LAUSR

Introduction: In the two-process model of sleep regulation, slow-wave activity (SWA, EEG power in the 0.5–4 Hz band) is a direct indicator of sleep need. SWA builds up during NREM sleep, declines before the onset of REM sleep, remains low during REM and the level of increase in successive NREM episodes gets progressively lower. The sleep regulation model of Borbely et al, 1999, states that the rate of decrease in sleep need S(t) is proportional to SWA, i.e. dS(t)/dt =-γSWA(t) where γ is the decay rate. The sleep need after T minutes of sleep is: S(T)=S0-γCSWA(T), where S0 is the sleep need at sleep-onset and CSWA(T) is the integral of SWA from sleep onset to time T. The goal in this research is to assess the effect of age on the dynamics of sleep need dissipation. Methods: Sleep EEG and EOG data were collected from 25 subjects (10M and 15F; 37.1 ± 6.5 years old) for 3 nights at home. The data was manually scored into sleep stages according to AASM rules. SWA was calculated for each 6-second epoch of NREM sleep. In this model, sleep need dissipation is completely determined by S0 and γ. To estimate these, two boundary conditions were used: 1) the final value of S(t) is 0, and 2) S(t*) coincides with SWA(t*) at time t* where SWA is maximum in the first sleep cycle. Results: Two age groups were defined using as threshold the median age (38) of subjects in the study. S0 did not significantly differ between groups while γ was significantly different (γ group1=2.82 and γ group2=2.12; p=0.006). These results suggest that the efficiency of sleep need dissipation significantly decreases in the older group by 25%. Conclusion: The rate of sleep need dissipation is proportional to slow wave activity. The proportionality coefficient γ (decay rate) can be estimated using a differential model. It was found that γ is significantly lower, by 25%, in the age group 38 to 47 as compared to the age group 22 to 38. The initial sleep need did not differ between groups.