Sleep and thermoregulation

Targeting Sleep Physiology to Modulate Glymphatic Brain Clearance

Sleep has been postulated to play an important role in the removal of potentially neurotoxic molecules, such as amyloid-β, from the brain via the glymphatic system. Disturbed sleep, on the other hand, may contribute to the accumulation of neurotoxins in brain tissue, eventually leading to neuronal death. A bidirectional relationship has been proposed between impaired sleep and neurodegenerative processes, which start years before the onset of clinical symptoms associated with conditions like Alzheimer's and Parkinson's diseases. Given the heavy burden these conditions place on society, it is imperative to develop interventions that promote efficient brain clearance, thereby potentially aiding in the prevention or slowing of neurodegeneration. In this review, we explore whether the metabolic clearance function of sleep can be enhanced through sensory (e.g., auditory, vestibular) or transcranial (e.g., magnetic, ultrasound, infrared light) stimulation, as well as pharmacological (e.g., antiepileptics) and behavioral (e.g., sleeping position, physical exercise, cognitive intervention) modulation of sleep physiology. A particular focus is placed on strategies to enhance slow-wave activity during nonrapid eye movement sleep as a driver of glymphatic brain clearance. Overall, this review provides a comprehensive overview on the potential preventative and therapeutic applications of sleep interventions in combating neurodegeneration, cognitive decline, and dementia.

Linking ringed seal foraging behaviour to environmental variability

BACKGROUND

Foraging rates directly influence animals' energetic intake and expenditure and are thus linked to body condition and the ability to survive and reproduce. Further, understanding the underlying processes driving a species' behaviour and habitat use is important as changes in behaviour could result from changes in environmental conditions.

METHODS

In this study, the dives of Saimaa ringed seals (Pusa hispida saimensis) were classified for the first time using hidden Markov models and telemetry data collected on individual dives, and the behavioural states of the diving seals were estimated. In addition, we used generalized additive mixed models on the foraging probability of the seals to identify environmental and temporal drivers of foraging behaviour.

RESULTS

We inferred three (in winter) or four (in summer) different dive types: sleeping/resting dives, shallow inactive dives, transiting dives and foraging dives, based on differences in dive metrics logged by or derived from data from telemetry tags. Long and relatively deep sleeping/resting dives were missing entirely in the winter, compensated by an increased proportion of time used for haul-out. We found profound differences in the behaviour of Saimaa ringed seals during the open water season compared to the ice-covered winter, with the greatest proportion of time allocated to foraging during the summer months (36%) and the lowest proportion in the winter (21%). The seals' foraging probability peaked in summer (July) and was highest during the daytime during both summer and winter months. Moreover, foraging probability was highest at lake depths of 7-30 m in the winter and at depths > 15 m in the summer. We also found some evidence of sex-specific foraging strategies that are adapted seasonally, with females preferring more sheltered water areas during winter.

CONCLUSIONS

We suggest that the foraging behaviour of Saimaa ringed seals is largely influenced by diel vertical movements and availability of fish, and that the seals optimize their energy acquisition while conserving energy, especially during the cold winter months. Further, the seals display some flexibility in foraging strategies, a feature that may help this endangered subspecies to cope with the ongoing climate change.

NKCC1 inhibition improves sleep quality and EEG information content in a Down syndrome mouse model

In several brain disorders, the hyperpolarizing/inhibitory effects of GABA signaling through Cl-permeable GABAA receptors are compromised, leading to an imbalance between neuronal excitation and inhibition. For example, the Ts65Dn mouse model of Down syndrome (DS) exhibits increased expression of the Cl- importer NKCC1, leading to depolarizing gamma aminobutyric acid (GABA) signaling in the mature hippocampus and cortex. Inhibiting NKCC1 with the Food and Drug Administration (FDA)-approved diuretic bumetanide rescues inhibitory GABAergic transmission, synaptic plasticity, and cognitive functions in adult Ts65Dn mice. Given that DS individuals and Ts65Dn mice show sleep disturbances, and considering the key role of GABAergic transmission in sleep, we investigated whether NKCC1 upregulation contributes to sleep abnormalities in adult Ts65Dn mice. Chronic oral administration of bumetanide ameliorated the spectral profile of sleep, sleep architecture, and electroencephalogram (EEG) entropy/complexity, accompanied by a lower hyperactivity in trisomic mice. These results offer a potential avenue for addressing common sleep disturbances in DS.

World Sleep Society recommendations for the use of wearable consumer health trackers that monitor sleep

Wearable consumer health trackers (CHTs) are increasingly used for sleep monitoring, yet their utility remains debated within the sleep community. To navigate these perspectives, we propose pragmatic, actionable recommendations for users, clinicians, researchers, and manufacturers to support CHT usage and development. We provide an overview of the evolution of multi-sensor CHTs, detailing common sensors and sleep-relevant metrics. We advocate for standardized 'fundamental sleep measures' across manufacturers, distinguishing these from proprietary exploratory metrics with future potential. We outline best practices for using CHT-derived sleep data in healthy individuals while addressing current device limitations. Additionally, we explore their role in evaluating and managing individuals at risk for or diagnosed with insomnia, sleep apnea, or circadian rhythm sleep-wake disorders. Guidance is provided on device selection to align with their intended use and on conducting and interpreting performance evaluation studies. Collaboration with manufacturers is needed to balance feature comprehensiveness with clinical utility and usability. Finally, we examine challenges in integrating heterogeneous sleep data into clinical health records and discuss medical device certification for specific wearable CHT features. By addressing these issues, our recommendations aim to inform the usage of CHTs in the global community and to begin bridging the gap between consumer technology and clinical application, maximizing the potential of CHTs to enhance both personal and community sleep health.

Imperatives and co-benefits of research into climate change and neurological disease

Evidence suggests that anthropogenic climate change is accelerating and is affecting human health globally. Despite urgent calls to address health effects in the context of the additional challenges of environmental degradation, biodiversity loss and ageing populations, the effects of climate change on specific health conditions are still poorly understood. Neurological diseases contribute substantially to the global burden of disease, and the possible direct and indirect consequences of climate change for people with these conditions are a cause for concern. Unaccustomed temperature extremes can impair the systems of resilience of the brain, thereby exacerbating or increasing susceptibility to neurological disease. In this Perspective, we explore how changing weather patterns resulting from climate change affect sleep - an essential restorative human brain activity, the quality of which is important for people with neurological diseases. We also consider the pervasive and complex influences of climate change on two common neurological conditions: stroke and epilepsy. We highlight the urgent need for research into the mechanisms underlying the effects of climate change on the brain in health and disease. We also discuss how neurologists can respond constructively to the climate crisis by raising awareness and promoting mitigation measures and research - actions that will bring widespread co-benefits.

Phasic Dopamine Release in the Nucleus Accumbens Influences REM Sleep Timing

Based on the activity of dopamine (DA) neurons during behavioral states, the DA system has long been thought to be foundational in regulating sleep-wake behavior; over the past decade, advances in circuit manipulation and recording techniques have strengthened this perspective. Recently, several studies have demonstrated that DA release in regions of the limbic system is important in the promotion of REM sleep. Yet how DA dynamics change within bouts of sleep, how these changes are regulated, and whether they influence future state changes remains unclear. To address these questions, in mice of both sexes we used in vivo fiber photometry and inhibitory optogenetics to identify a specific role of DA transients in the nucleus accumbens (NAcc) in state transitions from NREM sleep. We found that DA transients increase their frequency and amplitude over the duration of NREM sleep and that this increase is more pronounced during NREM bouts that transition into REM sleep. Next, we found that DA transients in NREM sleep are influenced by changes in REM sleep pressure. Finally, we show that transient DA release in the NAcc plays a functional role in regulating the timing of REM sleep entrances, as inhibition of midbrain DA neuron terminals in the NAcc prolonged bouts of NREM sleep and decreased the frequency of bouts of REM sleep. These findings demonstrate that DA release in the NAcc is dynamically regulated by sleep pressure and has a functional role in transitions from NREM sleep, particularly those into REM sleep.

Does body cooling facilitated by bedding compared to control condition improve sleep among adults (18-64 years old)? A systematic review and meta-analysis

INTRODUCTION

The relationship between blood distribution, body temperature, and sleep/wakefulness states is still unclear. The aim of the present study is to systematically review the potential beneficial effects of bedding strategies (e.g., mattress, mattress topper or pillow) on body cooling and night-time sleep.

MATERIAL & METHODS

This systematic review with meta-analysis searched PubMed, ScienceDirect and Web of Science, from inception until March 4, 2024. We included randomized controlled trials aiming to investigate any type of bedding that induced body cooling compared to habitual sleep environment on sleep parameters in healthy adults. Two reviewers independently extracted data, appraised risk of bias by Cochrane tool, and estimated the mean differences between groups with 95% confidence interval. Meta-analyses and proportional meta-analyses were performed depending on the type of variable. The certainty of evidence was assessed using the Grades of Recommendation, Assessment, Development and Evaluation system.

RESULTS

From 3454 articles screened, 9 studies met the inclusion criteria. Overall, with the certainty of the evidence ranging from very low to low we found no differences between groups on sleep onset latency, sleep efficiency, sleep proportion spent in each sleep stage (i.e. N1, N2, N3 and REM), wake after sleep onset, and total sleep time. Results could be interpreted with caution due to high heterogeneity in the estimated effects.

CONCLUSION

With uncertainty of evidence, that ranged from very low to low, different bedding strategies had no effects on night-time sleep characteristics; however, the studies included into the qualitative synthesis suggested an effect of different bedding strategies on body cooling (i.e., lower core body temperature, p < 0.05) from an acute perspective. Future studies on various forms of bedding interventions susceptible to favour and maintain sleep through a positive body thermal effect are highly warranted.

PROSPERO REGISTRATION

CRD42021275369.

Rising global temperatures and its impact on sleep behavior of male redheaded bunting (Emberiza bruniceps)

Anthropogenic global warming is one of the most pervasive threats to nature and biodiversity. The magnitude with which earths' temperature is rising is affecting every lifeform uniquely; however, the studies highlighting the impacts of global warming on avian sleep are scarce. To this end, the present study was aimed at analyzing the impact of global warming on sleep behavior of a nocturnal migrant, Emberiza bruniceps. For this purpose, the birds were divided into two groups (N = 15 each), subjected to high (35 ± 1 °C) and low (19 ± 1 °C) temperature schedule with concurrent exposure to 8L:16D (short day; SD) photoperiod followed by 13L:11D (long day; LD). The experiment continued till 7 cycles of zugunruhe (LD) in birds. The results reveal significant impact of temperature treatment on initiation and quality of zugunruhe. Temporal distribution of activity and rest varied according to the temperature provided. Focusing on rest and specifically on sleep of birds, high ambient temperatures resulted in greater sleep fragmentation (evident by increased awakenings during night), whereas low temperature created a sleep conducive environment (evident by abundance of back sleep). Besides postural differences, high temperature resulted in reduced sleep duration, sleep onset latency and circulating plasma melatonin levels in comparison with low temperature suggesting the negative impact of high temperature on different sleep attributes. Not only sleep, seasonal physiology of birds such as hyperphagia, gain in body mass, and fat stores showed significant reduction in high temperature condition. Besides behavioral and physiological alterations, high ambient temperature led to elevated expression of temperature sensitive (trpv4, trpm8, hspa8, and hsp70) genes. Enhanced expression of chrm3 (responsible for wakefulness) also affirms sleep fragmentation in response to high temperature. Thus, the study highlights the negative impact of high temperature on birds' sleep behavior and seasonal physiology.

Huddling substates in mice facilitate dynamic changes in body temperature and are modulated by Shank3b and Trpm8 mutation

Social thermoregulation is a means of maintaining homeostatic body temperature. While adult mice are a model organism for studying both social behavior and energy regulation, the relationship between huddling and core body temperature (Tb) is poorly understood. Here, we develop a behavioral paradigm and computational tools to identify active-huddling and quiescent-huddling as distinct thermal substates. We find that huddling is an effective thermoregulatory strategy in female but not male groups. At 23 °C (room temperature), but not 30 °C (near thermoneutrality), huddling facilitates large reductions in Tb and Tb-variance. Notably, active-huddling is associated with bidirectional changes in Tb, depending on its proximity to bouts of quiescent-huddling. Further, group-housed animals lacking the synaptic scaffolding gene Shank3b have hyperthermic Tb and spend less time huddling. In contrast, individuals lacking the cold-sensing gene Trpm8 have hypothermic Tb - a deficit that is rescued by increased huddling time. These results reveal how huddling behavior facilitates acute adjustments of Tb in a state-dependent manner.

Isotemporal substitution analysis of time between sedentary behavior, and physical activity on sleep quality in younger adults: a multicenter study

OBJECTIVE

To evaluate the effects of replacing time spent in sedentary behavior (SB) with moderate to vigorous physical activity on sleep quality in young adults.

METHODS

Multicenter cross-sectional study, carried out with students enrolled in undergraduate courses at universities in Brazil. Sleep quality was assessed using a question of the World Health Organization Quality of Life (WHOQOL-brief) and classified as good or poor sleep quality. SB was evaluated by self-reported total sitting time, and the level of leisure-time PA was classified according to the intensity of moderate-intensity physical activity (MPA) and vigorous-intensity physical activity (VPA), which were assessed using a self-reported questionnaire. An isotemporal replacement logistic model was used to evaluate the effects of different SB, MPA, and VPA sessions on sleep quality.

RESULTS

A total of 8,059 study participants were evaluated, the majority had poor sleep quality (64.79%), were physically inactive (48.28%, defined as practicing < 150 min of MPA or < 75 min of VPA per week), and spent ≥ 9 h/day in SB (55.08%). The multivariate model showed an association between non-adherence to wake-based movement guidelines and poor sleep quality, where those with one altered behavior were 43% more likely to have poor sleep quality (OR:1.43;95%CI:1.27 to 1.60), while individuals with two altered behaviors were 97% more likely (OR:1.97;95%CI:1.73 to 2.24). In the isotemporal analysis, replacing MPA and VPA with equivalent time in SB increased the odds of poor sleep at all times assessed, with peaks of 56% for MPA and 68% for VPA.

CONCLUSION

The results of the present study indicate that replacing SB with the same amount of MPA or VPA may reduce poor sleep quality.

Volumetric analysis of the hypothalamic subunits in obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) is a prevalent sleep disorder that is associated with structural brain damage and cognitive impairment. The hypothalamus plays a crucial role in regulating sleep and wakefulness. We aimed to evaluate hypothalamic subunit volumes in patients with OSA.

METHODS

We enrolled 30 participants (15 patients with OSA and 15 healthy controls (HC)). Patients with OSA underwent complete overnight polysomnography (PSG) examination. All the participants underwent MRI. The hypothalamic subunit volumes were calculated using a segmentation technique that trained a 3D convolutional neural network.

RESULTS

Although hypothalamus subunit volumes were comparable between the HC and OSA groups (lowest p = .395), significant negative correlations were found in OSA patients between BMI and whole left hypothalamus volume (R = -0.654, p = .008), as well as between BMI and left posterior volume (R = -0.556, p = .032). Furthermore, significant positive correlations were found between ESS and right anterior inferior volume (R = 0.548, p = .042), minimum SpO2 and the whole left hypothalamus (R = 0.551, p = .033), left tubular inferior volumes (R = 0.596, p = .019), and between the percentage of REM stage and left anterior inferior volume (R = 0.584, p = .022).

CONCLUSIONS

While there were no notable differences in the hypothalamic subunit volumes between the OSA and HC groups, several important correlations were identified in the OSA group. These relationships suggest that factors related to sleep apnea severity could affect hypothalamic structure in patients.

From Garden to Pillow: Understanding the Relationship between Plant-Based Nutrition and Quality of Sleep

The effect of diet on sleep quality has been addressed in many studies; however, whether/how plant-based diets (PBDs) impact sleep-related parameters has not been explored in detail. This review aims to give an overview of the components of PBDs and the possible mechanisms through which PBDs may improve sleep quality. Studies have indicated that diets such as PBDs, which are typically high in fruits, vegetables, nuts, seeds, whole grains, and fiber, are associated with better sleep outcomes, including less fragmented sleep and improved sleep duration. Several mechanisms may explain how PBDs impact and/or improve sleep outcomes. Firstly, PBDs are characteristically rich in certain nutrients, such as magnesium and vitamin B6, which have been associated with improved sleep patterns. Secondly, PBDs are often lower in saturated fats and higher in fiber, which may contribute to better overall health, including sleep quality. Additionally, plant bioactive compounds like phytochemicals and antioxidants in fruits, vegetables, and herbs may have sleep-promoting effects. According to available data, PBD and Mediterranean diet elements promise to enhance sleep quality; however, it is crucial to note that diets should be customized based on each person's needs.

Promoting healthy sleep among older adults

As people age, their sleep patterns and needs naturally change in response to developmental and health-related factors. However, attaining sufficient restorative sleep remains crucial for overall well-being in older adults. This manuscript provides an overview of common sleep alterations that tend to emerge with advancing age, such as shifts in circadian rhythms, decreases in deeper sleep stages, fragmented sleep architecture and an association between comorbidities and sleep disruption. Practical recommendations that target environmental, behavioral and lifestyle modifications may optimize sleep initiation, maintenance, and duration for the older population. By enhancing understanding of the sleep changes that occur in the aged population, geriatric nurses are better able to provide respectful, patient-centered care to older adults that are experiencing sleep difficulties.

Huddling substates in mice facilitate dynamic changes in body temperature and are modulated by Shank3b and Trpm8 mutation

Social thermoregulation is a means of maintaining homeostatic body temperature. While adult mice are a model organism for studying both social behavior and energy regulation, the relationship between huddling and core body temperature (Tb) is poorly understood. Here, we develop a behavioral paradigm and computational tools to identify active-huddling and quiescent-huddling as distinct thermal substates. We find that huddling is an effective thermoregulatory strategy in female but not male groups. At 23°C (room temperature), but not 30°C (near thermoneutrality), huddling facilitates large reductions in Tb and Tb-variance. Notably, active-huddling is associated with bidirectional changes in Tb, depending on its proximity to bouts of quiescent-huddling. Further, group-housed animals lacking the synaptic scaffolding gene Shank3b have hyperthermic Tb and spend less time huddling. In contrast, individuals lacking the cold-sensing gene Trpm8 have hypothermic Tb - a deficit that is rescued by increased huddling time. These results reveal how huddling behavior facilitates acute adjustments of Tb in a state-dependent manner.

Thermoneutral temperature exposure enhances slow-wave sleep with a correlated improvement in amyloid pathology in a triple-transgenic mouse model of Alzheimer's disease

Accumulation of amyloid-β (Aβ) plays an important role in Alzheimer's disease (AD) pathology. There is growing evidence that disordered sleep may accelerate AD pathology by impeding the physiological clearance of Aβ from the brain that occurs in normal sleep. Therapeutic strategies for improving sleep quality may therefore help slow disease progression. It is well documented that the composition and dynamics of sleep are sensitive to ambient temperature. We therefore compared Aβ pathology and sleep metrics derived from polysomnography in 12-month-old female 3xTg-AD mice (n = 8) exposed to thermoneutral temperatures during the light period over 4 weeks to those of age- and sex-matched controls (n = 8) that remained at normal housing temperature (22°C) during the same period. The treated group experienced greater proportions of slow wave sleep (SWS)-i.e. epochs of elevated 0.5-2 Hz EEG slow wave activity during non-rapid eye movement (NREM) sleep-compared to controls. Assays performed on mouse brain tissue harvested at the end of the experiment showed that exposure to thermoneutral temperatures significantly reduced levels of DEA-soluble (but not RIPA- or formic acid-soluble) Aβ40 and Aβ42 in the hippocampus, though not in the cortex. With both groups pooled together and without regard to treatment condition, NREM sleep continuity and any measure of SWS within NREM at the end of the treatment period were inversely correlated with DEA-soluble Aβ40 and Aβ42 levels, again in the hippocampus but not in the cortex. These findings suggest that experimental manipulation of SWS could offer useful clues into the mechanisms and treatment of AD.

Neural cell-types and circuits linking thermoregulation and social behavior

Understanding how social and affective behavioral states are controlled by neural circuits is a fundamental challenge in neurobiology. Despite increasing understanding of central circuits governing prosocial and agonistic interactions, how bodily autonomic processes regulate these behaviors is less resolved. Thermoregulation is vital for maintaining homeostasis, but also associated with cognitive, physical, affective, and behavioral states. Here, we posit that adjusting body temperature may be integral to the appropriate expression of social behavior and argue that understanding neural links between behavior and thermoregulation is timely. First, changes in behavioral states-including social interaction-often accompany changes in body temperature. Second, recent work has uncovered neural populations controlling both thermoregulatory and social behavioral pathways. We identify additional neural populations that, in separate studies, control social behavior and thermoregulation, and highlight their relevance to human and animal studies. Third, dysregulation of body temperature is linked to human neuropsychiatric disorders. Although body temperature is a "hidden state" in many neurobiological studies, it likely plays an underappreciated role in regulating social and affective states.

Sleep in the wild: the importance of individual effects and environmental conditions on sleep behaviour in wild boar

Sleep serves vital physiological functions, yet how sleep in wild animals is influenced by environmental conditions is poorly understood. Here we use high-resolution biologgers to investigate sleep in wild animals over ecologically relevant time scales and quantify variability between individuals under changing conditions. We developed a robust classification for accelerometer data and measured multiple dimensions of sleep in the wild boar (Sus scrofa) over an annual cycle. In support of the hypothesis that environmental conditions determine thermoregulatory challenges, which regulate sleep, we show that sleep quantity, efficiency and quality are reduced on warmer days, sleep is less fragmented in longer and more humid days, while greater snow cover and rainfall promote sleep quality. Importantly, this longest and most detailed analysis of sleep in wild animals to date reveals large inter- and intra-individual variation. Specifically, short-sleepers sleep up to 46% less than long-sleepers but do not compensate for their short sleep through greater plasticity or quality, suggesting they may pay higher costs of sleep deprivation. Given the major role of sleep in health, our results suggest that global warming and the associated increase in extreme climatic events are likely to negatively impact sleep, and consequently health, in wildlife, particularly in nocturnal animals.

'Staying Hot': Investigating the influence of overnight conditions on the penile skin temperature during male sexual arousal-A novel methodology for nocturnal erection detection

Objective

The objective of this study is to assess the impact of overnight environmental conditions on erectile penile temperature within a controlled setting, with the aim of investigating the feasibility of using temperature measurements for nocturnal erection detection in erectile dysfunction diagnostics.

Subjects/patients and methods

We conducted a proof-of-concept study involving 10 healthy male participants aged 20 to 25. The study was carried out at the Department of Urology, St. Antonius Ziekenhuis, the Netherlands. Penile temperature thermistor measurements were taken during visually aroused erections of participants in naked state and in simulated overnight condition (underwear and blankets). Main outcome variables were peak and baseline temperature during erectile periods. To minimize the impact of differences in erectile strength and duration between consecutive measurements, we applied randomization to the order of the environmental conditions.

Results

We observed a significant increase in penile temperature during erection in both the naked (p < 0.01) and simulated overnight condition (p < 0.01). The mean temperature increase was 1.70 and 0.67°C, respectively. While penile temperature returned to baseline immediately after naked erections, the 'Staying Hot effect' was noted in the simulated overnight condition measurements, where the temperature remained elevated at peak temperature for the entire 30-min period following the erection.

Conclusions

The findings from this study indicate that the penile temperature not only significantly increases during naked sexual arousal but is also detectable under simulated overnight conditions. This underscores the potential of using temperature measurements for nocturnal erection detection, representing a crucial initial step in developing a modernized, non-invasive sensor system for ambulatory erectile dysfunction diagnostics. Further research, including an overnight study, is needed to gain insights into the feasibility of utilizing penile temperature measurements for nocturnal erection detection and to assess the impact of the 'Staying Hot effect' on subsequent erection detection.

Optimal bilayer composites for temperature-tracking wireless electronics

Modern silicone-based epidermal electronics engineered for body temperature sensing represent a pivotal development in the quest for advancing preventive medicine and enhancing post-surgical monitoring. While these compact and highly flexible electronics empower real-time monitoring in dynamic environments, a noteworthy limitation is the challenge in regulating the infiltration or obstruction of heat from the external environment into the surface layers of these electronics. The study presents a cost-effective temperature sensing solution by embedding wireless electronics in a multi-layered elastomeric composite to meet the dual needs of enhanced thermal insulation for encapsulation in contact with air and improved thermal conductivity for the substrate in contact with the skin. The encapsulating composite benefits from the inclusion of hollow silica microspheres, which reduce the thermal conductivity by 40%, while non-spherical aluminum nitride enhances the thermal conductivity of the substrate by 370%. The addition of particles to the respective composites inevitably leads to an increase in modulus. Two composite elements are engineered to coexist while maintaining a matching low modulus of 3.4 MPa and a stretchability exceeding 30%, all without compromising the optimized thermal properties. Consecutive thermal, electrical, and mechanical characterization confirms the sensor's capacity for precise body temperature monitoring during a single day's lifespan, while also assessing the influence of behavioral factors on body temperature.

Can the Brain's Thermostatic Mechanism Generate Sleep-Wake and NREM-REM Sleep Cycles? A Nested Doll Model of Sleep-Regulating Processes

Evidence is gradually accumulating in support of the hypothesis that a process of thermostatic brain cooling and warming underlies sleep cycles, i.e., the alternations between non-rapid-eye-movement and rapid-eye-movement sleep throughout the sleep phase of the sleep-wake cycle. A mathematical thermostat model predicts an exponential shape of fluctuations in temperature above and below the desired temperature setpoint. If the thermostatic process underlies sleep cycles, can this model explain the mechanisms governing the sleep cyclicities in humans? The proposed nested doll model incorporates Process s generating sleep cycles into Process S generating sleep-wake cycles of the two-process model of sleep-wake regulation. Process s produces ultradian fluctuations around the setpoint, while Process S turns this setpoint up and down in accord with the durations of the preceding wake phase and the following sleep phase of the sleep-wake cycle, respectively. Predictions of the model were obtained in an in silico study and confirmed by simulations of oscillations of spectral electroencephalographic indexes of sleep regulation obtained from night sleep and multiple napping attempts. Only simple-inverse exponential and exponential-functions from the thermostatic model were used for predictions and simulations of rather complex and varying shapes of sleep cycles during an all-night sleep episode. To further test the proposed model, experiments on mammal species with monophasic sleep are required. If supported, this model can provide a valuable framework for understanding the involvement of sleep-wake regulatory processes in the mechanism of thermostatic brain cooling/warming.

Sleep and circadian rhythmicity as entangled processes serving homeostasis

Sleep is considered essential for the brain and body. A predominant concept is that sleep is regulated by circadian rhythmicity and sleep homeostasis, processes that were posited to be functionally and mechanistically separate. Here we review and re-evaluate this concept and its assumptions using findings from recent human and rodent studies. Alterations in genes that are central to circadian rhythmicity affect not only sleep timing but also putative markers of sleep homeostasis such as electroencephalogram slow-wave activity (SWA). Perturbations of sleep change the rhythmicity in the expression of core clock genes in tissues outside the central clock. The dynamics of recovery from sleep loss vary across sleep variables: SWA and immediate early genes show an early response, but the recovery of non-rapid eye movement and rapid eye movement sleep follows slower time courses. Changes in the expression of many genes in response to sleep perturbations outlast the effects on SWA and time spent asleep. These findings are difficult to reconcile with the notion that circadian- and sleep-wake-driven processes are mutually independent and that the dynamics of sleep homeostasis are reflected in a single variable. Further understanding of how both sleep and circadian rhythmicity contribute to the homeostasis of essential physiological variables may benefit from the assessment of multiple sleep and molecular variables over longer time scales.

Increased risk of sleep disturbances in patients with rosacea: A nationwide population-based cohort study

Rosacea is a chronic inflammatory skin disorder linked to various mental disorders, but little is known about the impact of rosacea on sleep disorders. The aim of this study is to confirm the association of rosacea with sleep disorders using a large administrative data set. This nationwide population-based retrospective cohort study enrolled 1129 individuals with rosacea and 11 017 age- and sex-matched controls without rosacea from the Korean National Health Insurance System database from 2002 to 2015. The prevalence of sleep disorder (7.8%) was significantly higher in patients with rosacea than in controls (5.81%; p < 0.001). Rosacea was associated with an increased risk of sleep disorder (adjusted odds ratio [aOR], 1.287 [95% confidence interval (CI), 1.022-1.623]). Among a variety of sleep disorders, patients with rosacea were likely to have an increased risk of insomnia (aOR, 1.318 [95% CI, 1.002-1.743]). In subgroup analysis, female patients with rosacea (aOR, 1.297 [95% CI, 1.010-1.722]) and those with rosacea and dyslipidemia (aOR, 1.417 [95% CI, 1.062-1.891]) were at a higher risk of having a sleep disorder. Rosacea is associated with an increased risk of having sleep disorders. The management of modifiable risk factors is important for managing sleep disorders in patients with rosacea.

Temperature-induced Artifacts in Tau Phosphorylation: Implications for Reliable Alzheimer's Disease Research

In preclinical research on Alzheimer's disease and related tauopathies, tau phosphorylation analysis is routinely employed in both cellular and animal models. However, recognizing the sensitivity of tau phosphorylation to various extrinsic factors, notably temperature, is vital for experimental accuracy. Hypothermia can trigger tau hyperphosphorylation, while hyperthermia leads to its dephosphorylation. Nevertheless, the rapidity of tau phosphorylation in response to unintentional temperature variations remains unknown. In cell cultures, the most significant temperature change occurs when the cells are removed from the incubator before harvesting, and in animal models, during anesthesia prior to euthanasia. In this study, we investigate the kinetics of tau phosphorylation in N2a and SH-SY5Y neuronal cell lines, as well as in mice exposed to anesthesia. We observed changes in tau phosphorylation within the few seconds upon transferring cell cultures from their 37°C incubator to room temperature conditions. However, cells placed directly on ice post-incubation exhibited negligible phosphorylation changes. In vivo, isoflurane anesthesia rapidly resulted in tau hyperphosphorylation within the few seconds needed to lose the pedal withdrawal reflex in mice. These findings emphasize the critical importance of preventing temperature variation in researches focused on tau. To ensure accurate results, we recommend avoiding anesthesia before euthanasia and promptly placing cells on ice after removal from the incubator. By controlling temperature fluctuations, the reliability and validity of tau phosphorylation studies can be significantly enhanced.

Application of Braided Piezoelectric Poly-l-Lactic Acid Cord Sensor to Sleep Bruxism Detection System with Less Physical or Mental Stress

For many years, we have been developing flexible sensors made of braided piezoelectric poly-l-lactic acid (PLLA) fibers that can be tied and untied for practical applications in society. To ensure good quality of sleep, the occurrence of bruxism has been attracting attention in recent years. Currently, there is a need for a system that can easily and accurately measure the frequency of bruxism at home. Therefore, taking advantage of the braided piezoelectric PLLA cord sensor's unique characteristic of being sewable, we aimed to provide a system that can measure the frequency of bruxism using the braided piezoelectric PLLA cord sensor simply sewn onto a bed sheet on which the subject lies down. After many tests using trial and error, the sheet sensor was completed with zigzag stitching. Twenty subjects slept overnight in a hospital room on sheets integrated with a braided piezoelectric PLLA cord. Polysomnography (PSG) was simultaneously performed on these subjects. The results showed that their bruxism could be detected with an accuracy of more than 95% compared with PSG measurements, which can only be performed in a hospital by a physician and are more burdensome for the subjects, with the subjects simply lying on the bed sheet with a braided piezoelectric PLLA cord sensor sewn into it.

Sleep and the hypothalamus

Neural substrates of wakefulness, rapid eye movement sleep (REMS), and non-REMS (NREMS) in the mammalian hypothalamus overlap both anatomically and functionally with cellular networks that support physiological and behavioral homeostasis. Here, we review the roles of sleep neurons of the hypothalamus in the homeostatic control of thermoregulation or goal-oriented behaviors during wakefulness. We address how hypothalamic circuits involved in opposing behaviors such as core body temperature and sleep compute conflicting information and provide a coherent vigilance state. Finally, we highlight some of the key unresolved questions and challenges, and the promise of a more granular view of the cellular and molecular diversity underlying the integrative role of the hypothalamus in physiological and behavioral homeostasis.

Somatostatin neurons in prefrontal cortex initiate sleep-preparatory behavior and sleep via the preoptic and lateral hypothalamus

The prefrontal cortex (PFC) enables mammals to respond to situations, including internal states, with appropriate actions. One such internal state could be 'tiredness'. Here, using activity tagging in the mouse PFC, we identified particularly excitable, fast-spiking, somatostatin-expressing, γ-aminobutyric acid (GABA) (PFCSst-GABA) cells that responded to sleep deprivation. These cells projected to the lateral preoptic (LPO) hypothalamus and the lateral hypothalamus (LH). Stimulating PFCSst-GABA terminals in the LPO hypothalamus caused sleep-preparatory behavior (nesting, elevated theta power and elevated temperature), and stimulating PFCSst-GABA terminals in the LH mimicked recovery sleep (non-rapid eye-movement sleep with higher delta power and lower body temperature). PFCSst-GABA terminals had enhanced activity during nesting and sleep, inducing inhibitory postsynaptic currents on diverse cells in the LPO hypothalamus and the LH. The PFC also might feature in deciding sleep location in the absence of excessive fatigue. These findings suggest that the PFC instructs the hypothalamus to ensure that optimal sleep takes place in a suitable place.

Activation of Basal Forebrain Astrocytes Induces Wakefulness without Compensatory Changes in Sleep Drive

Mammalian sleep is regulated by a homeostatic process that increases sleep drive and intensity as a function of prior wake time. Sleep homeostasis has traditionally been thought to be a product of neurons, but recent findings demonstrate that this process is also modulated by glial astrocytes. The precise role of astrocytes in the accumulation and discharge of sleep drive is unknown. We investigated this question by selectively activating basal forebrain (BF) astrocytes using designer receptors exclusively activated by designer drugs (DREADDs) in male and female mice. DREADD activation of the Gq-protein-coupled pathway in BF astrocytes produced long and continuous periods of wakefulness that paradoxically did not cause the expected homeostatic response to sleep loss (e.g., increases in sleep time or intensity). Further investigations showed that this was not because of indirect effects of the ligand that activated DREADDs. These findings suggest that the need for sleep is not only driven by wakefulness per se, but also by specific neuronal-glial circuits that are differentially activated in wakefulness.SIGNIFICANCE STATEMENT Sleep drive is controlled by a homeostatic process that increases sleep duration and intensity based on prior time spent awake. Non-neuronal brain cells (e.g., glial astrocytes) influence this homeostatic process, but their precise role is unclear. We used a genetic technique to activate astrocytes in the basal forebrain (BF) of mice, a brain region important for sleep and wake expression and sleep homeostasis. Astroglial activation induced prolonged wakefulness without the expected homeostatic increase in sleep drive (i.e., sleep duration and intensity). These findings indicate that our need to sleep is also driven by non-neuronal cells, and not only by time spent awake.

The neighborhood environment and sleep health in adolescents

OBJECTIVE

Neighborhood-level factors, including education, health and environment, and socioeconomic exposures, are important contextual determinants of child health. We explored whether these factors, measured via the Childhood Opportunity Index 2.0, were associated with sleep health in adolescents.

METHODS

Actigraphy was used to assess sleep duration, timing, and efficiency among 110 adolescents in eighth (13.9 (0.4)) and ninth (14.9 (0.4)) grade. Home addresses were geocoded and linked to Childhood Opportunity Index 2.0 scores (including 3 subtype scores and the 29 individual factor Z-scores). Mixed-effects linear regression was used to determine associations between the Childhood Opportunity Index 2.0 scores and the sleep outcomes, adjusting for sex, race, parent education, household income, school grade and weeknight status. Interactions were also tested by school grade, weeknight status, sex, and race.

RESULTS

No associations were observed between overall or subtype scores with sleep outcomes in adolescents. However, we detected associations between select individual Childhood Opportunity Index 2.0 Z-scores, spanning health & environment and education domains, and sleep outcomes. For example, greater fine particulate matter was associated with later timing of sleep onset and offset; ozone concentration was associated with earlier sleep onset and offset; greater exposure to extreme temperature was associated with later sleep onset and offset and increased odds of optimal sleep efficiency.

CONCLUSIONS

Specific neighborhood factors indexed by the Childhood Opportunity Index 2.0 were associated with sleep health among adolescents. In particular, neighborhood air quality measures were associated with sleep timing and efficiency, warranting further investigation.

Molecular and Neural Mechanisms of Temperature Preference Rhythm in Drosophila melanogaster

Temperature influences animal physiology and behavior. Animals must set an appropriate body temperature to maintain homeostasis and maximize survival. Mammals set their body temperatures using metabolic and behavioral strategies. The daily fluctuation in body temperature is called the body temperature rhythm (BTR). For example, human body temperature increases during wakefulness and decreases during sleep. BTR is controlled by the circadian clock, is closely linked with metabolism and sleep, and entrains peripheral clocks located in the liver and lungs. However, the underlying mechanisms of BTR are largely unclear. In contrast to mammals, small ectotherms, such as Drosophila, control their body temperatures by choosing appropriate environmental temperatures. The preferred temperature of Drosophila increases during the day and decreases at night; this pattern is referred to as the temperature preference rhythm (TPR). As flies are small ectotherms, their body temperature is close to that of the surrounding environment. Thus, Drosophila TPR produces BTR, which exhibits a pattern similar to that of human BTR. In this review, we summarize the regulatory mechanisms of TPR, including recent studies that describe neuronal circuits relaying ambient temperature information to dorsal neurons (DNs). The neuropeptide diuretic hormone 31 (DH31) and its receptor (DH31R) regulate TPR, and a mammalian homolog of DH31R, the calcitonin receptor (CALCR), also plays an important role in mouse BTR regulation. In addition, both fly TPR and mammalian BTR are separately regulated from another clock output, locomotor activity rhythms. These findings suggest that the fundamental mechanisms of BTR regulation may be conserved between mammals and flies. Furthermore, we discuss the relationships between TPR and other physiological functions, such as sleep. The dissection of the regulatory mechanisms of Drosophila TPR could facilitate an understanding of mammalian BTR and the interaction between BTR and sleep regulation.

Chronic social stress blunts core body temperature and molecular rhythms of Rbm3 and Cirbp in mouse lateral habenula

Chronic social stress in mice causes behavioural and physiological changes that result in perturbed rhythms of body temperature, activity and sleep-wake cycle. To further understand the link between mood disorders and temperature rhythmicity in mice that are resilient or susceptible to stress, we measured core body temperature (Tcore) before and after exposure to chronic social defeat stress (CSDS). We found that Tcore amplitudes of stress-resilient and susceptible mice are dampened during exposure to CSDS. However, following CSDS, resilient mice recovered temperature amplitude faster than susceptible mice. Furthermore, the interdaily stability (IS) of temperature rhythms was fragmented in stress-exposed mice during CSDS, which recovered to control levels following stress. There were minimal changes in locomotor activity after stress exposure which correlates with regular rhythmic expression of Prok2 - an output signal of the suprachiasmatic nucleus. We also determined that expression of thermosensitive genes Rbm3 and Cirbp in the lateral habenula (LHb) were blunted 1 day after CSDS. Rhythmic expression of these genes recovered 10 days later. Overall, we show that CSDS blunts Tcore and thermosensitive gene rhythms. Tcore rhythm recovery is faster in stress-resilient mice, but Rbm3 and Cirbp recovery is uniform across the phenotypes.

Cold temperature extends longevity and prevents disease-related protein aggregation through PA28γ-induced proteasomes

Aging is a primary risk factor for neurodegenerative disorders that involve protein aggregation. Because lowering body temperature is one of the most effective mechanisms to extend longevity in both poikilotherms and homeotherms, a better understanding of cold-induced changes can lead to converging modifiers of pathological protein aggregation. Here, we find that cold temperature (15 °C) selectively induces the trypsin-like activity of the proteasome in Caenorhabditis elegans through PSME-3, the worm orthologue of human PA28γ/PSME3. This proteasome activator is required for cold-induced longevity and ameliorates age-related deficits in protein degradation. Moreover, cold-induced PA28γ/PSME-3 diminishes protein aggregation in C. elegans models of age-related diseases such as Huntington's and amyotrophic lateral sclerosis. Notably, exposure of human cells to moderate cold temperature (36 °C) also activates trypsin-like activity through PA28γ/PSME3, reducing disease-related protein aggregation and neurodegeneration. Together, our findings reveal a beneficial role of cold temperature that crosses evolutionary boundaries with potential implications for multi-disease prevention.

ER proteostasis regulators cell-non-autonomously control sleep

Sleep is regulated by peripheral tissues under fatigue. The molecular pathways in peripheral cells that trigger systemic sleep-related signals, however, are unclear. Here, a forward genetic screen in C. elegans identifies 3 genes that strongly affect sleep amount: sel-1, sel-11, and mars-1. sel-1 and sel-11 encode endoplasmic reticulum (ER)-associated degradation components, whereas mars-1 encodes methionyl-tRNA synthetase. We find that these machineries function in non-neuronal tissues and that the ER unfolded protein response components inositol-requiring enzyme 1 (IRE1)/XBP1 and protein kinase R-like ER kinase (PERK)/eukaryotic initiation factor-2α (eIF2α)/activating transcription factor-4 (ATF4) participate in non-neuronal sleep regulation, partly by reducing global translation. Neuronal epidermal growth factor receptor (EGFR) signaling is also required. Mouse studies suggest that this mechanism is conserved in mammals. Considering that prolonged wakefulness increases ER proteostasis stress in peripheral tissues, our results suggest that peripheral ER proteostasis factors control sleep homeostasis. Moreover, based on our results, peripheral tissues likely cope with ER stress not only by the well-established cell-autonomous mechanisms but also by promoting the individual's sleep.

Altered Core Temperature and Salivary Melatonin in Athletes with a Cervical Spinal Cord Injury

Sleep disturbances are common in athletes with a cervical spinal cord injury (cSCI) and may be associated with circadian alterations. Therefore, the purpose of this study was to compare physiological circadian outputs between athletes with a cSCI and non-disabled controls (CON). Eight male wheelchair athletes with a cSCI and eight male CON (30±4 and 30±6 yrs, respectively) had their core body temperature (T_core), skin temperature (T_skin), and salivary melatonin measured during a 24 h period. In the cSCI group, daytime T_core was significantly lower (36.5 (0.2) vs 36.9 (0.3)°C; p=0.02) and time of the T_core sleep minimum was significantly earlier (23:56±00:46 vs 02:39 ± 02:57; p=0.04). The athletes with a cSCI had significantly lower T_core values during the beginning of the night compared with the CON group, but their T_core increased at a greater rate, thereafter, indicated by a significant time/group interaction (p=0.04). Moreover, the cSCI group did not display a salivary melatonin response and exhibited significantly lower concentrations at 22:00 (p=0.01) and 07:00 (p=0.01) compared with the CON group. Under natural living conditions, athletes with a cSCI displayed circadian changes in the T_core rhythm and nocturnal melatonin production.

Peripheral body temperature rhythm as a marker of the severity of depression symptoms in fibromyalgia

BACKGROUND

Circadian rhythm alterations have been reported in fibromyalgia (FM) and depression. Peripheral body temperature (PBT) is a reliable measure of the circadian system, so we compared the PBT rhythm between persons with FM and controls. We evaluated PBT correlation with depression symptoms and pain severity in women with FM.

METHODS

We included 101 women aged 30-65 with FM diagnosis (FM group, n = 83) and controls (n = 18). Twenty-four-hour PBT was assessed by actigraphy. For the analysis, in the FM group, the PBT measurement was divided into four periods: morning (6 a.m.-noon), afternoon (noon-6 p.m.), evening (6 p.m.-midnight), and night (midnight-6 a.m.). According to their scores on the Hamilton Depression Rating Scale (HDRS), participants were classified as having mild or moderate to severe depression symptoms.

RESULTS

There was no difference in PBT between FM and controls. Subjects with FM and moderate to severe depression symptoms showed a higher PBT (p = .003) during the evening period (p = .004). The analysis of PBT rhythm revealed an interaction between time and group according to mild or moderate to severe depression symptoms (χ2 (3) = 12.79, p < .005). The pain severity was positively correlated with PBT (ß=0.22, [CI 95%, 0.07-0.37], p = .003).

CONCLUSIONS

PBT rhythm was not a sensitive measure for discriminating persons with FM from controls. In FM, PBT is related to the severity of depression symptoms and pain intensity.

Hyperhidrosis in sleep disorders - A narrative review of mechanisms and clinical significance

Hyperhidrosis is characterized by excessive sweating beyond thermoregulatory needs that affects patients' quality of life. It results from an excessive stimulation of eccrine sweat glands in the skin by the sympathetic nervous system. Hyperhidrosis may be primary or secondary to an underlying cause. Nocturnal hyperhidrosis is associated with different sleep disorders, such as obstructive sleep apnea, insomnia, restless legs syndrome/periodic limb movement during sleep and narcolepsy. The major cause of the hyperhidrosis is sympathetic overactivity and, in the case of narcolepsy type 1, orexin deficiency may also contribute. In this narrative review, we will provide an outline of the possible mechanisms underlying sudomotor dysfunction and the resulting nocturnal hyperhidrosis in these different sleep disorders and explore its clinical relevance.

Chronic social stress blunts core body temperature and molecular rhythms ofRbm3andCirbpin mouse lateral habenula.. [DOI: 10.1101/2023.01.02.522528]

Chronic social stress in mice causes behavioral and physiological changes that result in perturbed rhythms of body temperature, activity and sleep-wake cycle. To further understand the link between mood disorders and temperature rhythmicity in mice that are resilient or susceptible to stress, we measured core body temperature (Tcore) before and after exposure to chronic social defeat stress (CSDS). We found that Tcore amplitudes of stress-resilient and susceptible mice are dampened during exposure to CSDS. However, following CSDS, resilient mice recovered temperature amplitude faster than susceptible mice. Furthermore, the interdaily stability (IS) of temperature rhythms was fragmented in stress-exposed mice during CSDS, which recovered to control levels following stress. There were minimal changes in locomotor activity after stress exposure which correlates with regular rhythmic expression ofProk2- an output signal of the suprachiasmatic nucleus. We also determined that expression of thermosensitive genesRbm3andCirbpin the lateral habenula (LHb) were blunted 1-day after CSDS. Rhythmic expression of these genes recovered 10 days later. Overall, we show that CSDS blunts Tcore and thermosensitive gene rhythms. Tcore rhythm recovery is faster in stress-resilient mice, butRbm3andCirbprecovery is uniform across the phenotypes.

Understanding Sleep Regulation in Normal and Pathological Conditions, and Why It Matters

Sleep occupies a peculiar place in our lives and in science, being both eminently familiar and profoundly enigmatic. Historically, philosophers, scientists and artists questioned the meaning and purpose of sleep. If Shakespeare's verses from MacBeth depicting "Sleep that soothes away all our worries" and "relieves the weary laborer and heals hurt minds" perfectly epitomize the alleviating benefits of sleep, it is only during the last two decades that the growing understanding of the sophisticated sleep regulatory mechanisms allows us to glimpse putative biological functions of sleep. Sleep control brings into play various brain-wide processes occurring at the molecular, cellular, circuit, and system levels, some of them overlapping with a number of disease-signaling pathways. Pathogenic processes, including mood disorders (e.g., major depression) and neurodegenerative illnesses such Huntington's or Alzheimer's diseases, can therefore affect sleep-modulating networks which disrupt the sleep-wake architecture, whereas sleep disturbances may also trigger various brain disorders. In this review, we describe the mechanisms underlying sleep regulation and the main hypotheses drawn about its functions. Comprehending sleep physiological orchestration and functions could ultimately help deliver better treatments for people living with neurodegenerative diseases.

How people wake up is associated with previous night's sleep together with physical activity and food intake

How people wake up and regain alertness in the hours after sleep is related to how they are sleeping, eating, and exercising. Here, in a prospective longitudinal study of 833 twins and genetically unrelated adults, we demonstrate that how effectively an individual awakens in the hours following sleep is not associated with their genetics, but instead, four independent factors: sleep quantity/quality the night before, physical activity the day prior, a breakfast rich in carbohydrate, and a lower blood glucose response following breakfast. Furthermore, an individual's set-point of daily alertness is related to the quality of their sleep, their positive emotional state, and their age. Together, these findings reveal a set of non-genetic (i.e., not fixed) factors associated with daily alertness that are modifiable.

Brain temperature affects quantitative features of hippocampal sharp wave ripples

Biochemical mechanisms are temperature dependent. Brain temperature shows wide variations across brain states, and such changes may explain quantitative changes in network oscillations. Here, we report on the relationship between various hippocampal sharp wave ripple features to brain temperature. Ripple frequency, occurrence rate, and duration correlated with temperature dynamics. By focal manipulation of the brain temperature in the hippocampal CA1 region, we show that ripple frequency can be increased and decreased by local heating and cooling, respectively. Changes of other parameters, such as the rate of sharp wave-ripple complex (SPW-R) and ripple duration were not consistently affected. Our findings suggest that brain temperature in the CA1 region plays a leading role in affecting ripple frequency, whereas other parameters of SPW-Rs may be determined by mechanisms upstream from the CA1 region. These findings illustrate that physiological variations of brain temperature exert important effects on hippocampal circuit operations.NEW & NOTEWORTHY During physiological conditions, brain temperature fluctuates approximately 3°C between sleep and active waking. Here, we show that features of hippocampal ripples, including the rate of occurrence, peak frequency, and duration are correlated with brain temperature variations. Focal bidirectional manipulation of temperature in the hippocampal CA1 region in awake rodents show that ripple frequency can be altered in the direction expected from the correlational observations, implying that temperature plays a significant role.

The Sleep-Promoting Ventrolateral Preoptic Nucleus: What Have We Learned over the Past 25 Years?

For over a century, the role of the preoptic hypothalamus and adjacent basal forebrain in sleep-wake regulation has been recognized. However, for years, the identity and location of sleep- and wake-promoting neurons in this region remained largely unresolved. Twenty-five years ago, Saper and colleagues uncovered a small collection of sleep-active neurons in the ventrolateral preoptic nucleus (VLPO) of the preoptic hypothalamus, and since this seminal discovery the VLPO has been intensively investigated by labs around the world, including our own. Herein, we first review the history of the preoptic area, with an emphasis on the VLPO in sleep-wake control. We then attempt to synthesize our current understanding of the circuit, cellular and synaptic bases by which the VLPO both regulates and is itself regulated, in order to exert a powerful control over behavioral state, as well as examining data suggesting an involvement of the VLPO in other physiological processes.

The hypothalamic link between arousal and sleep homeostasis in mice

Sleep and wakefulness are not simple, homogenous all-or-none states but represent a spectrum of substates, distinguished by behavior, levels of arousal, and brain activity at the local and global levels. Until now, the role of the hypothalamic circuitry in sleep-wake control was studied primarily with respect to its contribution to rapid state transitions. In contrast, whether the hypothalamus modulates within-state dynamics (state "quality") and the functional significance thereof remains unexplored. Here, we show that photoactivation of inhibitory neurons in the lateral preoptic area (LPO) of the hypothalamus of adult male and female laboratory mice does not merely trigger awakening from sleep, but the resulting awake state is also characterized by an activated electroencephalogram (EEG) pattern, suggesting increased levels of arousal. This was associated with a faster build-up of sleep pressure, as reflected in higher EEG slow-wave activity (SWA) during subsequent sleep. In contrast, photoinhibition of inhibitory LPO neurons did not result in changes in vigilance states but was associated with persistently increased EEG SWA during spontaneous sleep. These findings suggest a role of the LPO in regulating arousal levels, which we propose as a key variable shaping the daily architecture of sleep-wake states.

A forebrain neural substrate for behavioral thermoregulation

Thermoregulatory behavior is a basic motivated behavior for body temperature homeostasis. Despite its fundamental importance, a forebrain region or defined neural population required for this process has yet to be established. Here, we show that Vgat-expressing neurons in the lateral hypothalamus (LH^Vgat neurons) are required for diverse thermoregulatory behaviors. The population activity of LH^Vgat neurons is increased during thermoregulatory behavior and bidirectionally encodes thermal punishment and reward (P&R). Although this population also regulates feeding and caloric reward, inhibition of parabrachial inputs selectively impaired thermoregulatory behaviors and encoding of thermal stimulus by LH^Vgat neurons. Furthermore, two-photon calcium imaging revealed a subpopulation of LH^Vgat neurons bidirectionally encoding thermal P&R, which is engaged during thermoregulatory behavior, but is largely distinct from caloric reward-encoding LH^Vgat neurons. Our data establish LH^Vgat neurons as a required neural substrate for behavioral thermoregulation and point to the key role of the thermal P&R-encoding LH^Vgat subpopulation in thermoregulatory behavior.

An open-source, high-performance tool for automated sleep staging

The clinical and societal measurement of human sleep has increased exponentially in recent years. However, unlike other fields of medical analysis that have become highly automated, basic and clinical sleep research still relies on human visual scoring. Such human-based evaluations are time-consuming, tedious, and can be prone to subjective bias. Here, we describe a novel algorithm trained and validated on +30,000 hr of polysomnographic sleep recordings across heterogeneous populations around the world. This tool offers high sleep-staging accuracy that matches human scoring accuracy and interscorer agreement no matter the population kind. The software is designed to be especially easy to use, computationally low-demanding, open source, and free. Our hope is that this software facilitates the broad adoption of an industry-standard automated sleep staging software package.

Nitric Oxide Synthase Neurons in the Preoptic Hypothalamus Are NREM and REM Sleep-Active and Lower Body Temperature

When mice are exposed to external warmth, nitric oxide synthase (NOS1) neurons in the median and medial preoptic (MnPO/MPO) hypothalamus induce sleep and concomitant body cooling. However, how these neurons regulate baseline sleep and body temperature is unknown. Using calcium photometry, we show that NOS1 neurons in MnPO/MPO are predominantly NREM and REM active, especially at the boundary of wake to NREM transitions, and in the later parts of REM bouts, with lower activity during wakefulness. In addition to releasing nitric oxide, NOS1 neurons in MnPO/MPO can release GABA, glutamate and peptides. We expressed tetanus-toxin light-chain in MnPO/MPO NOS1 cells to reduce vesicular release of transmitters. This induced changes in sleep structure: over 24 h, mice had less NREM sleep in their dark (active) phase, and more NREM sleep in their light (sleep) phase. REM sleep episodes in the dark phase were longer, and there were fewer REM transitions between other vigilance states. REM sleep had less theta power. Mice with synaptically blocked MnPO/MPO NOS1 neurons were also warmer than control mice at the dark-light transition (ZT0), as well as during the dark phase siesta (ZT16-20), where there is usually a body temperature dip. Also, at this siesta point of cooled body temperature, mice usually have more NREM, but mice with synaptically blocked MnPO/MPO NOS1 cells showed reduced NREM sleep at this time. Overall, MnPO/MPO NOS1 neurons promote both NREM and REM sleep and contribute to chronically lowering body temperature, particularly at transitions where the mice normally enter NREM sleep.

Dim light in the evening causes coordinated realignment of circadian rhythms, sleep, and short-term memory

In modern societies, people are regularly exposed to artificial light (e.g., light-emitting electronic devices). Dim light in the evening (DLE) imposes an artificial extension of the solar day, increasing our alertness before bedtime, delaying melatonin timing and sleep onset, and increasing sleepiness in the next morning. Using laboratory mice as a model organism, we show that 2 wk of 4-h, 20-lux DLE postpones rest–activity rhythms, delays molecular rhythms in the brain and body, and reverses the diurnal pattern of short-term memory performance. These results highlight the biological impact of DLE and emphasize the need to optimize our evening light exposure if we are to avoid shifting our biological clocks.

Light provides the primary signal for entraining circadian rhythms to the day/night cycle. In addition to rods and cones, the retina contains a small population of photosensitive retinal ganglion cells (pRGCs) expressing the photopigment melanopsin (OPN4). Concerns have been raised that exposure to dim artificial lighting in the evening (DLE) may perturb circadian rhythms and sleep patterns, and OPN4 is presumed to mediate these effects. Here, we examine the effects of 4-h, 20-lux DLE on circadian physiology and behavior in mice and the role of OPN4 in these responses. We show that 2 wk of DLE induces a phase delay of ∼2 to 3 h in mice, comparable to that reported in humans. DLE-induced phase shifts are unaffected in Opn4^−/− mice, indicating that rods and cones are capable of driving these responses in the absence of melanopsin. DLE delays molecular clock rhythms in the heart, liver, adrenal gland, and dorsal hippocampus. It also reverses short-term recognition memory performance, which is associated with changes in preceding sleep history. In addition, DLE modifies patterns of hypothalamic and cortical cFos signals, a molecular correlate of recent neuronal activity. Together, our data show that DLE causes coordinated realignment of circadian rhythms, sleep patterns, and short-term memory process in mice. These effects are particularly relevant as DLE conditions―due to artificial light exposure―are experienced by the majority of the populace on a daily basis.

Local administration of bicuculline into the ventrolateral and medial preoptic nuclei modifies sleep and maternal behavior in lactating rats

The preoptic area (POA) is a brain structure classically involved in a wide variety of animal behavior including sleep and maternal care. In the current study, we evaluate the specific effect of disinhibition of two specific regions of the POA, the medial POA nucleus (mPOA) and the ventrolateral POA area (VLPO) on sleep and maternal behavior in lactating rats. For this purpose, mother rats on postpartum day 1 (PPD1) were implanted for polysomnographic recordings and with bilateral cannulae either in the mPOA or in the VLPO. The rats were tested for sleep and maternal behavior on PPD4-8 after the infusion of the GABA-A antagonist, bicuculline (0, 10 or 30 ng/0.2 µl/side). Infusion of bicuculline into the mPOA augmented retrieving and nest building behaviors and reduced both nursing and milk ejections but had almost no effect on sleep. When bicuculine was microinjected into the VLPO, the rats significantly increase the number of retrievings and mouthings and reduced the nursing time without changes in milk ejections, which was associated with an increase in wakefulness and a reduction in light sleep. Our results show that disinhibition of the mPOA, a key area in the control of maternal behavior, increased active maternal behaviors and reduced nursing without affecting wakefulness or sleep time. In contrast, the enhancement of some active maternal behaviors when the drug was infused into the VLPO, a sleep-promoting area, with a concomitant increase in wakefulness suggests that mother rats devote this additional waking time in the active maternal care of the pups. We hypothesize that maternal behavior changes after bicuculine microinjection into the VLPO are caused by a reduction in the sleep drive, rather than a direct effect on maternal behavior.

Deconstructing Commercial Wearable Technology: Contributions toward Accurate and Free-Living Monitoring of Sleep

Despite prolific demands and sales, commercial sleep assessment is primarily limited by the inability to "measure" sleep itself; rather, secondary physiological signals are captured, combined, and subsequently classified as sleep or a specific sleep state. Using markedly different approaches compared with gold-standard polysomnography, wearable companies purporting to measure sleep have rapidly developed during recent decades. These devices are advertised to monitor sleep via sensors such as accelerometers, electrocardiography, photoplethysmography, and temperature, alone or in combination, to estimate sleep stage based upon physiological patterns. However, without regulatory oversight, this market has historically manufactured products of poor accuracy, and rarely with third-party validation. Specifically, these devices vary in their capacities to capture a signal of interest, process the signal, perform physiological calculations, and ultimately classify a state (sleep vs. wake) or sleep stage during a given time domain. Device performance depends largely on success in all the aforementioned requirements. Thus, this review provides context surrounding the complex hardware and software developed by wearable device companies in their attempts to estimate sleep-related phenomena, and outlines considerations and contributing factors for overall device success.

The role of anxiety and depression in the relationship between physical activity and sleep quality: A serial multiple mediation model

BACKGROUND

Physical inactivity exacerbates poorer sleep quality, but potential underlying mechanisms of this association remain unknown. The present study aims to disentangle the pathways linking psychical activity to sleep quality through the serial mediation effect of anxiety and depression in a Chinese population.

METHODS

Data analyzed were from Guangdong Sleep and Psychosomatic Health Survey, a cross-sectional population-based study with a representative sample of adult inhabitants aged 18-85 years living in Guangdong province, China. A total of 13,768 participants were included with the response rate of 80.4%. Singe and serial mediation analyses were conducted to examine whether anxiety and depression mediated the relationship between physical activity and sleep quality, independently and jointly.

RESULTS

Both direct and indirect effects of physical activity on sleep quality were found. As predicted, anxiety and depression mediated the relationship between physical activity and sleep quality (B _Anxiety = -0.17, 95% bootstrap CI: -0.20 to -0.15; B _Depression= -0.25, 95% bootstrap CI: -0.28 to -0.21), respectively. In addition, serial mediation analyses indicated that the association of physical activity and sleep quality is mediated by anxiety and depression in a sequential manner (B = -0.13, 95% bootstrap CI: -0.15 to -0.11).

LIMITATIONS

The primary limitation of the study is the cross-sectional design, which limits the causal inference ability.

CONCLUSIONS

These findings highlight the role of anxiety and depression as serial mediators of the relationship between physical activity and sleep quality. Thus, exercise-based programs focusing on improving sleep could benefit from a multi-faceted approach therapeutically targeting psychiatric disorders.

The Promise of Sleep: A Multi-Sensor Approach for Accurate Sleep Stage Detection Using the Oura Ring

Consumer-grade sleep trackers represent a promising tool for large scale studies and health management. However, the potential and limitations of these devices remain less well quantified. Addressing this issue, we aim at providing a comprehensive analysis of the impact of accelerometer, autonomic nervous system (ANS)-mediated peripheral signals, and circadian features for sleep stage detection on a large dataset. Four hundred and forty nights from 106 individuals, for a total of 3444 h of combined polysomnography (PSG) and physiological data from a wearable ring, were acquired. Features were extracted to investigate the relative impact of different data streams on 2-stage (sleep and wake) and 4-stage classification accuracy (light NREM sleep, deep NREM sleep, REM sleep, and wake). Machine learning models were evaluated using a 5-fold cross-validation and a standardized framework for sleep stage classification assessment. Accuracy for 2-stage detection (sleep, wake) was 94% for a simple accelerometer-based model and 96% for a full model that included ANS-derived and circadian features. Accuracy for 4-stage detection was 57% for the accelerometer-based model and 79% when including ANS-derived and circadian features. Combining the compact form factor of a finger ring, multidimensional biometric sensory streams, and machine learning, high accuracy wake-sleep detection and sleep staging can be accomplished.