Sleep, circadian rhythms, and delayed phase in adolescence
Introduction
This review describes changes to sleep/wake behavior during adolescent development and the contribution of the circadian and sleep/wake homeostatic systems to this changing behavior. We also review delayed sleep phase syndrome (DSPS), which may be an extreme manifestation of these changes or may be a distinct clinical entity. Last, we describe approaches to treat DSPS in adolescents. For the purpose of this review, we consider biological adolescence to span the second decade of life.
Section snippets
Developmental changes in sleep/wake (light/dark) patterns
Sleep/wake patterns of developing adolescents are often described in the context of a school year and have been described separately for school (weekday) and non-school (weekend) days. Sleep timing is often quite different during school vacations. Describing sleep patterns during both school and vacation times provides a more comprehensive account of developmental sleep/wake behavior changes, yet few studies have examined vacation sleep patterns.
Table 1 summarizes adolescent self-reported sleep
The circadian timing system
The circadian timing system provides temporal organization for regulatory mechanisms to facilitate adaptive behavior, such as feeding, reproduction, and sleep/wake cycles [23]. These coordinated temporal patterns, or circadian rhythms, are self-sustained and oscillate with a period of about 24 h. The internal mechanism (pacemaker) that organizes these rhythms in mammals has been localized to a small paired nucleus in the hypothalamus, the suprachiasmatic nucleus (SCN; [24]). Biological events or
The homeostatic sleep system
The homeostatic sleep/wake system is thought to be relatively independent of circadian timing. A simple way to characterize the process is that sleep pressure increases the longer one is awake and dissipates as one sleeps. Slow wave sleep (SWS, stages 3 and 4) and electroencephalographic (EEG) slow wave activity (SWA, power in the 0.75–4.5 Hz range) have been used as physiological markers for “sleep pressure.” Thus, SWA is high at the beginning of the nocturnal sleep episode when sleep pressure
Process C
The circadian timing system undergoes developmental changes during adolescence. Although sleep/wake patterns have long been known to delay in adolescents, behavioral factors (e.g., social and scholastic obligations) were assumed to be entirely responsible. The notion that circadian timing may change was noted by Carskadon and colleagues in a study of circadian phase preference in young adolescents [52]. Phase preference, or morningness/eveningness is a behavioral construct related to the time
Delayed sleep phase syndrome (DSPS)
The developmental changes in the circadian and sleep systems we have described may be exaggerated in adolescents who receive a diagnosis of delayed sleep phase syndrome (DSPS). DSPS is a disorder with a typical onset in the second decade of life or earlier [75]. Weitzman, Czeisler, and colleagues [76], [77] first described delayed sleep phase insomnia as a distinct syndrome characterized by a cluster of features including a chronic inability to fall asleep and wake at a desired clock time,
Conclusions
Developmental delays in sleep/wake behavior across adolescence are associated with extrinsic and intrinsic factors. Investigations of circadian timing mechanisms and homeostatic sleep processes may provide insights into biological underpinnings of behavioral changes. Future research is needed to identify whether DSPS is an exaggeration of a typical developmental delay or whether the pathophysiology of DSPS has other pathways. Furthermore, efficacy studies of chronotherapy, phototherapy, and
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