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Review
. 2012 Mar 13;31(1):5.
doi: 10.1186/1880-6805-31-5.

Daily rhythms of the sleep-wake cycle

Jim Waterhouse  1 , Yumi Fukuda, Takeshi Morita
Affiliations
Review

Daily rhythms of the sleep-wake cycle

Jim Waterhouse et al. J Physiol Anthropol. .

Abstract

The amount and timing of sleep and sleep architecture (sleep stages) are determined by several factors, important among which are the environment, circadian rhythms and time awake. Separating the roles played by these factors requires specific protocols, including the constant routine and altered sleep-wake schedules. Results from such protocols have led to the discovery of the factors that determine the amounts and distribution of slow wave and rapid eye movement sleep as well as to the development of models to determine the amount and timing of sleep. One successful model postulates two processes. The first is process S, which is due to sleep pressure (and increases with time awake) and is attributed to a 'sleep homeostat'. Process S reverses during slow wave sleep (when it is called process S'). The second is process C, which shows a daily rhythm that is parallel to the rhythm of core temperature. Processes S and C combine approximately additively to determine the times of sleep onset and waking. The model has proved useful in describing normal sleep in adults. Current work aims to identify the detailed nature of processes S and C. The model can also be applied to circumstances when the sleep-wake cycle is different from the norm in some way. These circumstances include: those who are poor sleepers or short sleepers; the role an individual's chronotype (a measure of how the timing of the individual's preferred sleep-wake cycle compares with the average for a population); and changes in the sleep-wake cycle with age, particularly in adolescence and aging, since individuals tend to prefer to go to sleep later during adolescence and earlier in old age. In all circumstances, the evidence that sleep times and architecture are altered and the possible causes of these changes (including altered S, S' and C processes) are examined.

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Figures

Figure 1
Figure 1
The daily rhythm of core temperature in a group of eight young men. Full line: under normal conditions (sleep from 12 a.m. to 7 a.m., indicated by bar). Dashed line: undergoing a 24-hour constant routine starting at 4 a.m. (From [2]).
Figure 2
Figure 2
Times of sleep and wake (top, separated by the double vertical lines). The C component is represented by two curves (Upper C and Lower C). Sleep pressure increases exponentially in the wake phase (Process S, dotted line) and decreases at a faster exponential rate in the sleep phase (S', dashed line). For more details, see text. (Based on [21]).
Figure 3
Figure 3
Morningness-Eveningness Questionnaire (chronotype) scores in male and female school children of different ages. Filled bars, boys; open bars, girls. Scores indicate: range 16 to 30, definitely evening-type; 31 to41, moderately evening-type; 42 to 58, neither or intermediate-type; 59 to 69, moderately morning-type; and 70 to 86, definitely morning-type.
Figure 4
Figure 4
Pittsburgh Sleep Quality Index scores in male and female school children of different ages. Filled bars, boys; open bars, girls. Scores > 5 indicate some problems with sleep.
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