Light sensitivity as a physiological factor that promotes irregular sleep/wake patterns: a model-based investigation

Kurzfassung

Introduction: Irregular sleep is a health risk factor. However, we currently have a poor understanding of physiological factors that contribute to individuals having irregular sleep/wake patterns. We used a validated mathematical model of sleep-wake and circadian physiology to systematically examine the influence of circadian, sleep homeostatic, and light sensitivity parameters on sleep regularity. Materials and Methods: Sleep-wake patterns were generated by a computational model, assuming a 5-day work schedule with enforced wakefulness from 7:00 to 19:00. We introduced daily random variation σ in the model’s sleep-onset threshold to mimic observed intra-individual variability in sleep/wake patterns. The Sleep Regularity Index (SRI) was calculated, ranging from 0 (random pattern) to 100 (perfectly regular pattern). Eight model parameters were varied to determine their effects on SRI: circadian period (τ); circadian amplitude (νvc); sleep homeostatic time constant (χ); and five light sensitivity parameters: delay bias of the phase response curve (b), sensitivity of the dose response curve (p), retinal output strength (G), photoreceptor recovery rate (β), and photoreceptor activation rate (α0). Results: Sleep regularity was meaningfully affected by six of the eight parameters. Responses occurred in three clusters: (1) light sensitivity parameters G and β had no effect on SRI; (2) circadian amplitude νvc modulated the effect of σ, such that weaker amplitude resulted in lower SRI (less regular patterns) for the same σ; and (3) the remaining five parameters τ, χ, b, p, and α0 all generated maximal SRI scores (most regular patterns) for default parameter values, with lower SRI scores when parameters deviated from default values. Conclusions: This is the first study to systematically investigate potential mechanisms of irregular sleep using mathematical modeling. Our findings suggest that irregular sleep can result from individual differences in the sensitivity to the timing and intensity of light exposure, as well as differences in circadian and sleep homeostatic parameters.