Daytime light exposure is a strong predictor of seasonal variation in sleep and circadian timing of university students.

In the absence of electric light, sleep for humans typically starts soon after dusk and at higher latitudes daily sleep timing changes seasonally as photoperiod changes. However, access to electric light shields humans from natural photoperiod changes, and whether seasonal changes in sleep occur despite this isolation from the natural light-dark cycle remains a matter of controversy. We measured sleep timing in over 500 university students living in the city of Seattle, WA (47.6°N) throughout the four seasons; we show that even when students are following a school schedule, sleep timing is delayed during the fall and winter. For instance, during the winter school days, students fell asleep 35 min later and woke up 27 min later (under daylight-savings time) than students during the summer school days, a change that is an hour larger relative to solar midnight. Furthermore, chronotype defined by mid-sleep on free days corrected for oversleep (MSFc), an indirect estimate of circadian phase, was more than 30 min later in the winter compared with the summer. Analysis of the effect of light exposure showed that the number of hours of light exposure to at least 50 lux during the daytime was a stronger predictor of MSFc than the exposure time to this illuminance after dusk. Specifically, MSFc was advanced by 30 min for each additional hour of light exposure during daytime and delayed by only 15 min for each additional hour of postdusk exposure to light. Additionally, the time of the day of exposure to high light intensities was more predictive of MSFc when daytime exposure was considered than when exposure for the full 24-h day was considered. Our results show that although sleep time is highly synchronized to social time, a delayed timing of sleep is evident during the winter months. They also suggest that daily exposure to daylight is key to prevent this delayed phase of the circadian clock and thus circadian disruption that is typically exacerbated in high-latitude winters.

Active learning narrows achievement gaps for underrepresented students in undergraduate science, technology, engineering, and math.

We tested the hypothesis that underrepresented students in active-learning classrooms experience narrower achievement gaps than underrepresented students in traditional lecturing classrooms, averaged across all science, technology, engineering, and mathematics (STEM) fields and courses. We conducted a comprehensive search for both published and unpublished studies that compared the performance of underrepresented students to their overrepresented classmates in active-learning and traditional-lecturing treatments. This search resulted in data on student examination scores from 15 studies (9,238 total students) and data on student failure rates from 26 studies (44,606 total students). Bayesian regression analyses showed that on average, active learning reduced achievement gaps in examination scores by 33% and narrowed gaps in passing rates by 45%. The reported proportion of time that students spend on in-class activities was important, as only classes that implemented high-intensity active learning narrowed achievement gaps. Sensitivity analyses showed that the conclusions are robust to sampling bias and other issues. To explain the extensive variation in efficacy observed among studies, we propose the heads-and-hearts hypothesis, which holds that meaningful reductions in achievement gaps only occur when course designs combine deliberate practice with inclusive teaching. Our results support calls to replace traditional lecturing with evidence-based, active-learning course designs across the STEM disciplines and suggest that innovations in instructional strategies can increase equity in higher education.

Real-time mobile monitoring of bipolar disorder: a review of evidence and future directions.

Rapidly accumulating data from mobile assessments are facilitating our ability to track patterns of emotions, behaviors, biologic rhythms, and their contextual influences in real time. These approaches have been widely applied to study the core features, traits, changes in states, and the impact of treatments in bipolar disorder (BD). This paper reviews recent evidence on the application of both passive and active mobile technologies to gain insight into the role of the circadian system and patterns of sleep and motor activity in people with BD. Findings of more than two dozen studies converge in demonstrating a broad range of sleep disturbances, particularly longer duration and variability of sleep patterns, lower average and greater variability of motor activity, and a shift to later peak activity and sleep midpoint, indicative of greater evening orientation among people with BD. The strong associations across the domains tapped by real-time monitoring suggest that future research should shift focus on sleep, physical/motor activity, or circadian patterns to identify common biologic pathways that influence their interrelations. The development of novel data-driven functional analytic tools has enabled the derivation of individualized multilevel dynamic representations of rhythms of multiple homeostatic regulatory systems. These multimodal tools can inform clinical research through identifying heterogeneity of the manifestations of BD and provide more objective indices of treatment response in real-world settings. Collaborative efforts with common protocols for the application of multimodal sensor technology will facilitate our ability to gain deeper insight into mechanisms and multisystem dynamics, as well as environmental, physiologic, and genetic correlates of BD.

Moonstruck sleep: Synchronization of human sleep with the moon cycle under field conditions.

Before the availability of artificial light, moonlight was the only source of light sufficient to stimulate nighttime activity; still, evidence for the modulation of sleep timing by lunar phases is controversial. Here, we use wrist actimetry to show a clear synchronization of nocturnal sleep timing with the lunar cycle in participants living in environments that range from a rural setting with and without access to electricity in indigenous Toba/Qom communities in Argentina to a highly urbanized postindustrial setting in the United States. Our results show that sleep starts later and is shorter on the nights before the full moon when moonlight is available during the hours following dusk. Our data suggest that moonlight likely stimulated nocturnal activity and inhibited sleep in preindustrial communities and that access to artificial light may emulate the ancestral effect of early-night moonlight.

Afternoon School Start Times Are Associated with a Lack of Both Social Jetlag and Sleep Deprivation in Adolescents.

The delayed circadian timing of adolescents creates a conflict with early school start times (SSTs). We used wrist actimetry to compare sleep parameters and routine nighttime activities in middle school students attending either a morning (0700 to 1200 h) or an afternoon (1230 to 1730 h) school shift. On school days, students from both shifts (n = 21 for morning shift, n = 20 for afternoon shift, ages 12-14 years) had a similar sleep onset, but morning-shift students had an earlier sleep offset and a 1 h 45 min shorter sleep duration than their afternoon peers, who slept the recommended 8 to 10 h of daily sleep. Only morning-shift students had afternoon naps, but this afternoon sleep was not sufficient to overcome sleep deprivation. On weekends, sleep onsets and offsets did not differ between shifts. Because only morning-shift students woke up later and slept longer (2 h 3 min) on weekends, they were also the only ones who experienced social jetlag. Daily surveys on their nighttime (from 1800 to 0600 h) activities indicated there was no difference between shifts in the time spent on leisure or using electronic media during school days, but students from both shifts spent more time in these activities during the weekend. Our study confirms that early SST in adolescents is associated with sleep deprivation and suggests that schedules that start much later than typically considered may be needed to eliminate sleep deprivation in adolescents.

Association of Outdoor Artificial Light at Night With Mental Disorders and Sleep Patterns Among US Adolescents.

Importance: Indoor nighttime light exposure influences sleep and circadian rhythms and is known to affect mood-associated brain circuits in animals. However, little is known about the association between levels of nighttime outdoor light and sleep and mental health in the population, especially among adolescents. Objective: To estimate associations of outdoor artificial light at night (ALAN) with sleep patterns and past-year mental disorder among US adolescents. Design, Setting, and Participants: This population-based, cross-sectional study of US adolescents used the National Comorbidity Survey-Adolescent Supplement, a nationally representative cross-sectional survey conducted from February 2001 through January 2004. A probability sample of adolescents aged 13 to 18 years was included. Analyses were conducted between February 2019 and April 2020. Exposures: Levels of outdoor ALAN, measured by satellite, with means calculated within census block groups. ALAN values were transformed into units of radiance (nW/cm2/sr). Main Outcomes and Measures: Self-reported habitual sleep patterns (weeknight bedtime, weeknight sleep duration, weekend bedtime delay, and weekend oversleep) and past-year mood, anxiety, behavior, and substance use disorders, measured via an in-person structured diagnostic interview. Parent-reported information was included in behavior disorder diagnoses. Results: Among 10 123 adolescents (4953 boys [51.3%]; mean [SE] age, 15.2 [0.06] years [weighted]; 6483 for behavior disorder outcomes), ALAN was positively associated with indicators of social disadvantage, such as racial/ethnic minority status (median [IQR] ALAN: white adolescents, 12.96 [30.51] nW/cm2/sr; Hispanic adolescents: 38.54 [47.84] nW/cm2/sr; non-Hispanic black adolescents: 37.39 [51.88] nW/cm2/sr; adolescents of other races/ethnicities: 30.94 [49.93] nW/cm2/sr; P < .001) and lower family income (median [IQR] ALAN by family income-to-poverty ratio ≤1.5: 26.76 [52.48] nW/cm2/sr; >6: 21.46 [34.38] nW/cm2/sr; P = .005). After adjustment for several sociodemographic characteristics, as well as area-level population density and socioeconomic status, this study found that higher ALAN levels were associated with later weeknight bedtime, and those in the lowest quartile of ALAN reported the longest weeknight sleep duration. Those in the highest quartile of ALAN went to bed 29 (95% CI, 15-43) minutes later and reported 11 (95% CI, 19-2) fewer minutes of sleep than those in the lowest quartile. ALAN was also positively associated with prevalence of past-year mood and anxiety disorder: each median absolute deviation increase in ALAN was associated with 1.07 (95% CI, 1.00-1.14) times the odds of mood disorder and 1.10 (95% CI, 1.05-1.16) times the odds of anxiety disorder. Further analyses revealed associations with bipolar disorder (odds ratio [OR], 1.19 [95% CI, 1.05-1.35]), specific phobias (OR, 1.18 [95% CI, 1.11-1.26]), and major depressive disorder or dysthymia (OR, 1.07 [95% CI, 1.00-1.15]). Among adolescent girls, differences in weeknight bedtime by ALAN (third and fourth quartiles vs first quartile) were greater with increasing years since menarche (F3, 8.15; P < .001). Conclusions and Relevance: In this study, area-level outdoor ALAN was associated with less favorable sleep patterns and mood and anxiety disorder in adolescents. Future studies should elucidate whether interventions to reduce exposure to ALAN may positively affect mental and sleep health.

Sleepmore in Seattle: Later school start times are associated with more sleep and better performance in high school students.

Most teenagers are chronically sleep deprived. One strategy proposed to lengthen adolescent sleep is to delay secondary school start times. This would allow students to wake up later without shifting their bedtime, which is biologically determined by the circadian clock, resulting in a net increase in sleep. So far, there is no objective quantitative data showing that a single intervention such as delaying the school start time significantly increases daily sleep. The Seattle School District delayed the secondary school start time by nearly an hour. We carried out a pre-/post-research study and show that there was an increase in the daily median sleep duration of 34 min, associated with a 4.5% increase in the median grades of the students and an improvement in attendance.

Influence of temperature on daily locomotor activity in the crab Uca pugilator.

Animals living in the intertidal zone are exposed to prominent temperature changes. To cope with the energetic demands of environmental thermal challenges, ectotherms rely mainly on behavioral responses, which may change depending on the time of the day and seasonally. Here, we analyze how temperature shapes crabs' behavior at 2 different times of the year and show that a transition from constant cold (13.5°C) to constant warm (17.5°C) water temperature leads to increased locomotor activity levels throughout the day in fiddler crabs (Uca pugilator) collected during the summer. In contrast, the same transition in environmental temperature leads to a decrease in the amplitude of the daily locomotor activity rhythm in crabs collected during the winter. In other words, colder temperatures during the cold season favor a more prominent diurnal behavior. We interpret this winter-summer difference in the response of daily locomotor activity to temperature changes within the framework of the circadian thermoenergetics hypothesis, which predicts that a less favorable energetic balance would promote a more diurnal activity pattern. During the winter, when the energetic balance is likely less favorable, crabs would save energy by being more active during the expected high-temperature phase of the day-light phase-and less during the expected low-temperature phase of the day-dark phase. Our results suggest that endogenous rhythms in intertidal ectotherms generate adaptive behavioral programs to cope with thermoregulatory demands of the intertidal habitat.