title: 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.
authors.affiliation: Department of Mathematics, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK. Electronic address: a.skeldon@surrey.ac.uk.
authors.forename: Anne C
authors.initials: AC
authors.lastname: Skeldon
authors.affiliation: Department of Mathematics, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK.
authors.forename: Gianne
authors.initials: G
authors.lastname: Derks
authors.affiliation: Surrey Sleep Research Centre, Faculty of Health and Medical Sciences, University of Surrey, Guildford GU2 7XP, UK.
authors.forename: Derk-Jan
authors.initials: DJ
authors.lastname: Dijk
mesh_terms: D002940:Circadian Rhythm / Q000502:physiology*; D000073656:Healthy Aging / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D012890:Sleep / Q000502:physiology*; D013997:Time Factors
keywords: Adolescence; Chronobiology; Circadian; Development; Models; Sleepiness