Movements and behaviors during spontaneous arousals in healthy young adults: an intermediary stage between wakefulness and sleep?

Background: Arousals are common, sudden and transient elevations of the vigilance level during normal sleep, but arousal-associated behaviors have not yet been studied. Objective: We aimed to describe the duration as well as motor and autonomic patterns associated with arousals across sleep stages in normal subjects. Methods: The spontaneous arousals of 25 healthy young adults were randomly analyzed on poly-somnography with body- and face-oriented video cameras. The duration of the heart rate response as well as the frequency, amplitude, speed, body segment and semiology of associated movements were measured. Results: Among 624 arousals (258 in N2, 140 in N3 and 226 in REM sleep), REM sleep arousals had the shortest duration, and N3 arousals were associated with greater heart rate acceleration. Movements and behaviors (mostly involving the head and neck, then the upper limbs, with rare eyes opening and no turning in bed) were frequent during arousals (69.4% during N2 sleep, 89.3% during N3 and 93.8% during REM sleep). Arousals more frequently included ample, prolonged and whole-body movements during N3 sleep and fast movements and facial expressions during REM sleep. During N2 arousals, chewing was the most prevalent behavior. Some movements resembled orientation and comfort behaviors (flexing/rotating the neck and trunk, scratching, pulling the sheets, rubbing the nose, yawning, smiling, frowning and speaking), whereas others resembled sleep-associated automatisms (swallowing, chewing). Conclusion: In contrast with previous assumptions, most arousals are associated with movements. The type of movements suggests that arousal is an intermediary state between wakefulness and sleep. (C) 2021 Elsevier B.V. All rights reserved.