The impact of prior wake duration on motor wake inertia in different age groups

The two-process model of sleep regulation posits that sleep-wake behavior results from the interaction between circadian (process C) and homeostatic (process S) mechanisms. While the developmental modulation of sleep architecture is well documented, less is known about how the behavioral expression of process S varies across the lifespan under ecological conditions. Using an innovative actigraphic approach, the present study examined the effect of prior wakefulness duration on motor wake inertia-the transition from wakefulness to sleep-across different age groups. Actigraphic data were collected during everyday life from children (8-10 years), young adults (18-24 years), and adults over 40 years of age. Functional linear modeling was applied to motor activity patterns surrounding bedtime, with total prior wake time as a covariate. The results revealed age-dependent differences in the influence of prior wakefulness on motor wake inertia. In particular, a significant effect in children with low motor activity in the first few minutes after bedtime associated with a longer duration of the previous wake, a reversed pattern in young adults, and no clear modulation in the over-40s group support the hypothesis that the interaction between processes C and S undergoes age-related changes.