Abstract
Studies in adult mammals (rats, cats, mice, and humans) have revealed a surprising regularity in the duration of sleep and wake bouts. In particular, wake bout durations exhibit a power-law distribution whereas sleep bout durations exhibit an exponential distribution. Moreover, in rodents, sleep bouts exhibit an exponential distribution at all ages examined, whereas wake bout durations exhibit exponential distributions early in ontogeny with a clear power-law emerging only at the older ages. Thus, the data examined thus far suggests a similar developmental trajectory for a wide range of mammals which in turn may offer a novel metric to directly compare human and animal sleep–wake data. Therefore, we tested the generalizability of these findings by examining the distributions of sleep and wake bouts during the night in a healthy human sample – from premature infants to 70-year-olds. We find that sleep bouts elongate over the first years. At the same time wake bouts shorten but elongate again with increasing age. Moreover, sleep bout durations exhibit exponential distributions at all ages tested, except for the youngest (premature infants). Wake bouts exhibit a power-law distribution – but only during a restricted time window during adulthood. We conclude that the developmental trajectory of human sleep–wake cycles does not map well onto those of rodents; however, the method of characterizing sleep–wake cycles, using bout distribution, holds great promise for classifying sleep, its disorders, and tracking its developmental milestones across the lifespan in humans.
Highlights
In all age groups total sleep time, rapid eye movement (REM) and NREM amounts represent normal values (Bliwise, 2005; Carskadon and Dement, 2005), ESS scores do not indicate daytime sleepiness (Johns, 1991), and low oxygen desaturation index (ODI) values suggest the absence of sleep disordered breathing (Chiner et al, 1999)
The current findings offer support for the notion that sleep bout durations exhibit exponential behavior virtually throughout the lifespan; in contrast to what might be expected from prior rodent data (Blumberg et al, 2005), wake bout durations only exhibit power-law behavior during a restricted developmental time window
In the current study sleep data is collected at night only and the participants were instructed to closely follow their normal routine
Summary
Brief periods of wakefulness frequently interrupt the much longer sleep bouts during, what to most of us seems to be, an uninterrupted night’s sleep. These awakenings have recently been shown to be non-random events (Lo et al, 2002, 2004); the durations of the alternating bouts of sleep and wakefulness, which echo changes in the activity of neural mechanisms generating the behavioral states, exhibit a statistical regularity (Lo et al, 2002, 2004; Blumberg et al, 2005). The inclusion of the structure of durations of bouts of wakefulness as well as sleep, holds information on the neural substrates of sleep and wakefulness and offers insights not included in many other models of sleep regulation (Borbély and Acherman, 2006)
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