0175 Light Improves Alertness and Mood During the Sleep Inertia Period Following Slow Wave Sleep

Funded by Naval Postgraduate SchoolThe article of record as published may be found at https://doi.org/10.1093/sleep/zsaa056.173Introduction: Waking from sleep, especially slow wave sleep (SWS), is associated with reduced alertness known as sleep inertia. Light improves alertness during sleep deprivation and circadian misalignment. In this study, we assessed the efficacy of light to improve alertness and mood immediately after waking from SWS. Methods: Twelve participants kept a sleep schedule of 8.5 h for 5 nights and 5 h for one night prior to the overnight laboratory visit (confirmed by actigraphy). Participants went to bed at their scheduled habitual bedtime in the laboratory and were monitored by standard polysomnography. After at least 5 min of SWS, participants were awoken and exposed to either red ambient light (control) or blue-enriched bright light (light) for 1 h. During this time, participants completed a subjective scale of alertness (Karolinska Sleepiness Scale, KSS) and visual analogue scales (VAS) of mood at 2 min, 17 min, 32 min, and 47 min after waking. Following this sleep inertia measurement period, all lights were turned off and participants were allowed to return to sleep. They were then awoken again from their subsequent SWS period and exposed to the opposite condition (control or light). A linear mixed-effects model with fixed effects of condition, time, and condition*time and a random effect of participant was used to determine the impact of light across the testing period. An average of baseline responses (pre-sleep) was included as a covariate. Results: Compared to the control condition, participants exposed to blue-enriched bright light reported feeling more alert (KSS: F1,77=4.955, p=.029; VASalert: F1,77=8.226, p=.005), more cheerful (VAScheerful: F1,77=8.615, p=.004), less depressed (VASdepressed: F1,77=4.649, p=.034), and less lethargic (VASlethargic: F1,77=5.652, p=.020). Conclusion: Exposure to blue-enriched bright light immediately after waking from SWS may help to improve subjective alertness and mood. Future analyses will explore whether these findings extend to effects on cognitive performance.Naval Postgraduate School Grant. NASA Airspace Operations and Safety Program, System-Wide Safety Project

Stability of the timing of food intake at daily and monthly timescales in young adults

Cross-sectional observations have shown that the timing of eating may be important for health-related outcomes. Here we examined the stability of eating timing, using both clock hour and relative circadian time, across one semester (n = 14) at daily and monthly time-scales. At three time points ~ 1 month apart, circadian phase was determined during an overnight in-laboratory visit and eating was photographically recorded for one week to assess timing and composition. Day-to-day stability was measured using the Composite Phase Deviation (deviation from a perfectly regular pattern) and intraclass correlation coefficients (ICC) were used to determine individual stability across months (weekly average compared across months). Day-to-day clock timing of caloric events had poor stability within individuals (~ 3-h variation; ICC = 0.12–0.34). The timing of eating was stable across months (~ 1-h variation, ICCs ranging from 0.54–0.63), but less stable across months when measured relative to circadian timing (ICC = 0.33–0.41). Our findings suggest that though day-to-day variability in the timing of eating has poor stability, the timing of eating measured for a week is stable across months within individuals. This indicates two relevant timescales: a monthly timescale with more stability in eating timing than a daily timescale. Thus, a single day’s food documentation may not represent habitual (longer timescale) patterns

Star clusters near and far; tracing star formation across cosmic time

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00690-x.Star clusters are fundamental units of stellar feedback and unique tracers of their host galactic properties. In this review, we will first focus on their constituents, i.e.\ detailed insight into their stellar populations and their surrounding ionised, warm, neutral, and molecular gas. We, then, move beyond the Local Group to review star cluster populations at various evolutionary stages, and in diverse galactic environmental conditions accessible in the local Universe. At high redshift, where conditions for cluster formation and evolution are more extreme, we are only able to observe the integrated light of a handful of objects that we believe will become globular clusters. We therefore discuss how numerical and analytical methods, informed by the observed properties of cluster populations in the local Universe, are used to develop sophisticated simulations potentially capable of disentangling the genetic map of galaxy formation and assembly that is carried by globular cluster populations.Peer reviewedFinal Accepted Versio

Light in ecological settings: entrainment, circadian disruption, and interventions

Light is the predominant signal for the human circadian clock to synchronize to the solar 24-h day through an active process called entrainment. Modern light profiles are characterized by exposure to both natural daylight and artificial lighting. A mismatch between these self-selected light profiles and the solar day-night alternation can disrupt the circadian system, resulting in acute and chronic effects for health and safety. In this chapter, we describe (i) how entrainment works in the real world, illustrating the major role of light for this process; (ii) ways in which the circadian system can be disrupted by (external) factors such as irregular sleep, shift work, daylight saving time, and longitudinal position in a time zone; and (iii) how field studies have used light interventions to reduce direct and indirect effects of circadian disruption in ecological settings

Jet Lag, Sleep Timing, and Sleep Inertia

This chapter explores the causes, consequences, and countermeasures of jet lag, mistimed sleep, and sleep inertia. Jet lag can occur when rapidly crossing multiple time zones (e.g., trans-meridian travel for long-haul pilots). The desynchrony between the body’s biological clock, or circadian rhythm, and the new day-night cycle can lead to indigestion, sleep disturbances, fatigue, and cognitive impairments. Mistimed sleep can also occur within a time zone. In the case of night shiftwork, sleep is displaced to the daytime which leads to poor sleep and increased fatigue at night due to the combination of pressures from the two-process model of sleep regulation: sleep loss (homeostatic pressure) and being awake when the body is promoting sleep (circadian pressure). There is also a third process of sleep regulation called sleep inertia, which refers to the brief period of fatigue and impaired cognitive performance experienced after waking. Sleep inertia can be a fatigue risk for transportation workers who work on-call (e.g., emergency services) or who nap on shift (e.g., long-haul truck drivers) and are required to perform a safety-critical task soon after waking. For each of these fatigue risks, strategic exposure to bright light can be used to help realign sleep timing and to promote alertness

Maintaining health and performance in challenging spatial and temporal environments

Summary: Humans have always aspired to reach new frontiers, both spatial and temporal. We have illuminated the night and started working around the clock, we have conquered the skies and explored space, and we are connected on a global scale never seen before. As a consequence, our lives and work conditions have become more challenging in many ways, with sleep and biological rhythms challenged by irregular work hours, early school start times, artificial light, and, most recently, pandemic-induced lockdowns. While associated risks to health and performance are well-documented, we want to shift the focus to potential solutions and present novel findings on how to stay healthy and maintain performance in challenging environments, including operational settings (i.e., spaceflight, aviation, and shift work) and ecological settings (i.e., schools and the COVID-19 pandemic). Specifically, Dr. Cassie Hilditch (San José State University, USA) will present findings from a series of translational studies investigating the use of light as a countermeasure to sleep inertia following abrupt awakenings at night, with applications for space flight. Dr. Julia Stone (Monash University, Australia) will talk about recent advances in modeling sleep and circadian timing, including model individualization, and how they are being applied to real-world settings with significant circadian disruption, such as shift work. Dr. Dorothee Fischer (German Aerospace Center, Germany) will present data from helicopter pilots in the emergency medical services working two different duty rosters, illustrating how shift scheduling can be used to improve sleep and cognitive performance. Dr. Anna Biller (Technical University Munich, Germany) will present a novel, inter-disciplinary framework of light exposure as an active human behavior and outline both structural and behavior-focused interventions to improve sleep and academic performance in educational settings, such as schools and universities. Dr. Luísa Klaus Pilz (Federal University of Rio Grande do Sul, Brazil) will present findings from rest-activity rhythms, sleep, and mental health data collected in 2020 and 2022 of the COVID-19 pandemic in Brazil, discussing strategies to preserve mental health. This symposium features an all-female cast of up-and-coming researchers from four different continents (Europe, North and South America, Australia), who are advancing novel research on how to stay healthy and maintain performance in environments that challenge sleep and circadian rhythms. We believe that this group of speakers are uniquely qualified to shed light on this important topic, bringing together diverse backgrounds and expertise, with the common goal to advance solution-oriented research