Systematic individual differences in sleep homeostatic and circadian rhythm contributions to neurobehavioral impairment during sleep deprivation

Dim light melatonin onset following simulated eastward travel is earlier in young males genotyped as PER35/5 than PER34/4

Inter-individual variability exists in recovery from jetlag following travel across time zones. Part of this variation may be due to genetic differences at the variable number tandem repeat (VNTR) polymorphism of the PERIOD3 (PER3) gene as this polymorphism has been associated with chronotype and sleep, as well as sensitivity to blue light on melatonin suppression. To test this hypothesis we conducted a laboratory-based study to compare re-entrainment in males genotyped as PER3^4/4 (n = 8) and PER3^5/5 (n = 8) following simulated eastward travel across six time zones. The recovery strategy included morning blue-enriched light exposure and appropriately-timed meals during the first 24 h after simulated travel. Dim light melatonin onset (DLMO), sleep characteristics, perceived sleepiness levels (Stanford Sleepiness Scale), and resting metabolic parameters were measured during constant routine periods before and after simulated travel. While DLMO time was similar between the two groups prior to simulated eastward travel (p = .223), it was earlier in the PER3^5/5 group (17h23 (17h15; 17h37)) than the PER3^4/4 group (18h05 (17h53; 18h12)) afterwards (p = .046). During resynchronisation, perceived sleepiness and metabolic parameters were similar to pre-travel in both groups but sleep was more disturbed in the PER3^5/5 group (total sleep time: p = .008, sleep efficiency: p = .008, wake after sleep onset: p = .023). The PER3 VNTR genotype may influence the efficacy of re-entrainment following trans-meridian travel when blue-enriched light exposure is incorporated into the recovery strategy on the first day following travel.

Arousal-Mediated Sleep Disturbance Persists During Cocaine Abstinence in Male Mice

Acute cocaine disturbs sleep on a dose-dependent basis; however, the consequences of chronic cocaine remain unclear. While the arousal promotion following cocaine has been well-established, effects of cocaine on sleep after termination of chronic cocaine exposure appear variable in human subjects with few studies in non-human subjects. Here, a within-subjects design (outcomes normalized to baseline, undisturbed behavior) and between-subjects design (repeated experimenter-administered cocaine vs. experimenter-administered saline) was used to investigate sleep homeostasis and sleep/waking under repeated cocaine/saline exposure and prolonged forced abstinence conditions in mice. Overall, during the forced abstinence period increases in arousal, as determined by sleep latency and gamma energy, persisted for 2 weeks. However, the sleep response to externally enforced sleep deprivation was unchanged suggesting that sleep disruptions during the forced abstinence period were driven by enhancement of arousal in the absence of changes in sleep homeostatic responses.

Working around the Clock: Is a Person’s Endogenous Circadian Timing for Optimal Neurobehavioral Functioning Inherently Task-Dependent?

Neurobehavioral task performance is modulated by the circadian and homeostatic processes of sleep/wake regulation. Biomathematical modeling of the temporal dynamics of these processes and their interaction allows for prospective prediction of performance impairment in shift-workers and provides a basis for fatigue risk management in 24/7 operations. It has been reported, however, that the impact of the circadian rhythm—and in particular its timing—is inherently task-dependent, which would have profound implications for our understanding of the temporal dynamics of neurobehavioral functioning and the accuracy of biomathematical model predictions. We investigated this issue in a laboratory study designed to unambiguously dissociate the influences of the circadian and homeostatic processes on neurobehavioral performance, as measured during a constant routine protocol preceded by three days on either a simulated night shift or a simulated day shift schedule. Neurobehavioral functions were measured every 3 h using three functionally distinct assays: a digit symbol substitution test, a psychomotor vigilance test, and the Karolinska Sleepiness Scale. After dissociating the circadian and homeostatic influences and accounting for inter-individual variability, peak circadian performance occurred in the late biological afternoon (in the “wake maintenance zone”) for all three neurobehavioral assays. Our results are incongruent with the idea of inherent task-dependent differences in the endogenous circadian impact on performance. Rather, our results suggest that neurobehavioral functions are under top-down circadian control, consistent with the way they are accounted for in extant biomathematical models.

Prediction of shiftworker alertness, sleep, and circadian phase using a model of arousal dynamics constrained by shift schedules and light exposure

STUDY OBJECTIVES

The study aimed to, for the first time, (1) compare sleep, circadian phase, and alertness of intensive care unit (ICU) nurses working rotating shifts with those predicted by a model of arousal dynamics; and (2) investigate how different environmental constraints affect predictions and agreement with data.

METHODS

The model was used to simulate individual sleep-wake cycles, urinary 6-sulphatoxymelatonin (aMT6s) profiles, subjective sleepiness on the Karolinska Sleepiness Scale (KSS), and performance on a Psychomotor Vigilance Task (PVT) of 21 ICU nurses working day, evening, and night shifts. Combinations of individual shift schedules, forced wake time before/after work and lighting, were used as inputs to the model. Predictions were compared to empirical data. Simulations with self-reported sleep as an input were performed for comparison.

RESULTS

All input constraints produced similar prediction for KSS, with 56%-60% of KSS scores predicted within ±1 on a day and 48%-52% on a night shift. Accurate prediction of an individual's circadian phase required individualized light input. Combinations including light information predicted aMT6s acrophase within ±1 h of the study data for 65% and 35%-47% of nurses on diurnal and nocturnal schedules. Minute-by-minute sleep-wake state overlap between the model and the data was between 81 ± 6% and 87 ± 5% depending on choice of input constraint.

CONCLUSIONS

The use of individualized environmental constraints in the model of arousal dynamics allowed for accurate prediction of alertness, circadian phase, and sleep for more than half of the nurses. Individual differences in physiological parameters will need to be accounted for in the future to further improve predictions.

Zebrafish as a tool in the study of sleep and memory-related disorders

Sleep is an evolutionarily conserved phenomenon, being an essential biological necessity for the learning process and memory consolidation. The brain displays two types of electrical activity during sleep: slow-wave activity or non-rapid eye movement (NREM) sleep and desynchronized brain wave activity or rapid eye movement (REM) sleep. There are many theories about "Why we need to sleep?" among them the synaptic homeostasis. This theory proposes that the role of sleep is the restoration of synaptic homeostasis, which is destabilized by synaptic strengthening triggered by learning during waking and by synaptogenesis during development. Sleep diminishes the plasticity load on neurons and other cells to normalize synaptic strength. In contrast, it re-establishes neuronal selectivity and the ability to learn, leading to the consolidation and integration of memories. The use of zebrafish as a tool to assess sleep and its disorders is growing, although sleep in this animal is not yet divided, for example, into REM and NREM states. However, zebrafish are known to have a regulated daytime circadian rhythm. Their sleep state is characterized by periods of inactivity accompanied by an increase in arousal threshold, preference for resting place, and the "rebound sleep effect" phenomenon, which causes an increased slow-wave activity after a forced waking period. In addition, drugs known to modulate sleep, such as melatonin, nootropics, and nicotine, have been tested in zebrafish. In this review, we discuss the use of zebrafish as a model to investigate sleep mechanisms and their regulation, demonstrating this species as a promising model for sleep research.

Quantifying Cognitive Impairment After Sleep Deprivation at Different Times of Day: A Proof of Concept Using Ultra-Short Smartphone-Based Tests

Cognitive functioning is known to be impaired following sleep deprivation and to fluctuate depending on the time of day. However, most methods of assessing cognitive performance remain impractical for environments outside of the lab. This study investigated whether 2-min smartphone-based versions of commonly used cognitive tests could be used to assess the effects of sleep deprivation and time of day on diverse cognitive functions. After three nights of normal sleep, participants (N = 182) were randomised to either one night of sleep deprivation or a fourth night of normal sleep. Using the Karolinska WakeApp (KWA), participants completed a battery of 2-min cognitive tests, including measures of attention, arithmetic ability, episodic memory, working memory, and a Stroop test for cognitive conflict and behavioural adjustment. A baseline measurement was completed at 22:30 h, followed by three measurements the following day at approximately 08:00 h, 12:30 h, and 16:30 h. Sleep deprivation led to performance impairments in attention, arithmetic ability, episodic memory, and working memory. No effect of sleep deprivation was observed in the Stroop test. There were variations in attention and arithmetic test performance across different times of day. The effect of sleep deprivation on all cognitive tests was also found to vary at different times of day. In conclusion, this study shows that the KWA's 2-min cognitive tests can be used to detect cognitive impairments following sleep deprivation, and fluctuations in cognitive performance relating to time of day. The results demonstrate the potential of using brief smartphone-based tasks to measure a variety of cognitive abilities within sleep and fatigue research.

Sensitivity and specificity of the driver sleepiness detection methods using physiological signals: A systematic review

Driver sleepiness is a major contributor to road crashes. A system that monitors and warns the driver at a certain, critical level of arousal, could aid in reducing sleep-related crashes. To determine how driver sleepiness detection systems perform, a systematic review of the sensitivity and specificity outcomes was performed. In total, 21 studies were located that met inclusion criteria for the review. The range of sensitivity outcomes was between 39.0-98.8 % and between 73.0-98.9 % for specificity outcomes. There was considerable variation in the outcomes of the studies employing only one physiological measure (mono-signal approach), whereas, a poly-signal approach with multiple physiological signals resulted in more consistency with higher outcomes on both sensitivity and specificity metrics. Only six of the 21 studies had both sensitivity and specificity outcomes above 90.0 %, which included mono- and poly-signal approaches. Moreover, increases in the number of features used in the sleepiness detection system did not result in higher sensitivity and specificity outcomes. Overall, there was considerable variability between the studies reviewed, including measures of ground truth, the features employed and the machine learning approach of the systems. A critical need for progressing any system is a revalidation of the system on a new sample of users. These aspects indicate considerable progress is needed with physiological-based driver sleepiness systems before they are at a sufficient standard to be deployed on-road.

The Iowa Resistance to Sleeplessness Test (iREST)

INTRODUCTION

Despite considerable individual differences in the vulnerability vs resistance to effects of sleep loss, there is no practical self-report tool to predict these differences across domains and only limited evidence whether they are general or domain-specific. To address this need, we developed the Iowa Resistance to Sleeplessness Test (iREST).

METHODS

A construct-validation approach was employed. During the substantive phase, self-report items were generated to capture vulnerability vs resistance to sleep loss across various psycho-behavioral domains. During the structural phase, analyses identified the underlying factor structure and examined reliability of individual scale scores. Finally, the external phase used convergent and discriminant analyses to evaluate the factors in light of related sleep and personality measures, and tested criterion validity of the scale scores in predicting neurocognitive and affective responses to experimental sleep restriction (Total N = 1018).

RESULTS

Analyses yielded discriminant and reliable scale scores that reflected resistance across cognitive, affective, and somatic responses, while also marking a general resistance factor. Convergent and discriminant probes revealed moderate associations of scale scores with daytime sleepiness and sleep-related distress, but small to negligible associations with other measures of sleep behavior, perceptions, and personality. Critically, criterion analyses yielded validity evidence for predicting cognitive and affective impairments in response to experimental sleep loss.

CONCLUSION

Scores on the iREST show validity in capturing cognitive and affective resistance to moderate sleep loss among young adults, supporting its further exploration as a practical tool for predicting behavior due to lost sleep.

The Role of the Thalamus in the Neurological Mechanism of Subjective Sleepiness: An fMRI Study

PURPOSE

The thalamus, the region that forms the attentional network and transmits external sensory signals to the entire brain, is important for sleepiness. Herein, we examined the relationship between activity in the thalamus-seed brain network and subjective sleepiness.

MATERIALS AND METHODS

Fifteen healthy male participants underwent an experiment comprising a baseline evaluation and two successive interventions, a 9-day sleep extension followed by 1-night total sleep deprivation. Pre- and post-intervention tests included the Karolinska sleepiness scale and neuroimaging for arterial spin labeling and functional connectivity. We examined the association between subjective sleepiness and the functional magnetic resonance imaging indices.

RESULTS

The functional connectivity between the left or right thalamus and various brain regions displayed a significant negative association with subjective sleepiness, and the functional connectivity between the left and right thalamus displayed a significant positive association with subjective sleepiness. The graph theory analysis indicated that the number of positive functional connectivity related to the thalamus showed a strong negative association with subjective sleepiness, and conversely, the number of negative functional connectivity showed a positive association with subjective sleepiness. Arterial spin labeling analysis indicated that the blood flow in both the left and right thalami was significantly negatively associated with subjective sleepiness. Functional connectivity between the anterior cingulate cortex and salience network areas of the left insular cortex, and that between the anterior and posterior cingulate cortices showed a strong positive and negative association with subjective sleepiness, respectively.

CONCLUSION

Subjective sleepiness and the thalamic-cortical network dynamics are strongly related, indicating the application of graph theory to study sleepiness and consciousness. These results also demonstrate that resting functional connectivity largely reflects the "state" of the subject, suggesting that the control of sleep and conscious states is essential when using functional magnetic resonance imaging indices as biomarkers.

Sleep as a Target for Optimized Response to Smoking Cessation Treatment

Declining national rates of current tobacco use to an all-time low of 15.1% represents a public health victory. Undermining this progress, however, are smoking rates of up to 50% among high-risk, low-income populations. Current FDA-approved treatments for nicotine dependence are ineffective with between 70-95% of treatment-seekers relapsing within the first year of attempted abstinence. Thus, identification of novel intervention targets to optimize response to currently available treatments for nicotine dependence is a critical next step. One such target may be sleep insomnia. Insomnia is a clinically verified nicotine withdrawal symptom but, to date, addressing insomnia or other sleep disturbance symptoms as an adjunctive smoking cessation therapy has yet to be fully considered. To this end, this manuscript presents a narrative review of: (1) sleep continuity and architecture in smokers versus nonsmokers; (2) effects of nicotine abstinence on sleep; (3) possible mechanisms linking sleep with smoking cessation outcomes; (4) plausible adjunctive sleep therapies to promote smoking cessation; (5) possible treatments for unhealthy sleep in smokers; and (6) directions for future research. Taken together, this will provide conceptual support for sleep therapy as an adjunctive treatment for smoking cessation.

Implications

This narrative literature review presents a comprehensive discussion of the relationship between habitual sleep and cigarette smoking. The extent to which unhealthy sleep in smokers may be a viable intervention target for promoting response to smoking cessation treatment is considered. Ultimately, this review provides conceptual support for sleep therapy as an adjunctive treatment for smoking cessation.

Precision Medicine for Sleep Loss and Fatigue Management

Sleep loss is a widespread phenomenon and a public health threat. Sleep disorders, medical conditions, lifestyles, and occupational factors all contribute to insufficient sleep. Regardless of the underlying cause, insufficient sleep has well-defined consequences and the severity of said consequences partially influenced by individual characteristics. It is here where precision medicine needs to understand and define sleep insufficiency in hopes for personalizing medical approach to improve patient outcomes. Following a discussion on causes and consequences of sleep loss, this article discusses tools for assessing sleep sufficiency, mitigating strategies to sleep loss, and sleep loss in the context of fatigue management.

Vulnerability to mood degradation during sleep deprivation is influenced by white-matter compactness of the triple-network model

Sleep deprivation (SD) is often associated with significant shifts in mood state relative to baseline functioning. Prior work suggests that there are consistent trait-like differences among individuals in the degree to which their mood and performances are affected by sleep loss. The goal of this study was to determine the extent to which trait-like individual differences in vulnerability/resistance to mood degradation during a night of SD are dependent upon region-specific white and grey matter (WM/GM) characteristics of a triple-network model, including the default-mode network (DMN), control-execution network (CEN) and salience network (SN). Diffusion-weighted and anatomical brain data were collected from 45 healthy individuals several days prior to a 28-h overnight SD protocol. During SD, a visual analog mood scale was administered every hour from 19:15 (time point1; TP1) to 11:15 (TP17) the following morning to measure two positive and six negative mood states. Four core regions within the DMN, five within the CEN, and seven within the SN were used as regions of interest (ROIs). An index of mood resistance (IMR) was defined as the averaged differences between positive and negative mood states over 12 TPs (TP5 to TP16) relative to baseline (TP1 to TP4). For each ROI, characteristics of WM - quantitative anisotropy (QA) and mean curvature index (WM-MCI), and GM - cortical volume (CV) and GM-MCI were estimated, and used to predict IMR. WM characteristics, particularly QA, of all of regions within the DMN, and most of the regions within the CEN and SN predicted IMR during SD. In contrast, most ROIs did not show significant association between IMR and any of the GM characteristics (CV and MCI) or WM MCI. Our findings suggest that greater resilience to mood degradation induced by total SD appears to be associated with more compact axonal pathways within the DMN, CEN and SN.

Analysis of the Effects of Day-Time vs. Night-Time Surgery on Renal Transplant Patient Outcomes

Sleep deprivation and disruption of the circadian rhythms could impair individual surgical performance and decision making. For this purpose, this study identified potential confounding factors on surgical renal transplant patient outcomes during day and night. Our retrospective cohort study of 215 adult renal cadaver transplant recipients, of which 132 recipients were allocated in the “day-time” group and 83 recipients in the “night-time” group, primarily stratified the patients into two cohorts, depending on the start time. Within a 24 h operational system, “day-time” was considered as being from 8 a.m. to 8 p.m. and “night-time” from 8 p.m. to 8 a.m.. Primary outcomes examined patient and graft survival after three months and one year. Secondary outcomes included the presence of acute rejection (AR) and delayed graft function (DGF), as well as the rate of postoperative complications. In log-rank testing, “day-time” surgery was associated with a significantly higher risk of patient death (p = 0.003), whereas long-term graft survival was unaffected by the operative time of day. The mean cold ischemia time (CIT), which was 12.4 ± 5.3 h in the “night-time” group, was significantly longer compared to 10.7 ± 3.6 for those during the day (p = 0.01). We observed that “night-time” kidney recipients experienced more wound complications. From our single-centre data, we conclude that night-time kidney transplantation does not increase the risk of adverse events or predispose the patient to a worse outcome. Nevertheless, further research is required to explore the effect of fatigue on nocturnal surgical performance.

Performance and sleepiness in nurses working 12-h day shifts or night shifts in a community hospital

Hospitals are around-the-clock operations and nurses are required to care for patients night and day. The nursing shortage and desire for a more balanced work-to-home life has popularized 12-h shifts for nurses. The present study investigated sleep/wake cycles and fatigue levels in 22 nurses working 12-h shifts, comparing day versus night shifts. Nurses (11day shift and 11 night shift) were recruited from a suburban acute-care medical center. Participants wore a wrist activity monitor and kept a diary to track their sleep/wake cycles for 2 weeks. They also completed a fatigue test battery, which included the Psychomotor Vigilance Test (PVT) and the Karolinska Sleepiness Scale (KSS), at the beginning, middle and end of 4 duty shifts. Daily sleep duration was 7.1h on average. No overall difference in mean daily sleep duration was found between nurses working day shifts versus night shifts. Objective performance on the PVT remained relatively good and stable at the start, middle, and end of duty shifts in day shift workers, but gradually degraded across duty time in night shift workers. Compared to day shift workers, night shift workers also exhibited more performance variability among measurement days and between participants at each testing time point. The same pattern was observed for subjective sleepiness on the KSS. However, congruence between objective and subjective measures of fatigue was poor. Our findings suggest a need for organizations to evaluate practices and policies to mitigate the inevitable fatigue that occurs during long night shifts, in order to improve patient and healthcare worker safety. Examination of alternative shift lengths or sanctioned workplace napping may be strategies to consider.

Sleeping hours: what is the ideal number and how does age impact this?

The objective of this narrative review paper is to discuss about sleep duration needed across the lifespan. Sleep duration varies widely across the lifespan and shows an inverse relationship with age. Sleep duration recommendations issued by public health authorities are important for surveillance and help to inform the population of interventions, policies, and healthy sleep behaviors. However, the ideal amount of sleep required each night can vary between different individuals due to genetic factors and other reasons, and it is important to adapt our recommendations on a case-by-case basis. Sleep duration recommendations (public health approach) are well suited to provide guidance at the population-level standpoint, while advice at the individual level (eg, in clinic) should be individualized to the reality of each person. A generally valid assumption is that individuals obtain the right amount of sleep if they wake up feeling well rested and perform well during the day. Beyond sleep quantity, other important sleep characteristics should be considered such as sleep quality and sleep timing (bedtime and wake-up time). In conclusion, the important inter-individual variability in sleep needs across the life cycle implies that there is no "magic number" for the ideal duration of sleep. However, it is important to continue to promote sleep health for all. Sleep is not a waste of time and should receive the same level of attention as nutrition and exercise in the package for good health.

An improved model to predict performance under mental fatigue

Fatigue has become an increasing problem in our modern society. Using MATLAB as a generic modelling tool, a fatigue model was developed based on an existing one and compared with a commercial fatigue software for prediction of cognitive performance under total and partial sleep deprivation. The flexibility of our fatigue model allowed additions of new algorithms and mechanisms for non-sleep factors and countermeasures and thus improved model predictions and usability for both civilian and military applications. This was demonstrated by model simulations of various scenarios and comparison with experimental studies. Our future work will be focused on model validation and integration with other modelling tools. Practitioner Summary: Mental fatigue affects health, safety and quality of life in our modern society. In this paper, we reported a cognitive fatigue model based on existing models with newly incorporated components taking both the operator's state of alertness and task demand into account. The model provided the additional capability for prediction of cognitive performance in scenarios involving pharmaceutical countermeasures, different task demands and shift work.

Computational cognitive modeling of the temporal dynamics of fatigue from sleep loss

Computational models have become common tools in psychology. They provide quantitative instantiations of theories that seek to explain the functioning of the human mind. In this paper, we focus on identifying deep theoretical similarities between two very different models. Both models are concerned with how fatigue from sleep loss impacts cognitive processing. The first is based on the diffusion model and posits that fatigue decreases the drift rate of the diffusion process. The second is based on the Adaptive Control of Thought - Rational (ACT-R) cognitive architecture and posits that fatigue decreases the utility of candidate actions leading to microlapses in cognitive processing. A biomathematical model of fatigue is used to control drift rate in the first account and utility in the second. We investigated the predicted response time distributions of these two integrated computational cognitive models for performance on a psychomotor vigilance test under conditions of total sleep deprivation, simulated shift work, and sustained sleep restriction. The models generated equivalent predictions of response time distributions with excellent goodness-of-fit to the human data. More importantly, although the accounts involve different modeling approaches and levels of abstraction, they represent the effects of fatigue in a functionally equivalent way: in both, fatigue decreases the signal-to-noise ratio in decision processes and decreases response inhibition. This convergence suggests that sleep loss impairs psychomotor vigilance performance through degradation of the quality of cognitive processing, which provides a foundation for systematic investigation of the effects of sleep loss on other aspects of cognition. Our findings illustrate the value of treating different modeling formalisms as vehicles for discovery.

Exploring gene expression biomarker candidates for neurobehavioral impairment from total sleep deprivation

Background

Although sleep deprivation is associated with neurobehavioral impairment that may underlie significant risks to performance and safety, there is no reliable biomarker test to detect dangerous levels of impairment from sleep loss in humans. This study employs microarrays and bioinformatics analyses to explore candidate gene expression biomarkers associated with total sleep deprivation (TSD), and more specifically, the phenotype of neurobehavioral impairment from TSD. Healthy adult volunteers were recruited to a sleep laboratory for seven consecutive days (six nights). After two Baseline nights of 10 h time in bed, 11 subjects underwent an Experimental phase of 62 h of continuous wakefulness, followed by two Recovery nights of 10 h time in bed. Another six subjects underwent a well-rested Control condition of 10 h time in bed for all six nights. Blood was drawn for measuring gene expression on days two, four, and six at 4 h intervals from 08:00 to 20:00 h, corresponding to 12 timepoints across one Baseline, one Experimental, and one Recovery day.

Results

Altogether 212 genes changed expression in response to the TSD Treatment, with most genes exhibiting down-regulation during TSD. Also, 28 genes were associated with neurobehavioral impairment as measured by the Psychomotor Vigilance Test. The results support previous findings associating TSD with the immune response and ion signaling, and reveal novel candidate biomarkers such as the Speedy/RINGO family of cell cycle regulators.

Conclusions

This study serves as an important step toward understanding gene expression changes during sleep deprivation. In addition to exploring potential biomarkers for TSD, this report presents novel candidate biomarkers associated with lapses of attention during TSD. Although further work is required for biomarker validation, analysis of these genes may aid fundamental understanding of the impact of TSD on neurobehavioral performance.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4664-3) contains supplementary material, which is available to authorized users.

Executive functioning is preserved in healthy young adults under acute sleep restriction

OBJECTIVES

This study aimed to evaluate if a partial morning or evening sleep restriction protocol could affect executive functioning in healthy young adults.

METHODS

Participants were assigned to one of three groups: control (n=18), in which participants maintained their habitual sleep/wake cycle; morning restriction (n=17), in which volunteers terminated sleep approximately three hours earlier than the usual on the experimental night, and evening restriction (n=13), in which volunteers initiated sleep approximately three hours later than the usual on the experimental night. On the day of the experiment, they performed the Stroop Test, the Go-NoGo Test and the Iowa Gambling Task (IGT).

RESULTS

When compared to the control group, neither morning nor evening sleep-restricted individuals displayed any significant deficits in: a) selective attention as assessed by the interference index (H=3.38; p=0.18) and time to performed the interference card (H=2.61; p=0.27) on the Stroop test; b) motor response inhibition as assessed by number of false alarms (H=0.8; p=0.67) on the Go-NoGo Test; and c) in decision-making as assessed by total won (H=2.64; p=0.26) and number of selected advantageous cards (H=4.43; p=0.11) on the IGT.

CONCLUSION

These findings suggest that the ability to pay attention, inhibit a motor response and make decisions is preserved following approximately 3 hours of sleep restriction, regardless of its timing (in the morning or in the evening).

Interindividual variability in neurobehavioral response to sleep loss: A comprehensive review

Stable trait-like responding is well established for neurobehavioral performance measures across repeated exposures to total sleep deprivation and partial chronic sleep restriction. These observed phenotypes are task-dependent, suggesting that there are distinct cognitive profiles of responding with differential vulnerability to sleep loss within the same individual. Numerous factors have been investigated as potential markers of phenotypic vulnerability to the effects of sleep loss but none fully account for this phenomenon. Observed interindividual differences in performance during extended wakefulness may be driven by underlying deficits in the wake-promoting system resulting in greater performance instability due to failure to counteract increased homeostatic pressure. Further work would benefit from a systems approach to the study of interindividual vulnerability in which behavioral, neurobiological, and genetic data are integrated in a larger framework delineating the relationships between genes, proteins, neurobiology, and behavior.

Catechol-O-methyltransferase (COMT) genotype affects cognitive control during total sleep deprivation

Adaptive decision making is profoundly impaired by total sleep deprivation (TSD). This suggests that TSD impacts fronto-striatal pathways involved in cognitive control, where dopamine is a key neuromodulator. In the prefrontal cortex (PFC), dopamine is catabolized by the enzyme catechol-O-methyltransferase (COMT). A functional polymorphism (Val158Met) influences COMT's enzymatic activity, resulting in markedly different levels of prefrontal dopamine. We investigated the effect of this polymorphism on adaptive decision making during TSD. Sixty-six healthy young adults participated in one of two in-laboratory studies. After a baseline day, subjects were randomized to either a TSD group (n = 32) with 38 h or 62 h of extended wakefulness or a well-rested control group (n = 34) with 10 h nighttime sleep opportunities. Subjects performed a go/no-go reversal learning (GNGr) task at well-rested baseline and again during TSD or equivalent control. During the task, subjects were required to learn stimulus-response relationships from accuracy feedback. The stimulus-response relationships were reversed halfway through the task, which required subjects to learn the new stimulus-response relationships from accuracy feedback. Performance on the GNGr task was quantified by discriminability (d') between go and no-go stimuli before and after the stimulus-response reversal. GNGr performance did not differ between COMT genotypes when subjects were well-rested. However, TSD exposed a significant vulnerability to adaptive decision making impairment in subjects with the Val allele. Our results indicate that sleep deprivation degrades cognitive control through a fronto-striatal, dopaminergic mechanism.

Interindividual differences in the dynamics of the homeostatic process are trait-like and distinct for sleep versus wakefulness

The sleep homeostatic Process S reflects the build-up of sleep pressure during waking and its dissipation during sleep. Process S is modelled as a saturating exponential function during waking and a decreasing exponential function during sleep. Slow wave activity is a physiological marker for non-rapid eye movement (non-REM) sleep intensity and serves as an index of Process S. There is considerable interindividual variability in the sleep homeostatic responses to sleep and sleep deprivation. The aim of this study was to investigate whether interindividual differences in Process S are trait-like. Polysomnographic recordings of 8 nights (12-h sleep opportunities, 22:00-10:00 hours) interspersed with three 36-h periods of sustained wakefulness were performed in 11 healthy young adults. Empirical mean slow wave activity per non-REM sleep episode at episode mid-points were used for parameter estimation. Parameters of Process S were estimated using different combinations of consecutive sleep recordings, resulting in two to three sets of parameters per subject. Intraclass correlation coefficients were calculated to assess whether the parameters were stable across the study protocol and they showed trait-like variability among individuals. We found that the group-average time constants of the build-up and dissipation of Process S were 19.2 and 2.7 h, respectively. Intraclass correlation coefficients ranged from 0.48 to 0.56, which reflects moderate trait variability. The time constants of the build-up and dissipation varied independently among subjects, indicating two distinct traits. We conclude that interindividual differences in the parameters of the dynamics of the sleep homeostatic Process S are trait-like.

Acute Sleep Deprivation Blocks Short- and Long-Term Operant Memory in Aplysia

STUDY OBJECTIVES

Insufficient sleep in individuals appears increasingly common due to the demands of modern work schedules and technology use. Consequently, there is a growing need to understand the interactions between sleep deprivation and memory. The current study determined the effects of acute sleep deprivation on short and long-term associative memory using the marine mollusk Aplysia californica, a relatively simple model system well known for studies of learning and memory.

METHODS

Aplysia were sleep deprived for 9 hours using context changes and tactile stimulation either prior to or after training for the operant learning paradigm, learning that food is inedible (LFI). The effects of sleep deprivation on short-term (STM) and long-term memory (LTM) were assessed.

RESULTS

Acute sleep deprivation prior to LFI training impaired the induction of STM and LTM with persistent effects lasting at least 24 h. Sleep deprivation immediately after training blocked the consolidation of LTM. However, sleep deprivation following the period of molecular consolidation did not affect memory recall. Memory impairments were independent of handling-induced stress, as daytime handled control animals demonstrated no memory deficits. Additional training immediately after sleep deprivation failed to rescue the induction of memory, but additional training alleviated the persistent impairment in memory induction when training occurred 24 h following sleep deprivation.

CONCLUSIONS

Acute sleep deprivation inhibited the induction and consolidation, but not the recall of memory. These behavioral studies establish Aplysia as an effective model system for studying the interactions between sleep and memory formation.

Differential Kinetics in Alteration and Recovery of Cognitive Processes from a Chronic Sleep Restriction in Young Healthy Men

Chronic sleep restriction (CSR) induces neurobehavioral deficits in young and healthy people with a morning failure of sustained attention process. Testing both the kinetic of failure and recovery of different cognitive processes (i.e., attention, executive) under CSR and their potential links with subject's capacities (stay awake, baseline performance, age) and with some biological markers of stress and anabolism would be useful in order to understand the role of sleep debt on human behavior. Twelve healthy subjects spent 14 days in laboratory with 2 baseline days (B1 and B2, 8 h TIB) followed by 7 days of sleep restriction (SR1-SR7, 4 h TIB), 3 sleep recovery days (R1-R3, 8 h TIB) and two more ones 8 days later (R12-R13). Subjective sleepiness (KSS), maintenance of wakefulness latencies (MWT) were evaluated four times a day (10:00, 12:00 a.m. and 2:00, 4:00 p.m.) and cognitive tests were realized at morning (8:30 a.m.) and evening (6:30 p.m.) sessions during B2, SR1, SR4, SR7, R2, R3 and R13. Saliva (B2, SR7, R2, R13) and blood (B1, SR6, R1, R12) samples were collected in the morning. Cognitive processes were differently impaired and recovered with a more rapid kinetic for sustained attention process. Besides, a significant time of day effect was only evidenced for sustained attention failures that seemed to be related to subject's age and their morning capacity to stay awake. Executive processes were equally disturbed/recovered during the day and this failure/recovery process seemed to be mainly related to baseline subject's performance and to their capacity to stay awake. Morning concentrations of testosterone, cortisol and α-amylase were significantly decreased at SR6-SR7, but were either and respectively early (R1), tardily (after R2) and not at all (R13) recovered. All these results suggest a differential deleterious and restorative effect of CSR on cognition through biological changes of the stress pathway and subject's capacity (ClinicalTrials-NCT01989741).

Sex differences in the circadian regulation of sleep and waking cognition in humans

The sleep-wake cycle and circadian rhythmicity both contribute to brain function, but whether this contribution differs between men and women and how it varies across cognitive domains and subjective dimensions has not been established. We examined the circadian and sleep-wake-dependent regulation of cognition in 16 men and 18 women in a forced desynchrony protocol and quantified the separate contributions of circadian phase, prior sleep, and elapsed time awake on cognition and sleep. The largest circadian effects were observed for reported sleepiness, mood, and reported effort; the effects on working memory and temporal processing were smaller. Although these effects were seen in both men and women, there were quantitative differences. The amplitude of the circadian modulation was larger in women in 11 of 39 performance measures so that their performance was more impaired in the early morning hours. Principal components analysis of the performance measures yielded three factors, accuracy, effort, and speed, which reflect core performance characteristics in a range of cognitive tasks and therefore are likely to be important for everyday performance. The largest circadian modulation was observed for effort, whereas accuracy exhibited the largest sex difference in circadian modulation. The sex differences in the circadian modulation of cognition could not be explained by sex differences in the circadian amplitude of plasma melatonin and electroencephalographic slow-wave activity. These data establish the impact of circadian rhythmicity and sex on waking cognition and have implications for understanding the regulation of brain function, cognition, and affect in shift-work, jetlag, and aging.

Modeling circadian and sleep-homeostatic effects on short-term interval timing

Short-term interval timing i.e., perception and action relating to durations in the seconds range, has been suggested to display time-of-day as well as wake dependent fluctuations due to circadian and sleep-homeostatic changes to the rate at which an underlying pacemaker emits pulses; pertinent human data being relatively sparse and lacking in consistency however, the phenomenon remains elusive and its mechanism poorly understood. To better characterize the putative circadian and sleep-homeostatic effects on interval timing and to assess the ability of a pacemaker-based mechanism to account for the data, we measured timing performance in eighteen young healthy male subjects across two epochs of sustained wakefulness of 38.67 h each, conducted prior to (under entrained conditions) and following (under free-running conditions) a 28 h sleep-wake schedule, using the methods of duration estimation and duration production on target intervals of 10 and 40 s. Our findings of opposing oscillatory time courses across both epochs of sustained wakefulness that combine with increasing and, respectively, decreasing, saturating exponential change for the tasks of estimation and production are consistent with the hypothesis that a pacemaker emitting pulses at a rate controlled by the circadian oscillator and increasing with time awake determines human short-term interval timing; the duration-specificity of this pattern is interpreted as reflecting challenges to maintaining stable attention to the task that progressively increase with stimulus magnitude and thereby moderate the effects of pacemaker-rate changes on overt behavior.

Patient safety, resident well-being and continuity of care with different resident duty schedules in the intensive care unit: a randomized trial

BACKGROUND

Shorter resident duty periods are increasingly mandated to improve patient safety and physician well-being. However, increases in continuity-related errors may counteract the purported benefits of reducing fatigue. We evaluated the effects of 3 resident schedules in the intensive care unit (ICU) on patient safety, resident well-being and continuity of care.

METHODS

Residents in 2 university-affiliated ICUs were randomly assigned (in 2-month rotation-blocks from January to June 2009) to in-house overnight schedules of 24, 16 or 12 hours. The primary patient outcome was adverse events. The primary resident outcome was sleepiness, measured by the 7-point Stanford Sleepiness Scale. Secondary outcomes were patient deaths, preventable adverse events, and residents' physical symptoms and burnout. Continuity of care and perceptions of ICU staff were also assessed.

RESULTS

We evaluated 47 (96%) of 49 residents, all 971 admissions, 5894 patient-days and 452 staff surveys. We found no effect of schedule (24-, 16- or 12-h shifts) on adverse events (81.3, 76.3 and 78.2 events per 1000 patient-days, respectively; p = 0.7) or on residents' sleepiness in the daytime (mean rating 2.33, 2.61 and 2.30, respectively; p = 0.3) or at night (mean rating 3.06, 2.73 and 2.42, respectively; p = 0.2). Seven of 8 preventable adverse events occurred with the 12-hour schedule (p = 0.1). Mortality rates were similar for the 3 schedules. Residents' somatic symptoms were more severe and more frequent with the 24-hour schedule (p = 0.04); however, burnout was similar across the groups. ICU staff rated residents' knowledge and decision-making worst with the 16-hour schedule.

INTERPRETATION

Our findings do not support the purported advantages of shorter duty schedules. They also highlight the trade-offs between residents' symptoms and multiple secondary measures of patient safety. Further delineation of this emerging signal is required before widespread system change.

TRIAL REGISTRATION

ClinicalTrials.gov, no. NCT00679809.

Insights into behavioral vulnerability to differential sleep pressure and circadian phase from a functional ADA polymorphism

Sleep loss affects human behavior in a nonuniform manner, depending on the cognitive domain and also the circadian phase. Besides, evidence exists about stable interindividual variations in sleep loss-related performance impairments. Despite this evidence, only a few studies have considered both circadian phase and neurobehavioral domain when investigating trait-like vulnerability to sleep manipulation. By applying a randomized, crossover design with 2 sleep pressure conditions (40 h sleep deprivation vs. 40 h multiple naps), we investigated the influence of a human adenosine deaminase (ADA) polymorphism (rs73598374) on several behavioral measures throughout nearly 2 circadian cycles. Confirming earlier studies, we observed that under sleep deprivation the previously reported vulnerable G/A-allele carriers felt overall sleepier than G/G-allele carriers. As expected, this difference was no longer present when sleep pressure was reduced by the application of multiple naps. Concomitantly, well-being was worse in the G/A genotype under sleep loss when compared to the nap protocol, and n-back working memory performance appeared to be specifically susceptible to sleep-wake manipulation in this genotype. When considering psychomotor vigilance performance, however, a higher sensitivity to sleep-wake manipulation was detected in homozygous participants, but specifically at the end of the night and only for optimal task performance. Although these data are based on a small sample size and hence require replication (12 G/A- and 12 G/G-allele carriers), they confirm the assumption that interindividual differences regarding the effect of sleep manipulation highly depend on the cognitive task and circadian phase, and thus emphasize the necessity of a multimethodological approach. Moreover, they indicate that napping might be suitable to counteract endogenously heightened sleep pressure depending on the neurobehavioral domain.

Daytime sleepiness associated with poor sustained attention in middle and late adulthood

OBJECTIVE

We aimed to determine the association between psychomotor vigilance task (PVT) performance and sleep-related factors including sleep duration, daytime sleepiness, poor sleep quality, insomnia, and habitual snoring in a population-based sample.

METHODS

This was a cross-sectional analysis from the ongoing prospective cohort study, the Korean Genome and Epidemiology Study. We measured PVT performance and documented demographics, sleep-related factors, life style, and medical conditions in community dwelling adults (N = 2499; mean age 57.1 ± 7.3; male 1259). Associations between PVT parameters and sleep-related factors were tested, adjusting for age, gender, smoking, alcohol use, education, body mass index, hypertension, diabetes, depression, and the interval between mid-sleep time and PVT test.

RESULTS

High Epworth Sleepiness Scale (ESS, ≥8) was associated with slower mean reciprocal response speed (mean RRT) (3.69 ± 0.02 vs. 3.77 ± 0.01, p < 0.001), higher probability for increased lapses (≥4) (OR 1.48, CI 1.12-1.88, p = 0.001), and more negative RRT slope (-0.036 ± 0.002 vs. -0.030 ± 0.001, p = 0.02). Older age, female gender, low education level, depressive mood, and the interval between mid-sleep and PVT test were also associated with poor performance. Sleep duration, habitual snoring, insomnia, or poor sleep quality (the Pittsburgh Sleep Quality Index score > 5) was not related to PVT parameters.

CONCLUSIONS

At the population level, our results revealed important modifiers of PVT performance, which included subjective reports of daytime sleepiness.

Sleep ability mediates individual differences in the vulnerability to sleep loss: evidence from a PER3 polymorphism

Sleep deprivation is highly prevalent in our 24/7 society with harmful consequences on daytime functioning on the individual level. Genetically determined, trait-like vulnerability contributes to prominent inter-individual variability in the behavioral responses to sleep loss and adverse circadian phase. We aimed at investigating the effects of differential sleep pressure levels (high vs low) on the circadian modulation of neurobehavioral performance, sleepiness correlates, and nap sleep in individuals genotyped for a polymorphism in the clock gene PERIOD3. Fourteen homozygous long (PER3(5/5)) and 15 homozygous short (PER3(4/4)) allele carriers underwent both a 40-h sleep deprivation and multiple nap protocol under controlled laboratory conditions. We compared genotypes regarding subjective and ocular correlates of sleepiness, unintentional sleep episodes as well as psychomotor vigilance during both protocols. Nap sleep was monitored by polysomnography and visually scored according to standard criteria. The detrimental effects of high sleep pressure on sleepiness correlates and psychomotor vigilance were more pronounced in PER3(5/5) than PER3(4/4) carriers. Under low sleep pressure, both groups showed similar circadian time courses. Concomitantly, nap sleep efficiency and subjective sleep quality across all naps tended to be higher in the more vulnerable PER3(5/5) carriers. In addition, PER3-dependent sleep-loss-related attentional lapses were mediated by sleep efficiency across the circadian cycle. Our data corroborate a greater detrimental impact of sleep deprivation in PER3(5/5) compared to PER3(4/4) carriers. They further suggest that the group with greater attentional performance impairment due to sleep deprivation (PER3(5/5) carriers) is superior at initiating sleep over the 24-h cycle. This higher sleep ability may mirror a faster sleep pressure build-up between the multiple sleep opportunities and thus a greater flexibility in sleep initiation. Finally, our data show that this higher nap sleep efficiency is positively related to attentional failures under sleep loss conditions and might thus be used as a marker for inter-individual vulnerability to elevated sleep pressure.

Disrupted directed connectivity along the cingulate cortex determines vigilance after sleep deprivation

The cingulate cortex is regarded as the backbone of structural and functional connectivity of the brain. While its functional connectivity has been intensively studied, little is known about its effective connectivity, its modulation by behavioral states, and its involvement in cognitive performance. Given the previously reported effects on cingulate functional connectivity, we investigated how eye-closure and sleep deprivation changed cingulate effective connectivity, estimated from resting-state high-density electroencephalography (EEG) using a novel method to calculate Granger Causality directly in source space. Effective connectivity along the cingulate cortex was dominant in the forward direction. Eyes-open connectivity in the forward direction was greater compared to eyes-closed, in well-rested participants. The difference between eyes-open and eyes-closed connectivity was attenuated and no longer significant after sleep deprivation. Individual variability in the forward connectivity after sleep deprivation predicted subsequent task performance, such that those subjects who showed a greater increase in forward connectivity between the eyes-open and the eyes-closed periods also performed better on a sustained attention task. Effective connectivity in the opposite, backward, direction was not affected by whether the eyes were open or closed or by sleep deprivation. These findings indicate that the effective connectivity from posterior to anterior cingulate regions is enhanced when a well-rested subject has his eyes open compared to when they are closed. Sleep deprivation impairs this directed information flow, proportional to its deleterious effect on vigilance. Therefore, sleep may play a role in the maintenance of waking effective connectivity.

Efficient driver drowsiness detection at moderate levels of drowsiness

Previous research on driver drowsiness detection has focused primarily on lane deviation metrics and high levels of fatigue. The present research sought to develop a method for detecting driver drowsiness at more moderate levels of fatigue, well before accident risk is imminent. Eighty-seven different driver drowsiness detection metrics proposed in the literature were evaluated in two simulated shift work studies with high-fidelity simulator driving in a controlled laboratory environment. Twenty-nine participants were subjected to a night shift condition, which resulted in moderate levels of fatigue; 12 participants were in a day shift condition, which served as control. Ten simulated work days in the study design each included four 30-min driving sessions, during which participants drove a standardized scenario of rural highways. Ten straight and uneventful road segments in each driving session were designated to extract the 87 different driving metrics being evaluated. The dimensionality of the overall data set across all participants, all driving sessions and all road segments was reduced with principal component analysis, which revealed that there were two dominant dimensions: measures of steering wheel variability and measures of lateral lane position variability. The latter correlated most with an independent measure of fatigue, namely performance on a psychomotor vigilance test administered prior to each drive. We replicated our findings across eight curved road segments used for validation in each driving session. Furthermore, we showed that lateral lane position variability could be derived from measured changes in steering wheel angle through a transfer function, reflecting how steering wheel movements change vehicle heading in accordance with the forces acting on the vehicle and the road. This is important given that traditional video-based lane tracking technology is prone to data loss when lane markers are missing, when weather conditions are bad, or in darkness. Our research findings indicated that steering wheel variability provides a basis for developing a cost-effective and easy-to-install alternative technology for in-vehicle driver drowsiness detection at moderate levels of fatigue.

Effect of airline travel on performance: a review of the literature

The need for athletes to travel long distances has spurred investigation into the effect of air travel across multiple time zones on athletic performance. Rapid eastward or westward travel may negatively affect the body in many ways; therefore, strategies should be employed to minimise these effects which may hamper athletic performance. In this review, the fundamentals of circadian rhythm disruption are examined along with additional effects of airline travel including jet lag, sleep deprivation, travel at altitude and nutritional considerations that negatively affect performance. Evidence-based recommendations are provided at the end of the manuscript to minimise the effects of airline travel on performance.

Overlapping prefrontal systems involved in cognitive and emotional processing in euthymic bipolar disorder and following sleep deprivation: a review of functional neuroimaging studies

Prefrontal cortex (PFC) mediated cognitive and emotional processing deficits in bipolar disorder lead to functional limitations even during periods of mood stability. Alterations of sleep and circadian functioning are well-documented in bipolar disorder, but there is little research directly examining the mechanistic role of sleep and/or circadian rhythms in the observed cognitive and emotional processing deficits. We systematically review the cognitive and emotional processing deficits reliant upon PFC functioning of euthymic patients with bipolar disorder and in healthy individuals deprived of sleep. The evidence from two parallel lines of investigation suggests that sleep and circadian rhythms may be involved in the cognitive and emotional processing deficits seen in bipolar disorder through overlapping neurobiological systems. We discuss current models of bipolar highlighting the PFC-limbic connections and discuss inclusion of sleep-related mechanisms. Sleep and circadian dysfunction is a core feature of bipolar disorder and models of neurobiological abnormalities should incorporate chronobiological measures. Further research into the role of sleep and circadian rhythms in cognition and emotional processing in bipolar disorder is warranted.

Reduced neurobehavioral impairment from sleep deprivation in older adults: contribution of adenosinergic mechanisms

A night without sleep is followed by enhanced sleepiness, increased low-frequency activity in the waking EEG, and reduced vigilant attention. The magnitude of these changes is highly variable among healthy individuals. Findings in young men of low and high subjective caffeine sensitivity suggest that adenosinergic mechanisms contribute to inter-individual differences in sleep deprivation-induced changes in EEG theta activity, as well as optimal performance on the psychomotor vigilance task (PVT). In comparison to young subjects, healthy adults of older age typically feel less sleepy after sleep deprivation, and show fewer response lapses, and faster reaction times on the PVT, especially in the morning after the night without sleep. We hypothesized that age-related changes in adenosine signal transmission underlie reduced vulnerability to sleep deprivation in older individuals. To test this hypothesis, the combined effects of prolonged wakefulness and the adenosine receptor antagonist, caffeine, on an antero-posterior power gradient in EEG theta activity and PVT performance were analyzed in healthy older and caffeine-insensitive and -sensitive young men. The results show that age-related differences in sleep loss-induced changes in brain rhythmic activity and neurobehavioral functions are mirrored in young individuals of low and high sensitivity to the stimulant effects of caffeine. Moreover, the effects of sleep deprivation and caffeine on regional theta power and vigilant attention are inversely correlated across older and young age groups. Genetic variants of the adenosine A_2A receptor gene contribute to individual differences in neurobehavioral performance in rested and sleep deprived state, and modulate the actions of caffeine in wakefulness and sleep. Based upon this evidence, we propose that age-related differences in A_2A receptor-mediated signal transduction could be involved in age-related changes in the vulnerability to acute sleep deprivation.

Time-of-day modulation of homeostatic and allostatic sleep responses to chronic sleep restriction in rats

To study sleep responses to chronic sleep restriction (CSR) and time-of-day influences on these responses, we developed a rat model of CSR that takes into account the polyphasic sleep patterns in rats. Adult male rats underwent cycles of 3 h of sleep deprivation (SD) and 1 h of sleep opportunity (SO) continuously for 4 days, beginning at the onset of the 12-h light phase ("3/1" protocol). Electroencephalogram (EEG) and electromyogram (EMG) recordings were made before, during, and after CSR. During CSR, total sleep time was reduced by ∼60% from baseline levels. Both rapid eye movement sleep (REMS) and non-rapid eye movement sleep (NREMS) during SO periods increased initially relative to baseline and remained elevated for the rest of the CSR period. In contrast, NREMS EEG delta power (a measure of sleep intensity) increased initially, but then declined gradually, in parallel with increases in high-frequency power in the NREMS EEG. The amplitude of daily rhythms in NREMS and REMS amounts was maintained during SO periods, whereas that of NREMS delta power was reduced. Compensatory responses during the 2-day post-CSR recovery period were either modest or negative and gated by time of day. NREMS, REMS, and EEG delta power lost during CSR were not recovered by the end of the second recovery day. Thus the "3/1" CSR protocol triggered both homeostatic responses (increased sleep amounts and intensity during SOs) and allostatic responses (gradual decline in sleep intensity during SOs and muted or negative post-CSR sleep recovery), and both responses were modulated by time of day.

Fatigue research in 2011: from the bench to practice

Over the last 20 years, academic, industry and community stakeholders have been meeting at a biennial scientific conference to discuss fatigue-related research and policy in the transportation, resources and health sectors. During this period, the research conducted around the world has progressed substantially: we now better understand the basic processes of sleep and circadian physiology that underpin performance; we better understand that fatigue risk management in the absence of any discussion about sleep is fruitless at worst and inadequate at best; and we are improving the capacity of models and other technologies to assist us to predict, monitor, identify, minimise and mitigate fatigue-related risk. At the same time however, the relationship between performance on simple cognitive tasks in laboratory settings and performance on complex tasks required to operate efficiently and safely in the workplace, remains a stumbling block. This special issue brings together fifteen papers that cover the range of areas in the field of fatigue research and challenges us as researchers, regulators, industry representatives and community members to continue the work of managing the risk of fatigue.