The two-process model of sleep regulation: a reappraisal

Cortical parvalbumin neurons are responsible for homeostatic sleep rebound through CaMKII activation

The homeostatic regulation of sleep is characterized by rebound sleep after prolonged wakefulness, but the molecular and cellular mechanisms underlying this regulation are still unknown. In this study, we show that Ca2+/calmodulin-dependent protein kinase II (CaMKII)-dependent activity control of parvalbumin (PV)-expressing cortical neurons is involved in homeostatic regulation of sleep in male mice. Prolonged wakefulness enhances cortical PV-neuron activity. Chemogenetic suppression or activation of cortical PV neurons inhibits or induces rebound sleep, implying that rebound sleep is dependent on increased activity of cortical PV neurons. Furthermore, we discovered that CaMKII kinase activity boosts the activity of cortical PV neurons, and that kinase activity is important for homeostatic sleep rebound. Here, we propose that CaMKII-dependent PV-neuron activity represents negative feedback inhibition of cortical neural excitability, which serves as the distributive cortical circuits for sleep homeostatic regulation.

Effects of non-rapid eye movement sleep on the cortical synaptic expression of GluA1-containing AMPA receptors

Converging electrophysiological, molecular and ultrastructural evidence supports the hypothesis that sleep promotes a net decrease in excitatory synaptic strength, counteracting the net synaptic potentiation caused by ongoing learning during waking. However, several outstanding questions about sleep-dependent synaptic weakening remain. Here, we address some of these questions by using two established molecular markers of synaptic strength, the levels of the AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors containing the GluA1 subunit and the phosphorylation of GluA1 at serine 845 (p-GluA1(845)). We previously found that, in the rat cortex and hippocampus, these markers are lower after 6-8 h of sleep than after the same time spent awake. Here, we measure GluA1 and p-GluA1(845) levels in synaptosomes of mouse cortex after 5 h of either sleep, sleep deprivation, recovery sleep after sleep deprivation or selective REM sleep deprivation (32 C57BL/B6 adult mice, 16 females). We find that relative to after sleep deprivation, these synaptic markers are lower after sleep independent of whether the mice were allowed to enter REM sleep. Moreover, 5 h of recovery sleep following acute sleep deprivation is enough to renormalize their expression. Thus, the renormalization of GluA1 and p-GluA1(845) expression crucially relies on NREM sleep and can occur in a few hours of sleep after acute sleep deprivation.

The role of ATP in sleep-wake regulation: In adenosine-dependent and -independent manner

ATP plays a crucial role as an energy currency in the body's various physiological functions, including the regulation of the sleep-wake cycle. Evidence from genetics and pharmacology demonstrates a strong association between ATP metabolism and sleep. With the advent of new technologies such as optogenetics, genetically encoded biosensors, and novel ATP detection methods, the dynamic changes in ATP levels between different sleep states have been further uncovered. The classic mechanism for regulating sleep by ATP involves its conversion to adenosine, which increases sleep pressure when accumulated extracellularly. However, emerging evidence suggests that ATP can directly bind to P2 receptors and influence sleep-wake regulation through both adenosine-dependent and independent pathways. The outcome depends on the brain region where ATP acts and the expression type of P2 receptors. This review summarizes the experimental evidence on the relationship between ATP levels and changes in sleep states and outlines the mechanisms by which ATP is involved in regulating the sleep-wake cycle through both adenosine-dependent and independent pathways. Hopefully, this review will provide a comprehensive understanding of the current research basis and progress in this field and promote further investigations into the specific mechanisms of ATP in regulating sleep.

The Complex Relationship between Sleep and Cognitive Reserve: A Narrative Review Based on Human Studies

Sleep and brain/cognitive/neural reserve significantly impact well-being and cognition throughout life. This review aims to explore the intricate relationship between such factors, with reference to their effects on human cognitive functions. The specific goal is to understand the bidirectional influence that sleep and reserve exert on each other. Up to 6 February 2024, a methodical search of the literature was conducted using the PubMed database with terms related to brain, cognitive or neural reserve, and healthy or disturbed sleep. Based on the inclusion criteria, 11 articles were selected and analyzed for this review. The articles focus almost exclusively on cognitive reserve, with no explicit connection between sleep and brain or neural reserve. The results evidence sleep's role as a builder of cognitive reserve and cognitive reserve's role as a moderator in the effects of physiological and pathological sleep on cognitive functions. In conclusion, the findings of the present review support the notion that both sleep and cognitive reserve are critical factors in cognitive functioning. Deepening comprehension of the interactions between them is essential for devising strategies to enhance brain health and resilience against age- and pathology-related conditions.

Sleep and Oxidative Stress: Current Perspectives on the Role of NRF2

Sleep is a fundamental conserved physiological state across evolution, suggesting vital biological functions that are yet to be fully clarified. However, our understanding of the neural and molecular basis of sleep regulation has increased rapidly in recent years. Among various processes implicated in controlling sleep homeostasis, a bidirectional relationship between sleep and oxidative stress has recently emerged. One proposed function of sleep may be the mitigation of oxidative stress in both brain and peripheral tissues, contributing to the clearance of reactive species that accumulate during wakefulness. Conversely, reactive species, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS), at physiological levels, may act as signaling agents to regulate redox-sensitive transcriptional factors, enzymes, and other effectors involved in the regulation of sleep. As a primary sensor of intracellular oxidation, the transcription factor NRF2 is emerging as an indispensable component to maintain cellular redox homeostasis during sleep. Indeed, a number of studies have revealed an association between NRF2 dysfunction and the most common sleep conditions, including sleep loss, obstructive sleep apnea, and circadian sleep disturbances. This review examines the evidence of the intricate link between oxidative stress and NRF2 function in the context of sleep, and highlights the potential of NRF2 modulators to alleviate sleep disturbances.

FlyVISTA, an Integrated Machine Learning Platform for Deep Phenotyping of Sleep in Drosophila

Animal behavior depends on internal state. While subtle movements can signify significant changes in internal state, computational methods for analyzing these "microbehaviors" are lacking. Here, we present FlyVISTA, a machine-learning platform to characterize microbehaviors in freely-moving flies, which we use to perform deep phenotyping of sleep. This platform comprises a high-resolution closed-loop video imaging system, coupled with a deep-learning network to annotate 35 body parts, and a computational pipeline to extract behaviors from high-dimensional data. FlyVISTA reveals the distinct spatiotemporal dynamics of sleep-associated microbehaviors in flies. We further show that stimulation of dorsal fan-shaped body neurons induces micromovements, not sleep, whereas activating R5 ring neurons triggers rhythmic proboscis extension followed by persistent sleep. Importantly, we identify a novel microbehavior ("haltere switch") exclusively seen during quiescence that indicates a deeper sleep stage. These findings enable the rigorous analysis of sleep in Drosophila and set the stage for computational analyses of microbehaviors.

Considerations towards a neurobiologically-informed EEG measurement of sleepiness

Sleep is a daily experience across humans and other species, yet our understanding of how and why we sleep is presently incomplete. This is particularly prevalent in research examining the neurophysiological measurement of sleepiness in humans, where several electroencephalogram (EEG) phenomena have been linked with prolonged wakefulness. This leaves researchers without a solid basis for the measurement of homeostatic sleep need and complicates our understanding of the nature of sleep. Recent theoretical and technical advances may allow for a greater understanding of the neurobiological basis of homeostatic sleep need: this may result from increases in neuronal excitability and shifts in excitation/inhibition balance in neuronal circuits and can potentially be directly measured via the aperiodic component of the EEG. Here, we review the literature on EEG-derived markers of sleepiness in humans and argue that changes in these electrophysiological markers may actually result from neuronal activity represented by changes in aperiodic markers. We argue for the use of aperiodic markers derived from the EEG in predicting sleepiness and suggest areas for future research based on these.

Current Aspects of Selected Factors to Modulate Brain Health and Sports Performance in Athletes

This review offers a comprehensive evaluation of current aspects related to nutritional strategies, brain modulation, and muscle recovery, focusing on their applications and the underlying mechanisms of physiological adaptation for promoting a healthy brain, not only in athletes but also for recreationally active and inactive individuals. We propose that applying the rule, among others, of good sleep, regular exercise, and a properly balanced diet, defined as "SPARKS", will have a beneficial effect on the function and regeneration processes of the gut-brain-muscle axis. However, adopting the formula, among others, of poor sleep, stress, overtraining, and dysbiosis, defined as "SMOULDER", will have a detrimental impact on the function of this axis and consequently on human health as well as on athletes. Understanding these dynamics is crucial for optimizing brain health and cognitive function. This review highlights the significance of these factors for overall well-being, suggesting that adopting the "SPARKS" approach may benefit not only athletes but also older adults and individuals with health conditions.

A metabolic perspective to sleep genetics

The metabolic signals that regulate sleep and the metabolic functions that occur during sleep are active areas of research. Prior studies have focused on sugars and nucleotides but new genetic evidence suggests novel functions of lipid and amino acid metabolites in sleep. Additional genetic studies of energetic signaling pathways and the circadian clock transcription factor network have increased our understanding of how sleep responds to changes in the metabolic state. This review focuses on key recent insights from genetic experiments in humans and model organisms to improve our understanding of the interrelationship between metabolism and sleep.

The interplay between sleep and ecophysiology, behaviour and responses to environmental change in fish

Evidence of behavioural sleep has been observed in every animal species studied to date, but current knowledge of the behaviour, neurophysiology and ecophysiology associated with sleep is concentrated on mammals and birds. Fish are a hugely diverse group that can offer novel insights into a variety of sleep-related behaviours across environments, but the ecophysiological relevance of sleep in fish has been largely overlooked. Here, we systematically reviewed the literature to assess the current breadth of knowledge on fish sleep, and surveyed the diverse physiological effects and behaviours associated with sleep. We also discuss possible ways in which unstudied external factors may alter sleep behaviours. For example, predation risk may alter sleep patterns, as has been shown in mammalian, avian and reptilian species. Other environmental factors - such as water temperature and oxygen availability - have the potential to alter sleep patterns in fish differently than for terrestrial endotherms. Understanding the ecological influences on sleep in fish is vital, as sleep deprivation has the potential to affect waking behaviour and fitness owing to cognitive and physiological impairments, possibly affecting ecological phenomena and sensitivity to environmental stressors in ways that have not been considered.

Objectively assessed sleep quality parameters in Multiple Sclerosis at home: Association to disease, disease severity and physical activity

BACKGROUND

Multiple Sclerosis (MS) is a chronic inflammatory autoimmune, neurodegenerative disease that affects regular mobility and leads predominantly to physical disability. Poor sleep quality, commonly reported in MS patients, impacts their physical activity (PA). Accelerometers monitor 24-h activity patterns, offering insights into disease progression in daily life.

OBJECTIVE

To test if the sleep quality variables of MS patients, as assessed with wrist-worn accelerometers, differ from those of controls and are associated with PA and disease severity variables.

METHODS

Seven-day raw accelerometer data collected from 40 MS patients and 24 controls was processed using an open-source GGIR package, from which variables of sleep quality (sleep efficiency, wake after sleep onset (WASO), sleep regularity index (SRI), intradaily variability (IV)) and PA (of different intensities: inactivity, light (LPA), moderate (MPA), vigorous (VPA)) were analyzed. The variables were compared between the two study groups and in MS patients, correlation tested associations among the variables of sleep quality, PA, and disease severity (assessed with the Expanded Disability Status Scale, EDSS).

RESULTS

Sleep efficiency was the only variable that differed significantly between MS patients and controls (lower in MS, p = 0.01). Both SRI (positively) and IV (negatively) correlated with the time spent in LPA and MPA. WASO correlated negatively with inactivity.

CONCLUSION

This is one of the few studies with a wrist-worn accelerometer that shows a difference in sleep efficiency between MS patients and controls and, in MS, an association of sleep quality variables with PA variables.

Sleep and local field potential effect of the D2 receptor agonist bromocriptine during the estrus cycle and postpartum period in female rats

BACKGROUND

Pituitary lactotrophs are under tonic dopaminergic inhibitory control and bromocriptine treatment blocks prolactin secretion.

METHODS

Sleep and local field potential were addressed for 72 h after bromocriptine treatments applied during the different stages of the estrus cycle and for 24 h in the early- and middle postpartum period characterized by spontaneously different dynamics of prolactin release in female rats.

RESULTS

Sleep changes showed strong dependency on the estrus cycle phase of the drug application. Strongest increase of wakefulness and reduction of slow wave sleep- and rapid eye movements sleep appeared during diestrus-proestrus and middle postpartum treatments. Stronger sleep-wake effects appeared in the dark phase in case of the estrus cycle treatments, but in the light phase in postpartum treatments. Slow wave sleep and REM sleep loss in case of estrus cycle treatments was not compensated at all and sleep loss seen in the first day post-injection was gained further later. In opposition, slow wave sleep loss in the light phase after bromocriptine injections showed compensation in the postpartum period treatments. Bromocriptine treatments resulted in a depression of local field potential delta power during slow wave sleep while an enhancement in beta and gamma power during wakefulness regardless of the treatment timing.

CONCLUSIONS

These results can be explained by the interplay of dopamine D2 receptor agonism, lack of prolactin release and the spontaneous homeostatic sleep drive being altered in the different stages of the estrus cycle and the postpartum period.

Effects of acute exposure to hypoxia on sleep structure in healthy adults: A systematic review

The sleep quality of lowlanders in hypoxic environments has become increasingly important with an increase in highland and alpine activities. This study aimed to identify the effects of acute exposure to hypoxia on the sleep structure of lowlanders and to analyze the changes in sleep indicators at varying levels of hypoxia. This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Twenty-three studies were screened and included in the quantitative analysis. The results showed that acute exposure to hypoxia reduced sleep quality in lowlanders. Post-sleep arousal events and the percentage of N1 were significantly increased, whereas total sleep time, sleep efficiency, and the percentage of N3 and rapid eye movement sleep were significantly decreased in hypoxic environments. Acute exposure to hypoxia had the greatest negative impact on wakefulness after sleep onset (WASO). In addition, a larger decrease in sleep efficiency and higher increase in the percentages of N1 and WASO were observed when lowlanders were exposed to higher levels of hypoxia. This study clarifies the quantitative effects of acute hypoxic exposure on sleep in lowlanders based on original studies and explains the sleep disorders faced by lowlanders in hypoxic environments.

Efficacy of Morning Shorter Wavelength Lighting in the Visible (Blue) Range and Broad-Spectrum or Blue-Enriched Bright White Light in Regulating Sleep, Mood, and Fatigue in Traumatic Brain Injury: A Systematic Review

Traumatic brain injury (TBI) profoundly affects sleep, mood, and fatigue, impeding daily functioning and recovery. This systematic review evaluates the efficacy of morning shorter wavelength lighting in the visible (blue) range and broad-spectrum or blue-enriched bright white light exposure in mitigating these challenges among TBI patients. Through electronic database searches up to May 2023, studies assessing sleep, circadian rhythm, sleepiness, mood, and fatigue outcomes in TBI patients exposed to morning shorter wavelength lighting in the visible (blue) range and broad-spectrum or blue-enriched bright white light were identified. Seven studies involving 309 participants met the inclusion criteria. Results indicated consistent advancement in sleep timing among individuals with mild TBI, alongside improvements in total sleep time, mood, and reduced sleepiness with both types of light exposure, particularly in mild TBI cases. Notably, two studies demonstrated alleviation of fatigue exclusively in severe TBI cases following light exposure. Despite promising findings, evidence remains limited, emphasizing the need for future research with standardized protocols to confirm the potential and optimize the benefits of light therapy for TBI recovery.

The association of sleep duration and leukocyte telomere length in middle-aged and young-old adults: A cross-sectional study of UK Biobank

BACKGROUND

The relationships between sleep duration and aging-associated diseases are intricate. Leukocyte telomere length (LTL) is a biomarker of aging, while the association of sleep duration and LTL is unclear.

METHODS

The 310,091 study participants from UK Biobank were enrolled in this cross-sectional study. Restricted cubic splines (RCS) analysis was firstly performed to assess the nonlinear relationship between sleep duration and LTL. Sleep duration was then categorized into three groups: <7 h (short sleep duration), 7-8 h (reference group), and >8 h (long sleep duration) and multiple linear regression was applied to analyze the association of short sleep and long sleep duration with LTL. We further performed subgroup analyses stratified by sex, age, chronotype and snoring.

RESULTS

RCS showed an inverted J-shaped relationship between sleep duration and LTL. Compared with the reference group, the inverse association of long sleep duration and LTL was statistically significant in fully-adjusted model (P = 0.001). Subgroup analyses showed that this association was more apparent in people over 50 years (51-60 y: P = 0.002; >60 y: P = 0.005), in men (P = 0.022), and in people preferred evening chronotype (P = 0.001).

CONCLUSION

Compared with participants sleeping 7-8 h, those sleep longer than 8 h had shorter LTL in middle-aged and young-old adults. The negative association between long sleep duration and LTL was more apparent in older people, in men, and in people preferred evening chronotype.

Resting-State EEG Reveals Abnormal Microstate Characteristics of Depression with Insomnia

Previous research revealed various aspects of resting-state EEG for depression and insomnia. However, the EEG characteristics of depressed subjects with insomnia are rarely studied, especially EEG microstates that capture the dynamic activities of the large-scale brain network. To fill these research gaps, the present study collected resting-state EEG data from 32 subclinical depression subjects with insomnia (SDI), 31 subclinical depression subjects without insomnia (SD), and 32 healthy controls (HCs). Four topographic maps were generated from clean EEG data after clustering and rearrangement. Temporal characteristics were obtained for statistical analysis, including cross-group variance analysis (ANOVA) and intra-group correlation analysis. In our study, the global clustering of all individuals in the EEG microstate analysis revealed the four previously discovered categories of microstates (A, B, C, and D). The occurrence of microstate B was lower in SDI than in SD and HC subjects. The correlation analysis showed that the total Pittsburgh Sleep Quality Index (PSQI) score negatively correlated with the occurrence of microstate C in SDI (r = - 0.415, p < 0.05). Conversely, there was a positive correlation between Self-rating Depression Scale (SDS) scores and the duration of microstate C in SD (r = 0.359, p < 0.05). These results indicate that microstates reflect altered large-scale brain network dynamics in subclinical populations. Abnormalities in the visual network corresponding to microstate B are an electrophysiological characteristic of subclinical individuals with symptoms of depressive insomnia. Further investigation is needed for microstate changes related to high arousal and emotional problems in people suffering from depression and insomnia.

An integrative sensor of body states: how the mushroom body modulates behavior depending on physiological context

The brain constantly compares past and present experiences to predict the future, thereby enabling instantaneous and future behavioral adjustments. Integration of external information with the animal's current internal needs and behavioral state represents a key challenge of the nervous system. Recent advancements in dissecting the function of the Drosophila mushroom body (MB) at the single-cell level have uncovered its three-layered logic and parallel systems conveying positive and negative values during associative learning. This review explores a lesser-known role of the MB in detecting and integrating body states such as hunger, thirst, and sleep, ultimately modulating motivation and sensory-driven decisions based on the physiological state of the fly. State-dependent signals predominantly affect the activity of modulatory MB input neurons (dopaminergic, serotoninergic, and octopaminergic), but also induce plastic changes directly at the level of the MB intrinsic and output neurons. Thus, the MB emerges as a tightly regulated relay station in the insect brain, orchestrating neuroadaptations due to current internal and behavioral states leading to short- but also long-lasting changes in behavior. While these adaptations are crucial to ensure fitness and survival, recent findings also underscore how circuit motifs in the MB may reflect fundamental design principles that contribute to maladaptive behaviors such as addiction or depression-like symptoms.

The effects of exercise programs on sleep architecture in obstructive sleep apnea: a meta-analysis of randomized controlled trials

OBJECTIVES

Exercise is an effective intervention for obstructive sleep apnea (OSA). However, the effects of exercise on objective sleep architecture in patients with OSA remain unknown. This meta-analysis aimed to collect data from randomized controlled trials of exercise interventions in patients with OSA, with a specific focus on objective sleep parameters derived from polysomnography.

METHODS

Randomized control trials that targeted patients with OSA aged >18 years, measured sleep using polysomnography after exercise programs, and reported the proportion of sleep stages were included for meta-analysis. Bias was assessed using the revised Cochrane risk-of-bias tool and funnel plots. The random effects model was applied.

RESULTS

Six studies with a total of 236 patients were included in the meta-analysis. There were no significant differences in the total sleep time (TST), sleep efficiency, sleep onset latency, stage N1 sleep, or rapid eye movement sleep between the exercise and control groups. Participation in an exercise program lasting >12 weeks significantly decreased stage N2 and increased stage N3 sleep as observed in the subgroup analysis. Although this tendency did not reach statistical significance in the total-group analysis, it was significant after excluding the possible confounding effects of heart disease.

CONCLUSIONS

The exercise program decreased N2 and increased N3 proportions over the TST among patients with OSA, which may correspond to subjective sleep quality. The beneficial effects were significant when the program lasted >12 weeks and after excluding the confounding effects of heart disease. Exercise program duration should be considered when providing clinical advice.

Promoting adolescent sleep and circadian function: A narrative review on the importance of daylight access in schools

Adolescent sleep disturbances and circadian delays pose significant challenges to mood and daytime functioning. In this narrative review, we explore the impact of light on sleep and highlight the importance of monitoring and managing light exposure in adolescents throughout the day and night. The benefits of daylight exposure in mitigating sleep and circadian disruptions are well-established; however, interventions targeting access to daylight in adolescents remain understudied and underutilized. The primary aim of this narrative review is to bring attention to this gap in the literature and propose the need for institutional-level interventions that promote access to daylight, especially considering adolescents' early school start times and substantial time spent indoors on weekdays. School-led interventions, such as active commuting to school and outdoor curriculums, have promising effects on sleep and circadian rhythms. Additionally, practical measures to optimize natural light in classrooms, including managing blinds and designing conducive environments, should also be considered. While future studies are necessary to facilitate the implementation of interventions, the potential for these school-level interventions to support adolescent sleep health is evident. Aiming for integration of individual-level regulation and institutional-level intervention of light exposure is necessary for optimal outcomes.

High stability of EEG spectral power across polysomnography and multiple sleep latency tests in good sleepers and chronic insomniacs

To assess the stability of electroencephalographic (EEG) spectral features across overnight polysomnography (PSG) and daytime multiple sleep latency tests (MSLTs) in chronic insomniacs (CIs) and normal controls (NCs). A total of 20 NCs and 22 CIs underwent standard PSG and MSLTs. Spectral analyses were performed on EEG data from PSG and MSLTs and absolute and relative power in central, frontal and occipital channels were obtained for wake (W) and non-rapid eye movement sleep stage 1 and 2 (N1, N2). Intraclass correlation coefficients (ICCs) were used to assess the stability of EEG spectral power across PSG and MSLTs for W, N1 and N2. The absolute power of all frequency bands except delta exhibited high stability across PSG and MSLTs in both NCs and CIs (ICCs ranged from 0.430 to 0.978). Although delta absolute power was stable in NCs during N1 and N2 stages (ICCs ranged from 0.571 to 0.835), it tended to be less stable in CIs during W and sleep stages (ICCs ranged from 0.042 to 0.807). We also observed lower stability of relative power compared to absolute power though the majority of relative power outcomes maintained high stability in both groups (ICCs in relative power ranged from 0.044 to 0.962). Most EEG spectral bandwidths across PSG and MSLT in W, N1 and N2 show high stability in good sleepers and chronic insomniacs. EEG signals from either an overnight PSG or a daytime MSLT may be useful for reliably exploring EEG spectral features during wakefulness or sleep.

Human Prosocial Preferences Are Related to Slow-Wave Activity in Sleep

Prosocial behavior is crucial for the smooth functioning of the society. Yet, individuals differ vastly in the propensity to behave prosocially. Here, we try to explain these individual differences under normal sleep conditions without any experimental modulation of sleep. Using a portable high-density EEG, we measured the sleep data in 54 healthy adults (28 females) during a normal night's sleep at the participants' homes. To capture prosocial preferences, participants played an incentivized public goods game in which they faced real monetary consequences. The whole-brain analyses showed that a higher relative slow-wave activity (SWA, an indicator of sleep depth) in a cluster of electrodes over the right temporoparietal junction (TPJ) was associated with increased prosocial preferences. Source localization and current source density analyses further support these findings. Recent sleep deprivation studies imply that sleeping enough makes us more prosocial; the present findings suggest that it is not only sleep duration, but particularly sufficient sleep depth in the TPJ that is positively related to prosociality. Because the TPJ plays a central role in social cognitive functions, we speculate that sleep depth in the TPJ, as reflected by relative SWA, might serve as a dispositional indicator of social cognition ability, which is reflected in prosocial preferences. These findings contribute to the emerging framework explaining the link between sleep and prosocial behavior by shedding light on the underlying mechanisms.

Sleep regulation and host genetics

Due to the multifactorial and complex nature of rest, we focus on phenotypes related to sleep. Sleep regulation is a multifactorial process. In this chapter, we focus on those phenotypes inherent to sleep that are highly prevalent in the population, and that can be modulated by lifestyle, such as sleep quality and duration, insomnia, restless leg syndrome and daytime sleepiness. We, therefore, leave in the background those phenotypes that constitute infrequent pathologies or for which the current level of scientific evidence does not favour the implementation of practical approaches of this type. Similarly, the regulation of sleep quality is intimately linked to the regulation of the circadian rhythm. Although this relationship is discussed in the sections that require it, the in-depth study of circadian rhythm regulation at the molecular level deserves a separate chapter, and this is how it is dealt with in this volume.

Sleep and Ultramarathon: Exploring Patterns, Strategies, and Repercussions of 1,154 Mountain Ultramarathons Finishers

BACKGROUND

Sleep and physical performance are strongly related and mutually influence each other. Athletes, particularly in disciplines like offshore sailing and ultra-endurance sports, often suffer from sleep deprivation due to factors like irregular training times, travel, and the extended duration of events like 100-mile mountain races. Despite growing interest in sleep's role in sports science, few studies have specifically investigated the sleep patterns of ultramarathon runners. This study aimed to investigate sleep patterns and sleep management strategies in ultramarathons, and the repercussions of sleep deprivation during and after races.

METHODS

This cross-sectional study using e-survey was conducted on 1154 runners from two ultramarathons (a 165 km race with 9,576 m positive elevation; 2018 finish time [23:18:48-66:04:00], and a 111 km race with 6,433 m elevation; [15:34:56 - 41:54:16]).

RESULTS

The results revealed that 58% of the runners reported implementing sleep management strategies before or during the race. Most runners began the race with some level of sleep debt (-50 min a week before the race). During the races, 77% of runners slept, with the cumulative sleep duration varying based on race duration and the number of nights spent on the race (76 min at 165 km and 27 min at 111 km). Short naps lasting less than 30 min were the most popular strategy. The prevalence of symptoms attributed to sleep deprivation during the race was high (80%), with reported falls and hallucinations. After the race, runners reported recovering a normal state of wakefulness relatively quickly (within two days); 22% believed that sleep deprivation during the race increased the risk of accidents in everyday life.

CONCLUSION

This study provides valuable insights into sleep patterns and strategies in ultramarathon running and emphasizes the importance of adequate sleep management for performance and post-race recovery.

Neuroligin-2 shapes individual slow waves during slow-wave sleep and the response to sleep deprivation in mice

BACKGROUND

Sleep disturbances are a common comorbidity to most neurodevelopmental disorders and tend to worsen disease symptomatology. It is thus crucial to understand mechanisms underlying sleep disturbances to improve patients' quality of life. Neuroligin-2 (NLGN2) is a synaptic adhesion protein regulating GABAergic transmission. It has been linked to autism spectrum disorders and schizophrenia in humans, and deregulations of its expression were shown to cause epileptic-like hypersynchronized cerebral activity in rodents. Importantly, the absence of Nlgn2 (knockout: KO) was previously shown to alter sleep-wake duration and quality in mice, notably increasing slow-wave sleep (SWS) delta activity (1-4 Hz) and altering its 24-h dynamics. This type of brain oscillation is involved in memory consolidation, and is also a marker of homeostatic sleep pressure. Sleep deprivation (SD) is notably known to impair cognition and the physiological response to sleep loss involves GABAergic transmission.

METHODS

Using electrocorticographic (ECoG) recordings, we here first aimed to verify how individual slow wave (SW; 0.5-4 Hz) density and properties (e.g., amplitude, slope, frequency) contribute to the higher SWS delta activity and altered 24-h dynamics observed in Nlgn2 KO mice. We further investigated the response of these animals to SD. Finally, we tested whether sleep loss affects the gene expression of Nlgn2 and related GABAergic transcripts in the cerebral cortex of wild-type mice using RNA sequencing.

RESULTS

Our results show that Nlgn2 KO mice have both greater SW amplitude and density, and that SW density is the main property contributing to the altered 24-h dynamics. We also found the absence of Nlgn2 to accelerate paradoxical sleep recovery following SD, together with profound alterations in ECoG activity across vigilance states. Sleep loss, however, did not modify the 24-h distribution of the hypersynchronized ECoG events observed in these mice. Finally, RNA sequencing confirmed an overall decrease in cortical expression of Nlgn2 and related GABAergic transcripts following SD in wild-type mice.

CONCLUSIONS

This work brings further insight into potential mechanisms of sleep duration and quality deregulation in neurodevelopmental disorders, notably involving NLGN2 and GABAergic neurotransmission.

Temporal pathways between circadian rhythm, depression and anxiety in the transition from adolescence to early adulthood

BACKGROUND

Sleep and circadian rhythm problems intertwine with affective disorders. Adolescents are particularly vulnerable to developing sleep and affective problems. Yet, the temporal pathways between circadian rhythm, depression and anxiety in the transition phase from adolescence to early adulthood are not fully understood.

METHODS

233 adolescents (76 % females) participated at two time points (T1 and T2) at an interval of 19-months (aged 16.8 and 18.4 years). We used The Beck Depression Inventory-II, Generalized Anxiety Disorder Assessment, GENEActiv actigraphy across 8 days (delayed sleep phase (DSP), sleep duration, midpoint, and regularity), and iButton 1922L thermologgers across 3 days (intrinsic circadian period length, amplitude, and mesor).

RESULTS

A shorter sleep duration at T1 associated with an increase in affective problems at T2, and affective problems at T1 associated with an increase in sleep irregularity at T2. A longer circadian period at T1 associated with an increase in males' affective problems at T2. Moderate to severe depression and anxiety at T1 associated with a 2.69-fold risk (95 % CI 1.38-5.26, p = 0.004) and 2.11-fold risk (95 % CI 1.04-4.25, p = 0.038) of poor sleep quality at T2. Moderate to severe generalized anxiety associated with a 3.17-fold risk (95 % CI 1.35-7.41, p = 0.008) of DSP at T2.

LIMITATIONS

The follow-up period is short.

CONCLUSIONS

The results revealed bidirectional temporal links between sleep and affective problems. Novel observations include a heightened risk of future DSP following a current anxiety disorder and a heightened risk of affective problems following a longer circadian period measured from the 24-hour temperature variation in males.

Sleep architecture of elite soccer players surrounding match days as measured by WHOOP straps

This study aimed to quantify and compare sleep architecture before and after home and away matches in elite soccer players from the English Premier League. Across two seasons, 6 male players (age 28 ± 5 y; body mass 85.1 ± 9.5 kg; height 1.86 ± 0.09 m) wore WHOOP straps to monitor sleep across 13 matches that kicked off before 17:00 h. For each, sleep was recorded the night before (MD-1), after (MD) and following the match (MD +1). Across these 3 days total sleep time (TST), sleep efficiency (SE), sleep disturbances, wake time, light sleep, deep sleep, REM sleep, sleep and wake onsets, alongside external load, were compared. TST was reduced after MD versus MD +1 (392.9 ± 76.4 vs 459.1 ± 66.7 min, p = 0.003) but no differences existed in any other sleep variables between days (p > 0.05). TST did not differ after home (386.9 ± 75.7 min) vs. away matches (401.0 ± 78.3 min) (p = 0.475), nor did other sleep variables (p > 0.05). GPS-derived external load peaked on MD (p < 0.05). In conclusion, despite reduced TST on MD, sleep architecture was unaffected after matches played before 17:00 h, suggesting sleep quality was not significantly compromised.

Embracing sleep-onset complexity

Sleep is crucial for many vital functions and has been extensively studied. By contrast, the sleep-onset period (SOP), often portrayed as a mere prelude to sleep, has been largely overlooked and remains poorly characterized. Recent findings, however, have reignited interest in this transitional period and have shed light on its neural mechanisms, cognitive dynamics, and clinical implications. This review synthesizes the existing knowledge about the SOP in humans. We first examine the current definition of the SOP and its limits, and consider the dynamic and complex electrophysiological changes that accompany the descent to sleep. We then describe the interplay between internal and external processing during the wake-to-sleep transition. Finally, we discuss the putative cognitive benefits of the SOP and identify novel directions to better diagnose sleep-onset disorders.

Selective REM sleep restriction in mice using a device designed for tunable somatosensory stimulation

BACKGROUND

Sleep perturbation is widely used to investigate the physiological mechanisms that mediate sleep-wake dynamics, and to isolate the specific roles of sleep in health and disease. However, state-of-the-art methods to accomplish sleep perturbation in preclinical models are limited in their throughput, flexibility, and specificity.

NEW METHOD

A system was developed to deliver vibro-tactile somatosensory stimulation aimed at controlled, selective sleep perturbation. The frequency and intensity of stimulation can be tuned to target a variety of experimental applications, from sudden arousal to sub-threshold transitions between light and deep stages of NREM sleep. This device was activated in closed-loop to selectively interrupt REM sleep in mice.

RESULTS

Vibro-tactile stimulation effectively and selectively interrupted REM sleep - significantly reducing the average REM bout duration relative to matched, unstimulated baseline recordings. As REM sleep was repeatedly interrupted, homeostatic mechanisms prompted a progressively quicker return to REM sleep. These effects were dependent on the parameters of stimulation applied.

COMPARISON WITH EXISTING METHODS

Existing sleep perturbation systems often require moving parts within the cage and/or restrictive housing. The system presented is unique in that it interrupts sleep without invading the animal's space. The ability to vary stimulation parameters is a great advantage over existing methods, as it allows for adaptation in response to habituation and/or circadian/homeostatic changes in arousal threshold.

CONCLUSIONS

The proposed method of stimulation demonstrates feasibility in affecting mouse sleep within a standard home cage environment, thus limiting environmental stress. Furthermore, the ability to tune frequency and intensity of stimulation allows for graded control over the extent of sleep perturbation, which potentially expands the utility of this technology beyond applications related to sleep.

Circadian Mechanisms in Brain Fluid Biology

The brain is a complex organ, fundamentally changing across the day to perform basic functions like sleep, thought, and regulating whole-body physiology. This requires a complex symphony of nutrients, hormones, ions, neurotransmitters and more to be properly distributed across the brain to maintain homeostasis throughout 24 hours. These solutes are distributed both by the blood and by cerebrospinal fluid. Cerebrospinal fluid contents are distinct from the general circulation because of regulation at brain barriers including the choroid plexus, glymphatic system, and blood-brain barrier. In this review, we discuss the overlapping circadian (≈24-hour) rhythms in brain fluid biology and at the brain barriers. Our goal is for the reader to gain both a fundamental understanding of brain barriers alongside an understanding of the interactions between these fluids and the circadian timing system. Ultimately, this review will provide new insight into how alterations in these finely tuned clocks may lead to pathology.

Light and dopamine impact two circadian neurons to promote morning wakefulness

In both mammals and flies, circadian brain neurons orchestrate physiological oscillations and behaviors like wake and sleep; these neurons can be subdivided by morphology and by gene expression patterns. Recent single-cell sequencing studies identified 17 Drosophila circadian neuron groups. One of these include only two lateral neurons (LNs), which are marked by the expression of the neuropeptide ion transport peptide (ITP). Although these two ITP+ LNs have long been grouped with five other circadian evening activity cells, inhibiting the two neurons alone strongly reduces morning activity; this indicates that they are prominent morning neurons. As dopamine signaling promotes activity in Drosophila like in mammals, we considered that dopamine might influence this morning activity function. Moreover, the ITP+ LNs express higher mRNA levels than other LNs of the type 1-like dopamine receptor Dop1R1. Consistent with the importance of Dop1R1, CRISPR/Cas9 mutagenesis of this receptor only in the two ITP+ LNs renders flies significantly less active in the morning, and ex vivo live imaging shows that dopamine increases cAMP levels in these two neurons; cell-specific mutagenesis of Dop1R1 eliminates this cAMP response to dopamine. Notably, the response is more robust in the morning, reflecting higher morning Dop1R1 mRNA levels in the two neurons. As morning levels are not elevated in constant darkness, this suggests light-dependent upregulation of morning Dop1R1 transcript levels. Taken together with enhanced morning cAMP response to dopamine, the data indicate how light stimulates morning wakefulness in flies, which mimics the important effect of light on morning wakefulness in humans.

Lipopolysaccharide-Mediated Effects of the Microbiota on Sleep and Body Temperature

Background

Recent research suggests that microbial molecules translocated from the intestinal lumen into the host's internal environment may play a role in various physiological functions, including sleep. Previously, we identified that butyrate, a short-chain fatty acid, produced by intestinal bacteria, and lipoteichoic acid, a cell wall component of gram-positive bacteria induce sleep when their naturally occurring translocation is mimicked by direct delivery into the portal vein. Building upon these findings, we aimed to explore the sleep signaling potential of intraportally administered lipopolysaccharide, a primary component of gram-negative bacterial cell walls, in rats.

Results

Low dose of lipopolysaccharide (1 μg/kg) increased sleep duration and prolonged fever, without affecting systemic lipopolysaccharide levels. Interestingly, administering LPS systemically outside the portal region at a dose 20 times higher did not affect sleep, indicating a localized sensitivity within the hepatoportal region, encompassing the portal vein and liver, for the sleep and febrile effects of lipopolysaccharide. Furthermore, both the sleep- and fever-inducing effects of LPS were inhibited by indomethacin, a prostaglandin synthesis inhibitor, and replicated by intraportal administration of prostaglandin E2 or arachidonic acid, suggesting the involvement of the prostaglandin system in mediating these actions.

Conclusions

These findings underscore the dynamic influence of lipopolysaccharide in the hepatoportal region on sleep and fever mechanisms, contributing to a complex microbial molecular assembly that orchestrates communication between the intestinal microbiota and brain. Lipopolysaccharide is a physiological component of plasma in both the portal and extra-portal circulation, with its levels rising in response to everyday challenges like high-fat meals, moderate alcohol intake, sleep loss and psychological stress. The increased translocation of lipopolysaccharide under such conditions may account for their physiological impact in daily life, highlighting the intricate interplay between microbial molecules and host physiology.

Sex-specific regulation of the cortical transcriptome in response to sleep deprivation

Multiple studies have documented sex differences in sleep behaviour, however, the molecular determinants of such differences remain unknown. Furthermore, most studies addressing molecular mechanisms have been performed only in males, leaving the current state of knowledge biased towards the male sex. To address this, we studied the differences in the transcriptome of the cerebral cortex of male and female C57Bl/6 J mice after 6 h of sleep deprivation. We found that several genes, including the neurotrophin growth factor Bdnf, immediate early genes Fosb and Fosl2, and the adenylate cyclase Adcy7 are differentially upregulated in males compared to females. We identified the androgen-receptor activating transcription factor EZH2 as the upstream regulatory element specifying sex differences in the sleep deprivation transcriptome. We propose that the pathways downstream of these transcripts, which impact on cellular re-organisation, synaptic signalling, and learning may underpin the differential response to sleep deprivation in the two sexes.

Activation of locus coeruleus noradrenergic neurons rapidly drives homeostatic sleep pressure

Homeostatic sleep regulation is essential for optimizing the amount and timing of sleep, but the underlying mechanism remains unclear. Optogenetic activation of locus coeruleus noradrenergic neurons immediately increased sleep propensity following transient wakefulness. Fiber photometry showed that repeated optogenetic or sensory stimulation caused rapid declines of locus coeruleus calcium activity and noradrenaline release. This suggests that functional fatigue of noradrenergic neurons, which reduces their wake-promoting capacity, contributes to sleep pressure.

Fundamentals of sleep regulation: Model and benchmark values for fractal and oscillatory neurodynamics

Homeostatic, circadian and ultradian mechanisms play crucial roles in the regulation of sleep. Evidence suggests that ratios of low-to-high frequency power in the electroencephalogram (EEG) spectrum indicate the instantaneous level of sleep pressure, influenced by factors such as individual sleep-wake history, current sleep stage, age-related differences and brain topography characteristics. These effects are well captured and reflected in the spectral exponent, a composite measure of the constant low-to-high frequency ratio in the periodogram, which is scale-free and exhibits lower interindividual variability compared to slow wave activity, potentially serving as a suitable standardization and reference measure. Here we propose an index of sleep homeostasis based on the spectral exponent, reflecting the level of membrane hyperpolarization and/or network bistability in the central nervous system in humans. In addition, we advance the idea that the U-shaped overnight deceleration of oscillatory slow and fast sleep spindle frequencies marks the biological night, providing somnologists with an EEG-index of circadian sleep regulation. Evidence supporting this assertion comes from studies based on sleep replacement, forced desynchrony protocols and high-resolution analyses of sleep spindles. Finally, ultradian sleep regulatory mechanisms are indicated by the recurrent, abrupt shifts in dominant oscillatory frequencies, with spindle ranges signifying non-rapid eye movement and non-spindle oscillations - rapid eye movement phases of the sleep cycles. Reconsidering the indicators of fundamental sleep regulatory processes in the framework of the new Fractal and Oscillatory Adjustment Model (FOAM) offers an appealing opportunity to bridge the gap between the two-process model of sleep regulation and clinical somnology.

Just Let Me Sleep in: Identifying and Treating Delayed Sleep Phase Disorder in Adolescents

Individuals with delayed sleep phase disorder (DSPD) are unable to naturally fall asleep and awake at conventional times; for this reason, DSPD is often mistaken for insomnia. However, unlike many patients with insomnia, those with DSPD struggle to get up at appropriate times. DSPD is associated with school refusal, academic difficulties, and lower employment rate. DSPD in youth has prevalence as high as 16%, and is often comorbid with other psychiatric disorders. Treatments include appropriate light exposure during the day, melatonin use, developing an evening routine that minimizes arousal-increasing activities, and gradually shifting sleep-wake times toward more functional ones.

Sleep deprivation and medication administration errors in registered nurses-A scoping review

AIM

To explore whether sleep deprivation contributes to medication errors in registered nurses (RNs).

BACKGROUND

Sleep deprivation is a potential issue for RNs, particularly those who work shifts. Sleep deprivation has been found to have a negative impact on numerous cognitive processes. Nurses administer several medications to patients a day, potentially while sleep deprived-anecdotal reports suggest that this could result in an increased risk of error occurring.

DESIGN

A scoping review was conducted using the Prisma-ScR extension framework to explore what is known about the effect of RNs' sleep deprivation on medication administration errors.

METHODS

A search of databases generated 171 results. When inclusion and exclusion criteria were applied, 18 empirical studies were analysed. Studies included retrospective analysis of errors, surveys of perceptions of causes and observational studies.

RESULTS

Data indicated that RNs consider fatigue, which may be caused by sleep deprivation, to be a contributing factor to medication errors. The search only identified three observer studies, which provided conflicting results as to whether lack of sleep contributes to the error rate. Of the numerous tools used to measure sleep, the Pittsburgh Sleep Quality Index was the most frequently used.

CONCLUSION

Although RNs anecdotally consider a lack of sleep potentially contributes to medication errors, there is insufficient research to provide robust evidence to confirm this assumption.

NO PATIENT OR PUBLIC CONTRIBUTIONS

Patient or public contributions were not required for this scoping review.

RELEVANCE TO CLINICAL PRACTICE

Sleep deprivation is a potential issue for nurses, especially those who work shifts. Poor sleep impacts cognitive processes that potentially could increase errors. Nurses should be aware of the impact sleep may have on patient safety.

Light exposure during sleep is bidirectionally associated with irregular sleep timing: The multi-ethnic study of atherosclerosis (MESA)

Exposure to light at night (LAN) may influence sleep timing and regularity. Here, we test whether greater light exposure during sleep (LEDS) is bidirectionally associated with greater irregularity in sleep onset timing in a large cohort of older adults in cross-sectional and short-term longitudinal (days) analyses. Light exposure and activity patterns, measured via wrist-worn actigraphy (ActiWatch Spectrum), were analyzed in 1933 participants with 6+ valid days of data in the Multi-Ethnic Study of Atherosclerosis (MESA) Exam 5 Sleep Study. Summary measures of LEDS averaged across nights were evaluated in linear and logistic regression analyses to test the association with standard deviation (SD) in sleep onset timing (continuous variable) and irregular sleep onset timing (SD > 90 min, binary). Night-to-night associations between LEDS and absolute differences in nightly sleep onset timing were also evaluated with distributed lag non-linear models and mixed models. In between-individual linear and logistic models adjusted for demographic, health, and seasonal factors, every 5-lux unit increase in LEDS was associated with a 7.8-min increase in sleep onset SD (β = 0.13 h, 95%CI:0.09-0.17) and 32% greater odds (OR = 1.32, 95%CI:1.17-1.50) of irregular sleep onset. In within-individual night-to-night mixed model analyses, every 5-lux unit increase in LEDS the night prior was associated with a 2.2-min greater deviation of sleep onset the next night (β = 0.036 h, p < 0.05). Conversely, every 1-h increase in sleep deviation was associated with a 0.35-lux increase in future LEDS (β = 0.348 lux, p < 0.05). LEDS was associated with greater irregularity in sleep onset in between-individual analyses and subsequent deviation in sleep timing in within-individual analyses, supporting a role for LEDS in irregular sleep onset timing. Greater deviation in sleep onset was also associated with greater future LEDS, suggesting a bidirectional relationship. Maintaining a dark sleeping environment and preventing LEDS may promote sleep regularity and following a regular sleep schedule may limit LEDS.

Persistently short or long sleep duration increases the risk of sensory impairment in Chinese older adults

Background

Cross-sectional evidence suggests that persistently short or long sleep duration is associated with sensory impairment. Thus, this study was conducted to investigate the associations between sleep duration and altered sleep duration with sensory impairment in Chinese older adults.

Methods

Longitudinal data (2008-2014) obtained through the Chinese Longitudinal Healthy Longevity Survey (CLHLS) were analyzed. Sleep duration was classified as normal (7-8 h), short (<7 h), or long (≥9 h). Sensory impairment was assessed using individuals' self-reported data on visual and hearing functions. Cox regression was performed to evaluate the effects of sleep duration and altered sleep duration on sensory impairment, including visual impairment (VI) and hearing impairment (HI).

Results

This study included 3,578 older adults (mean age: 78.12 ± 9.59 years). Among them, 2,690 (75.2%) were aged 65-84 years and 1798 (50.3%) were women. The risks of VI (hazard ratio [HR]: 1.14; 95% confidence interval [CI]: 1.02-1.29), HI (HR: 1.14; 95% CI: 1.00-1.30), and dual sensory impairment (both VI and HI; HR: 1.26; 95% CI: 1.03-1.55) were high in older adults with long sleep duration. In addition, the risks of VI, HI, and dual sensory impairment were high in individuals whose sleep duration changed from normal to short or long (HR: 1.20 [95% CI: 1.02-1.42], 1.26 [95% CI: 1.03-1.53], and 1.54 [95% CI: 1.11-2.12], respectively) and those with persistently short or long sleep duration (HR: 1.25 [95% CI: 1.07-1.46], 1.34 [95% CI: 1.11-1.61], and 1.67 [95% CI: 1.22-2.27], respectively).

Conclusion

A prospective association was identified between altered sleep duration and sensory impairment in Chinese older adults. Our findings highlight the importance of optimal sleep duration and healthy sleep habits in preventing sensory impairment in older adults.

Wake EEG oscillation dynamics reflect both sleep need and brain maturation across childhood and adolescence

An objective measure of brain maturation is highly insightful for monitoring both typical and atypical development. Slow wave activity, recorded in the sleep electroencephalogram (EEG), reliably indexes changes in brain plasticity with age, as well as deficits related to developmental disorders such as attention-deficit hyperactivity disorder (ADHD). Unfortunately, measuring sleep EEG is resource-intensive and burdensome for participants. We therefore aimed to determine whether wake EEG could likewise index developmental changes in brain plasticity. We analyzed high-density wake EEG collected from 163 participants 3-25 years old, before and after a night of sleep. We compared two measures of oscillatory EEG activity, amplitudes and density, as well as two measures of aperiodic activity, intercepts and slopes. Furthermore, we compared these measures in patients with ADHD (8-17 y.o., N=58) to neurotypical controls. We found that wake oscillation amplitudes behaved the same as sleep slow wave activity: amplitudes decreased with age, decreased after sleep, and this overnight decrease decreased with age. Oscillation densities were also substantially age-dependent, decreasing overnight in children and increasing overnight in adolescents and adults. While both aperiodic intercepts and slopes decreased linearly with age, intercepts decreased overnight, and slopes increased overnight. Overall, our results indicate that wake oscillation amplitudes track both development and sleep need, and overnight changes in oscillation density reflect some yet-unknown shift in neural activity around puberty. No wake measure showed significant effects of ADHD, thus indicating that wake EEG measures, while easier to record, are not as sensitive as those during sleep.

A two-process model of Drosophila sleep reveals an inter-dependence between circadian clock speed and the rate of sleep pressure decay

Sleep is controlled by two processes-a circadian clock that regulates its timing and a homeostat that regulates the drive to sleep. Drosophila has been an insightful model for understanding both processes. For four decades, Borbély and Daan's two-process model has provided a powerful framework for understanding sleep regulation. However, the field of fly sleep has not employed such a model as a framework for the investigation of sleep. To this end, we have adapted the two-process model to the fly and established its utility by showing that it can provide empirically testable predictions regarding the circadian and homeostatic control of fly sleep. We show that the ultradian rhythms previously reported for loss-of-function clock mutants in the fly are robustly detectable and a predictable consequence of a functional sleep homeostat in the absence of a functioning circadian system. We find that a model in which the circadian clock speed and homeostatic rates act without influencing each other provides imprecise predictions regarding how clock speed influences the strength of sleep rhythms and the amount of daily sleep. We also find that quantitatively good fits between empirical values and model predictions were achieved only when clock speeds were positively correlated with rates of decay of sleep pressure. Our results indicate that longer sleep bouts better reflect the homeostatic process than the current definition of sleep as any inactivity lasting 5 minutes or more. This two-process model represents a powerful framework for work on the molecular and physiological regulation of fly sleep.

Exposure to indoor light at night in relation to multiple dimensions of sleep health: findings from the Sister Study

STUDY OBJECTIVE

To examine the association between light at night (LAN) and multiple sleep health dimensions.

METHODS

Among 47 765 Sister Study participants, indoor LAN (TV on in the room, light(s) on in room, light from outside the room, nightlight, no light) and sleep dimensions were self-reported at baseline (2003-2009). We used Poisson regression with robust variance to estimate adjusted prevalence ratios (PR) and 95% confidence intervals (CI) for the cross-sectional associations between LAN and short sleep duration (<7 hours/night), insomnia symptoms (difficulty falling or staying asleep), frequent napping (≥3 naps/week), inconsistent sleep/wake time (differed day-to-day and week-to-week), sleep debt (≥2 hours between longest and shortest duration), recent sleep medication use, and a cumulative poor sleep score (≥3 poor sleep dimensions). Population-attributable risks (PARs) were determined for any light exposure vs. none by race/ethnicity.

RESULTS

Compared to sleeping with no light in the bedroom, sleeping with a TV on was associated with a higher prevalence of most dimensions of poor sleep (e.g. short sleep duration: PR = 1.38, 95% CI: 1.32 to 1.45; inconsistent sleep/wake time: PR = 1.55, 95% CI: 1.44 to 1.66; sleep debt: PR = 1.36, 95% CI: 1.29 to 1.44; poor sleep score: PR = 1.58, 95% CI: 1.48-1.68). PARs tended to be higher for non-Hispanic black women compared to non-Hispanic white women.

CONCLUSIONS

Sleeping with a TV on was associated with poor sleep health among US women, and non-Hispanic black women may be disproportionately burdened.

The Negative Effects of Travel on Student Athletes Through Sleep and Circadian Disruption

Collegiate athletes must satisfy the academic obligations common to all undergraduates, but they have the additional structural and social stressors of extensive practice time, competition schedules, and frequent travel away from their home campus. Clearly such stressors can have negative impacts on both their academic and athletic performances as well as on their health. These concerns are made more acute by recent proposals and decisions to reorganize major collegiate athletic conferences. These rearrangements will require more multi-day travel that interferes with the academic work and personal schedules of athletes. Of particular concern is additional east-west travel that results in circadian rhythm disruptions commonly called jet lag that contribute to the loss of amount as well as quality of sleep. Circadian misalignment and sleep deprivation and/or sleep disturbances have profound effects on physical and mental health and performance. We, as concerned scientists and physicians with relevant expertise, developed this white paper to raise awareness of these challenges to the wellbeing of our student-athletes and their co-travelers. We also offer practical steps to mitigate the negative consequences of collegiate travel schedules. We discuss the importance of bedtime protocols, the availability of early afternoon naps, and adherence to scheduled lighting exposure protocols before, during, and after travel, with support from wearables and apps. We call upon departments of athletics to engage with sleep and circadian experts to advise and help design tailored implementation of these mitigating practices that could contribute to the current and long-term health and wellbeing of their students and their staff members.

Schizophrenia and disruption of circadian rhythms: An overview of genetic, metabolic and clinical signs

A molecular clock in the suprachiasmatic nucleus of the anterior hypothalamus, which is entrained by the dark-light cycle and controls the sleep-wake cycle, regulates circadian rhythms. The risk of developing mental disorders, such as schizophrenia, has long been linked to sleep abnormalities. Additionally, a common aspect of mental disorders is sleep disturbance, which has a direct impact on the intensity of the symptoms and the quality of life of the patient. This relationship can be explained by gene alterations such as CLOCK in schizophrenia which are also important components of the physiological circadian rhythm. The function of dopamine and adenosine in circadian rhythm should also be noted, as these hypotheses are considered to be the most popular theories explaining schizophrenia pathogenesis. Therefore, determining the presence of a causal link between the two can be key to identifying new potential targets in schizophrenia therapy, which can open new avenues for clinical research as well as psychiatric care. We review circadian disruption in schizophrenia at the genetic, metabolic, and clinical levels. We summarize data about clock and clock-controlled genes' alterations, neurotransmitter systems' impairments, and association with chronotype in schizophrenia patients. Our findings demonstrate that in schizophrenia either homeostatic or circadian processes of sleep regulation are disturbed. Also, we found an insufficient number of studies aimed at studying the relationship between known biological phenomena of circadian disorders and clinical signs of schizophrenia.

Sleep restores an optimal computational regime in cortical networks

Sleep is assumed to subserve homeostatic processes in the brain; however, the set point around which sleep tunes circuit computations is unknown. Slow-wave activity (SWA) is commonly used to reflect the homeostatic aspect of sleep; although it can indicate sleep pressure, it does not explain why animals need sleep. This study aimed to assess whether criticality may be the computational set point of sleep. By recording cortical neuron activity continuously for 10-14 d in freely behaving rats, we show that normal waking experience progressively disrupts criticality and that sleep functions to restore critical dynamics. Criticality is perturbed in a context-dependent manner, and waking experience is causal in driving these effects. The degree of deviation from criticality predicts future sleep/wake behavior more accurately than SWA, behavioral history or other neural measures. Our results demonstrate that perturbation and recovery of criticality is a network homeostatic mechanism consistent with the core, restorative function of sleep.

Validation of the Chinese version of the Sleep Regularity Questionnaire (SRQ) and analysis of influencing factors

BACKGROUND

Currently, there is no instrument to measure sleep regularity in China. In this study, the Sleep Regularity Questionnaire（SRQ） was translated into Chinese, tested for reliability and validity, and analyzed for factors affecting sleep regularity.

METHODS

The English version of the SRQ was translated into Chinese, and a total of 3642 individuals were included in this research. Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were used to examine the underlying factor structure of the Chinese version of the SRQ and to measure its reliability and validity. In addition, the correlations between sleep regularity and general information, personal habits, self-control, stress, anxiety, and depression were explored.

RESULTS

The Cronbach's α of the Chinese SRQ was 0.858, supporting the two-factor structure. Sleep regularity was statistically different between gender and ethnicity (p < 0.05), and personal habits (exercise, continued eating after dinner, smoking and drinking) had an effect on sleep regularity. Sleep regularity was positively associated with individual self-control and negatively associated with stress, anxiety, and depression.

CONCLUSIONS

The Chinese version of the SRQ has excellent reliability and validity. There are two dimensions, namely circadian regularity and sleep continuity regularity, which can be used to assess the sleep regularity of Chinese adults. The results of this study showed that males and Han Chinese having better sleep regularity. And people with good lifestyle habits and greater self-control sleep more regularly, while stress, anxiety and depression can affect individuals' sleep regularity.

Orexin Receptor Antagonism: Normalizing Sleep Architecture in Old Age and Disease

Sleep is essential for human well-being, yet the quality and quantity of sleep reduce as age advances. Older persons (>65 years old) are more at risk of disorders accompanied and/or exacerbated by poor sleep. Furthermore, evidence supports a bidirectional relationship between disrupted sleep and Alzheimer's disease (AD) or related dementias. Orexin/hypocretin neuropeptides stabilize wakefulness, and several orexin receptor antagonists (ORAs) are approved for the treatment of insomnia in adults. Dysregulation of the orexin system occurs in aging and AD, positioning ORAs as advantageous for these populations. Indeed, several clinical studies indicate that ORAs are efficacious hypnotics in older persons and dementia patients and, as in adults, are generally well tolerated. ORAs are likely to be more effective when administered early in sleep/wake dysregulation to reestablish good sleep/wake-related behaviors and reduce the accumulation of dementia-associated proteinopathic substrates. Improving sleep in aging and dementia represents a tremendous opportunity to benefit patients, caregivers, and health systems.

Regularity of bedtime, wake-up time, and time in bed in mid-life: associations with cardiometabolic health markers with adjustment for physical activity and sedentary time

BACKGROUND

Insufficient sleep has been linked to the accumulation of cardiometabolic risks while physical activity acts as a protective factor. Also, sleep regularity may play a critical role in maintaining optimal cardiometabolic health. This cross-sectional study examined the association between device-based sleep regularity, waking activity behaviors, and cardiometabolic health markers, including blood pressure level; abdominal adiposity level; and blood glucose, insulin, and cholesterol.

METHODS

We included 3698 members of the Northern Finland Birth cohort 1966 who participated in the follow-up study at the age of 46 years between 2012 and 2014 (women 61%). We used seven-day standard deviations of device-based bedtime, wake-up time, and time in bed to reflect sleep regularities. As covariates in linear regression models, we used commonly known potential risk factors in (gender, education, marital status, work schedule, smoking status, alcohol risk use, seven-day time in bed mean, chronotype). In addition to the previous, we used either sedentary time or total physical activity as a covariate (B coefficients with 95% confidence intervals CI).

RESULTS

When we considered sedentary time with other covariates, irregularities in bedtime, wake-up time, and time in bed were associated with unfavorable cardiometabolic health markers, such as higher body mass index (bedtime regularity: 0.194, 95% CI [0.072, 0.316], p = 0.002); higher diastolic blood pressure levels (time in bed regularity: 0.175, 95% CI [0.044, 0.306], p = 0.009); and higher 2-h glucose levels (wake-up time regularity: 0.107, 95% CI [0.030, 0.184], p = 0.006). When we considered total physical activity with other covariates, only irregular bedtime was associated with higher waist circumference (B 0.199, 95% CI [0.042, 0.356], p = 0.013). Irregularities in bedtime and wake-up time were not associated with higher diastolic blood pressure, higher visceral fat area or higher fasting insulin level after considering sedentary time or total physical activity with other covariates (in all, p > 0.05).

CONCLUSIONS

In middle-aged, physical activity appears to weaken the adverse relationship between irregular sleep and cardiometabolic health markers, although the interpretation of the impact of sedentary time remains less conclusive. The clinical significance and extent of the observed associations warrant further investigation.

A pilot time-in-bed restriction intervention behaviorally enhances slow-wave activity in older adults

Introduction

Identifying intervention methods that target sleep characteristics involved in memory processing is a priority for the field of cognitive aging. Older adults with greater sleep efficiency and non-rapid eye movement slow-wave activity (SWA) (0.5-4 Hz electroencephalographic activity) tend to exhibit better memory and cognitive abilities. Paradoxically, long total sleep times are consistently associated with poorer cognition in older adults. Thus, maximizing sleep efficiency and SWA may be a priority relative to increasing mere total sleep time. As clinical behavioral sleep treatments do not consistently enhance SWA, and propensity for SWA increases with time spent awake, we examined with a proof-of concept pilot intervention whether a greater dose of time-in-bed (TiB) restriction (75% of habitual TiB) would increase both sleep efficiency and SWA in older adults with difficulties staying asleep without impairing memory performance.

Methods

Participants were adults ages 55-80 with diary-reported sleep efficiency <90% and wake after sleep onset (WASO) >20 min. Sleep diary, actigraphy, polysomnography (PSG), and paired associate memory acquisition and retention were assessed before and after a week-long TiB restriction intervention (n = 30). TiB was restricted to 75% of diary-reported habitual TiB. A comparison group of n = 5 participants repeated assessments while following their usual sleep schedule to obtain preliminary estimates of effect sizes associated with repeated testing.

Results

Subjective and objective sleep measures robustly improved in the TiB restriction group for sleep quality, sleep depth, sleep efficiency and WASO, at the expense of TiB and time spent in N1 and N2 sleep. As hypothesized, SWA increased robustly with TiB restriction across the 0.5-4 Hz range, as well as subjective sleep depth, subjective and objective WASO. Despite increases in sleepiness ratings, no impairments were found in memory acquisition or retention.

Conclusion

A TiB restriction dose equivalent to 75% of habitual TiB robustly increased sleep continuity and SWA in older adults with sleep maintenance difficulties, without impairing memory performance. These findings may inform long-term behavioral SWA enhancement interventions aimed at improving memory performance and risk for cognitive impairments.