Sleep Stages Research Articles

Classification of cyclic alternating patterns of sleep using EEG signals

Cyclic alternating patterns (CAP) occur in electroencephalogram (EEG) signals during non-rapid eye movement sleep. The analysis of CAP can offer insights into various sleep disorders. The first step is the identification of phases A and B for the CAP cycles. In this work, we develop an easy-to-implement accurate system to differentiate between CAP A and CAP B. Small segments of the EEG signal are processed using Gaussian filters to obtain sub-band components. Features are extracted using some statistical characteristics of these signal components. Minimum redundancy maximum relevance test is employed to identify the more significant features. Three different machine learning classifiers are considered and their performance is compared. The results are analyzed for both the balanced and unbalanced datasets. The k-nearest neighbour (kNN) classifier achieves 79.14% accuracy and F-1 score of 79.24% for the balanced dataset. The proposed method outperforms the existing methods for CAP classification. It is easy-to-implement and can be considered as a candidate for real-time deployment.

The Impact of Alpha-s1 Casein Hydrolysate On Chronic Insomnia: A Randomized, Double-Blind Controlled Trial

BackgroundAlpha-s1 casein hydrolysate (ACH; Lactium®) is recognized as a supplementary treatment to enhance sleep quality. However, limited studies utilizing objective sleep assessment tools have resulted in a lack of substantial validation. This study aimed to assess the effects of ACH on both subjective sleep assessments and objective polysomnography (PSG) recordings in a hospital-based cohort of Taiwanese individuals with chronic insomnia. MethodsIn this 4-week randomized, double-blind, placebo-controlled trial, 36 participants diagnosed with chronic insomnia were enrolled and randomly assigned to either the ACH or placebo groups. Initially, participants in the ACH group received 600 mg of ACH daily, which was reduced to 300 mg for the latter two weeks; the placebo group received maltodextrin capsules throughout the study. The study utilized polysomnography (PSG), along with detailed sleep questionnaires including the Insomnia Severity Index (ISI), Global Sleep Disorders Score (GSDS), Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), and Hospital Anxiety and Depression Scale (HADS), to assess improvements in sleep quality and related health markers. The efficacy of the intervention was assessed through measures of sleep efficiency, stage distribution, and psychological well-being, comparing results from before to after the treatment phase. ResultsThe study demonstrated that ACH treatment notably enhanced sleep quality, evidenced by significant improvements in ISI, GSDS, PSQI, ESS, and HADS scores at both week 2 and 4 (all p-values < 0.05) compared with baseline scores. When compared to the placebo group, the ACH group experienced a marked reduction in GSDS scores over time (p = 0.045). Furthermore, PSG data revealed a significant decrease in sleep onset latency from baseline in the ACH group compared to the placebo group (p = 0.012; -7.7 ± 16.0 minutes vs. 6.1 ± 17.7 minutes for ACH and placebo groups, respectively). These results indicate that ACH treatment effectively improved sleep initiation and overall sleep quality. ConclusionACH Supplementation significantly improved sleep quality, particularly by reducing GSDS scores and sleep onset latency, demonstrating its potential as an effective intervention for chronic insomnia. Future studies with larger samples and exploration of long-term effects are needed to confirm these results.

Neither fifty percent slow-wave sleep suppression nor fifty percent rapid eye movement sleep suppression does impair memory consolidation

Establishing well-defined relationships between sleep features and memory consolidation is essential in comprehending the pathophysiology of cognitive decline commonly seen in patients with insomnia, depression, and other sleep-disrupting conditions.Twenty-eight volunteers participated in two experimental sessions: a session with selective SWS suppression during one night and a session with undisturbed night sleep (as a control condition). Fifteen of them also participated in a third session with REM suppression. Suppression was achieved by presenting an acoustic tone. In the evening and the morning, the participants completed procedural and declarative memory tasks and the Psychomotor vigilance task (PVT). Heart rate variability analysis and salivary cortisol were used to control possible stress reactions to sleep interference.SWS and REM suppression led to more than 50 percent reduction in the amount of these stages. Neither vigilance nor memory consolidation was impaired after SWS or REM suppression. Unexpectedly, a beneficial effect of selective SWS suppression on PVT performance was found. Similarly, after a night with SWS suppression, the overnight improvement in procedural skills was higher than after a night with REM suppression and after a night with undisturbed sleep.Our data brings into question the extent to which SWS and REM are truly necessary for effective memory consolidation to proceed. Moreover, SWS suppression may even improve the performance of some tasks, possibly by reducing sleep inertia associated with undisturbed sleep.

Low-Frequency Deep Brain Stimulation in Non-Rapid Eye Movement Sleep Modifies Memory Retention in Parkinson's Disease.

Memory impairment is a frequent and debilitating symptom in neurodegenerative disorders. The objective of this study was to provide proof-of-principle that deep brain stimulation during sleep can modify memory consolidation in people with Parkinson's disease depending on the stimulation frequency that is applied. Twenty-four patients with Parkinson's disease who were treated with deep brain stimulation of the subthalamic nucleus were included in this single-blind pilot study. Six patients had to be excluded because of insomnia on the night of testing. Patients were randomized (1:1 ratio) to receiving either low frequency deep brain stimulation (4 Hz) or clinically used high frequency deep brain stimulation (130 Hz) during early non-rapid eye movement (NREM) sleep. The main outcome measure was overnight memory retention as measured by a validated declarative memory task. Patients receiving low frequency deep brain stimulation during early NREM sleep (n = 9, 4 females, mean age 61.1 ± 4.3 years) showed improved overnight memory retention (z = 2.549, P = 0.011). Patients receiving clinically used high frequency deep brain stimulation (n = 9, 2 females, mean age 62.2 ± 7.1) did not show any improvement (z = 1.023, P = 0.306) leading to a significant difference between groups (z = 2.214, P = 0.027). Stronger improvement in memory function was correlated with increased cortical low frequency activity after low frequency deep brain stimulation as measured by electroencephalography (ρ = 0.711, P = 0.037). These results provide proof-of-principle that memory can be modulated by frequency-specific deep brain stimulation during sleep. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Stimulation-Evoked Resonant Neural Activity in the Subthalamic Nucleus Is Modulated by Sleep.

Deep brain stimulation is a treatment for advanced Parkinson's disease and currently tuned to target motor symptoms during daytime. Parkinson's disease is associated with multiple nocturnal symptoms such as akinesia, insomnia, and sleep fragmentation, which may require adjustments of stimulation during sleep for best treatment outcome. There is a need for a robust biomarker to guide stimulation titration across sleep stages. This study aimed to investigate whether evoked resonant neural activity (ERNA) is modulated by sleep. We recorded local field potentials from the subthalamic nucleus of four Parkinson's patients with externalized electrodes while applying single stimulation pulses to investigate the effect of sleep on ERNA. We found that ERNA features change with wakefulness and sleep stages and are correlated with canonical frequency bands and heart rate. Given that ERNA modulates with sleep, it could be used as a robust marker for automatic stimulation titration during sleep. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Thalamic spindles and Up states coordinate cortical and hippocampal co-ripples in humans.

In the neocortex, ~90 Hz ripples couple to ~12 Hz sleep spindles on the ~1 Hz Down-to-Up state transition during non-rapid eye movement sleep. This conjunction of sleep waves is critical for the consolidation of memories into long-term storage. The widespread co-occurrences of ripples ("co-ripples") may integrate information across the neocortex and hippocampus to facilitate consolidation. While the thalamus synchronizes spindles and Up states in the cortex for memory, it is not known whether it may also organize co-ripples. Using human intracranial recordings during NREM sleep, we investigated whether cortico-cortical co-ripples and hippocampo-cortical co-ripples are either: (1) driven by directly projected thalamic ripples; or (2) coordinated by propagating thalamic spindles or Up states. We found ripples in the anterior and posterior thalamus, with similar characteristics as hippocampal and cortical ripples, including having a center frequency of ~90 Hz and coupling to local spindles on the Down-to-Up state transition. However, thalamic ripples rarely co-occur or phase-lock with cortical or hippocampal ripples. By contrast, spindles and Up states that propagate from the thalamus strongly coordinate co-ripples in the cortex and hippocampus. Thus, thalamo-cortical spindles and Up states, rather than thalamic ripples, may provide input facilitating spatially distributed co-rippling that integrates information for memory consolidation during sleep in humans.

Differential effects of sleep position and sleep stage on the severity of obstructive sleep apnea.

This study compared the effects of sleeping in the supine position and rapid eye movement sleep on the severity of obstructive sleep apnea, and investigated the effect of sleep stage on position-dependent obstructive sleep apnea, and of sleep position on rapid eye movement-dependent obstructive sleep apnea. We analysed epoch-labelled polysomnographic readouts of 3843 patients, and calculated the apnea-hypopnea index for each sleep position and sleep stage. Subgroup analyses were performed to evaluate whether the proportion of position-dependent obstructive sleep apnea patients changed during rapid eye movement and non-rapid eye movement sleep, and whether that of rapid eye movement-dependent obstructive sleep apnea patients changed during supine/lateral sleep. The apnea-hypopnea index was highest in the rapid eye movement-supine position (50.7 ± 22.6 events per hr), followed by non-rapid eye movement-supine, rapid eye movement-lateral and non-rapid eye movement-lateral (39.2 ± 25.3, 22.9 ± 24.4, 15.9 ± 21.9 events per hr, respectively; p < 0.001). Patients with position-dependent obstructive sleep apnea had a higher ratio of rapid eye movement sleep, and those with rapid eye movement-dependent obstructive sleep apnea had a higher ratio of sleep time in the supine position (p < 0.001). During rapid eye movement sleep, position-dependent obstructive sleep apnea was not observed in 21.1% of patients who otherwise had position-dependent obstructive sleep apnea. In the lateral position, 36.9% of patients with rapid eye movement-dependent obstructive sleep apnea did not retain rapid eye movement dependency. Although sleeping in the supine position and rapid eye movement sleep were both associated with more frequent respiratory events, this was the first study to demonstrate that the former had a stronger correlation with obstructive sleep apnea severity. Position dependency in patients with obstructive sleep apnea decreased during rapid eye movement sleep, and worsening of rapid eye movement dependency was alleviated in the lateral position, suggesting potential for personalized obstructive sleep apnea management.

A Single Night in Hypoxia Either with or without Ketone Ester Ingestion Reduces Sleep Quality Without Impacting Next Day Exercise Performance

ABSTRACT Background Sleeping at altitude is highly common in athletes as an integral part of altitude training camps or sport competitions. However, concerns have been raised due to expected negative effects on sleep quality, thereby potentially hampering exercise recovery and next-day exercise performance. We recently showed that ketone ester (KE) ingestion beneficially impacted sleep following strenuous, late evening exercise in normoxia, and alleviated hypoxemia. Therefore, we hypothesized that KE ingestion may be an effective strategy to attenuate hypox(em)ia-induced sleep dysregulations. Methods Eleven healthy, male participants completed three experimental sessions including normoxic training and subsequent sleep in normoxia or at a simulated altitude of 3,000 m while receiving either KE or placebo post-exercise and pre-sleep. Sleep was evaluated using polysomnography, while next-day exercise performance was assessed through a 30-min all-out time trial (TT30’). Physiological measurements included oxygen status, heart rate variability, ventilatory parameters, blood acid-base balance and capillary blood gases. Results Hypoxia caused a ~3% drop in sleep efficiency, established through a doubled wakefulness after sleep onset and a ~22% reduction in slow wave sleep. KE ingestion alleviated the gradual drop in SpO2 throughout the first part of the night, but did not alter hypoxia-induced sleep dysregulations. Neither KE, nor nocturnal hypoxia affected TT30’ performance, but nocturnal hypoxia hampered heart rate recovery following TT30’. Conclusions We observed that sleeping at 3,000 m altitude impairs sleep efficiency. Although this hypoxia-induced sleep disruption was too subtle to limit exercise performance, we for the first time indicate that sleeping at altitude might impair next-day exercise recovery. KE alleviated nocturnal hypoxemia only when SpO2 values dropped below ~85%, but this did not translate into improved sleep or next-day exercise performance.

The Combination of Topological Data Analysis and Mathematical Modeling Improves Sleep Stage Prediction From Consumer-Grade Wearables

Wearable devices have become commonplace tools for tracking behavioral and physiological parameters in real-world settings. Nonetheless, the practical utility of these data for clinical and research applications, such as sleep analysis, is hindered by their noisy, large-scale, and multidimensional characteristics. Here, we develop a neural network algorithm that predicts sleep stages by tracking topological features (TFs) of wearable data and model-driven clock proxies (CPs) reflecting the circadian propensity for sleep. To evaluate its accuracy, we apply it to motion and heart rate data from the Apple Watch worn by young subjects undergoing polysomnography (PSG) and compare the predicted sleep stages with the corresponding ground truth PSG records. The neural network that includes TFs and CPs along with raw wearable data as inputs shows improved performance in classifying Wake/REM/NREM sleep. For example, it shows significant improvements in identifying REM and NREM sleep (AUROC/AUPRC improvements &gt;13% and REM/NREM accuracy improvement of 12%) compared with the neural network using only raw data inputs. We find that this improvement is mainly attributed to the heart rate TFs. To further validate our algorithm on a different population, we test it on elderly subjects from the Multi-ethnic Study of Atherosclerosis cohort. This confirms that TFs and CPs contribute to the improvements in Wake/REM/NREM classification. We next compare the performance of our algorithm with previous state-of-the-art wearable-based sleep scoring algorithms and find that our algorithm outperforms them within and across different populations. This study demonstrates the benefits of combining topological data analysis and mathematical modeling to extract hidden inputs of neural networks from puzzling wearable data.

Assessing the impact of 24-hour activity behaviors on cardiorespiratory fitness in the older adult: a component analysis approach

BackgroundCardiorespiratory fitness (CRF) serves as a critical measure of the cardiovascular system’s efficiency in delivering oxygenated blood to tissues and organs. Understanding the relationship between various activity behaviors and CRF is essential for devising effective health interventions for the older adult population.ObjectiveThis study aimed to investigate the association between 24-h activity behaviors and CRF in older adult individuals, utilizing compositional data analysis.MethodsWe utilized baseline data from the “Fifth National Physical Fitness Monitoring Cohort Study in Tianjin, China,” which included 540 older adult participants. Physical activity and sedentary behavior were objectively measured using a three-dimensional accelerometer, and CRF was assessed via a gas metabolism analyzer. Compositional data analysis was employed to examine the relationships between 24-h activity behaviors—specifically, moderate-to-vigorous physical activity (MVPA), light physical activity (LPA), sedentary behavior (SB), and sleep (SLP)—and CRF.ResultsThe analysis demonstrated that MVPA was significantly positively associated with CRF (βMVPA = 5.36, p &amp;lt; 0.01), whereas SB was significantly negatively associated (βSB = −3.97, p &amp;lt; 0.01). No significant associations were observed for LPA and SLP with CRF. The isochronous substitution model revealed that reallocating 15 min of MVPA to SB, LPA, or SLP significantly decreased CRF by 0.31, 0.27, and 0.23 mL/kg/min, respectively. Conversely, substituting 15 min of SB, LPA, or SLP with MVPA resulted in increases in CRF by 0.29, 0.22, and 0.17 mL/kg/min, respectively. Additionally, replacing SB with LPA or SLP led to improvements in CRF, though these changes were not significant, underscoring the potential benefits of reducing sedentary time and enhancing physical activity levels.ConclusionThese findings underscore the critical role of increasing MVPA and reducing SB in improving CRF among the older adult. This study provides a robust scientific foundation for health promotion and intervention strategies targeting older adults. Comprehensive modifications to daily activity patterns are imperative for optimizing cardiovascular health in this population.

Mineralocorticoid Receptor and Sleep Quality in Chronic Kidney Disease

The classical function of the mineralocorticoid receptor (MR) is to maintain electrolytic homeostasis and control extracellular volume and blood pressure. The MR is expressed in the central nervous system (CNS) and is involved in the regulation of the hypothalamic–pituitary–adrenal (HPA) axis as well as sleep physiology, playing a role in the non-rapid eye movement (NREM) phase of sleep. Some patients with psychiatric disorders have very poor sleep quality, and a relationship between MR dysregulation and this disorder has been found in them. In addition, the MR is involved in the regulation of the renal peripheral clock. One of the most common comorbidities observed in patients with chronic kidney disease (CKD) is poor sleep quality. Patients with CKD experience sleep disturbances, including reduced sleep duration, sleep fragmentation, and insomnia. To date, no studies have specifically investigated the relationship between MR activation and CKD-associated sleep disturbances. However, in this review, we analyzed the environment that occurs in CKD and proposed two MR-related mechanisms that may be responsible for these sleep disturbances: the circadian clock disruption and the high levels of MR agonist observed in CKD.

Monocytes migrate to the brain after MI to promote deep sleep to aid cardiac healing.

Monocytes migrate to the brain after MI to promote deep sleep to aid cardiac healing.

Influence of sleep on seizures and interictal epileptiform discharges in epilepsy.

Sleep significantly influences seizure occurrence and interictal epileptiform discharges (IEDs) in patients with epilepsy. Sleep-related epilepsy, where seizures occur exclusively or predominantly during sleep, has been observed in various epilepsy syndromes. Understanding the influence of sleep on seizures and IEDs is crucial in the diagnosis, classification, and management of epilepsy. Although there is a bidirectional relationship between sleep and epilepsy, this review focuses on the influence of sleep on seizures and IEDs in epilepsy. Seizures are more common during non-rapid eye movement (NREM) sleep, particularly during stage N2, and are suppressed during rapid eye movement (REM) sleep. Sleep also activates IEDs, increasing the diagnostic yield of EEG recordings. The rate of IEDs increases during NREM sleep, reaches its maximum during stage N3, and decreases during REM sleep. Sleep affects the electrical field of IEDs, with an increase of spiking fields during NREM sleep and a decrease during REM sleep. In the localization of epileptogenic foci, REM sleep is less sensitive but more specific than NREM sleep. Thalamocortical EEG synchronization during NREM sleep and desynchronization during REM sleep underlie their opposing effects on seizures and IEDs. Accumulating evidence has suggested an antiseizure effect of orexinergic antagonism in animal studies. Interventions that promote REM sleep, including orexinergic antagonists, should be studied in the future as novel treatment strategies for epilepsy.

A sleepy cannabis constituent: cannabinol and its active metabolite influence sleep architecture in rats.

Medicinal cannabis is being used worldwide and there is increasing use of novel cannabis products in the community. Cannabis contains the major cannabinoids, Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), but also an array of minor cannabinoids that have undergone much less pharmacological characterization. Cannabinol (CBN) is a minor cannabinoid used in the community in "isolate' products and is claimed to have pro-sleep effects comparable to conventional sleep medications. However, no study has yet examined whether it impacts sleep architecture using objective sleep measures. The effects of CBN on sleep in rats using polysomnography were therefore examined. CBN increased total sleep time, although there was evidence of biphasic effects with initial sleep suppression before a dramatic increase in sleep. CBN increased both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. The magnitude of the effect of CBN on NREM was comparable to the sleep aid zolpidem, although, unlike CBN, zolpidem did not influence REM sleep. Following CBN dosing, 11-hydroxy-CBN, a primary metabolite of CBN surprisingly attained equivalently high brain concentrations to CBN. 11-hydroxy-CBN was active at cannabinoid CB1 receptors with comparable potency and efficacy to Δ9-THC, however, CBN had much lower activity. We then discovered that the metabolite 11-hydroxy-CBN also influenced sleep architecture, albeit with some subtle differences from CBN itself. This study shows CBN affects sleep using objective sleep measures and suggests an active metabolite may contribute to its hypnotic action.

Interleukin-12 modulates sleep–wake activity and improves performance in a memory task

Abstract Background Cytokines, known for their pro- and anti-inflammatory roles, are also key regulators of sleep–wake cycles. Classical pro-inflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-α), are associated with increased sleep, particularly slow-wave sleep (SWS), while anti-inflammatory cytokines, like interleukin-10 (IL-10), generally reduce sleep duration. Given the essential role of sleep in memory consolidation, this study aimed to investigate whether interleukin-12 (IL-12), a pro-inflammatory cytokine, could increase sleep duration following a memory acquisition task and subsequently improve memory performance. Male Swiss mice were surgically implanted with electrodes for electrocorticogram (ECoG) and electromyogram (EMG) recordings to track their sleep–wake cycles. After a recovery period, baseline sleep–wake activity was recorded. The mice were then randomly assigned to two groups and treated with either IL-12 (0.5 µg, i.p.) or a phosphate-buffered saline (PBS, i.p.) control, administered immediately before the multiple-trial inhibitory avoidance (MTIA) task, a behavioral test used to assess memory performance. Following the memory acquisition session, sleep–wake activity was immediately recorded for a continuous 24-h period. Results Mice treated with IL-12 exhibited longer latency to cross into the dark compartment during the MTIA test, indicating improved memory retention compared to the control group. Interestingly, this improved performance was associated with prolonged wakefulness, particularly in the first three hours after task acquisition. Conclusion The study shows that IL-12 can improve memory retention through prolonged wake episodes rather than increased sleep. This finding challenges the conventional understanding that sleep is the primary state for memory consolidation, suggesting that under specific conditions, wakefulness may also play a key role in supporting memory processes. Further research is needed to explore the underlying mechanisms of IL-12's cognitive effects.

Based -evidence, an intervention study to improve sleep quality in awake adult ICU patients: a prospective, single-blind, clustered controlled trial.

Evidence-based guidelines advocate promoting sleep in intensive care unit (ICU) patients, yet many patients experience poor sleep quality. We sought to develop a collaborative evidence-based intervention with healthcare providers and assess whether evidence-based sleep interventions could improve sleep quality in awake adult ICU patients. We conducted a prospective, nonrandomized cluster control trial in two intensive care units (ICUs) at a tertiary general teaching hospital in China. Patients aged 18years or older who stayed in the ICU for one night or more and were conscious were eligible for enrollment. We only blinded the patients, not the outcome assessors. On the basis of evidence-based practice and clinical reality, we developed intervention measures for the intervention group, which mainly included four aspects: reducing environmental noise in the ICU, adjusting nursing actions, modifying nighttime lighting, and other measures. The assessment tools used were wearable actigraphy sleep monitoring devices and the Richards-Campbell Sleep Questionnaire (RCSQ). The primary outcomes were patient sleep quality, including total sleep time, deep sleep time, light sleep time, rapid eye movement (REM) time, number of awakenings, overall sleep score, and patients' self-assessment of their sleep quality that night. The data collected were analyzed via SPSS and Mplus statistical software for between-group analysis, pre-post comparison, profile analysis, and calculation of the intervention effect size. From September 1, 2023, to January 31, 2024, 713 patients underwent eligibility assessment, and ultimately 246 patients were included in the analysis, with 125 in the intervention group and 121 in the control group. Comparative analysis revealed no statistically significant differences in sleep quality between the two groups when the duration in the ICU = 1 night (P > 0.05), with a small intervention effect size. However, the intervention group had higher sleep quality scores (sleep monitoring wristband: 57.74 ± 22.55 > 57.72 ± 19.39; RCSQ questionnaire: 60.58 ± 22.14 > 57.61 ± 24.4) and total sleep time (440.42 ± 262.11 > 420.31 ± 236.89), a lower awakening frequency (3.98 ± 2.69 < 6.09 ± 4.66) and a lower awakening frequency (3.976 ± 2.693 < 6.09 ± 4.664) than did the control group. The sleep quality of patients who stayed in the ICU for > 1 night significantly improved in all the parameters except rapid eye movement time (min) according to the pre-post-test analyses (P < 0.05), with a medium to large intervention effect size and favorable intervention effects. Evidence-based interventions significantly improve sleep quality in ICU patients hospitalized for more than one day. However, our results do not support the improvement of sleep quality in patients admitted to the ICU for one day. ChiCTR2300075763, Registered 14 September 2023-Retrospectively registered, https://www.chictr.org.cn/bin/userProject.

Exploration of an intrinsically explainable self-attention based model for prototype generation on single-channel EEG sleep stage classification.

Prototype-based methods in deep learning offer interpretable explanations for decisions by comparing inputs to typical representatives in the data. This study explores the adaptation of SESM, a self-attention-based prototype method successful in electrocardiogram (ECG) tasks, for electroencephalogram (EEG) signals. The architecture is evaluated on sleep stage classification, exploring its efficacy in predicting stages with single-channel EEG. The model achieves comparable test accuracy compared to EEGNet, a state-of-the-art black-box architecture for EEG classification. The generated prototypical components are exaimed qualitatively and using the area over the perterbation curve (AOPC) indicate some alignment with expected bio-markers for different sleep stages such as alpha spindles and slow waves in non-REM sleep, but the results are severely limited by the model's ability to only extract and present information in the time-domain. Ablation studies are used to explore the impact of kernel size, number of heads, and diversity threshold on model performance and explainability. This study represents the first application of a self-attention based prototype method to EEG data and provides a step forward in explainable AI for EEG data analysis.

Changes to human sleep architecture during long-duration spaceflight.

Both rapid eye movement and non-rapid eye movement sleep are important for cognitive function and well-being, yet few studies have examined whether human sleep architecture is affected by long-duration spaceflight. We recorded 256 nights of sleep from five crew members before (n = 112 nights), during (n = 83 nights) and after (n = 61 nights) ~6-month missions aboard the Mir space station, using the Nightcap sleep monitor. We compared sleep outcomes (including total sleep time, efficiency, latency, rapid eye movement and non-rapid eye movement) during spaceflight with those on Earth. We also evaluated longitudinal changes over time in space. We found that wakefulness increased by 1 hr in space compared with on Earth. Over time in space, rapid eye movement was initially reduced and then recovered to near preflight levels at the expense of non-rapid eye movement sleep. Upon return to Earth, sleep architecture returned to preflight distribution. Our findings suggest that spaceflight may alter sleep architecture and should be explored further.

The effect of restricted and free-living conditions on light exposure and sleep in older adults

ABSTRACT During the COVID-19 pandemic, studies reported that restricted living conditions were associated with worse subjective sleep quality. This effect might have been caused by reduced light exposure during lockdowns. We investigated light exposure levels, subjective and objective sleep and physical activity levels in older adults during restricted and free-living conditions after the pandemic. Ninety-one participants (62.7 ± 8.4 years) recruited from the community using social media with 44 participants (63.4 ± 8.9 years) completed follow-up during free-living conditions. Participants wore an actigraphy device and completed sleep diaries for 7 days during each condition. Light values were extracted in hourly bins across the 24-h period and objective and subjective sleep were compared between the conditions. There was an increase in mean 24-h light exposure during restricted-living (1103.7 ± 1024.8 lux) compared to free-living (803.0 ± 803.6 lux; p < 0.001). This was partially related to participants spending 18 min more in bright light conditions (>1,000 lux) during wakefulness in restricted living (2.6 ± 1.9 h) compared to free-living (2.3 ± 2.0 h; p = 0.036). Despite differences in light exposure, there were no significant differences in objective and subjective sleep parameters between the two conditions. More research is required to better understand behaviours related to light exposure and how this may impact on sleep.

Characterising the power spectrum dynamics of the non-REM to REM sleep transition.

The transition from non-rapid eye movement (NREM) to rapid eye movement (REM) sleep is considered a transitional or intermediate stage (IS), characterised by high amplitude spindles in the frontal cortex and theta activity in the occipital cortex. Early reports in rats showed an IS lasting from 1 to 5 s, but recent studies suggested a longer duration of this stage of up to 20 s. To further characterise the IS, we analysed its spectral characteristics on electrocorticogram (ECoG) recordings of the olfactory bulb (OB), primary motor (M1), primary somatosensory (S1), and secondary visual cortex (V2) in 12 Wistar male adult rats. By comparing the IS with consolidated NREM/REM epochs, our results reveal that the IS has specific power spectral patterns that fall out of the NREM and REM sleep state power distribution. Specifically, the main findings were that sigma (11-16 Hz) power in OB, M1, S1, and V2 increased during the IS compared with NREM and REM sleep, which started first in the frontal part of the brain (OB -54 s, M1 -53 s) prior to the last spindle occurrence. The beta band (17-30 Hz) power showed a similar pattern to that of the sigma band, starting -54 s before the last spindle occurrence in the M1 cortex. Notably, sigma infraslow coupling (~0.02 Hz) increased during the IS but occurred at a slower frequency (~0.01 Hz) compared with NREM sleep. Thus, we argue that the NREM to REM transition contains its own local spectral profile, in accordance with previous reports, and is more extended than described previously.