[Regulation of sleep]

Abstract

Sleep regulation calls for 3 processes: the first one is the homeostatic process increasing during wakefulness and decreasing during sleep, the second one is the circadian process depending on the circadian oscillator which controls temperature and alertness rhythms, and the third one is the ultradian process: it determines the NREM/REM periodicity. In the 2 process model of sleep regulation, the power density of the delta band (0.75-4.5 Hz) called slow wave activity (SWA) and obtained by spectral analysis, is supposed to reflect the variations of a homeostatic recovery process (process S) that increases in a saturating exponential way during wakefulness. Its decrease is expressed by the exponential decline of SWA during sleep. Process S interacts with the circadian process (process S) that determines the sleep timing. The 2 process model has been further modified to account for the semicircadian sleep propensity, although no satisfactory fit has been obtained with laboratory data. No impairment of NREM sleep homeostatic sleep regulation can be evidenced in narcoleptic patients who seem more sensitive to homeostatic regulation of sleep than normal subjects. On the other hand the circadian process appears to be weaker in narcoleptic patients than in normal subjects; this permits the occurrence of a strong ultradian component explaining diurnal sleep episodes.