Circadian control of the sleep–wake cycle

Abstract

It is beyond doubt that the timing of sleep is under control of the circadian pacemaker. Humans are a diurnal species; they sleep mostly at night, and they do so at approximately 24-h intervals. If they do not adhere to this general pattern, for instance when working night shifts or when travelling across time zones, they experience the stubborn influence of their circadian clock.In recent years much has been discovered about the organisation of the circadian clock. New photoreceptor cells in the retina have been found to influence the input to the clock, and much of the molecular machinery of the clock has been unravelled. It is now known that the circadian rhythm of sleep and wakefulness is only loosely coupled to the circadian rhythm of the pacemaker. New theories have been proposed for the functions of sleep and the sites at which those functions are executed. In spite of this rapid increase in knowledge of the circadian clock and of sleep regulatory processes, much remains to be discovered concerning the precise interaction between the biological clock and sleep timing. This is particularly unfortunate in view of the 24-h demands of our society for 7 days a week. Too little is known about the negative consequences of the societal pressures on well-being and performance.

The Effect of 40 Hours of Constant Wakefulness on Number Comparison Performance

“…Harmonic regression analyses revealed a circadian modulation in both simple RT performance (i.e., PVT) and choice RT performance (i.e., symbolic distance task), with fastest responses observed during the daytime and slowest responses observed during the nighttime. Moreover, there was a close phase relationship between decrements in RT performance, self-report measures of sleepiness (Akerstedt et al, 2008b), and onset of melatonin secretion, which is considered the most important physiological marker of the circadian phase (e.g., Beersma & Gordijn, 2007;Cajochen et al, 2003). The fact that the performance impairments during the nighttime, that is, from 00:00 h to 6:00 h, recovered afterwards during the next day supports the view that overall performance, including perceptual, cognitive, and motor processes, is essentially modulated by the rhythmic activity of the circadian clock and not only by the cumulative effects of sleep loss (Carrier & Monk, 2000;Rogers et al, 2003).…”

P-glycoprotein Function in the Rodent Brain Displays a Daily Rhythm, a Quantitative In Vivo PET Study

“…Ultimately, rhythms in the regulation of gene expression, protein synthesis, hormone levels, or neurotransmitter release could affect P-gp expression and function. Moreover, the endogenous circadian clock might not only affect P-gp function through direct physiological mechanisms, but a daily rhythm in P-gp function might also be related to sleep, which is itself under control of the SCN (13,14).…”

You are only coming through in waves: wakefulness variability and assessment in patients with impaired consciousness

“…Indeed, mental performance is significantly worse in sleep deprivation conditions and during the night (Monk et al, 1997). It is important to state that these changes are related to the two main mechanisms responsible for the sleep-wake cycle, that is, the homeostatic (fatigue) component and the circadian (endogenous) proclivity to wakefulness or sleep (Beersma and Gordijn, 2007;Boivin et al, 1997;Borbely, 1982).…”

“…Indeed, mental performance is significantly worse in sleep deprivation conditions and during the night (Monk et al, 1997). It is important to state that these changes are related to the two main mechanisms responsible for the sleep-wake cycle, that is, the homeostatic (fatigue) component and the circadian (endogenous) proclivity to wakefulness or sleep (Beersma and Gordijn, 2007;Boivin et al, 1997;Borbely, 1982).Although sleep states and, certainly, pharmacological manipulations, have traditionally been linked to different consciousness levels (Broughton, 1982;Cantero and Atienza, 2005;Tung and Mendelson, 2004), no formal approach to circadian modulation of consciousness or, on the other hand, circadian alterations in altered consciousness states has been performed, except for a few studies in patients with different degrees of brain damage. In this aspect, core body temperature rhythms are significantly affected by both impaired physical activity and brain lesions (Takekawa et al, 2002) and, more importantly, circadian rhythms have been associated with diagnosis and neurological findings in patients with altered consciousness states derived from brain damage (Dauch and Bauer, 1990).…”