0014 The Circadian Timing of Sleep Affects the Rate of Accumulation of Objective Neurobehavioral Impairment Across Days of Sleep Restriction

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Abstract Introduction Chronic nighttime sleep restriction leads to the build-up of neurobehavioral impairment across days. Although it is known that the circadian timing of sleep mediates the effects of sleep loss, it is not known how the timing of restricted sleep influences the accumulation of neurobehavioral impairment over days. Here we investigated lapses on the psychomotor vigilance test (PVT) across days with restricted sleep placed in the late morning or late afternoon. Methods N=72 healthy young adults (ages 21-45y, 39% female) completed a 14-day in-laboratory study. After an 8h nighttime adaptation sleep opportunity (23:30–07:30) there was a baseline day with an 8h shifted sleep opportunity ending in late A) morning (11:30) or B) afternoon (19:30). Subjects were then randomized to 9 consecutive days of sleep restricted to 4h, 6h, or 8h time-in-bed (TIB) for late A) morning (11:30; n=19, 8, 8, respectively), or B) afternoon (19:30; n=13, 17, 7, respectively). Subjects were tested on a 10-minute PVT every ~2h during scheduled wakefulness. Daily averages for PVT lapses (RTs>500ms) observed 2-14h after scheduled awakening, expressed relative to average PVT lapses on theshifted baseline day, were analyzed with nonlinear mixed-effects regression to investigate differences in the build-up of neurobehavioral impairment between shifted sleep restriction doses. Results In the afternoon sleep conditions, PVT lapses showed a significant sleep dose-response effect (F=6.22, p=0.003), with the fastest accrual of impairment across days in the 4h condition (t=5.12, p< 0.001) and near-negligible impairment build-up in the 8h condition (t=1.00, p=0.32). However, in the morning sleep conditions, PVT lapses showed no sleep dose-response effect (F=0.01, p=0.99) with modest impairment growth across days overall (t=2.06, p=0.043) at just 43.7% the average rate observed in the afternoon sleep conditions. Conclusion In this sample of young adults, placing 6h and 4h daily sleep opportunities in the late morning appeared to provide resilience against the accumulation of neurobehavioral impairment from sustained sleep restriction. Our results suggest that afternoon circadian promotion of wakefulness can sustain objective neurobehavioral functioning for at least 14h of wakefulness daily across multiple days of sleep restriction. Support (if any) NIH R01-NR04281, M01-RR00040

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