Systematic review of light exposure impact on human circadian rhythm.

Light is necessary for life, and artificial light improves visual performance and safety, but there is an increasing concern of the potential health and environmental impacts of light. Findings from a number of studies suggest that mistimed light exposure disrupts the circadian rhythm in humans, potentially causing further health impacts. However, a variety of methods has been applied in individual experimental studies of light-induced circadian impacts, including definition of light exposure and outcomes. Thus, a systematic review is needed to synthesize the results. In addition, a review of the scientific evidence on the impacts of light on circadian rhythm is needed for developing an evaluation method of light pollution, i.e., the negative impacts of artificial light, in life cycle assessment (LCA). The current LCA practice does not have a method to evaluate the light pollution, neither in terms of human health nor the ecological impacts. The systematic literature survey was conducted by searching for two concepts: light and circadian rhythm. The circadian rhythm was searched with additional terms of melatonin and rapid-eye-movement (REM) sleep. The literature search resulted to 128 articles which were subjected to a data collection and analysis. Melatonin secretion was studied in 122 articles and REM sleep in 13 articles. The reports on melatonin secretion were divided into studies with specific light exposure (101 reports), usually in a controlled laboratory environment, and studies of prevailing light conditions typical at home or work environments (21 studies). Studies were generally conducted on adults in their twenties or thirties, but only very few studies experimented on children and elderly adults. Surprisingly many studies were conducted with a small sample size: 39 out of 128 studies were conducted with 10 or less subjects. The quality criteria of studies for more profound synthesis were a minimum sample size of 20 subjects and providing details of the light exposure (spectrum or wavelength; illuminance, irradiance or photon density). This resulted to 13 qualified studies on melatonin and 2 studies on REM sleep. Further analysis of these 15 reports indicated that a two-hour exposure to blue light (460 nm) in the evening suppresses melatonin, the maximum melatonin-suppressing effect being achieved at the shortest wavelengths (424 nm, violet). The melatonin concentration recovered rather rapidly, within 15 min from cessation of the exposure, suggesting a short-term or simultaneous impact of light exposure on the melatonin secretion. Melatonin secretion and suppression were reduced with age, but the light-induced circadian phase advance was not impaired with age. Light exposure in the evening, at night and in the morning affected the circadian phase of melatonin levels. In addition, even the longest wavelengths (631 nm, red) and intermittent light exposures induced circadian resetting responses, and exposure to low light levels (5-10 lux) at night when sleeping with eyes closed induced a circadian response. The review enables further development of an evaluation method of light pollution in LCA regarding the light-induced impacts on human circadian system.

Immediate effects of phototherapy on sleep in very preterm neonates: an observational study.

Process C (internal clock) and Process S (sleep-wake homeostasis) are the basis of sleep-wake regulation. In the last trimester of pregnancy, foetal heart rate is synchronized with the maternal circadian rhythm. At birth, this interaction fails and an ultradian rhythm appears. Light exposure is a strong factor influencing the synchronization of sleep-wake processes. However, little is known about the effects of phototherapy on the sleep rhythm of premature babies. It was hypothesized that sleep in preterm infants would not differ during phototherapy, but that a maturation effect would be seen. Sleep states were studied in 38 infants born < 32 weeks gestational age and/or < 1 500 g birth weight. Videos of 3 h were taken over the first 5 days of life. Based on breathing and movement patterns, behavioural states were defined as: awake; active sleep; or quiet sleep. Videos with and without phototherapy were compared for amounts of quiet sleep and active states (awake + active sleep). No significant association between phototherapy and amount of quiet sleep was found (P = 0.083). Analysis of videos in infants not under phototherapy revealed an increase in time spent awake with increasing gestational age. The current data suggest that the ultradian rhythm of preterm infants seems to be independent of phototherapy, supporting the notion that sleep rhythm in this population is mainly driven by their internal clock.

Arvicanthis ansorgei, a Novel Model for the Study of Sleep and Waking in Diurnal Rodents.

STUDY OBJECTIVES: Sleep neurobiology studies use nocturnal species, mainly rats and mice. However, because their daily sleep/wake organization is inverted as compared to humans, a diurnal model for sleep studies is needed. To fill this gap, we phenotyped sleep and waking in Arvicanthis ansorgei, a diurnal rodent widely used for the study of circadian rhythms. DESIGN: Video-electroencephalogram (EEG), electromyogram (EMG), and electrooculogram (EOG) recordings. SETTING: Rodent sleep laboratory. PARTICIPANTS: Fourteen male Arvicanthis ansorgei, aged 3 mo. INTERVENTIONS: 12 h light (L):12 h dark (D) baseline condition, 24-h constant darkness, 6-h sleep deprivation. MEASUREMENTS AND RESULTS: Wake and rapid eye movement (REM) sleep showed similar electrophysiological characteristics as nocturnal rodents. On average, animals spent 12.9 h ± 0.4 awake per 24-h cycle, of which 6.88 h ± 0.3 was during the light period. NREM sleep accounted for 9.63 h ± 0.4, which of 5.13 h ± 0.2 during dark period, and REM sleep for 89.9 min ± 6.7, which of 52.8 min ± 4.4 during dark period. The time-course of sleep and waking across the 12 h light:12 h dark was overall inverted to that observed in rats or mice, though with larger amounts of crepuscular activity at light and dark transitions. A dominant crepuscular regulation of sleep and waking persisted under constant darkness, showing the lack of a strong circadian drive in the absence of clock reinforcement by external cues, such as a running wheel. Conservation of the homeostatic regulation was confirmed with the observation of higher delta power following sustained waking periods and a 6-h sleep deprivation, with subsequent decrease during recovery sleep. CONCLUSIONS: Arvicanthis ansorgei is a valid diurnal rodent model for studying the regulatory mechanisms of sleep and so represents a valuable tool for further understanding the nocturnality/diurnality switch.

Sleep electroencephalographic characteristics of the Cynomolgus monkey measured by telemetry.

Cynomolgus monkeys are widely used as models of diseases and in pre-clinical studies to assess the impact of new pharmacotherapies on brain function and behaviour. However, the time course of electroencephalographic delta activity during sleep, which represents the main marker of sleep intensity associated with recovery during sleep, has never been described in this non-human primate. In this study, telemetry implants were used to record one spontaneous 24-h sleep-wake cycle in four freely-moving Cynomolgus monkeys, and to quantify the time course of electroencephalographic activity during sleep using spectral analysis. Animals presented a diurnal activity pattern interrupted by short naps. During the dark period, most of the time was spent in sleep with non-rapid eye movement sleep/rapid eye movement sleep alternations and sleep consolidation profiles intermediate between rodents and humans. Deep non-rapid eye movement sleep showed a typical predominance at the beginning of the night with decreased propensity in the course of the night, which was accompanied by a progressive increase in rapid eye movement sleep duration. Spectral profiles showed characteristic changes between vigilance states as reported in other mammalian species. Importantly, delta activity also followed the expected time course of variation, showing a build-up with wakefulness duration and dissipation across the night. Thus, Cynomolgus monkeys present typical characteristics of sleep architecture and spectral structure as those observed in other mammalian species including humans, validating the use of telemetry in this non-human primate model for translational sleep studies.

Selective slow wave sleep but not rapid eye movement sleep suppression impairs morning glucose tolerance in healthy men.

Shortened nocturnal sleep impairs morning glucose tolerance. The underlying mechanism of this effect is supposed to involve a reduced fraction of slow wave sleep (SWS). However, it remains unanswered if impaired glucose tolerance occurs due to specific SWS reduction or a general disturbance of sleep. Sixteen healthy men participated in three experimental conditions in a crossover design: SWS suppression, rapid eye movement (REM)-sleep disturbance, and regular sleep. Selective sleep stage disturbance was performed by means of an acoustic tone (532Hz) with gradually rising sound intensity. Blood concentrations of glucoregulatory parameters were measured upon an oral glucose tolerance test the next morning. Our data show that morning plasma glucose and serum insulin responses were significantly increased after selective SWS suppression. Moreover, SWS suppression reduced postprandial insulin sensitivity up to 20%, as determined by Matsuda Index. Contrastingly, disturbed REM-sleep did not affect glucose homeostasis. We conclude that specifically SWS reduction is critically involved in the impairment of glucose tolerance associated with disturbed sleep. Therefore, glucose metabolism in subjects predisposed to reduced SWS (e.g. depression, aging, obstructive sleep apnea, pharmacological treatment) should be thoroughly monitored.

Optogenetic disruption of sleep continuity impairs memory consolidation.

Memory consolidation has been proposed as a function of sleep. However, sleep is a complex phenomenon characterized by several features including duration, intensity, and continuity. Sleep continuity is disrupted in different neurological and psychiatric conditions, many of which are accompanied by memory deficits. This finding has raised the question of whether the continuity of sleep is important for memory consolidation. However, current techniques used in sleep research cannot manipulate a single sleep feature while maintaining the others constant. Here, we introduce the use of optogenetics to investigate the role of sleep continuity in memory consolidation. We optogenetically targeted hypocretin/orexin neurons, which play a key role in arousal processes. We used optogenetics to activate these neurons at different intervals in behaving mice and were able to fragment sleep without affecting its overall amount or intensity. Fragmenting sleep after the learning phase of the novel object recognition (NOR) task significantly decreased the performance of mice on the subsequent day, but memory was unaffected if the average duration of sleep episodes was maintained at 62-73% of normal. These findings demonstrate the use of optogenetic activation of arousal-related nuclei as a way to systematically manipulate a specific feature of sleep. We conclude that regardless of the total amount of sleep or sleep intensity, a minimal unit of uninterrupted sleep is crucial for memory consolidation.

Sleep after mobile phone exposure in subjects with mobile phone-related symptoms.

Several studies show increases in activity for certain frequency bands (10-14 Hz) and visually scored parameters during sleep after exposure to radiofrequency electromagnetic fields. A shortened REM latency has also been reported. We investigated the effects of a double-blind radiofrequency exposure (884 MHz, GSM signaling standard including non-DTX and DTX mode, time-averaged 10 g psSAR of 1.4 W/kg) on self-evaluated sleepiness and objective EEG measures during sleep. Forty-eight subjects (mean age 28 years) underwent 3 h of controlled exposure (7:30-10:30 PM; active or sham) prior to sleep, followed by a full-night polysomnographic recording in a sleep laboratory. The results demonstrated that following exposure, time in Stages 3 and 4 sleep (SWS, slow-wave sleep) decreased by 9.5 min (12%) out of a total of 78.6 min, and time in Stage 2 sleep increased by 8.3 min (4%) out of a total of 196.3 min compared to sham. The latency to Stage 3 sleep was also prolonged by 4.8 min after exposure. Power density analysis indicated an enhanced activation in the frequency ranges 0.5-1.5 and 5.75-10.5 Hz during the first 30 min of Stage 2 sleep, with 7.5-11.75 Hz being elevated within the first hour of Stage 2 sleep, and bands 4.75-8.25 Hz elevated during the second hour of Stage 2 sleep. No pronounced power changes were observed in SWS or for the third hour of scored Stage 2 sleep. No differences were found between controls and subjects with prior complaints of mobile phone-related symptoms. The results confirm previous findings that RF exposure increased the EEG alpha range in the sleep EEG, and indicated moderate impairment of SWS. Furthermore, reported differences in sensitivity to mobile phone use were not reflected in sleep parameters.

Melanopsin as a sleep modulator: circadian gating of the direct effects of light on sleep and altered sleep homeostasis in Opn4(-/-) mice.

Light influences sleep and alertness either indirectly through a well-characterized circadian pathway or directly through yet poorly understood mechanisms. Melanopsin (Opn4) is a retinal photopigment crucial for conveying nonvisual light information to the brain. Through extensive characterization of sleep and the electrocorticogram (ECoG) in melanopsin-deficient (Opn4(-/-)) mice under various light-dark (LD) schedules, we assessed the role of melanopsin in mediating the effects of light on sleep and ECoG activity. In control mice, a light pulse given during the habitual dark period readily induced sleep, whereas a dark pulse given during the habitual light period induced waking with pronounced theta (7-10 Hz) and gamma (40-70 Hz) activity, the ECoG correlates of alertness. In contrast, light failed to induce sleep in Opn4(-/-) mice, and the dark-pulse-induced increase in theta and gamma activity was delayed. A 24-h recording under a LD 1-hratio1-h schedule revealed that the failure to respond to light in Opn4(-/-) mice was restricted to the subjective dark period. Light induced c-Fos immunoreactivity in the suprachiasmatic nuclei (SCN) and in sleep-active ventrolateral preoptic (VLPO) neurons was importantly reduced in Opn4(-/-) mice, implicating both sleep-regulatory structures in the melanopsin-mediated effects of light. In addition to these acute light effects, Opn4(-/-) mice slept 1 h less during the 12-h light period of a LD 12ratio12 schedule owing to a lengthening of waking bouts. Despite this reduction in sleep time, ECoG delta power, a marker of sleep need, was decreased in Opn4(-/-) mice for most of the (subjective) dark period. Delta power reached after a 6-h sleep deprivation was similarly reduced in Opn4(-/-) mice. In mice, melanopsin's contribution to the direct effects of light on sleep is limited to the dark or active period, suggesting that at this circadian phase, melanopsin compensates for circadian variations in the photo sensitivity of other light-encoding pathways such as rod and cones. Our study, furthermore, demonstrates that lack of melanopsin alters sleep homeostasis. These findings call for a reevaluation of the role of light on mammalian physiology and behavior.

Differential numbers of foci of lymphocytes within the brains of Lewis rats exposed to weak complex nocturnal magnetic fields during development of experimental allergic encephalomyelitis.

To discern if specific structures of the rat brain contained more foci of lymphocytes following induction of experimental allergic encephalomyelitis and exposures to weak, amplitude-modulated magnetic fields for 6 min once per hour during the scotophase, the residuals between the observed and predicted values for the numbers of foci for 320 structures were obtained. Compared to the brains of sham-field exposed rats, the brains of rats exposed to 7-Hz 50 nT (0.5 mG) amplitude-modulated fields showed more foci within hippocampal structures and the dorsal central grey of the midbrain while those exposed to 7-Hz 500 nT (5 mG) fields showed greater densities within the hypothalamus and optic chiasm. The brains of rats exposed to either the 50 nT or 500 nT amplitude-modulated 40-Hz fields displayed greater densities of foci within the midbrain structures related to rapid eye movement. Most of the enhancements of infiltrations within the magnetic field-exposed rats occurred in structures within periventricular or periaqueductal regions and were both frequency- and intensity-dependent. The specificity and complexity of the configurations of the residuals of the numbers of infiltrated foci following exposures to the different fields suggest that the brain itself may be a "sensory organ" for the detection of these stimuli.

Neural substrates of awakening probed with optogenetic control of hypocretin neurons.

The neural underpinnings of sleep involve interactions between sleep-promoting areas such as the anterior hypothalamus, and arousal systems located in the posterior hypothalamus, the basal forebrain and the brainstem. Hypocretin (Hcrt, also known as orexin)-producing neurons in the lateral hypothalamus are important for arousal stability, and loss of Hcrt function has been linked to narcolepsy. However, it is unknown whether electrical activity arising from Hcrt neurons is sufficient to drive awakening from sleep states or is simply correlated with it. Here we directly probed the impact of Hcrt neuron activity on sleep state transitions with in vivo neural photostimulation, genetically targeting channelrhodopsin-2 to Hcrt cells and using an optical fibre to deliver light deep in the brain, directly into the lateral hypothalamus, of freely moving mice. We found that direct, selective, optogenetic photostimulation of Hcrt neurons increased the probability of transition to wakefulness from either slow wave sleep or rapid eye movement sleep. Notably, photostimulation using 5-30 Hz light pulse trains reduced latency to wakefulness, whereas 1 Hz trains did not. This study establishes a causal relationship between frequency-dependent activity of a genetically defined neural cell type and a specific mammalian behaviour central to clinical conditions and neurobehavioural physiology.

Carbachol induction of REM sleep in the rat is more effective at lights-out than lights-on.

Long-lasting increases in REM sleep are induced in the rat following injection of small amounts of muscarinic receptor agonists into the caudal oral pontine reticular formation. By injecting carbachol at the beginning of the light period or beginning of the dark period, we sought to determine whether the muscarinic, REM sleep induction is influenced by the time of day it is initiated. We found that carbachol is more effective at increasing REM sleep when administered at the beginning of the dark in 87% of the cases. Of these cases, 43% showed evidence of a decreased potency of carbachol by a shift in the dose-response curve to the right. The lack of agreement in efficacy and potency to increase REM sleep supports a conclusion that alterations in local muscarinic receptors are not mediating the effect of time of day. REM sleep control mechanisms down stream of the muscarinic receptors may be the responsible factors.

The effect of electromagnetic fields emitted by mobile phones on human sleep.

Previous research has suggested that exposure to radiofrequency electromagnetic fields increases electroencephalogram spectral power in non-rapid eye movement sleep. Other sleep parameters have also been affected following exposure. We examined whether aspects of sleep architecture show sensitivity to electromagnetic fields emitted by digital mobile phone handsets. Fifty participants were exposed to electromagnetic fields for 30 min prior to sleep. Results showed a decrease in rapid eye movement sleep latency and increased electroencephalogram spectral power in the 11.5-12.25 Hz frequency range during the initial part of sleep following exposure. These results are evidence that mobile phone exposure prior to sleep may promote rapid eye movement sleep and modify the sleep electroencephalogram in the first non-rapid eye movement sleep period.

Role of alpha and beta adrenoceptors in locus coeruleus stimulation-induced reduction in rapid eye movement sleep in freely moving rats.

Based on the results of independent studies the involvement of norepinephrine in REM sleep regulation was known. Isolated studies showed that the effect could be mediated through either one or more subtypes of adrenoceptors. Earlier we have reported that REM-OFF neurons continue firing during REM sleep deprivation and mild but continuous stimulation of locus coeruleus (LC) or picrotoxin injection into the LC, that did not allow the REM-OFF neurons in the LC to stop firing, reduced REM sleep. However, the mechanism of action and type of adrenoreceptors involved in REM sleep regulation were unknown. The possible mechanism of action has been investigated in this study. It was proposed that if LC stimulation-induced decrease in REM sleep was due to norepinephrine, adrenergic antagonist must prevent the effect. Therefore, in this study, the effects of alpha1, alpha2 and beta-antagonists, viz. prazosin, yohimbine and propranolol, respectively, and alpha2 agonist, clonidine, on LC stimulation-induced reduction in REM sleep were investigated. The results showed that stimulation of LC inhibited REM sleep by reducing the frequency of generation of REM sleep, although the duration per episode remained unaffected. This decrease in the frequency of REM sleep was blocked by beta-antagonist propranolol while the duration of REM sleep per episode was blocked by alpha1-antagonist, prazosin. Also, a critical level of norepinephrine in the system was required for the generation of REM sleep, however, a higher level may be inhibitory. Based on the results of this study and our earlier studies, an interaction between neurons, containing different neurotransmitters and their subtypes of receptors for LC-mediated regulation of REM sleep has been proposed.

Sleep responses to light and dark are shaped by early experience.

Light regulates sleep timing through circadian entrapment and by eliciting acute changes in behavior. These behaviors are mediated by the subcortical visual system, retinorecipient nuclei distinct from the geniculocortical system. To test the hypothesis that early visual experience shapes light regulation of behavior, the authors recorded sleep in albino rats reared in continuous dark, continuous light, or a 12-hr light-dark cycle. Dark rearing strengthened and light rearing weakened acute responses to light, including light modulation of REM sleep, a marker for pretectal function in albino rats. However, neither dark nor light rearing altered daily amounts of wakefulness, non-REM sleep, or REM sleep. Thus, light and dark rearing might differentially affect the balance between acute and circadian responses to light that, in concert, govern sleep timing.

The effect of restraint stress on paradoxical sleep is influenced by the circadian cycle.

It is well known that the physiological impact imposed by events or behaviors displayed during the waking period determines the way organisms sleep. Among the situations known to affect sleep both in its duration and quality, stress has been widely studied and it is now admitted that its effects on sleep architecture depend on several factors specific to the stressor or the individual itself. Although numerous reports have highlighted the prominent role of the circadian cycle in the physiological, endocrine and behavioral consequences of restraint stress, a possible circadian influence in the effects of stress on the sleep-wake cycle has never been studied. Thus the present study was designed to compare the effects on sleep of a 1 h-lasting restraint stress applied at light onset to those observed after the same stressor was applied at light offset. We report that in both conditions stress induced a marked paradoxical sleep increase, whereas wakefulness displayed a moderate decrease and slow wave sleep a moderate augmentation. Although the effects of stress at lights on were of similar magnitude than those of stress at lights off, important differences in the sleep rebound latencies were observed: whatever the time of day the stress was applied, its effects on sleep always occurred during the dark period. This result thus shows that restraint stress could be efficiently used to study the interaction between the circadian and homeostatic components of sleep regulation.

Enhancement of REM sleep during extraocular light exposure in humans.

This study examined the effects on sleep of light administered to an extraocular site. A 3-h photic stimulus was applied to the popliteal region during sleep in 14 human subjects. Each subject also underwent a control stimulus condition during a separate laboratory session. The proportion of rapid eye movement (REM) sleep during the 3-h light administration session increased by an average of 31% relative to the control condition. The frequency but not the duration of REM episodes was altered during light exposure, thereby shortening the REM/non-REM (NREM) cycle length. No other sleep stages were significantly affected during light administration nor was sleep architecture altered after the light-exposure interval. These results confirm that extraocular light is transduced into a signal that is received and processed by the human central nervous system. In addition, they expand to a novel sensory modality previous findings that REM sleep can be enhanced by sensory stimulation.

Exposure to pulsed high-frequency electromagnetic field during waking affects human sleep EEG.

The aim of the study was to investigate whether the electromagnetic field (EMF) emitted by digital radiotelephone handsets affects brain physiology. Healthy, young male subjects were exposed for 30 min to EMF (900 MHz; spatial peak specific absorption rate 1 W/kg) during the waking period preceding sleep. Compared with the control condition with sham exposure, spectral power of the EEG in non-rapid eye movement sleep was increased. The maximum rise occurred in the 9.75-11.25 Hz and 12.5-13.25 Hz band during the initial part of sleep. These changes correspond to those obtained in a previous study where EMF was intermittently applied during sleep. Unilateral exposure induced no hemispheric asymmetry of EEG power. The present results demonstrate that exposure during waking modifies the EEG during subsequent sleep. Thus the changes of brain function induced by pulsed high-frequency EMF outlast the exposure period.

REM sleep in response to light and dark in congenic albino and pigmented F344 rats.

Sleep was recorded in congenic F344 albino (c/c) and pigmented (c/+) rats while they were exposed to various light-dark schedules at 10, 50 and 100 lux. In short LD schedules (1:1 and 3:3), both c/c and c/+ rats had similar patterns of NREM and waking in the light and dark. NREM was higher in the light and there was more wakefulness in the dark. These differences were accentuated with increased light intensity. In contrast, substantial effects on REM sleep were seen only in the c/c rats and increased light levels also enhanced these effects. REM sleep in pigmented c/+ rats was virtually unaffected by lighting changes. These results indicate that different systems are involved in regulating sleep-waking and REM sleep responses to light and further that these systems are differentially affected by alleles at (or near) the c locus and/or albinism.

Bilirubin, REM sleep, and phototransduction of environmental time cues. A hypothesis.

The prevailing hypothesis for phototransduction is that visual (rod or cone) pigments mediate light's primary effects on biological clock systems. Common light-responsive chronobiological behavioral properties of plants and animals and some common molecular structures of plants and animals suggest the possibility that heme moieties and bile pigments in animals mediate some nonvisual influences of light on neuroactive gases and biological rhythms. As plant phytochrome resets the plant biological clock, the similar chromophore in bile pigments is proposed to transduce environmental light zeitgeber signals to endogenous biological clocks. The temporal association of plasma bilirubin and rapid-eye-movement (REM) sleep in populations, the correlation of secretion of biliary bilirubin with REM sleep among 10 different species (Spearman r = 0.89, p < 0.002), and the known responses of bilirubin to light lead to the hypothesis that bilirubin, in particular, plays an evolutionary role in the regulation of REM sleep and in mediating some of light's antidepressant effects.

Effects of pulsed high-frequency electromagnetic fields on human sleep.

In the present study we investigated the influence of pulsed high-frequency electromagnetic fields of digital mobile radio telephones on sleep in healthy humans. Besides a hypnotic effect with shortening of sleep onset latency, a REM suppressive effect with reduction of duration and percentage of REM sleep was found. Moreover, spectral analysis revealed qualitative alterations of the EEG signal during REM sleep with an increased spectral power density. Knowing the relevance of REM sleep for adequate information processing in the brain, especially concerning mnestic functions and learning processes, the results emphasize the necessity to carry out further investigations on the interaction of this type of electromagnetic fields and the human organism.