Midnight is no longer mid-night for individuals in the developed world. Many adolescents and young adults are awake and active at midnight. Artificial lighting, caffeine, and alarms have enabled this dissociation of sleep/wake+light/dark schedules from the external environment. In addition, many individuals have different schedules on work/school and non-work/non-school days, with later bedtimes, later wake times, and more frequent naps on non-work/non-school days. We and others have found correlations between irregular sleep/wake schedules and later circadian timing, poorer mood, poorer academic performance, and some health metrics, such as weight and psychiatric disorders. These, however, are correlations and not causal links. Identifying mechanisms by which modifiable behaviors, such as variable sleep timing, impact physiology is vital to developing effective educational or treatment-based strategies. We propose an experiment to test the effects of irregular and regular sleep/wake schedules on circadian timing, sleep, cognitive performance, mood, and learning. We will study a young adult population, as this is a time in human development when variable sleep schedules are prevalent and the consequences of irregular schedules on circadian timing, sleep propensity, performance, mood, and learning may be pronounced. The results from the proposed work will allow us to determine if it is the irregularity of the sleep/wake light/dark (SW/LD) schedule that delays circadian timing and disrupts performance, mood, and learning. Using our Sleep Regularity Index (SRI, a quantitative measure of sleep regularity), we will identify and select individuals with Irregular and Regular sleep/wake schedules based on the individual's sleep-wake pattern during three weeks of outpatient screening at home. Individuals from each group will then be randomly assigned to either an Irregular or Regular SW/LD schedule for an inpatient assessment. Assessments of circadian phase, sleep propensity, cognitive performance including vigilant attention, sleep-dependent and long-term learning, and mood will be conducted during the inpatient portion of the study. Our findings will help define physiological links among multiple physiological systems, including sleep/wake, light-sensitive processes (e.g., circadian rhythms, alertness, hormones), cognitive performance, and mood. Reducing scheduled sleep variability has no pharmacologic side-effects and may have additional health benefits. Designing effective therapeutic strategies for reducing variability requires an understanding of the physiological and environmental factors that may mediate and reinforce irregularity. Our results will help to elucidate these mechanisms and will be applicable to high school and college students, as well as adults working shift or night work or experiencing jet-lag. The findings may be utilized in public health forums, including educational campaigns about sleep timing and its effects on circadian rhythms, performance, learning, mood, and safety.

Public Health Relevance

Irregular sleep patterns are associated with delayed circadian phase, adverse health outcomes, and impaired cognitive performance, mood, and learning, but causation has not been established for any of these associations. Using both at-home and inpatient data from individuals keeping either an irregular or regular sleep schedule, we will determine the influence of sleep regularity on circadian timing, sleepiness, cognitive performance, mood, and learning. These findings are critical for the development of research-based strategies to improve learning and mood in adolescents, and performance and mood in individuals with shift- or night- work schedules or jet-lag.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Biobehavioral Mechanisms of Emotion, Stress and Health Study Section (MESH)
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Laposky, Aaron D
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Brigham and Women's Hospital
United States
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McHill, Andrew W; Hull, Joseph T; McMullan, Ciaran J et al. (2018) Chronic Insufficient Sleep Has a Limited Impact on Circadian Rhythmicity of Subjective Hunger and Awakening Fasted Metabolic Hormones. Front Endocrinol (Lausanne) 9:319
Asgari-Targhi, Ameneh; Klerman, Elizabeth B (2018) Mathematical modeling of circadian rhythms. Wiley Interdiscip Rev Syst Biol Med :e1439
McHill, Andrew W; Hull, Joseph T; Wang, Wei et al. (2018) Chronic sleep curtailment, even without extended (>16-h) wakefulness, degrades human vigilance performance. Proc Natl Acad Sci U S A 115:6070-6075
Phillips, Andrew J K; Clerx, William M; O'Brien, Conor S et al. (2017) Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing. Sci Rep 7:3216
Phillips, Andrew J K; Klerman, Elizabeth B; Butler, James P (2017) Modeling the adenosine system as a modulator of cognitive performance and sleep patterns during sleep restriction and recovery. PLoS Comput Biol 13:e1005759
McHill, Andrew W; Phillips, Andrew Jk; Czeisler, Charles A et al. (2017) Later circadian timing of food intake is associated with increased body fat. Am J Clin Nutr 106:1213-1219
Gupta, Manish; Beckett, Scott A; Klerman, Elizabeth B (2017) On-line EEG Denoising and Cleaning Using Correlated Sparse Recovery and Active Learning. Int J Wirel Inf Netw 24:109-123
McHill, Andrew W; Klerman, Elizabeth B; Slater, Bridgette et al. (2017) The Relationship Between Estrogen and the Decline in Delta Power During Adolescence. Sleep 40:
Klerman, Elizabeth B; Wang, Wei; Phillips, Andrew J K et al. (2017) Statistics for Sleep and Biological Rhythms Research. J Biol Rhythms 32:18-25
Swaminathan, Krithika; Klerman, Elizabeth B; Phillips, Andrew J K (2017) Are Individual Differences in Sleep and Circadian Timing Amplified by Use of Artificial Light Sources? J Biol Rhythms 32:165-176

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