RESUMO
STUDY OBJECTIVES: Sleep onset (SO) is cognitively and physiologically similar to rapid eye movement (REM) sleep, supporting the notion that REM sleep-related processes are 'covertly' active at this time. The objective was to determine if SO mentation is sensitive to REM sleep deprivation. DESIGN: Two-group cross-sectional design; sleep recordings for 3 nights. SETTING: Standard sleep laboratory with 24-channel polysomnography recording. PARTICIPANTS: Fourteen female, 13 male healthy volunteers (18-41 yrs, mean=24.8 +/- 6.07). INTERVENTIONS: On Night 2, half were and half were not partially REM sleep-deprived (REMD), recalled REM mentation, and rated it for dream-like quality (DLQ), sleepiness, and sensory attributes. On Night 3, all were awakened from SO substages 4 and 5 for mentation reports and further ratings. REMD measures were derived from scored sleep tracings. MEASUREMENTS AND RESULTS: REMD produced increases in DLQ for both REM and SO reports (P < .05); DLQ scores were higher for REM than for SO mentation (P < .001). Covarying sleepiness preserved the (REMD) effect but abolished the REM/SO difference. Whereas 2 sensory attributes (presence of self, visual intensity) tended to distinguish the REM-mentation reports of REMD and control subjects, only 1, self-movement, distinguished their SO mentation reports (P < .06). Multiple regression revealed that increased DLQ of both REM and SO mentation was associated with increased sleepiness and decreased REM sleep time on Night 2. CONCLUSIONS: SO mentation responds to REMD much like REM mentation does, a finding consistent with other work supporting the notion of covert REM-sleep processes at SO. DLQ may be mediated by both increases in REM-sleep propensity and a circadian process indexed by sleepiness ratings.
