Modelling changes in sleep timing and duration across the lifespan: Changes in circadian rhythmicity or sleep homeostasis?

Abstract

Sleep changes across the lifespan, with a delay in sleep timing and a reduction in slow wave sleep seen in adolescence, followed by further reductions in slow wave sleep but a gradual drift to earlier timing during healthy ageing. The mechanisms underlying changes in sleep timing are unclear: are they primarily related to changes in circadian processes, or to a reduction in the neural activity dependent build up of homeostatic sleep pressure during wake, or both? We review existing studies of age-related changes to sleep and explore how mathematical models can explain observed changes. Model simulations show that typical changes in sleep timing and duration, from adolesence to old age, can be understood in two ways: either as a consequence of a simultaneous reduction in the amplitude of the circadian wake-propensity rhythm and the neural activity dependent build-up of homeostatic sleep pressure during wake; or as a consequence of reduced homeostatic sleep pressure alone. A reduction in the homeostatic pressure also explains greater vulnerability of sleep to disruption and reduced daytime sleep-propensity in healthy ageing. This review highlights the important role of sleep homeostasis in sleep timing. It shows that the same phenotypic response may have multiple underlying causes, and identifies aspects of sleep to target to correct delayed sleep in adolescents and advanced sleep in later life.

The effects of self-selected light-dark cycles and social constraints on human sleep and circadian timing: a modeling approach

“…This model has been shown to describe changes in sleep timing and duration across the lifespan for a modern industrialized country29. We demonstrate that the model also agrees well with measurements of sleep timing and duration in pre-industrialized societies.…”

Future Directions in Sleep and Developmental Psychopathology

“…Thus relying on "average" sleep duration, or asking a single question about "typical" sleep routines, is not sufficient to determine how sleep variability within an individual contributes to the development of psychopathology. In addition to the experimental, longitudinal, and treatment trials that are needed to further examine the role of night-to-night 296 MELTZER variability on sleep, there is a role for more advanced statistical approaches to analysis, as well as mathematical modeling that may help shed light on sleep variability and changes across development (Becker, Sidol, et al, 2016;Skeldon, Derks, & Dijk, 2016).…”

Sleep behavior across the lifespan: How a model can expand our current understanding

“…In human adolescents, the melatonin rhythm was later in the participants who were late or postpubertal compared to those who were pre- and early-pubertal adolescents after both groups kept the same sleep/wake (and thus dark/light) pattern for at least a week before melatonin collection. As the analysis of Skeldon and colleagues (14) in this issue would predict, however, developmental changes to sleep homeostasis also partly explains the shift to later sleep times over the course of adolescence. Previous work illustrates that the dynamics of the homeostatic sleep system are altered during adolescence.…”

“…Finally, the model predictions of Skeldon and colleagues (14) could also inform the etiology of circadian rhythms sleep-wake disorders that emerge at different ages. The onset of symptoms of Delayed Sleep Phase Disorder (DSPD), for example, typically occurs during adolescence or emerging adulthood (44–46).…”

“…Importantly, the extended version of the model (11) incorporates feedback from the light/dark (wake/sleep) cycle, which determines phase of the self-sustaining circadian oscillator. In this issue of Sleep Medicine Reviews, Skeldon, Derks, and Dijk (14) explore how the Phillips-Robinson model (11) can explain observed changes in sleep timing and duration across the lifespan from adolescence to older adulthood. These data describe the relative impact of changes to sleep homeostasis and circadian processes on sleep behavior, continue to challenge the assumption that sleep timing is driven exclusively by the circadian system, and may provide insights into the etiology of circadian sleep-wake disorders that manifest at different ages.…”