Abstract
The two-process conceptualization of sleep-wake regulation suggests that the biological underpinnings of the differences between morning and evening types in sleep timing and duration might be related to either the circadian process or the homeostatic process or both. The purpose of this report was to test whether morning and evening types might have similar homeostatic processes to achieve such ultimate goal of homeostatic sleep regulation as taking an adequate amount of sleep on free days. Weekend and weekday rise- and bedtimes reported for 50 paired samples of morning and evening types were averaged and simulated with a model of sleep-wake regulation. In morning and evening types of the same age, the homeostatic components of the sleep-wake regulation were found to be identical. Therefore, the difference in the circadian process between chronotypes of similar age can account for the observed differences between them in sleep timing and duration on weekdays and weekends. It was also demonstrated that the model-based simulations might have practical implications for informing an individual about the extent of unrecoverable reduction of his/her sleep on weekdays.
Highlights
Knowledge of individual differences in the timing of human behavior and physiology seems to be of importance for the optimization of times for taking medications and for attending school, management of fatigue in occupational settings, prediction of performance and risk of accidents on the roads and in unsafe workplaces, diagnosis, and treatment of sleep and circadian rhythm disorders, etc
Given the complexity of the biological mechanisms controlling the phase characteristics of human behavioral and physiological rhythms, valuable insights into the causes of these inter- and intra-individual differences can be provided by mathematical modeling
The result suggested that the biologically determined differences between chronotypes do not change with advancing age, and significant age-associated changes in the difference in weekday sleep cannot be explained by the biological differences between chronotypes. They can be explained by the age-associated weakening of the social constraints placed on sleep-wake schedule of E-type participants
Summary
Knowledge of individual differences in the timing of human behavior and physiology seems to be of importance for the optimization of times for taking medications and for attending school, management of fatigue in occupational settings, prediction of performance and risk of accidents on the roads and in unsafe workplaces, diagnosis, and treatment of sleep and circadian rhythm disorders, etc. The recommendations about optimal timing for human activity are often challenged by the lack of information about the causes of the observed profound differences between individuals in the phase characteristics of their circadian rhythms. The phase characteristics of such rhythms as the sleep-wake cycle demonstrate notable changes across the lifespan These changes might cause conflicts between social and biological clocks. The two-process conceptualization of the mechanisms of sleep-wake regulation (Borbély, 1982) seems to be the major contributor to our current understanding of the causes of differences between individuals in their 24-h sleep-wake pattern It postulates that the cyclicity of sleep and wakefulness is determined by two regulation processes, a circadian process and a homeostatic process (Borbély, 1982; Daan et al, 1984). It was demonstrated that the exponential function might be applied for the quantitative description of the homeostatic process as the alternations of buildups and decays of SWA in the course of wakefulness and sleep, respectively (Daan et al, 1984; Duffy et al, 1999)
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