Article

Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle

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Abstract

The electric light is one of the most important human inventions. Sleep and other daily rhythms in physiology and behavior, however, evolved in the natural light-dark cycle [1], and electrical lighting is thought to have disrupted these rhythms. Yet how much the age of electrical lighting has altered the human circadian clock is unknown. Here we show that electrical lighting and the constructed environment is associated with reduced exposure to sunlight during the day, increased light exposure after sunset, and a delayed timing of the circadian clock as compared to a summer natural 14 hr 40 min:9 hr 20 min light-dark cycle camping. Furthermore, we find that after exposure to only natural light, the internal circadian clock synchronizes to solar time such that the beginning of the internal biological night occurs at sunset and the end of the internal biological night occurs before wake time just after sunrise. In addition, we find that later chronotypes show larger circadian advances when exposed to only natural light, making the timing of their internal clocks in relation to the light-dark cycle more similar to earlier chronotypes. These findings have important implications for understanding how modern light exposure patterns contribute to late sleep schedules and may disrupt sleep and circadian clocks.

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... Because we are operating under conditions far removed from how our internal timing systems evolved, Wright and colleagues sought to determine how the age of electronics has affected our circadian clocks (533). To accomplish this goal, Wright and his team examined light exposure, sleep, circadian activity, and melatonin profiles in participants during one week of their typical routines under artificial light exposure followed by one week of outdoor camping in the Rocky Mountains of Colorado with exposure only to natural light (533). ...
... Because we are operating under conditions far removed from how our internal timing systems evolved, Wright and colleagues sought to determine how the age of electronics has affected our circadian clocks (533). To accomplish this goal, Wright and his team examined light exposure, sleep, circadian activity, and melatonin profiles in participants during one week of their typical routines under artificial light exposure followed by one week of outdoor camping in the Rocky Mountains of Colorado with exposure only to natural light (533). As expected, relative to outdoor conditions, electrical lighting was associated with reduced exposure to sunlight during the day and increased lighting exposure after sunset. ...
... Remarkably, after just 1 week of camping, the onset of melatonin secretion started around sunset with sleep onset advancing around 1.2 h. This outdoor light exposure also led to comparable advancement of melatonin offset just after sunrise and earlier awakening (533). This first study was conducted in the summer and the authors wondered if people experience similar benefits of natural lighting in winter and whether the circadian system is sensitive to seasonal changes in lighting as seen in nonhuman species. ...
Chapter
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Circadian rhythms are endogenously generated, daily patterns of behavior and physiology that are essential for optimal health and disease prevention. Disruptions to circadian timing are associated with a host of maladies, including metabolic disease and obesity, diabetes, heart disease, cancer, and mental health disturbances. The circadian timing system is hierarchically organized, with a master circadian clock located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks throughout the CNS and periphery. The SCN receives light information via a direct retinal pathway, synchronizing the master clock to environmental time. At the cellular level, circadian rhythms are ubiquitous, with rhythms generated by interlocking, autoregulatory transcription-translation feedback loops. At the level of the SCN, tight cellular coupling maintains rhythms even in the absence of environmental input. The SCN, in turn, communicates timing information via the autonomic nervous system and hormonal signaling. This signaling couples individual cellular oscillators at the tissue level in extra-SCN brain loci and the periphery and synchronizes subordinate clocks to external time. In the modern world, circadian disruption is widespread due to limited exposure to sunlight during the day, exposure to artificial light at night, and widespread use of light-emitting electronic devices, likely contributing to an increase in the prevalence, and the progression, of a host of disease states. The present overview focuses on the circadian control of endocrine secretions, the significance of rhythms within key endocrine axes for typical, homeostatic functioning, and implications for health and disease when dysregulated. © 2022 American Physiological Society. Compr Physiol 12: 1-30, 2022.
... In fact, the same camps in the past have shown improved melatonin rhythms on several days after the camp started (Noi et al. 2013). Besides, a week-long camp for adults has also been observed to advance the melatonin rhythm (Wright et al. 2013). From these facts, we infer that the participants were not forced to wake-up during the camp, but did so of their own will. ...
... However, it was reported that there is no relationship between bedtime and the seasonality of sunset in daily living environment by Homma et al. (1992). In addition, Wright et al. (2013) reported that living in an electric lighting environment is associated with delayed biological rhythms, bedtime and wake-up time compared to camp. In fact, as shown in Figure 5(c), the longer the HLE from 19:00 to 24:00, the delayer the bedtime. ...
Article
This study aimed to clarify the situation of light exposure and examine the relationship between light exposure and bedtime/wake-up time during school days (SD), holidays (HD), and a long-stay camp period (CP) in Japanese children. After data cleaning, the final subjects were 29 children (10.2 ± 1.2 years old, 25 boys and 4 girls) who participated in paid long-term camp programs in the summers of 2019 and 2021. Data on light exposure, bedtime, and wake-up time were collected. The results of the comparison of the total high-intensity light exposure (HLE) hours for each survey period confirmed
... Masking is an important topic to understand within the field of biological rhythms because it is increasingly affecting human health (e.g., increased artificial light exposure at night, decreased natural light exposure during the day, increased use of melatonin) (Hölker et al., 2010;Wright et al., 2013;Kyba and Kantermann, 2016;Li et al., 2022). Thus, masking stands to have significant deleterious effects on human health when these exogenous stimuli occur at an inappropriate time-of-day, whereas masking is capable of having significant beneficial effects on human health when these stimuli occur at an appropriate or expected time-of-day that align with other exogenous arousalpromoting or sleep-promoting stimuli. ...
... Although some steps can be taken to reduce the negative health effects on these shift workers, such as aligning circadian rhythms with activity on work days and days off, there are still costs to consider such as social isolation and reduced natural light. Wright et al. (2013) have shown that artificial light at night is harmful to the expression of circadian rhythms in humans, and that natural light exposure during the day can help strengthen entrainment. While it is most beneficial for diurnal organisms to align their behavioral profiles to be active when the sun is out, we recognize that this is not always possible. ...
Article
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Environmental cues (e.g., light-dark cycle) have an immediate and direct effect on behavior, but these cues are also capable of “masking” the expression of the circadian pacemaker, depending on the type of cue presented, the time-of-day when they are presented, and the temporal niche of the organism. Masking is capable of complementing entrainment, the process by which an organism is synchronized to environmental cues, if the cues are presented at an expected or predictable time-of-day, but masking can also disrupt entrainment if the cues are presented at an inappropriate time-of-day. Therefore, masking is independent of but complementary to the biological circadian pacemaker that resides within the brain (i.e., suprachiasmatic nucleus) when exogenous stimuli are presented at predictable times of day. Importantly, environmental cues are capable of either inducing sleep or wakefulness depending on the organism’s temporal niche; therefore, the same presentation of a stimulus can affect behavior quite differently in diurnal vs. nocturnal organisms. There is a growing literature examining the neural mechanisms underlying masking behavior based on the temporal niche of the organism. However, the importance of these mechanisms in governing the daily behaviors of mammals and the possible implications on human health have been gravely overlooked even as modern society enables the manipulation of these environmental cues. Recent publications have demonstrated that the effects of masking weakens significantly with old age resulting in deleterious effects on many behaviors, including sleep and wakefulness. This review will clearly outline the history, definition, and importance of masking, the environmental cues that induce the behavior, the neural mechanisms that drive them, and the possible implications for human health and medicine. New insights about how masking is affected by intrinsically photosensitive retinal ganglion cells, temporal niche, and age will be discussed as each relates to human health. The overarching goals of this review include highlighting the importance of masking in the expression of daily rhythms, elucidating the impact of aging, discussing the relationship between dysfunctional masking behavior and the development of sleep-related disorders, and considering the use of masking as a non-invasive treatment to help treat humans suffering from sleep-related disorders.
... In humans, greater exposure to natural sunlight and less exposure to artificial lighting are associated with internal circadian clock synchronization such that bedtime and wake times are less variable and occur earlier, closer to sunset and sunrise [9]. Harmful effects of artificial lighting have been demonstrated in both industrial [10,11] and small-scale, non-industrial contexts [12,13], with the increased reports of sleep disturbance in metropolitan settings leading many to identify an emerging sleep loss epidemic [14,15]. ...
... These findings suggest that having more environmentally-buffered sleep sites, with reduced exposure to natural light and temperature fluctuations, combined with individual exposure to the natural environment, daily outdoor activities, and/or social regulation of sleep-wake timing may also influence circadian rhythm expression. If natural sunlight and limited use of artificial lighting are important for synchronization between environmental cues and physiology [9], it follows that urbanization and technological development could explain the increase in reports of sleep disturbance in metropolitan populations [49,50]. This increase may be due to circadian disruption. ...
Article
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Sleep duration, quality, and rest-activity pattern—a measure for inferring circadian rhythm—are influenced by multiple factors including access to electricity. Recent findings suggest that the safety and comfort afforded by technology may improve sleep but negatively impact rest-activity stability. According to the circadian entrainment hypothesis, increased access to electric lighting should lead to weaker and less uniform circadian rhythms, measured by stability of rest-activity patterns. Here, we investigate sleep in a Maya community in Guatemala who are in a transitional stage of industrialization. We predicted that (i) sleep will be shorter and less efficient in this population than in industrial settings, and that (ii) rest-activity patterns will be weaker and less stable than in contexts with greater exposure to the natural environment and stronger and more stable than in settings more buffered by technologic infrastructure. Our results were mixed. Compared to more industrialized settings, in our study population sleep was 4.87% less efficient (78.39% vs 83.26%). We found no significant difference in sleep duration. Rest-activity patterns were more uniform and less variable than in industrial settings (interdaily stability = 0.58 vs 0.43; intradaily variability = 0.53 vs 0.60). Our results suggest that industrialization does not inherently reduce characteristics of sleep quality; instead, the safety and comfort afforded by technological development may improve sleep, and an intermediate degree of environmental exposure and technological buffering may support circadian rhythm strength and stability.
... For instance, the amplitude of the light-dark cycle increases when the difference between day and night becomes more pronounced (e.g., with more sunlight exposure in summer) and decreases when the line between day and night is blurred (e.g., due to increased exposure to electrical light in the evening). The CIRC predicts that with increasing amplitude of the zeitgeber cycle, the distribution of phases of entrainment within a population will become narrower, which has been confirmed by studies in humans (Beale et al., 2017;Moreno et al., 2015;Pilz et al., 2018;Wright et al., 2013) and birds (Dominoni et al., 2013). Consequently, under strong and weak zeitgeber conditions, two individuals with identical τ will assume different phases of entrainment whereas two individuals with different τ can assume the same phase. ...
... The availability of artificial light allows individuals to create their own light-dark cycles, typically increasing their exposure to light in the evening, when it is already dark outside (Goulet et al., 2007;Phillips et al., 2019). This exposure to evening light weakens the zeitgeber strength (i.e., blurring the difference between day and night), delays the circadian clock and widens the chronotype distribution, with more later chronotypes than under stronger zeitgeber conditions (Chang et al., 2015;Roenneberg et al., 2010;Wright et al., 2013). The net result is a repeated shifting of sleep times between workdays and days off, that resembles sleep-wake patterns observed for travel crossing time zones but without the simultaneous change of the external light-dark cycle. ...
Chapter
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.
... Natural daylight is usually 100 to 1000 times brighter than artificial light and a lack of exposure to natural sunlight, even with the use of electrical lighting, has been shown to alter circadian physiology and sleep behavior (Wright Jr et al. 2013). Time of awakening is additionally correlated with sunrise and tends to be later in the winter (Hashizaki et al. 2018). ...
... This increase in darkness around the time of morning awakening is a strong argument against permanent DST (Roenneberg et al. 2019a, Roenneberg et al. 2019b, Rishi et al. 2020. In the absence of schedule constraints or artificial light, humans naturally awake around or after sunrise (Wright Jr et al. 2013, Skeldon et al. 2017. A mismatch between the timing of sleep due to schedule constraints and human's natural circadian rhythmicity can result in recurrent symptoms of fatigue known as "social jetlag" (Wittmann et al. 2006, Skeldon et al. 2017, McMahon et al. 2018. ...
... Through the route, the external light stimulus regulates the human circadian system as well as other non-visual effects [7] - [13]: daylight help synchronize the human body's circadian clock to match the earth's 24-hour light-dark cycle [14], while insufficient daytime light exposure or excessive evening light can disrupt the circadian system, leading to long-term effects of increased incidence of diseases, such as sleep disorders, seasonal affective disorder (SAD), and even increased risk of cancers [15], [16]. Such circadian-disruption-related problems become even more critical in modern society as people spend increased time indoors during the daytime [17], [18]. Therefore, to help people maintain a healthy circadian rhythm, a proper management of the lighting environment is needed for desired circadian stimulus at the right time, which requires accurate quantification of the circadian effect of light. ...
Article
Full-text available
Circadian stimulus ( CS ) is a popular metric for evaluating circadian effects of light. However, the determination of its value is complicated. In this work, the possibility of developing a simplified model to accurately estimate CS values has been investigated. It is found that: i) the $CS_{2018}$ model itself has an important limitation: a very small perturbation in spectrum could result in a significant change in CS value, which fundamentally limits the development of a simplified model based on photometric or colorimetric inputs. ii) such a limitation is effectively reduced by the latest $CS_{2021}$ model, and therefore a simplified model can be developed to estimate the value of $CS_{2021}$ based on illuminance, correlated color temperature, a constraint of color rending index, and the factors of the continuous light exposure duration t and the spatial distribution of circadian light exposure f . The simplified model is developed and validated by using a comprehensive data set containing 395923 lighting spectra. The small deviations in CS value, which is less than 0.087 and 0.052 for warm and cool white light sources, respectively, show that the proposed simplified model could serve as an accurate and convenient tool for practical circadian lighting design.
... As circadian clocks are entrained by the light-dark cycle (e.g., Berson et al., 2002;Wright Jr et al., 2013;Zeng et al., 1996), light intensity is likely a very important determinant for activity patterns in the wild (see also Sockman & Hurlbert, 2020 for a discussion on the role of active daylength on migratory behavior). In great tits and blue tits, light intensity at the nest box significantly influenced emergence time and awakening time in the morning, respectively (Steinmeyer et al., 2010;Stuber et al., 2015). ...
Article
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There is increasing evidence that individuals are consistent in the timing of their daily activities, and that individual variation in temporal behavior is related to the timing of reproduction. However, it remains unclear whether observed patterns relate to the timing of the onset of activity or whether an early onset of activity extends the time that is available for foraging. This may then again facilitate reproduction. Furthermore, the timing of activity onset and offset may vary across the breeding season, which may complicate studying the above-mentioned relationships. Here, we examined in a wild population of great tits (Parus major) whether an early clutch initiation date may be related to an early onset of activity and/or to longer active daylengths. We also investigated how these parameters are affected by the date of measurement. To test these hypotheses, we measured emergence and entry time from/into the nest box as proxies for activity onset and offset in females during the egg laying phase. We then determined active daylength. Both emergence time and active daylength were related to clutch initiation date. However, a more detailed analysis showed that the timing of activities with respect to sunrise and sunset varied throughout the breeding season both within and among individuals. The observed positive relationships are hence potentially statistical artifacts. After methodologically correcting for this date effect, by using data from the pre-egg laying phase, where all individuals were measured on the same days, neither of the relationships remained significant. Taking methodological pitfalls and temporal variation into account may hence be crucial for understanding the significance of chronotypes.
... Natural and artificial lights at night affect the human circadian clock, regulating the body's perception of day and night (Boivin et al., 1996). As such, light pollution in cities has been shown to disrupt the synchronicity between the sleep-wake and day-night cycles (Wright et al., 2013). As a result, city dwellers tend to sleep later and wake up later, with plausibly shorter sleep duration (Pilz et al., 2018). ...
Article
Receiving a healthy amount of sleep is essential to one's quality of life. Both sleep-wake timing preferences (chronotype) and sleep duration are implicated in health, academic achievement, and workplace performance. This study complements the existing sleep–politics literature by examining the associations between sleep duration, chronotype, and turnout with a representative cross-national survey dataset from nine national contexts. Our analyses demonstrate that greater sleep duration is non-linearly related to higher turnout; those who sleep too little or too much are less likely to vote. The results also show that morning chronotype is associated with higher turnout, but controlling for religiosity attenuates this relationship. We argue that healthy sleep duration and chronotype lay at the intersection of the socioeconomic and psychological resources necessary to participate in elections.
... The human circadian clock system is entrained to the Earth's 24 h rotation using signals from the environment, where daylight is the most powerful signal [20][21][22][23]. Daylight has fundamental and extensive effects on the circadian system governing daily human physiology and behavior, including alertness, sleep, mood, stress, cognition, and regulation of neuroendocrine, cardiovascular, and metabolic functions [20,[24][25][26][27][28][29][30]. ...
Article
Objective Circadian rhythm disruption is commonly observed in bipolar disorder (BD). Daylight is the most powerful signal to entrain the human circadian clock system. This exploratory study investigated if solar insolation at the onset location was associated with the polarity of the first episode of BD I. Solar insolation is the amount of electromagnetic energy from the Sun striking a surface area of the Earth. Methods Data from 7488 patients with BD I were collected at 75 sites in 42 countries. The first episode occurred at 591 onset locations in 67 countries at a wide range of latitudes in both hemispheres. Solar insolation values were obtained for every onset location, and the ratio of the minimum mean monthly insolation to the maximum mean monthly insolation was calculated. This ratio is largest near the equator (with little change in solar insolation over the year), and smallest near the poles (where winter insolation is very small compared to summer insolation). This ratio also applies to tropical locations which may have a cloudy wet and clear dry season, rather than winter and summer. Results The larger the change in solar insolation throughout the year (smaller the ratio between the minimum monthly and maximum monthly values), the greater the likelihood the first episode polarity was depression. Other associated variables were being female and increasing percentage of gross domestic product spent on country health expenditures. (All coefficients: P ≤ 0.001). Conclusion Increased awareness and research into circadian dysfunction throughout the course of BD is warranted.
... Light is the most potent zeitgeber for the entrainment of human circadian rhythms [1][2][3][4]. In the past, human circadian rhythms were clearly regulated by the periodic 24 h light/dark cycle of the sun [5,6], but the introduction of electric (artificial) light in modern industrialized societies over the last two centuries has significantly altered light exposure of the population [7,8]. Many people now receive lower levels of daytime bright light [9], due to longer periods of time being spent indoors, spending up to 90% of time per day under electric lights [10][11][12]. ...
Article
Full-text available
Light therapy is used to treat sleep and circadian rhythm disorders, yet there are limited studies on whether light therapy impacts electroencephalographic (EEG) activity during sleep. Therefore, we aimed to provide an overview of research studies that examined the effects of light therapy on sleep macro- and micro-architecture in populations with sleep and circadian rhythm disorders. We searched for randomized controlled trials that used light therapy and included EEG sleep measures using MEDLINE, PubMed, CINAHL, PsycINFO and Cochrane Central Register of Controlled Trials databases. Five articles met the inclusion criteria of patients with either insomnia or delayed sleep–wake phase disorder (DSWPD). These trials reported sleep macro-architecture outcomes using EEG or polysomnography. Three insomnia trials showed no effect of the timing or intensity of light therapy on total sleep time, wake after sleep onset, sleep efficiency and sleep stage duration compared to controls. Only one insomnia trial reported significantly higher sleep efficiency after evening light therapy (>4000 lx between 21:00–23:00 h) compared with afternoon light therapy (>4000 lx between 15:00–17:00 h). In the only DSWPD trial, six multiple sleep latency tests were conducted across the day (09:00 and 19:00 h) and bright light (2500 lx) significantly lengthened sleep latency in the morning (09:00 and 11:00 h) compared to control light (300 lx). None of the five trials reported any sleep micro-architecture measures. Overall, there was limited research about the effect of light therapy on EEG sleep measures, and studies were confined to patients with insomnia and DSWPD only. More research is needed to better understand whether lighting interventions in clinical populations affect sleep macro- and micro-architecture and objective sleep timing and quality.
... Circadian rhythms of lipid metabolism are modulated by light and food [5][6][7][8][9][10][11][12][13][14][15]. Furthermore, light and the extent of the day-night intensity differences modulate chronotype, sleep parameters, and circadian alignment [24][25][26][27][28]. This also occurs in glaucoma [29]. ...
Article
Full-text available
Lipid metabolism is intimately linked to circadian mechanisms and light signaling. Deteriorated photic transduction because of retinal ganglion cell (RGC) loss occurring with glaucoma progression reduces perceived light amplitude, causing circadian disruption. To investigate associations with RGCs, total cholesterol (TC), its low-density (LDL-C) and high-density (HDL-C) fractions, and triglycerides (TG) were measured, under a controlled meal regimen, during daytime hours in 114 patients diagnosed with primary open-angle glaucoma (POAG). RGC damage was assessed by high-definition optical coherence tomography (HD-OCT). Analysis of eight clock, clock-related, and melatonin receptor gene polymorphisms was performed on 19 patients. RGC loss was associated with changes in lipid metabolism in a time-dependent manner. Morning (08:00) values of HDL-C (r = 0.613, p < 0.0001) and TG (r = 0.568, p < 0.0001) correlated positively with RGC global loss, while LDL-C at 08:00 had a weak correlation (r = 0.235; p = 0.012) but showed a strong correlation in the evening (20:00) (r = 0.533, p < 0.0001). The morning–evening gradients (MEGs, changes at 20:00 versus 08:00) in TC and LDL-C changed sign from a negative to a positive association in patients exceeding the 15% two-eye mean GLV threshold. MEG (LDL-C higher in the evening than in the morning) was positive only in POAG patients with the CLOCK_3111 TT genotype.
... Worldwide, bedtime has been delayed by a growing number of nighttime activities (Billari et al. 2018), increased nocturnal light exposure (Wright et al. 2013), increased screen time on devices (Christensen et al. 2016), and the blurring of boundaries between study/work and sleep time. The effect of these trends was magnified during COVID-19 pandemic-related lockdowns, when most persons slept later given the opportunity to (Blume et al. 2020, Giuntella et al. 2021. ...
Article
The restorative function of sleep is shaped by its duration, timing, continuity, subjective quality, and efficiency. Current sleep recommendations specify only nocturnal duration and have been largely derived from sleep self-reports that can be imprecise and miss relevant details. Sleep duration, preferred timing, and ability to withstand sleep deprivation are heritable traits whose expression may change with age and affect the optimal sleep prescription for an individual. Prevailing societal norms and circumstances related to work and relationships interact to influence sleep opportunity and quality. The value of allocating time for sleep is revealed by the impact of its restriction on behavior, functional brain imaging, sleep macrostructure, and late-life cognition. Augmentation of sleep slow oscillations and spindles have been proposed for enhancing sleep quality, but they inconsistently achieve their goal. Crafting bespoke sleep recommendations could benefit from large-scale, longitudinal collection of objective sleep data integrated with behavioral and self-reported data. Expected final online publication date for the Annual Review of Psychology, Volume 74 is January 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Organisms have developed time measurement system, i.e., circadian clocks which allow them to entrain and align different behavioral and physiological activities to appropriate time of the day (Falcón et al. 2020). For instance, daily variations of sleep, locomotor activity, food intake, body temperature, hormone secretion, and gene expression are all fine-tuned by the light-dark cycle (Foster and Kreitzman 2005;Roenneberg et al. 2007;Wright et al. 2013;Azzi et al. 2014;Welbers et al. 2017). Studies from the past report the deleterious effects of LAN on animals ranging from invertebrates to vertebrates (Falcón et al. 2020). ...
Article
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Artificial light at night is constantly minimizing the span of dark nights from the natural light-dark cycle of earth. Over the past century, the “lightscape” of earth has completely changed owing to technological advancements which subsequently changed the lifestyle of human as well as the nearby animal species. This motivated the present study, wherein we investigated the impact of light at night (LAN) on behavior and physiology of a diurnal passerine finch, baya weaver (Ploceus philippinus). A group of bird (N=10) exposed to 12L:12D photoperiod was initially subjected to dark nights (0 lux) for a period of 1.5 weeks followed by 5 lux, night light for a span of 4 weeks. The first week in LAN served as acute treatment with respect to the fourth week (chronic). The results reveal significant increase in nighttime activity and sleep loss with respect to acute LAN, while significant inclusion of drowsiness behavior during the day in response to chronic LAN. Besides these behavioral alterations, changes in physiological parameters such as reduction in body mass, loss of gradient between pre- and post- prandial blood glucose levels, and elevation in plasma corticosterone levels were more prominent during acute exposure of LAN. Plasma metabolites such as triglycerides, total protein, serum glutamic-oxaloacetic transaminase (SGOT), and creatinine concentrations also hiked in response to acute LAN treatment. Thus, acute exposure of LAN seems to serve as a novel environment for the bird leading to more pronounced impacts on behavioral and physiological observations during the experiment. In chronic exposure, the birds sort of adapted themselves to the prevailing circumstances as evident by decreased nighttime activity, rebound of sleep and corticosterone levels, etc. Thus, the study clearly demonstrates the differential impact of acute and chronic exposure of LAN on behavior and physiology of birds.
... Several external cues pace the body's circadian clocks and light is considered the most important time giver, or zeitgeber , so spending time outside regularly in bright daylight keeps individuals entrained to the natural lightdarkness cycle (Wright et al., 2013;Stothard et al., 2017). Circadian rhythms are partially genetically determined (Schnell et al., 2014;Jones et al., 2019), environmentally cued , and, to some extent individually controlled (Richardson et al., 2017;Przepiórka et al., 2019). ...
Article
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Circadian rhythms relate to multiple aspects of health and wellbeing, including physical activity patterns. Susceptible circadian regulation predisposes to circadian misalignment, poor sleep, sleep deprivation, increased sleepiness, and thereby sedentary behavior. Adolescents’ circadian regulation is particularly vulnerable, and may lead to sedentary behavior. To investigate which factors associate strongest between physical activity (PA) and circadian behavior, we conducted multimodal circadian rhythm analyses. We investigate how individual characteristics of habitual circadian patterns associate with objectively measured PA. We studied 312 adolescents [70% females) (56% with delayed sleep phase (DSP)], mean age 16.9 years. Circadian period length, temperature mesor (estimated 24 h midline) and amplitude (difference between mesor and peak) were measured using distally attached thermologgers (ibutton 1922L, 3-day-measurement). We additionally utilized algorithm-formed clusters of circadian rhythmicity. Sleep duration, timing, DSP, and PA were measured using actigraphs (GeneActiv Original, 10-day-measurement). We found that continuous circadian period length was not associated with PA, but lower mesor and higher amplitude were consistently associated with higher levels of PA as indicated by mean Metabolic Equivalent (METmean) and moderate-to-vigorous PA (MVPA), even when controlling for sleep duration. Separate circadian clusters formed by an algorithm also reflected distinct patterns of PA accordingly. Late sleepers and those with DSP were less likely to engage in MVPA compared to non-DSP and had more sedentary behavior. Adolescents who engage in higher levels or high-intensity PA have better circadian regulation, as measured by different objective methods including distal temperature measurements as well as actigraphy-measured sleep-wake behavior.
... Not all scholars [40] agree on widespread segmented sleep in the Roman society 2000 years ago. However, if we consider that artificial lighting [41], because of its cost, was available only to the richest people, and, on the average, a human being needs to sleep for a total of 7 h (in summer) and 8 h (in winter), it can be assumed that segmented sleep was practiced by most people. ...
Article
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We have re-examined and discussed all chronological, historical and astronomical elements which can be referred to the year of Herod the Great’s death, which occurred—according to Josephus—after a lunar eclipse and before Passover. Since the XIX century, most scholars still assume the eclipse occurred on 13 March 4 BC, so that Dionysius Exiguus was wrong in calculating the beginning of the Christian era—by four years at least—because Herod the Great must have been alive when Jesus was born. We have solved the apparent incompatibility of the events narrated by Josephus, occurring between the eclipse of 13 March 4BC and a too-near Passover (12 April 4 BC), by determining another date after studying all eclipses visible from Jerusalem in near years. This analysis—supported by a novel simulation of naked–eye visibility of partial lunar eclipses—has shown that the most eligible eclipse associable to Herod’s death occurred in the night of 8–9 November 2 AD. Besides this astronomical finding, our conclusion is also supported by significant correlation between segmented sleep and eclipse intervals; by its compatibility with the long sequence of events narrated by Josephus and with the rabbinic tradition about Herod’s death. This dating also agrees with other historical facts connected to Roman and Jewish history. In conclusion, Herod the Great must have died in the first month of 3 AD and, very likely, Dionysius Exiguus was correct.
... The ideal field experiment to assess the impact of electric light on human circadian rhythms would be a longitudinal experiment in which a group of subjects living in the same place gain or lose access to electricity and their rhythms are monitored before and after the introduction of electric light. Such a scenario is difficult to come by, but a similar longitudinal approach was used by Wright and colleagues [11]. The team monitored their own actimetry-based sleep and DLMO in their typical urban setting during the summer, and later monitored the same rhythms during a camping trip in which they used no artificial sources of light. ...
Chapter
Human sleep is regulated by light in two fundamental ways: The light-dark (LD) cycle entrains a circadian clock that in turn regulates sleep timing, and light per se can acutely inhibit sleep. Throughout evolution, these sleep regulatory systems became highly sensitive to the effects of light and they can be affected by the relatively low light intensities that are used indoors. Thus, postindustrial living conditions have created built environments that have isolated humans from the natural LD cycle and exposed them to an artificial one that can affect daily sleep timing. Studying indigenous communities that have differential access to electricity, as well as communities living in highly urbanized areas, we and others have shown that human access to artificial light has delayed the daily onset of sleep but has had a smaller effect on its offset, leading to an overall reduction in sleep duration that is pervasive in modern societies. In this chapter we discuss these studies, highlight their main findings, and point to their limitations.
... Experiments by Hedge (2018) revealed that occupants seated within 10 feet of a window could experience 84% decrease in eyestrains given the fact that windows do not have glare. Brainard, et al. (2015), and Wright Jr, et al. (2013) showed that proper daylighting exposure and connections with outdoor environments through windows are essential for maintaining natural circadian rhythms. Daylighting can also reduce energy consumption in buildings. ...
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Daylight glare is one of the most intricate and dynamic phenomena to work with when designing architectural spaces. It has been researched across diverse fields including ophthalmology, photometry, architecture, environmental sciences, materials engineering, etc. Finding a comprehensive approach that interconnects these disciplines to inform real-world architectural practice, however, has proven elusive. Glare is defined as the excessive amount of light or high luminance ratios as perceived by the eye according to the Illuminating Engineering Society (IES 2018). Quantifying excessive light or luminance ratios, however, is challenging due to the eye's adaptability and constantly changing outdoor illumination. Daylight discomfort glare can be assessed using different methods addressed in previous research studies such as: luminance contrast ratio, daylight glare probability (DGP), vertical eye illuminance, etc. In this study, we synthesize findings through systematic literature review from ophthalmology and photometry to understand the structure of the eye and glare occurrence to assist architects and researchers conducting glare simulations. We analyze glare in an indoor space by performing various daylighting computer simulations and demonstrate how to mitigate it via different design strategies. A computer model of the space is created in Rhino and simulated in DIVA to obtain horizontal illumination data, and DGP metrics. In this study, we use a mixed methodological approach which includes selecting an existing library space and analyzing it via: (1) in-person field visits and collecting horizontal illumination data using a luminance meter, (2) performing two-level baseline simulations: [a] horizontal illuminance at 30" above finish floor level, and [b] a DGP analysis, (3) validating computer-simulated horizontal illuminations with corresponding field-measured data discussed in step 1, (5) assessing and evaluating the baseline and its glare conditions (6) proposing glare-mitigation strategies based on published studies, and (7) presenting an improved design case simulation which incorporates glare control and mitigation with daylighting strategies.
... Particularly, an upper limit associated with either the developmental stage achieved at the end of secondary school 59,60 or with the entrainment mechanism of the circadian clock 62 might explain the association of both school timing and baseline chronotype with ΔChronotype. Previous works showed that chronotype variability among adolescents depends on different factors, including genetics, culture, light exposure, schedules and age 2,[4][5][6][7][8][12][13][14][15][16][17]57 . On the one hand, advanced pubertal stages have been associated with later chronotypes 59,80 students with later baseline chronotypes might be the ones presenting the most advanced pubertal stages at the beginning of secondary school. ...
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The misalignment between late chronotypes and early school start times affect health, performance and psychological well-being of adolescents. Here we test whether, and how, the baseline chronotype (i.e. chronotype at the beginning of secondary school) and the school timing affect the magnitude and the direction of the developmental change in chronotype during adolescence. We evaluated a sample of Argentinian students (n = 259) who were randomly assigned to attend school in the morning (07:45 a.m.–12:05 p.m.), afternoon (12:40 p.m.–05:00 p.m.) or evening (05:20 p.m.–09:40 p.m.) school timings. Importantly, chronotype and sleep habits were assessed longitudinally in the same group of students along secondary school (at 13–14 y.o. and 17–18 y.o.). Our results show that: (1) although chronotypes partially align with class time, this effect is insufficient to fully account for the differences observed in sleep-related variables between school timings; (2) both school timing and baseline chronotype are independently associated with the direction and the magnitude of change in chronotype, with greater delays related to earlier baseline chronotypes and later school timings. The practical implications of these results are challenging and should be considered in the design of future educational timing policies to improve adolescents’ well-being.
... Regarding the etiology of poor sleep quality in these patients, several different factors may be implicated. Lockdown, quarantine, fear of the disease, atypical homework schedules, and reduced exposure to daylight can take a toll on the circadian rhythm [24][25][26][27][28]. Psychiatric conditions certainly seem to be a significant burden for COVID-19 survivors, and therefore they could be linked to the observed sleep disturbance. ...
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Background: To date, evidence about sleep disturbances among post-COVID-19 patients is limited. This study aimed to evaluate sleep quality after hospitalization due to SARS-CoV-2 infection. Methods: In-person follow-up was conducted in patients with prior hospitalization due to COVID-19 1(Τ1), 3(Τ2), and 6 (Τ3) months after hospital discharge. Patients were asked to complete questionnaires concerning sleep quality: the Pittsburgh Sleep Quality Index (PSQI), the Epworth Sleepiness Scale (ESS), the Athens Insomnia Scale (AIS), the Fatigue Severity Scale (FSS), and the Stop-BANG (S-B) questionnaire. Results: In total, 133 patients were enrolled (mean age: 56.0 ± 11.48 years, 59.4% males). The most frequently reported comorbidity was arterial hypertension (29.8% of patients), while 37.4% of patients had no comorbidities. The majority of participants exhibited poor sleep quality (global PSQI ≥ 5) at T1 (84.3%), T2 (75.7%), and T3 (77.4%). Insomnia was observed in 56.5%, 53.5%, and 39.2% of participants, respectively (AIS ≥ 6). An FSS score ≥ 4 was observed in 51.2%, 33.7%, and 29.1% of participants at T1, T2, T3, respectively. Elapsed time was found to be negatively and independently associated with the global PSQI, PSQI C5-Sleep disturbance, PSQI C7-Daytime dysfunctions, FSS, and AIS after adjustment for possible confounders. No significant difference was found between groups with good and poor sleep quality (based on the global PSQI) with respect to gender (p = 0.110), age (p = 0.528), BMI (p = 0.816), smoking status (p = 0.489), hypertension (p = 0.427), severity of disease (p = 0.224), the Charlson Comorbidity Index (p = 0.827), or the length of hospital stay (p = 0.162). Participants with excessive daytime sleepiness (EDS) and patients with severe fatigue (FSS ≥ 4) were significantly younger. Females presented a higher rate of insomnia symptoms (55.7% vs. 44.3%, p < 0.001). Conclusions: Several sleep disturbances were observed after hospital discharge for COVID-19 pneumonia at certain time points; However, the improvement over time was remarkable in most domains of the assessed questionnaires.
... As a result of direct connections between ipRGCs and the brain, the integrated information on environmental light is directly transduced from the retina to downstream areas, with the SCN as one of the main targets 83 . From an evolutionary perspective, ambient light solely consisted of sunlight, but since the introduction of electric light, the 24-h exposure profile is increasingly becoming a mixture of solar and artificial light 108 Findings from previous studies suggest that this 'light pollution' affects photoentrainment of the biological clock and may shift circadian rhythms 109,110 . ...
Thesis
The non-image forming effects of environmental light are critically mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs) that are characterized by their expression of melanopsin, which is a photopigment that is maximally responsive to light in the blue part of the spectrum. The ipRGC-mediated effects of light can typically endure far beyond light offset, with widespread functional consequences, including changes in various aspects of human sleep. The present thesis investigated such sleep-related post-illumination effects in the context of physiology and behavior. In chapter 2 and 3, we presented a post-illumination pupil response (PIPR) after blue light assessment method that yields a robust and feasible estimate of the functionality of an individual’s intrinsic melanopsin-based phototransduction circuitry. In chapter 4, we showed that the PIPR after blue light was more pronounced in individuals with a later sleep timing. Following red light, sleep propensity is promoted, as indicated by our physiological and behavioral findings in chapter 5. Chapter 6 added to chapter 2 and 5 indicating that task demands and mental effort should be taken into account in order to correctly interpret changes in physiological and behavioral reflections of the central and autonomic nervous system. It appears timely to consider large-scale follow-up studies to contribute to the multivariate fingerprint of the non-image forming effects of light on human physiology and behavior and to further evaluate the clinical application of light therapy in the treatment of sleep disorders.
... Winters in the Subarctic regions consist of dark periods while summers are marked by constant daylight [20]. It has been suggested that these light exposure patterns cause abnormalities of circadian rhythms and disturbed sleep [21][22][23]. Indeed, individuals who live near the Subarctic experience greater seasonal changes in insomnia and fatigue, compared to those who live near the equator [21]. ...
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Study objectives To date, few studies have assessed sleep problems among women residing in Subarctic regions. Therefore, the aim of this large-scale population-based study was to assess the prevalence of severe sleep problems and associated factors among Icelandic women, living at 63-66°N. Methods Participants were 29,681 women (18-69 years old) who took part in the Icelandic Stress-And-Gene-Analysis study in 2018–2019. Background information, health-related behaviour, and mental health symptoms were assessed with an online questionnaire. The Pittsburgh Sleep Quality Index (PSQI) was used to assess severe sleep problems during the past month. Adjusting for age, marital status, number of children, education, personal income, work schedule, region, and response period, we used modified Poisson log-linear models to obtain prevalence ratios (PRs) with 95% confidence intervals (CIs). Results Overall, 24.2% of women reported severe sleep problems (PSQI>10). Women responding in the winter presented with overall higher prevalence of severe sleep problems, compared to those responding in the summer (PR 1.21; 95% CI, 1.15-1.28). Severe sleep problems were more prevalent among young and late-midlife women, those who were single, had children, socio-economic challenges, worked shifts and flexible hours. Furthermore, obesity, suboptimal health behaviours, excessive screen time, and mental health problems were associated with severe sleep problems. Conclusion Severe sleep problems are more common among women in Subarctic regions than elsewhere, particularly during winter. These findings motivate development of preventive strategies and interventions for women in the Subarctic who suffer from sleep problems.
... These were informed by evidence-based research in Neurology, Photobiology, Neuroendocrinology, Neurobehavioral Studies, Psychophysiology of Perception, as well as aspects of Environmental Psychology, which all aimed at fostering accessibility and the implementation of the curriculum across Europe and overseas. Researchers from Thomas Jefferson University's Light Research Program, which included Dr George Brainard and his team, joined this project as experts to advise on the physiological effects of light [5][6][7][8][9]. They also provided guidance on the use of appropriate lighting metrics, which includes tutorials on the use of CIE α-opic Toolbox [10]. ...
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This paper presents the results of ‘Light4Health’ (L4H), a three-year EU Erasmus+ Strategic Partnership grant project (2019-2021), which investigated, systematized and taught health-related research on the impact of natural and artificial light on human health and well-being relevant to indoor lighting design. The objective was to re-think evidence-based lighting design approaches for residential, working/educational, and healthcare spaces, in order to develop a novel cross-disciplinary eLearning platform, that intersects lighting design and current peer-reviewed health research through a select combination of the most relevant research, methods, and tools. The content was developed through teaching workshops with international researchers, teachers, and students. Participating students were introduced to the application of relevant research and new metrics, in order to produce creative lighting design proposals. Students were able to inform lighting design approaches that support health and well-being without compromising creativity via the tools and methods developed through the health sciences. With this project, participants and consortium members have narrowed the gap that exists between research and the practice/application of lighting, by translating research from complex scientific jargon into various tools for designers to use. The knowledge gained, was consolidated into an open-access online curriculum for international lighting design students, educators and professionals via the free eLearning Moodle platform (https://course.light4health.net/).
... While jetlag is the most abrupt and obvious form of exogenously imposed circadian desynchrony, there are other more insidious forms, including what has been coined "social jetlag" (shifting sleep/wake rhythms several hours between weekend and weekday), 9 1 increased exposure to artificial light during the solar night, 92 and decreased natural light exposure during the solar day. 93 In all of these situations, the clock itself and its entrainment mechanisms function correctly, but the consequent behavior has a negative impact on health or well-being. Endogenous circadian dysfunction occurs when the circadian mechanism is itself dysfunctional. ...
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‘Management of Sleep Disorders in Psychiatry’ provides an in-depth and evidence-based review of sleep-wake disorders included in Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) that are associated with a range of psychiatric disorders including mood, anxiety, psychotic, neurocognitive, eating, and substance use disorders. It also includes special sections on sleep-wake disorders associated with pediatric and neurological disorders, and reviews forensic issues encountered in the practice of psychiatry as they relate to sleep disorders. The book is unique in its focus on clinical assessment and management of sleep-wake disorders, and provides in-depth insight into the impact of disturbed sleep and wakefulness on clinical course and treatment outcomes of comorbid psychiatric conditions. Treatments reviewed include both evidence-based pharmacological and behavioral strategies to address sleep-wake disorders in patients with psychiatric disorders. Case vignettes are added to assist in the understanding of key clinical concepts of sleep and psychiatric comorbidity and multiple-choice questions are added for self-assessment. This comprehensive text aims to cater to the needs of the clinicians in a wide range of medical specialties including psychiatrists, sleep medicine physicians, psychologists, primary care physicians, and neurologists who strive to improve the sleep and clinical outcomes of their patients with psychiatric disorders.
... Runner's demographics, environmental conditions [1][2][3], training status [4,5], time of day [6], sunlight exposure [7,8], wind [9], and perceptual comfort [10] are some of the myriad of factors that could influence marathon performance. In particular, marathon performance suffers as temperature rises, especially if held in hot and humid climates [1,2,11]. ...
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We examined marathon performance of the same group of runners in relation to small changes in dry bulb temperature (Tdb) and wet bulb temperature (Twb) across 3 consecutive y, and investigated whether performance was poorer during an evening marathon compared with morning marathons. Marathon results were obtained from the 2017, 2018, and 2019 Standard Chartered Singapore Marathons. Tdb, Twb, Td, relative humidity, and absolute humidity were gathered for each marathon. K-means clustering and linear regressions were performed on 610 runners who participated in all three marathons. Analysis of the 610 runners’ marathon performance was contrasted with Tdb and Twb. Linear regressions were also performed on 190 runners filtered by percentile, yielding similar results. For clusters with similar Tdb from all runners K-means clustering, an increase in mean Twb by 1.5°C coincided with an increase in finishing time by 559 s (9.3 min) (p < 0.033). Twb hinders marathon performance more than Tdb, with each percentage rise in Tdb and Twb resulting in an increase in net time by 7.6% and 39.1%, respectively (p < 0.025). Male and female runners’ response to Tdb and Twb changes were similar (overlap in 95% confidence intervals for the respective regression coefficients). In conclusion, small variations in environmental parameters affected marathon performance, with Twb impairing marathon performance more than Tdb. Marathon performance was likely better in the morning than evening, possibly due to time of day differences, along with unfavorable Tdb that superseded training effects and the effects of lower Twb.
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Light is the primary stimulus for synchronizing the circadian clock in humans. There are very large interindividual differences in the sensitivity of the circadian clock to light. Little is currently known about the genetic basis for these interindividual differences. We performed a genome-wide gene-by-environment interaction study (GWIS) in 280,897 individuals from the UK Biobank cohort to identify genetic variants that moderate the effect of daytime light exposure on chronotype (individual time of day preference), acting as light sensitivity variants for the impact of daylight on the circadian system. We identified a genome-wide significant SNP mapped to the ARL14EP gene (rs3847634; p < 5x10-8), where additional minor alleles were found to enhance the morningness effect of daytime light exposure (βGxE = -.03, SE = 0.005) and were associated with increased gene ARL14EP expression in brain and retinal tissues. Gene-property analysis showed light sensitivity loci were enriched for genes in the G protein-coupled glutamate receptor signaling pathway and in Per2+ hypothalamic neurons. Linkage disequilibrium score regression identified significant genetic correlations of the light sensitivity GWIS with chronotype and sleep duration, such that greater light sensitivity was associated with later chronotype, greater insomnia symptoms and shorter sleep duration. Greater light sensitivity was also genetically correlated with greater risk for PTSD. This study is the first to assess light as an important exposure in the genomics of chronotype and is a critical first step in uncovering the genetic architecture of human circadian light sensitivity and its links to sleep and mental health.
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Evening exposure to short-wavelength light has disruptive effects on circadian rhythms and sleep. These effects can be mitigated by blocking short-wavelength (blue) frequencies, which has led to the development of evening blue-depleted light environments (BDLEs). We have previously reported that residing 5 days in an evening BDLE, compared with residing in a normal indoor light environment of similar photopic lux, advances circadian rhythms and increases the duration of rapid eye movement (REM) sleep in a randomized cross-over trial with twelve healthy participants. The current study extends these findings by testing whether residing in the evening BDLE affects the consolidation and microstructure of REM sleep in the same sample. Evening BDLE significantly reduces the fragmentation of REM sleep (p = 0.0003), and REM sleep microarousals in (p = 0.0493) without significantly changing REM density or the latency to first REM sleep episode. Moreover, the increased accumulation of REM sleep is not at the expense of NREM stage 3 sleep. BDLE further has a unique effect on REM sleep fragmentation (p = 0.0479) over and above that of circadian rhythms phase-shift, indicating a non-circadian effect of BDLE. If these effects can be replicated in clinical populations, this may have a therapeutic potential in disorders characterized by fragmented REM sleep.
Article
The field of “circadian medicine” is a recent addition to chronobiology and sleep research efforts. It represents a logical step arising from the increasing insights into the circadian system and its interactions with life in urbanised societies; applying these insights to the health/disease balance at home and in the medical practice (outpatient) and clinic (inpatient). Despite its fast expansion and proliferating research efforts, circadian medicine lacks a formal framework to categorise the many observations describing interactions among the circadian system, sleep, and the health/disease balance. A good framework allows us to categorise observations and then assign them to one or more components with hypothesised interactions. Such assignments can lead to experiments that document causal (rather than correlational) relationships and move from describing observations to discovering mechanisms. This review details such a proposed formal framework for circadian medicine and will hopefully trigger discussion among our colleagues, so that the framework can be improved and expanded. As the basis of the framework for circadian medicine, we define “circadian health” and how it links to general health. We then define interactions among the circadian system, sleep, and the health/disease balance and put the framework into the context of the literature with examples from six domains of health/disease balance: fertility, cancer, immune system, mental health, cardiovascular, and metabolism.
Article
Chronobiology research has uncovered a host of maladies linked to social jetlag (SJL), the sleep-disrupting disconnect between solar time and social time. This interdisciplinary study applies chronobiology theory to the potential effect of misaligned time zones on motor-vehicle deaths. In the U.S. 53 million residents live in counties located outside their official time zones’ standard 15° span of longitude, based on degrees west of the prime meridian. We refer to these counties as eccentric time localities (ETLs), all of which lie west of their time zones’ standard western border in the U.S. In contrast, counties within 7.5° of their time zone’s standard geographic center are what we call solar zones. Solar zones do not vary more than 30 minutes from true solar time. ETL residents are forced to rise before dawn, possibly restricting their sleep-time and suppressing both morning and evening zeitgebers that would support their circadian entrainment. Hypothesizing that living in ETLs amplifies social jetlag, data on 417,399 traffic fatalities in the U.S. between 2006 and 2017 from the Fatality Analysis Reporting System (FARS) census were analyzed via GIS mapping and population-data statistics. Road fatalities among residents of solar zones were compared to those living in ETLs within the same official time zone. ETL residents across the U.S. indicated 21.8% higher fatality-rates than solar residents, with a mean of 1286 additional (i.e., unexpected) deaths-per-year. Results support circadian entrainment theory and are consistent with the SJL construct. The socio-political ramifications of these findings are discussed, as well as the subject of best practices when analyzing whole-population data. The authors conclude that the unquestioned rhetoric of time-zone boundaries should be reconsidered in social policy.
Article
Windows and shading devices occupy an essential part between inside and outside environment of buildings, for providing interior air quality and optimization of lighting and HVAC energy consumption. This paper aims to perform the thermal performance of double pane Electrochromic window (ECW) using Finite Element Method and the energy performance using the Building Information Modelling (BIM) tool. The thermal model of the ECW is simulated in COMSOL Multiphysics. Double pane glass with and without electrochromic (EC) layer is analyzed to obtain the average and maximum surface temperature between the top and bottom layers of the glazing. It is observed that the maximum temperature gradient is observed with EC layer. The energy performance with a double glazing and ECW for warm and humid climate is evaluated using eQUEST DOE tool. A 30 % reduction is observed in the annual energy consumption with an ECW compared to that with a double-glazing window. In addition, during the monthly evaluation of energy consumption, there is 10% reduction with the ECW compared to baseline. The appreciable thermal characteristics and the energy performance of the EC glazing proves it to be an alternative solution for normal window glazing in automated buildings for thermal comfort and lesser cooling load demand.
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The interplay of environmental, social, and behavioral factors influencing human circadian phase in ecological conditions remains elusive. The Uruguayan national dance school END-SODRE operating in two shifts (morning: 8:30-12:30 and night: 20:00-24:00) allowed us to evaluate how social demands, chronotype, environmental light, physical activity, and sleep patterns affected individual circadian phase measured by the onset of the nocturnal increase of melatonin (DLMO) in a single study. The DLMO was 1.5h earlier in morning-shift dancers (n=7) compared to night-shift dancers (n=11). Sleep time and chronotype (only in night-shift dancers) were associated with the circadian phase. In training days, during each participant’s phase-advance and phase-delay time windows, light exposure was similar between morning and night-shift dancers and did not correlate with DLMO. In contrast, the time spent in moderate-vigorous physical activity during each participant’s phase-lag time window was higher in night-shift dancers than in morning-shift dancers and positively correlated with DLMO.
Article
The circadian clock is a fundamental endogenous mechanism of adaptation that coordinates the physiology and behavior of most organisms with diel variations in the external environment to maintain temporal homeostasis. Diatoms are the major primary producers in the ocean. However, little is known about the circadian clock in marine diatoms compared with other organisms. Here, we investigated circadian clock genes, their expression patterns, and responses to environmental stimuli such as light, nitrogen and phosphorus in two marine diatoms, Skeletonema costatum and Phaeodactylum tricornutum, using a combination of qRT-PCR and bioinformatic analysis. We identified 17 and 18 circadian clock genes in P. tricornutum and S. costatum, respectively. Despite significant evolutionary differences, these genes were similar to those of the higher plant Arabidopsis. We also established a molecular model for the marine diatom circadian clock comprising an input pathway, core oscillator, output pathway, and valve effector. Notably, the expression patterns of core clock genes (circadian clock associated 1 (CCA1), late elongated hypocotyl (LHY) and timing of cab 1 (TOC1)) in both species differed from those of terrestrial plants. Furthermore, the expression of these genes was influenced by variations in ambient light, nitrogen and phosphorus availability. Although marine diatoms and higher plants share common circadian clock components, their clock genes have diverged throughout evolution, likely as a result of adapting to contrasting environments.
Article
Time-restricted eating (TRE) is a dietary intervention that limits food consumption to a specific time window each day. The effect of TRE on body weight and physiological functions has been extensively studied in rodent models, which have shown considerable therapeutic effects of TRE and important interactions among time of eating, circadian biology and metabolic homeostasis. In contrast, it is difficult to make firm conclusions regarding the effect of TRE in people because of the heterogeneity in results, TRE regimens, and study populations. In this review, we: i) provide a background of the history of meal consumption in people and the normal physiology of eating and fasting; ii) discuss the interaction between circadian molecular metabolism and TRE; iii) integrate the results of preclinical and clinical studies that evaluated the effects of TRE on body weight and physiological functions; iv) summarize other time-related dietary interventions that have been studied in people; and v) identify current gaps in knowledge and provide a framework for future research directions.
Article
Students spend more than 70% of their time in the classroom, and the quality of the classroom environment has an important impact on the physical and mental health of students in the growing stage. Drawing on Scopus, PubMed, China National Knowledge Infrastructure, and other databases, this paper sorts and summarizes 191 research articles on the impact of the classroom environment on the physical and mental health of schoolchildren in the past 20 years. Based on the aspects of acoustic, light, thermal, and air quality, eight key indicators and their impact on classroom indoor environments and thus student health are identified (background noise level, reverberation time, useful daylight illuminance, indoor air temperature and air velocity, ventilation rate, CO2 and PM2.5 concentrations). Corresponding classroom optimization design methods and potential improvements are proposed. Compared with related studies of adults, it is found that adolescents are suitable for cooler indoor temperatures, while their sensitivity to daylight illuminance, noise, and PM2.5 concentrations is higher than that of adults.
Article
Circadian rhythms alter with ageing and may be aetiologically linked to neurodegeneration. This study explored the association between clinical markers and 1) dim light melatonin onset (DLMO) time and 2) phase angle derived from sleep midpoint, in older adults with varying dementia risks. Participants completed 14 days of actigraphy followed by in-lab measurement of salivary melatonin, from which DLMO time and phase angle were computed. Eighty participants (age = 65.5, SD = 9.6), 44 males (55%), MMSE (28.6, SD = 1.5) were included in the analysis. Sex (t = 2.15, p = .04), sleep onset (r = 0.49, p < .001) and midpoint (r = 0.44, p < .001) also correlated with DLMO time. Multiple linear regression showed chronotype, average actigraphy-derived light exposure during the DLMO window (window 2 h prior to DLMO to 2 h post), early biological day (6–10 h post DLMO time) and late biological day (10–14 h post DLMO time) were predictive of DLMO time (adjusted R² = 0.75). Sleep offset, depression severity, average light exposure during the early biological night and early and late biological day were shown to be predictive variables in the estimation of phase angle (adjusted R² = 0.78). The current study highlights the potential use of clinical variables, such as actigraphy-derived light, as circadian markers in ageing which could be easily implemented into existing clinical practice and could yield potential targets focusing on chronotherapeutic interventions.
Article
Sleep is fundamental to life and essential to one’s health behavior, scholastic achievement, and work performance. Recent years have seen an increase in empirical investigations incorporating sleep research into political science. This study complements existing sleep-politics studies by examining the associations between chronotype (a person’s preferred time to sleep and wake up) and attitudinal and behavioral political outcomes (left–right ideology and social conservatism proxied by religious service attendance). We analyze representative samples from 10 national contexts (Finland, Greece, Ireland, Mexico, the Netherlands, New Zealand, the Philippines, Russia, South Korea, and Switzerland) to test our hypotheses. The results demonstrate that morning chronotype has significant links with political conservatism in six national contexts depending on model specification (most robustly in Switzerland). Unexpectedly, the morning chronotype may have links to liberalism in three other countries depending on model specification (most robustly in Russia). The results for religious observance are more uniform, indicating a link between morningness and greater religious observance across all cases in many specifications (excepting a reversed relationship in New Zealand in some models). Urbanization, seasonal effects, geographical characteristics, and religious denominations are explored as potential confounders.
Article
People in closed spaces without daylight for a long time are prone to circadian rhythm desynchrony and sleep disorders. To explore the effects of different lighting patterns on circadian rhythm and sleep, 20 adults were confined in an underground lab by within-subject design for four consecutive weeks with one lighting pattern per week. The static lighting pattern (SLP) was used in the 1st week, then the circadian forward lighting pattern (FLP) in the 2nd and 4th weeks, and the backward lighting pattern (BLP) in the 3rd week. Their salivary melatonin, Karolinska Sleepiness Scale(KSS),core body temperature (CBT), Pittsburgh Sleep Quality Index (PSQI), sleep latency and the number of awakenings were measured. The results showed dim light melatonin onset (DLMO) was delayed by 0.62 h during the 1st week, indicating the backward tendency of circadian rhythm but without significance (p = 0.295). In the 2 nd week, the schedule was forced to bring forward by 2 h, assisted with FLP. The BLP in the 3rd week resulted in a significant delay of 1.87 h in DLMO(p = 0.002) and lower melatonin at bedtime (p = 0.001), with progressively longer sleep latency, lower sleepiness at night and CBT when waking up, and PSQI increased day by day, meaning the gradually deteriorated sleep. In the 4th week, DLMO was significantly shifted forward by 2.13 h (p = 0.003), melatonin at bedtime was higher (p = 0.000), and sleep quality gradually improved. Lighting interventions on KSS, CBT, PSQI and sleep latency showed day-by-day cumulative effects, and the dynamic lighting interventions can help maintain circadian rhythm stability in closed spaces and adapt to shift hours.
Article
Traditional risk factors for obesity and the metabolic syndrome, such as excess energy intake and lack of physical activity, cannot fully explain the high prevalence of these conditions. Insufficient sleep and circadian misalignment predispose individuals to poor metabolic health and promote weight gain and have received increased research attention in the past 10 years. Insufficient sleep is defined as sleeping less than recommended for health benefits, whereas circadian misalignment is defined as wakefulness and food intake occurring when the internal circadian system is promoting sleep. This Review discusses the impact of insufficient sleep and circadian misalignment in humans on appetite hormones (focusing on ghrelin, leptin and peptide-YY), energy expenditure, food intake and choice, and risk of obesity. Some potential strategies to reduce the adverse effects of sleep disruption on metabolic health are provided and future research priorities are highlighted. Millions of individuals worldwide do not obtain sufficient sleep for healthy metabolic functions. Furthermore, modern working patterns, lifestyles and technologies are often not conducive to adequate sleep at times when the internal physiological clock is promoting it (for example, late-night screen time, shift work and nocturnal social activities). Efforts are needed to highlight the importance of optimal sleep and circadian health in the maintenance of metabolic health and body weight regulation.
Chapter
Synopsis This article presents and discusses the fundamentals of LED supplying through electronic circuits. The electrical and thermal characteristics of the LEDs are presented, and the main strategies of DC and AC LED supplying are detailed. Important topics as light flicker, dimming, useful life, LED efficacy, standards, and future trends in lighting are deeply discussed.
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For field research of non-visual effects of light, accurate measurement of personal light exposure is required. A consensus framework for light-dosimetry could improve non-visual field research and ensure comparability between studies. Here, we present a review of methodologies used in non-visual light-dosimetry studies published to date, focussing on considerations regarding the measurement and preparation of personal light exposure data. Overall, a large variability in the studies’ methodologies is observed, highlighting the need for a consensus framework. We propose methodological considerations that should be included in such a framework and that can guide future studies. Furthermore, we highlight important points that should be addressed in future research to ensure compatibility between different dosimetry studies. Taken together, this review effort underlines the importance of a systematic approach to light-dosimetry in order to harness all the power of integrative lighting research in real life.
Article
With virtual reality (VR) industries and research focusing on gaming, training and, somewhat, in healthcare, there seems to be a lack of VR as simpler form of relaxing leisure, despite its potential. When emotions are targeted, there appears to be a focus on visceral ones like jump scares, panic, high adrenaline, fears and anything related to bad feelings and instinctive reactions. This study explores and proves that VR can effectively relax the user. We conducted an experiment where the users were exposed to VR-based natural sceneries, and we measured its effect on their positive feelings and relaxation levels. We found evidence, with a high degree of significance, of an increase in calmness and a reduction of arousal and energy. This effect is present in short sessions. We also explored the possibility of VR sunsets affecting our subjects’ circadian rhythm.
Chapter
Circadian rhythms are modulated by age. The timing of the circadian clock under real-life conditions (i.e., chronotype) is progressively delayed during adolescence. However, schools start very early in the morning, when the adolescent’ clock is still not prepared to be awake. Consistently, the misalignment between early school timing and late chronotypes leads to poor sleep: both short and out-of-time, which is associated with adverse consequences for health and cognitive and academic performance. This situation worsens in some countries due to cultural differences: Argentinian adolescents have even later chronotypes than most of their peers around the globe. Later school start times are associated with better sleep and a lower impact of chronotype on academic performance. Several strategies are suggested to evaluate and to mitigate the consequences of the misalignment between chronotype and school timing. Importantly, local studies and interventions are the key to understand and improve adolescents’ education and well-being.
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Circadian timing affects sleep onset. Delayed sleep onset can reduce sleep duration in adolescents required to awake early for a fixed school schedule. The absence of short-wavelength ("blue") morning light, which helps entrain the circadian system, can hypothetically delay sleep onset and decrease sleep duration in adolescents. The goal of this study was to investigate whether removal of short-wavelength light during the morning hours delayed the onset of melatonin in young adults. Dim light melatonin onset (DLMO) was measured in eleven 8th-grade students before and after wearing orange glasses, which removed short-wavelength light, for a five-day school week. DLMO was significantly delayed (30 minutes) after the five-day intervention, demonstrating that short-wavelength light exposure during the day can be important for advancing circadian rhythms in students. Lack of short-wavelength light in the morning has been shown to delay the circadian clock in controlled laboratory conditions. The results presented here are the first to show, outside laboratory conditions, that removal of short-wavelength light in the morning hours can delay DLMO in 8th-grade students. These field data, consistent with results from controlled laboratory studies, are directly relevant to lighting practice in schools.
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Circadian rhythms are endogenous 24 h cycles that persist in the absence of external time cues. These rhythms provide an internal representation of day length and optimize physiology and behaviour to the varying demands of the solar cycle. These clocks require daily adjustment to local time and the primary time cue (zeitgeber) used by most vertebrates is the daily change in the amount of environmental light (irradiance) at dawn and dusk, a process termed photoentrainment. Attempts to understand the photoreceptor mechanisms mediating non-image-forming responses to light, such as photoentrainment, have resulted in the discovery of a remarkable array of different photoreceptors and photopigment families, all of which appear to use a basic opsin/vitamin A-based photopigment biochemistry. In non-mammalian vertebrates, specialized photoreceptors are located within the pineal complex, deep brain and dermal melanophores. There is also strong evidence in fish and amphibians for the direct photic regulation of circadian clocks in multiple tissues. By contrast, mammals possess only ocular photoreceptors. However, in addition to the image-forming rods and cones of the retina, there exists a third photoreceptor system based on a subset of melanopsin-expressing photosensitive retinal ganglion cells (pRGCs). In this review, we discuss the range of vertebrate photoreceptors and their opsin photopigments, describe the melanopsin/pRGC system in some detail and then finally consider the molecular evolution and sensory ecology of these non-image-forming photoreceptor systems.
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Light is considered the most potent synchronizer of the human circadian system and exerts many other non-image-forming effects, including those that affect brain function. These effects are mediated in part by intrinsically photosensitive retinal ganglion cells that express the photopigment melanopsin. The spectral sensitivity of melanopsin is greatest for blue light at approximately 480 nm. At present, there is little information on how the spectral composition of light to which people are exposed varies over the 24 h period and across seasons. Twenty-two subjects, aged 22+/-4 yrs (mean+/-SD) participated during the winter months (November-February), and 12 subjects aged 25+/-3 yrs participated during the summer months (April-August). Subjects wore Actiwatch-RGB monitors, as well as Actiwatch-L monitors, for seven consecutive days while living in England. These monitors measured activity and light exposure in the red, green, and blue spectral regions, in addition to broad-spectrum white light, with a 2 min resolution. Light exposure during the day was analyzed for the interval between 09:00 and 21:00 h. The time course of white-light exposure differed significantly between seasons (p = 0.0022), with light exposure increasing in the morning hours and declining in the afternoon hours, and with a more prominent decline in the winter. Overall light exposure was significantly higher in summer than winter (p = 0.0002). Seasonal differences in the relative contribution of blue-light exposure to overall light exposure were also observed (p = 0.0006), in particular during the evening hours. During the summer evenings (17:00-21:00 h), the relative contribution of blue light was significantly higher (p < 0.0001) (40.2+/-1.1%) than during winter evenings (26.6+/-0.9%). The present data show that in addition to overall light exposure, the spectral composition of light exposure varies over the day and with season.
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Differences in morningness-eveningness among humans are commonly ascribed to circadian parameters, such as circadian period and responsivity to environmental time cues, as well as homeostatic sleep drive. Light is the primary synchronizer of the human biological clock, and if circadian differences exist between morning and evening types, they should have different phase angles of entrainment to the light/dark cycle; that is, morning and evening types should have different patterns of light exposure relative to endogenous circadian phase (ECP). When phase angle of entrainment is strictly defined as the relationship between a marker of ECP and the timing of light exposure, such differences have been demonstrated in the laboratory under controlled light/dark cycles and have recently been shown under conditions of spring and summer light exposure outside the laboratory, taking into account the variable intensity of light. Here, we report similar results from a large (n=66), diverse cohort of morning and evening types across the age span studied at all different times of the year. Differences between morning and evening types in light exposure relative to ECP, indicative of a difference in the phase angle of entrainment to the external light/dark cycle, were found. Specifically, evening types, compared to morning types, had a higher ratio of phase advancing to phase delaying by light. We interpret this as indicating a longer circadian period (tau) in evening types.
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An English language self-assessment Morningness-Eveningness questionnaire is presented and evaluated against individual differences in the circadian vatiation of oral temperature. 48 subjects falling into Morning, Evening and Intermediate type categories regularly took their temperature. Circadian peak time were identified from the smoothed temperature curves of each subject. Results showed that Morning types and a significantly earlier peak time than Evening types and tended to have a higher daytime temperature and lower post peak temperature. The Intermediate type had temperatures between those of the other groups. Although no significant differences in sleep lengths were found between the three types, Morning types retired and arose significantly earlier than Evening types. Whilst these time significatly correlated with peak time, the questionnaire showed a higher peak time correlation. Although sleep habits are an important déterminant of peak time there are other contibutory factors, and these appear to be partly covered by the questionnaire. Although the questionnaire appears to be valid, further evaluation using a wider subject population is required.
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The authors treated winter depression in 13 patients with typical seasonal affective disorder by extending the length of winter days with bright and dim light in the morning and evening in a balanced-order crossover study. Bright light had a marked antidepressant effect, whereas the dim light did not. This response could not be attributed to sleep deprivation. Subsequent pilot studies indicated that bright evening light alone is probably also effective. Several patients were able to maintain the antidepressant response throughout the winter months by continuing daily light treatments.
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Two- to threefold variations in sleep length were observed in 12 subjects living on self-selected schedules in an environment free of time cues. The duration of polygraphically recorded sleep episodes was highly correlated with the circadian phase of the body temperature rhythm at bedtime and not with the length of prior wakefulness. Furthermore, the rate of REM (rapid eye movement) sleep accumulation , REM latency, bedtime selection, and self-rated alertness assessments were also correlated with the body temperature rhythm.
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The accuracy with which a circadian pacemaker can entrain to an environmental 24-h zeitgeber signal depends on (a) characteristics of the entraining signal and (b) response characteristics and intrinsic stability of the pacemaker itself. Position of the sun, weather conditions, shades, and behavioral variations (eye closure, burrowing) all modulate the light signal reaching the pacemaker. A simple model of a circadian pacemaker allows researchers to explore the impact of these factors on pacemaker accuracy. Accuracy is operationally defined as the reciprocal value of the day-to-day standard deviation of the clock times at which a reference phase (0) is reached. For the purpose of this exploration, the authors used a model pacemaker characterized solely by its momentary phase and momentary velocity. The average velocity determines the time needed to complete one pacemaker cycle and, therefore, is inversely proportional to pacemaker period. The model pacemaker responds to light by shifting phase and/or changing its velocity. The authors assumed further that phase and velocity show small random fluctuations and that the velocity is subject to aftereffects. Aftereffects were incorporated mathematically in a term allowing period to contract exponentially to a stable steady-state value, with a time constant of 69 d in the absence of light. The simulations demonstrate that a pacemaker reaches highest accuracy when it responds to light by simultaneous phase shifts and changes of its velocity. Phase delays need to coincide with slowing down and advances with speeding up; otherwise, no synchronization to the zeitgeber occurs. At maximal accuracy, the changes in velocity are such that the average period of the pacemaker under entrained conditions equals 24 h. The results suggest that during entrainment, the pacemaker adjusts its period to 24 h, after which daily phase shifts to compensate for differences between the periods of the zeitgeber and the clock are no longer necessary. On average, phase shifts compensate for maladjustments of phase and velocity changes compensate for maladjustments of period.
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The photopigment in the human eye that transduces light for circadian and neuroendocrine regulation, is unknown. The aim of this study was to establish an action spectrum for light-induced melatonin suppression that could help elucidate the ocular photoreceptor system for regulating the human pineal gland. Subjects (37 females, 35 males, mean age of 24.5 +/- 0.3 years) were healthy and had normal color vision. Full-field, monochromatic light exposures took place between 2:00 and 3:30 A.M. while subjects' pupils were dilated. Blood samples collected before and after light exposures were quantified for melatonin. Each subject was tested with at least seven different irradiances of one wavelength with a minimum of 1 week between each nighttime exposure. Nighttime melatonin suppression tests (n = 627) were completed with wavelengths from 420 to 600 nm. The data were fit to eight univariant, sigmoidal fluence-response curves (R(2) = 0.81-0.95). The action spectrum constructed from these data fit an opsin template (R(2) = 0.91), which identifies 446-477 nm as the most potent wavelength region providing circadian input for regulating melatonin secretion. The results suggest that, in humans, a single photopigment may be primarily responsible for melatonin suppression, and its peak absorbance appears to be distinct from that of rod and cone cell photopigments for vision. The data also suggest that this new photopigment is retinaldehyde based. These findings suggest that there is a novel opsin photopigment in the human eye that mediates circadian photoreception.
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The interaction of homeostatic and circadian processes in the regulation of waking neurobehavioral functions and sleep was studied in six healthy young subjects. Subjects were scheduled to 15–24 repetitions of a 20-h rest/activity cycle, resulting in desynchrony between the sleep-wake cycle and the circadian rhythms of body temperature and melatonin. The circadian components of cognitive throughput, short-term memory, alertness, psychomotor vigilance, and sleep disruption were at peak levels near the temperature maximum, shortly before melatonin secretion onset. These measures exhibited their circadian nadir at or shortly after the temperature minimum, which in turn was shortly after the melatonin maximum. Neurobehavioral measures showed impairment toward the end of the 13-h 20-min scheduled wake episodes. This wake-dependent deterioration of neurobehavioral functions can be offset by the circadian drive for wakefulness, which peaks in the latter half of the habitual waking day during entrainment. The data demonstrate the exquisite sensitivity of many neurobehavioral functions to circadian phase and the accumulation of homeostatic drive for sleep.
Conference Paper
Background: Morningness-eveningness refers to interindividual differences in preferred timing of behavior (ie, bed and wake times). Older people have earlier wake times and rate themselves as more morning-like than young adults. It has been reported that the phase of circadian rhythms is earlier in morning-types than in evening types, and that older people have earlier phases than young adults. These changes in phase have been considered to be the chronobiological basis of differences in preferred bed and wake times and age-related changes therein. Whether such differences in phase are associated with changes in the phase relationship between endogenous circadian rhythms and the sleep-wake cycle has not been investigated previously. Methods: We investigated the association between circadian phase, the phase relationship between the sleep-wake cycle and circadian rhythms, and morningness-eveningness, and their interaction with aging. In this circadian rhythm study, 68 young and 40 older subjects participated. Results: Among the young subjects, the phase of the melatonin and core temperature rhythms occurred earlier in morning than in evening types and the interval between circadian phase and usual wake time was longer in morning types. Thus, while evening types woke at a later clock hour than morning types, morning types actually woke at a later circadian phase. Comparing young and older morning types we found that older morning types had an earlier circadian phase and a shorter phase-wake time interval. The shorter phase-wake-time interval in older "morning types" is opposite to the change associated with morningness in young people, and is more similar to young evening types. Conclusions: These findings demonstrate an association between circadian phase, the relationship between the sleep-wake cycle and circadian phase, and morningness-eveningness in young adults. Furthermore, they demonstrate that age-related changes in phase angle cannot be attributed fully to an age-related shift toward morningness, These findings have important implications for understanding individual preferences in sleep-wake timing and age-related changes in the timing of sleep.
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This paper is an attempt to integrate in a general model the major findings reported earlier in this series on: lability and history dependence of circadian period, tau (Pittendrigh and Daan, 1976); dependence of tau and α on light intensity as described by Aschoff's Rule (Daan and Pittendrigh, 1976); the interrelationships between tau and phase response curves (Daan and Pittendrigh, 1976); and those inconsistencies between experimental facts on entrainment and theoretical predictions based on a single oscillator with fixed parameters tau and PRC, which pointed to a more complex system (Pittendrigh and Daan, 1976). The qualitative model developed consists of 2 oscillators. The evidence that 2 separate oscillators are involved in circadian activity rhythms rests largely on the 'splitting' phenomenon, known to occur in several species of mammals and birds. The empirical regularities of 'splitting' in hamsters exposed to constant illumination (LL) are described. Splitting, i.e., the dissociation of a single activity band into 2 components which become stably coupled in ca 180° antiphase, occurs in about 50% of the animals in 100 to 200 lux, and has not been observed in lower light intensities. Splitting never occurred before 40 days after the transition to LL, unless the pretreatment had been LL of low intensity. In some animals, the unsplit condition returned spontaneously. The attainment of antiphase is usually accompanied by a decrease in tau, and refusion of the 2 components by an increase in tau. These data show that both the split and the unsplit condition are metastable states, characterized by different phase relationships (psiEM) of 2 constituent oscillators. psiEM is history dependent and determines tau of the coupled system. Observations in Peromyscus leucopus transferred from LL to DD to LD 12:12 show that the 2 components of the bimodal activity peak in (LD) can for some time run at different frequencies (in DD), suggesting that bimodality of activity peaks and splitting are based on the same 2 oscillator systems. The model developed assumes the existence of 2 oscillators or principal groups of oscillators E and M, with opposite dependence of spontaneous frequency on light intensity. The dependence of the phase relationship (psiEM) between the 2 on light intensity and the dependence of tau and psiEM account for all the history dependent characteristics of circadian pacemakers, and for the interdependence of tau, PRC, and tau lability. The model qualitatively accommodates the interdependence of tau and α summarized in Aschoff's Rule. It is noted that the major intuitive elements in the model have been found to characterize an explicit version of it in computer stimulations. The relevance of the model to seasonal change in photoperiod is discussed. A pacemaker comprising 2 oscillators mutually interacting but coupled separately to sunrise and sunset enhances its competence to accommodate to seasonal change in the daily pattern of external conditions; and it could well be involved in the pacemaker's known ability to discriminate between daylengths in the phenomena of photoperiodic induction.
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gives an overview of the current understanding of how the output of the circadian pacemaker interacts with the sleep–wake-dependent oscillatory process to generate the daily time course of alertness and cognitive performance under normal entrained conditions, under free-running conditions, among night workers, and during desynchronization of the sleep–wake and circadian systems, such as is seen in blind individuals (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
1. The seasonal variations in time of daily onset and end of locomotor activity are described for 3 species of mammals and 5 species of birds kept in captivity at the arctic circle and at lower latitude. These variations are most pronounced at high latitude. 2. The duration of daily activity plotted versus the photoperiod can be described as an S-curve in all species studied so far, both in nature and in captivity. In both male and female fringillid birds activity times were longer before the summer solstice (spring) than after the summer solstice at equal photoperiods. 3. The seasonal changes in activity time result from roughly mirror-image changes in the times of onset and end of activity relative to sunrise and sunset, cancelling out each other. Therefore the midpoint of activity stays relatively stable; remaining minor changes in the midpoint of activity do not produce a general seasonal pattern. 4. At high latitude, a large seasonal fluctuation in the day-to-day variability (or precision) of activity timing is detected. These patterns of precision of the rhythm cannot be attributed to a single Zeitgeber property without complex assumptions. Onset and ends of activity become more precise when occurring during the civil twilight, i.e. at times of day with most rapid changes in light intensity. This may reflect direct action of light on the rhythm rather than a property of the entrainment mechanism. 5. The data do not give compelling evidence for any formal model of the oscillations driving the activity rhythms. Predictions concerning the relation between phase and activity time derived from a single oscillator model are not matched by the data. On the other hand, the general seasonal patterns can be easily described in terms of a two-oscillator model. 6. Seasonal variations in duration of activity are larger in birds than in mammals. Day-to-day variations in timing are larger in mammals than in birds. The implications for photoperiodic time measurement are discussed.
Article
1 Phase response curves for 15′ bright light pulses of four species of nocturnal rodents are described. All show delay phase shifts early in the subjective night, advance shifts in the late subjective night, and relative insensitivity during the subjective day. 2 The broad scatter in measured phase-shifts is largely due to error of measurement: the response of the pacemakers to light stimuli is more accurate than we observe. 3. Indications are found that the response to a resetting stimulus at a given phase of the rhythm is correlated with the individual {Mathematical expression} (freerunning period). Fast pacemakers (short {Mathematical expression}) tend to be more delayed or less advanced by the light than slow pacemakers (long {Mathematical expression}). 4. Within individual mice (Mus musculus) the circadian pacemaker adjusts its resetting response to variations in its frequency: when τ is long (induced as after-effect of prior light treatment) light pulses at a defined phase of the oscillation (ct 15) produce smaller delay phase shifts than when τ is short. 5. Among species there are conspicuous differences in the shape of the phase response curve: where {Mathematical expression} is long, advance phase shifts are large and delay phase shifts small (Mesocricetus auratus); where {Mathematical expression} is short, advance shifts are small, and delay shifts are large (Mus musculus;Peromyscus maniculatus). 6. The functional meaning of the interrelationships of τ and PRC is briefly discussed.
Article
1. In thefirst part of the paper, the model of non-parametric entrainment of circadian pacemakers is tested for the case of nocturnal rodents. The model makes use of the available data on freerunning period ([`(t)]\bar \tau is close to 24 h. Thus the verycircadian nature of these pacemakers helps to conserve[`(t)]\bar \tau =24 h. The effect of-instability is further reduced by entrainment with 2 pulses (dawn and dusk), made possible by the PRC's having both an advance and a delay section. 8. To analyze the contributions to-conservation with seasonally changing photoperiod, we have assumed that it is of functional significance to conserve the phase of activity with respect to dusk (nocturnal animals) or to dawn (diurnal animals). We distinguish three contributions of nocturnal pacemaker behaviour to this type of-conservation: increased amplitude of the PRC (i), asymmetry in the PRC, such that the slope of the delay-part is steeper than the slope of the advance-part (ii), and a short freerunning period in DD (iii). 9. A further contribution must derive from parametric effects of light, which are not traceable by the model, but certainly effective in preventing in complete photoperiods the-jump which is seen in skeleton photoperiods. The existence of parametric effects is further demonstrated by the change of with light intensity in LL, described by Aschoff's Rule, which presumably reflects differences in PRC-shape between nocturnal and diurnal animals (Daan and Pittendrigh, 1976b). 10. The paper concludes with an attempt to distinguish the features of circadian clocks that are analytically necessary for entrainment to occur (i), or have functional meaning, either in the measurement of the lapse of time (ii) or in the identification of local time (iii).
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We recently reported that humans have conserved mechanisms, like those that exist in other animals, which detect changes in day length and make corresponding adjustments in the duration of nocturnal periods of secretion of melatonin and of other functions. We detected these responses in individuals who were exposed to artificial "days" of different durations. The purpose of the present study was to determine whether men who are exposed to natural and artificial light in an urban environment at 39 degrees N are still able to detect and respond to seasonal changes in duration of the natural photoperiod. We measured profiles of circadian rhythms during 24-h periods of constant darkness (< 1 lx) and found no summer-winter differences in durations of nocturnal periods of active secretion of melatonin, rising levels of cortisol, high levels of thyrotropin, and low levels of rectal temperature. The results of this and our previous study suggest that modern men&apos;s use of artificial light suppresses responses to seasonal changes in the natural photoperiod that might otherwise occur at this latitude.
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