Examining the structure validity of the Pittsburgh Sleep Quality Index among female workers during New Zealand's initial COVID-19 lockdown.

Sleep is important for good physical and mental health. The COVID-19 pandemic lockdown created a unique context that impacted psychological and social drivers for sleeping well. The Pittsburgh Sleep Quality Index (PSQI) is a widely used measurement tool assessing subjective sleep quality. The traditional model of the PSQI (a one-factor model), whilst validated and used across different populations, has also been questioned with regards to data fit and representativeness of its global score in different social and work-related circumstances. Examination of the structure validity of the PSQI in the unique context of the pandemic has been scarce. This study determined the PSQI structure validity amongst employed women considered to experience increased stressors during the pandemic lockdown. The subjectively reported PSQI data from 498 female workers (mean age 44.6 years) collected during New Zealand's first national COVID-19 lockdown (April, 2020) was used. Confirmatory factor analyses compared the original one-factor model of the PSQI with the two- and three-factor models used by Jia et al. (2019) within this pandemic context. Results showed that the two-factor model provided a superior fit of the PSQI data compared to the original one-factor or a three-factor model. These findings suggest that a sub-score of the PSQI with two factors appears to be better at describing the sleep quality of healthy working women during the constrained situation of the pandemic lockdown compared to a single global sleep quality score. This indicates the importance of considering the validity of subjective sleep measures when used within unique social contexts and stressors.

Ultradian sleep cycles: Frequency, duration, and associations with individual and environmental factors-A retrospective study.

OBJECTIVE: Sleep varies between individuals in response to sleep-wake history and various environmental factors, including light and noise. Here we report on the intranight variation of the ultradian nonrapid eye movement-rapid eye movement (NREM-REM) sleep cycle in 369 participants who have contributed to different laboratory studies from 1994 to 2020 at the Centre for Chronobiology, Basel, Switzerland. RESULTS: We observed a large interindividual variability in sleep cycle duration, including NREM and REM sleep episodes in healthy participants who were given an 8-hour sleep opportunity at habitual bedtime in controlled laboratory settings. The median sleep cycle duration was 96 minutes out of 6064 polysomnographically-recorded cycles. The number and duration of cycles were not normally distributed, and the distribution became narrower for NREM sleep and wider for REM sleep later in the night. The first cycle was consistently shorter than subsequent cycles, and moderate presleep light or nocturnal noise exposure had no significant effects on ultradian sleep cycle duration. Age and sex significantly affected NREM and REM sleep duration, with older individuals having longer NREM and shorter REM sleep particularly in the end of the night, and females having longer NREM sleep episodes. High sleep pressure (ie, sleep deprivation) and low sleep pressure (ie, multiple naps) altered ultradian sleep cycles, with high sleep pressure leading to longer NREM sleep in the first cycle, and low sleep pressure leading to longer REM sleep episodes. Positive correlations were observed between N2 and NREM duration, and between N1 and REM duration. Weak intrasleep REM sleep homeostasis was also evident in our data set. CONCLUSIONS: We conclude that ultradian sleep cycles are endogenous biological rhythms modulated by age, sex, and sleep homeostasis, but not directly responsive to (moderate levels of) environmental cues in healthy good sleepers.

Circadian- and wake-dependent influences on face-name memory in healthy men and women over 3weeks of chronic sleep restriction.

OBJECTIVES: Facial recognition is one of the key functions of the human brain, and linking a face to a name is critical in many social and occupational settings. This study assessed circadian- and wake-dependent effects on face-name recognition in healthy adults. METHODS: Thirteen healthy adults (20-70years; 7 F) were studied in a 39-day inpatient protocol that included 3weeks of 28 hours forced desynchrony with sleep restriction (6.5:21.5 hours sleep:wake). Starting 3 hours after scheduled wake, 6 novel face-name pairs were presented every 4 waking hours; recognition was tested 2 hours later. Performance data were averaged across ∼4 hours circadian phase or time-awake bins. RESULTS: Face-name recognition deteriorated with increased time awake (p < .0001) and exhibited significant circadian variation (p < .0001), with worst performance shortly after the core temperature nadir. There was a significant interaction between sex and circadian phase (p = .0177), with women performing significantly better than men at all circadian phases except 60° and 120°. Women exhibited a significantly higher amplitude than men during the third week of forced desynchrony (p < .01). CONCLUSIONS: Like many other aspects of neurobehavioral performance, recalling face-name associations is impacted by both duration of time awake and circadian phase. These results have implications for face recognition testing in medical contexts, such as in testing for dementia, because performance may be impacted by sleep deficiency and the time of testing.

Preliminary evidence that daily light exposure enhances the antibody response to influenza vaccination in patients with dementia.

Enhancing lighting conditions in institutions for individuals with dementia improves their sleep, circadian rhythms and well-being. Here, we report first findings that exposure to brighter light during daytime may support the immune response to the annual influenza vaccination. Eighty older institutionalised patients suffering from dementia (54 women and 26 men) continuously wore an activity tracker for 8 weeks to assess individual light exposure and rest-activity cycles. We analysed the patients' immune response from two blood samples taken before and 4 weeks after the annual influenza vaccination. Individual antibody concentrations to three influenza virus strains (H3N2, H1N1, IB) were quantified via hemagglutination inhibition assays. By quantifying individual light exposure profiles (including daylight), we classified the patients into a low and a high light exposure group based on a median illuminance of 392.6 lux. The two light exposure groups did not differ in cognitive impairment severity, age or gender distribution. However, patients in the high light exposure group showed a significantly greater circadian rest-activity amplitude (i.e., more daytime activity and less nighttime activity) along with a significantly greater antibody titer increase to the H3N2 vaccine than patients in the low light exposure group, despite similar pre-vaccination concentrations. Sufficient seroprotective responses to all three influenza virus strains were attained for ≥75% of participants. These data provide preliminary evidence for a potentially enhanced immune response in patients with dementia when they received more daily light. Future studies are needed to determine whether regular daily light exposure may have beneficial effects on the human immune system, either directly or via a stabilising circadian sleep-wake rhythms.

Sleeping in a bubble: factors affecting sleep during New Zealand's COVID-19 lockdown.

New Zealand (NZ) enforced a rigorous lockdown in response to the outbreak of COVID-19 in 2020. Infection rates remained remarkably low, yet social and personal routines were affected. Factors associated with reporting worsening sleep were explored using an anonymous online survey launched during New Zealand's 2020 lockdown. Participants were 723 adults aged 20-85 years (median: 45 years, 82% women). Bed and wake times occurred significantly later compared to pre-lockdown estimates and resulted in shorter social jetlag (15 min). During lockdown, 54.5% were identified as "poor sleepers" [i.e. score > 5 on the Pittsburgh Sleep Quality Index (PSQI)]. Overall, 45% rated their sleep quality to worsen compared to pre-lockdown, 22% reported an improvement. Reports of worsening sleep were significantly related to increased sleep latency, reduced sleep efficiency, and heightened PSQI scores compared to those with better sleep or no change. Subjectively worse sleep was significantly associated with less time engaging in physical activity, less exposure to daylight, and social interactions compared to pre-lockdown estimates (p < .05). Logistic regression models identified significant relationships between having more vivid dreams and worsening sleep. Worse sleepers also had increased likelihoods of reporting poorer mood and they also scored higher for anxiety compared to those with no change or improved sleep during lockdown (p < .05). Pandemic-related restrictions contributed to poorer self-reported sleep which was linked to deterioration of mood. Negative affect was comparatively lower than reported elsewhere. These findings provide unique insights to the psychosocial impact of the initial COVID-19 lockdown in New Zealand, where the disease outbreak remained low.

Chronotype Differences in Body Composition, Dietary Intake and Eating Behavior Outcomes: A Scoping Systematic Review.

The timing and nutritional composition of food intake are important zeitgebers for the biological clocks in humans. Thus, eating at an inappropriate time (e.g., during the night) may have a desynchronizing effect on the biological clocks and, in the long term, may result in adverse health outcomes (e.g., weight gain, obesity, and poor metabolic function). Being a very late or early chronotype not only determines preferred sleep and wake times but may also influence subsequent mealtimes, which may affect the circadian timing system. In recent years, an increased number of studies have examined the relation between chronotype and health outcomes, with a main focus on absolute food intake and metabolic markers and, to a lesser extent, on dietary intake distribution and eating behavior. Therefore, this review aimed to systematically determine whether chronotype indirectly affects eating behaviors, dietary intake (timing, choice, nutrients), and biomarkers leading to body composition outcomes in healthy adults. A systematic literature search on electronic databases (PubMed, CINAHL, MEDLINE, SCOPUS, Cochrane library) was performed (International Prospective Register of Systematic Reviews number: CRD42020219754). Only studies that included healthy adults (aged >18 y), classified according to chronotype and body composition profiles, using outcomes of dietary intake, eating behavior, and/or biomarkers, were considered. Of 4404 articles, 24 met the inclusion criteria. The results revealed that late [evening type (ET)] compared with early [morning type (MT)] chronotypes were more likely to be overweight/obese with poorer metabolic health. Both MT and ET had similar energy and macronutrient intakes, consuming food during their preferred sleep-wake timing: later for ET than MT. Most of the energy and macronutrient intakes were distributed toward nighttime for ET and exacerbated by unhealthy eating behaviors and unfavorable dietary intakes. These findings from our systematic review give further insight why higher rates of overweight/obesity and unhealthier metabolic biomarkers are more likely to occur in ET.

Optimized office lighting advances melatonin phase and peripheral heat loss prior bedtime.

Improving indoor lighting conditions at the workplace has the potential to support proper circadian entrainment of hormonal rhythms, sleep, and well-being. We tested the effects of optimized dynamic daylight and electric lighting on circadian phase of melatonin, cortisol and skin temperatures in office workers. We equipped one office room with an automated controller for blinds and electric lighting, optimized for dynamic lighting (= Test room), and a second room without any automated control (= Reference room). Young healthy participants (n = 34) spent five consecutive workdays in each room, where individual light exposure data, skin temperatures and saliva samples for melatonin and cortisol assessments were collected. Vertical illuminance in the Test room was 1177 ± 562 photopic lux (mean ± SD) , which was 320 lux higher than in the Reference room (p < 0.01). Melanopic equivalent daylight (D65) illuminance was 931 ± 484 melanopic lux in the Test room and 730 ± 390 melanopic lux in the Reference room (p < 0.01). Individual light exposures resulted in a 50 min earlier time of half-maximum accumulated illuminance in the Test than the Reference room (p < 0.05). The melatonin secretion onset and peripheral heat loss in the evening occurred significantly earlier with respect to habitual sleeptime in the Test compared to the Reference room (p < 0.05). Our findings suggest that optimized dynamic workplace lighting has the potential to promote earlier melatonin onset and peripheral heat loss prior bedtime, which may be beneficial for persons with a delayed circadian timing system.

Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults.

Ocular light exposure has important influences on human health and well-being through modulation of circadian rhythms and sleep, as well as neuroendocrine and cognitive functions. Prevailing patterns of light exposure do not optimally engage these actions for many individuals, but advances in our understanding of the underpinning mechanisms and emerging lighting technologies now present opportunities to adjust lighting to promote optimal physical and mental health and performance. A newly developed, international standard provides a SI-compliant way of quantifying the influence of light on the intrinsically photosensitive, melanopsin-expressing, retinal neurons that mediate these effects. The present report provides recommendations for lighting, based on an expert scientific consensus and expressed in an easily measured quantity (melanopic equivalent daylight illuminance (melaponic EDI)) defined within this standard. The recommendations are supported by detailed analysis of the sensitivity of human circadian, neuroendocrine, and alerting responses to ocular light and provide a straightforward framework to inform lighting design and practice.

Reply to Bracke et al. Comment on "Prayag et al. Light Modulation of Human Clocks, Wake, and Sleep. Clocks&Sleep 2019, 1, 193-208".

We thank Bracke and colleagues [...].

The relevance of daylight for humans.

Daylight is ubiquitous and is crucial for mammalian vision as well as for non-visual input to the brain via the intrinsically photosensitive retinal ganglion cells (ipRGCs) that express the photopigment melanopsin. The ipRGCs project to the circadian clock in the suprachiasmatic nuclei and thereby ensure entrainment to the 24-hour day-night cycle, and changes in daylength trigger the appropriate seasonal behaviours. The ipRGCs also project to the perihabenular nucleus and surrounding brain regions that modulate mood, stress and learning in animals and humans. Given that light has strong direct effects on mood, cognition, alertness, performance, and sleep, light can be considered a "drug" to treat many clinical conditions. Light therapy is already well established for winter and other depressions and circadian sleep disorders. Beyond visual and non-visual effects via the retina, daylight contributes to prevent myopia in the young by its impact on eye development, and is important for Vitamin D synthesis and bone health via the skin. The sun is the most powerful light source and, dependent on dose, its ultraviolet radiance is toxic for living organisms and can be used as a disinfectant. Most research involves laboratory-based electric light, without the dynamic and spectral changes that daylight undergoes moment by moment. There is a gap between the importance of daylight for human beings and the amount of research being done on this subject. Daylight is taken for granted as an environmental factor, to be enjoyed or avoided, according to conditions. More daylight awareness in architecture and urban design beyond aesthetic values and visual comfort may lead to higher quality work and living environments. Although we do not yet have a factual basis for the assumption that natural daylight is overall "better" than electric light, the environmental debate mandates serious consideration of sunlight not just for solar power but also as biologically necessary for sustainable and healthy living.

The Role of Daylight for Humans: Gaps in Current Knowledge.

Daylight stems solely from direct, scattered and reflected sunlight, and undergoes dynamic changes in irradiance and spectral power composition due to latitude, time of day, time of year and the nature of the physical environment (reflections, buildings and vegetation). Humans and their ancestors evolved under these natural day/night cycles over millions of years. Electric light, a relatively recent invention, interacts and competes with the natural light-dark cycle to impact human biology. What are the consequences of living in industrialised urban areas with much less daylight and more use of electric light, throughout the day (and at night), on general health and quality of life? In this workshop report, we have classified key gaps of knowledge in daylight research into three main groups: (I) uncertainty as to daylight quantity and quality needed for "optimal" physiological and psychological functioning, (II) lack of consensus on practical measurement and assessment methods and tools for monitoring real (day) light exposure across multiple time scales, and (III) insufficient integration and exchange of daylight knowledge bases from different disciplines. Crucial short and long-term objectives to fill these gaps are proposed.

Sleep Restriction With Circadian Disruption Negatively Alter Bone Turnover Markers in Women.

PURPOSE: The purpose of this work is to determine whether an uncoupling of bone turnover markers (BTMs) occurs in women exposed to the combination of sleep restriction with circadian disruption (SRCD), as previously reported in men. METHODS: Four bone biomarkers (N-terminal propeptide of type I procollagen [P1NP] and osteocalcin = bone formation; C-telopeptide [CTX] = bone resorption; sclerostin = bone formation inhibitor) were measured in bihourly samples over 24 hours at baseline and after approximately 3 weeks of sleep restriction (~5.6 hours of sleep/24 hours) with concurrent circadian disruption (SRCD, recurring 28-hour "day" in dim light). Maximum likelihood estimation in a repeated-measures model was used to assess the effects of SRCD and age on bone biomarkers. RESULTS: Five women were young (22 ±â€…2.8 years) and four were older (58 ±â€…1.8 years). Baseline bone biomarker levels did not differ by age (all P ≥ .07). Bone formation markers were lower after SRCD (estimate ±â€…SEE, ΔP1NP = -9.5 ±â€…2.8 µg/L, P = .01; Δosteocalcin = -2.3 ±â€…0.9 ng/mL, P = .04). The P1NP decline was greater in young women (ΔP1NP = -12.9 ±â€…3.7 µg/L, P = .01). After SRCD, CTX was significantly higher in young women (0.182 ±â€…0.069 ng/mL, P = .04) but did not change in older women. CONCLUSIONS: These pilot data are similar to previous findings in men and suggest that SRCD negatively altered bone metabolism in women by decreasing markers of bone formation and, in young women, increasing a marker of bone resorption. If sustained, this pattern of BTM uncoupling may lead to bone loss and lower bone mineral density.

Can Extra Daytime Light Exposure Improve Well-Being and Sleep? A Pilot Study of Patients With Glaucoma.

Glaucoma damages retinal ganglion cells, including intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells modulate various non-visual physiological and psychological functions which are modulated by light. In patients with glaucoma, we assessed the effect of daily bright light exposure (LE) on several melanopsin-dependent functions, such as the pupil constriction, circadian rest-activity cycles, sleep and subjective well-being including relaxation, alertness and mood. Twenty patients participated in the study (9 women, 11 men, mean age = 67.6 ± 7.5 y). Pupillometry was performed before the LE weeks and repeated on the last day of LE. The post-illumination pupil response (PIPR) was calculated as a proxy for melanopsin-dependent activation. Participants continuously wore an activity monitor and self-assessed sleep quality, well-being and visual comfort for 7 days before and during 4 weeks of daily bright LE (30 min to 10,000 lux polychromatic bright white light). After the LE, there was a significantly greater PIPR and higher subjective sleep quality when compared to the pre-LE week (p < 0.05), but no significant changes in 24-h rhythms or sleep parameters. A greater PIPR was correlated with an increase in circadian amplitude and higher inter-daily stability (derived from rest-activity cycles; p < 0.05). In a small group of patients with glaucoma, scheduled daily bright light exposure could improve subjective sleep quality. These findings highlight the importance to evaluate and maintain non-visual functions at different levels in patients with progressive loss of ipRGCs.

Effects of a dawn-dusk simulation on circadian rest-activity cycles, sleep, mood and well-being in dementia patients.

Light is the most powerful "zeitgeber" signal to synchronize circadian sleep-wake cycles. In dementia, these rhythms are often fragmented - probably due to loss of neuronal function of the suprachiasmatic nuclei (the biological "master clock" in the brain) and/or weakness of external zeitgebers. We investigated the effects of a prototype dawn-dusk simulator (DDS) on circadian rest-activity cycles, sleep, mood and well-being in a balanced crossover design during fall and winter in 20 institutionalized patients with dementia (86 ±â€¯6 y, 17 f). All participants had one baseline week followed by exposure to individually timed DDS over their beds for 7-8 weeks. They spent 8 weeks without DDS as a control. Mood, self-reliant daily activity, social behavior, agitation, and quality of life were assessed by standardized questionnaires and visual analogue scales, regularly rated by trained caregivers. Circadian and sleep characteristics of their rest-activity cycles were analyzed by actimetry over 17 weeks. DDS exposure led to significantly better mood in the morning hours after waking. The effects were most pronounced in the second 4 weeks with DDS, indicating that positive effects emerged gradually. Differences in circadian rest-activity cycles and sleep were mainly age-dependent. We found statistically significant correlations between measures of higher quality of life and better mood, greater alertness and circadian rhythm stability. We conclude that continuous, long-term application of dawn-dusk simulation at the sleep-wake transitions appears to increase external zeitgeber strength in institutionalized patients with dementia. The DDS may provide an effective, non-invasive tool to improve mood and ameliorate patients' quality of life.

Living in Biological Darkness: Objective Sleepiness and the Pupillary Light Responses Are Affected by Different Metameric Lighting Conditions during Daytime.

Nighttime melatonin suppression is the most commonly used method to indirectly quantify acute nonvisual light effects. Since light is the principal zeitgeber in humans, there is a need to assess its strength during daytime as well. This is especially important since humans evolved under natural daylight but now often spend their time indoors under artificial light, resulting in a different quality and quantity of light. We tested whether the pupillary light response (PLR) could be used as a marker for nonvisual light effects during daytime. We also recorded the wake electroencephalogram to objectively determine changes in daytime sleepiness between different illuminance levels and/or spectral compositions of light. In total, 72 participants visited the laboratory 4 times for 3-h light exposures. All participants underwent a dim-light condition and either 3 metameric daytime light exposures with different spectral compositions of polychromatic white light (100 photopic lux, peak wavelengths at 435 nm or 480 nm, enriched with longer wavelengths of light) or 3 different illuminances (200, 600, and 1200 photopic lux) with 1 metameric lighting condition (peak wavelength at 435 nm or 480 nm; 24 participants each). The results show that the PLR was sensitive to both spectral differences between metameric lighting conditions and different illuminances in a dose-responsive manner, depending on melanopic irradiance. Objective sleepiness was significantly reduced, depending on melanopic irradiance, at low illuminance (100 lux) and showed fewer differences at higher illuminance. Since many people are exposed to such low illuminance for most of their day-living in biological darkness-our results imply that optimizing the light spectrum could be important to improve daytime alertness. Our results suggest the PLR as a noninvasive physiological marker for ambient light exposure effects during daytime. These findings may be applied to assess light-dependent zeitgeber strength and evaluate lighting improvements at workplaces, schools, hospitals, and homes.

Chronotype Genetic Variant in PER2 is Associated with Intrinsic Circadian Period in Humans.

The PERIOD2 (PER2) gene is a core molecular component of the circadian clock and plays an important role in the generation and maintenance of daily rhythms. Rs35333999, a missense variant of PER2 common in European populations, has been shown to associate with later chronotype. Chronotype relates to the timing of biological and behavioral activities, including when we sleep, eat, and exercise, and later chronotype is associated with longer intrinsic circadian period (cycle length), a fundamental property of the circadian system. Thus, we tested whether this PER2 variant was associated with circadian period and found significant associations with longer intrinsic circadian period as measured under forced desynchrony protocols, the 'gold standard' for intrinsic circadian period assessment. Minor allele (T) carriers exhibited significantly longer circadian periods when determinations were based on either core body temperature or plasma melatonin measurements, as compared to non-carriers (by 12 and 11 min, respectively; accounting for ~7% of inter-individual variance). These findings provide a possible underlying biological mechanism for inter-individual differences in chronotype, and support the central role of PER2 in the human circadian timing system.

Light Modulation of Human Clocks, Wake, and Sleep.

Light, through its non-imaging forming effects, plays a dominant role on a myriad of physiological functions, including the human sleep-wake cycle. The non-image forming effects of light heavily rely on specific properties such as intensity, duration, timing, pattern, and wavelengths. Here, we address how specific properties of light influence sleep and wakefulness in humans through acute effects, e.g., on alertness, and/or effects on the circadian timing system. Of critical relevance, we discuss how different characteristics of light exposure across the 24-h day can lead to changes in sleep-wake timing, sleep propensity, sleep architecture, and sleep and wake electroencephalogram (EEG) power spectra. Ultimately, knowledge on how light affects sleep and wakefulness can improve light settings at home and at the workplace to improve health and well-being and optimize treatments of chronobiological disorders.

Young adults are more vulnerable to chronic sleep deficiency and recurrent circadian disruption than older adults.

More than a third of US adults report fewer than 6 hours of sleep a night, making chronic sleep restriction a growing public health concern. Sleep curtailment is associated with an increase in industrial accidents, motor vehicle accidents, medical and other occupational errors. Young adults are more vulnerable to acute sleep deprivation than older adults, but less is known about how young vs. older adults respond to the more commonly experienced chronic sleep restriction. To test the hypothesis that young adults are more vulnerable to chronic sleep loss than older adults, we compared data from young and older adults who underwent three weeks of chronic sleep restriction (equivalent to 5.6 hours/24 hours) combined with recurrent circadian disruption in an experiment that enabled us to separate the influences of the sleep-wake homeostatic process, the circadian timing system, and the chronic sleep deficit. We found that while young and older adults reported similar levels of subjective sleepiness, objective measures of sleepiness revealed that young adults were more vulnerable and had more attentional failures than the older adults. These results have important public health implications, particularly related to prevention of sleep-related motor vehicle crashes in young drivers. Further research is needed to understand the neurobiological basis of these age-related differences.

The alerting effect of the wake maintenance zone during 40 hours of sleep deprivation.

Under entrained conditions, the accumulation of homeostatic sleep pressure in the evening is opposed by a strong circadian arousal signal prior to the dim light melatonin onset, called the Wake Maintenance Zone (WMZ). This study aimed at investigating the impact of the WMZ on different cognitive performance tests, as well as on subjective and objective sleepiness. Twelve young male participants completed a constant routine protocol with 40 h of extended wakefulness that included two WMZs. Cognitive tests and saliva samples were assessed hourly, while the electroencephalogram (EEG) was recorded continuously. Participants improved in cognitive response inhibition during WMZ1 (13.5 h awake) and sustained attention during WMZ2 (37.5 h awake), but not in higher executive function tests. There were significant EEG power density reductions in the delta/theta frequency range during WMZ1 and in delta/theta, alpha, and sigma/beta ranges during WMZ2, with a greater change in the sigma/beta range during WMZ2 compared to WMZ1. EEG power reductions coincided during WMZ1 with stable subjective sleepiness and sustained attention. During WMZ2, EEG power reductions were more pronounced and coincided with improved sustained attention. Our results suggest the circadian arousal signal in the evening differently modulates cognitive functions and EEG power depending on the duration of prior wakefulness.