progressive slowing of EEG activity across the lifespan. This large-scale, multicohort analysis provides a comprehensive characterization of REM sleep microstructure across aging and between sexes in healthy participants, constituting an important step toward its potential as a biomarker candidate in psychopathological and neurodegenerative disorders.