Tonic REM sleep EEG components predict better mood, cognition and reduce cortical excitability overnight

Rapid Eye Movement (REM) sleep makes up approximately 20% of sleep in the adult human and is altered in psychiatric and neurodegenerative conditions. REM sleep comprises two substates, during which eye movements do (phasic REM) and do not (tonic REM) occur. Tonic REM makes up 70-90% of REM sleep but its role in regulating brain function, mood and cognition remain underexplored. We investigated how seven nights of insufficient sleep (6 h time in bed), compared to sufficient sleep, alter periodic and aperiodic components of the phasic and tonic REM sleep electroencephalography (EEG), in 542 sleep recordings of 36 young adults. Associations between phasic and tonic REM sleep EEG and mood, cognitive performance, and overnight changes in cortical excitability as indexed by 1/f spectral slopes were assessed. Insufficient sleep predominantly affected tonic REM EEG components, specifically the density of theta, the amplitude, density, and frequency of alpha oscillations and the 1/f slope in the 30 to 45 Hz range. These changes associated with mood and cognitive performances, and with overnight reductions in cortical excitability. These results provide evidence for a role of tonic REM sleep in regulating mood and counteracting cognitive deterioration and excitability changes associated with insufficient sleep.