Effect of 60 days of head down tilt bed rest on amplitude and phase of rhythms in physiology and sleep in men

Twenty-four-hour rhythms in physiology and behaviour are shaped by circadian clocks, environmental rhythms, and feedback of behavioural rhythms onto physiology. In space, 24 h signals such as those associated with the light-dark cycle and changes in posture, are weaker, potentially reducing the robustness of rhythms. Head down tilt (HDT) bed rest is commonly used to simulate effects of microgravity but how HDT affects rhythms in physiology has not been extensively investigated. Here we report effects of -6° HDT during a 90-day protocol on 24 h rhythmicity in 20 men. During HDT, amplitude of light, motor activity, and wrist-temperature rhythms were reduced, evening melatonin was elevated, while cortisol was not affected during HDT, but was higher in the morning during recovery when compared to last session of HDT. During recovery from HDT, time in Slow-Wave Sleep increased. EEG activity in alpha and beta frequencies increased during NREM and REM sleep. These results highlight the profound effects of head-down-tilt-bed-rest on 24 h rhythmicity.

An online behavioural self-help intervention rapidly improves acute insomnia severity and subjective mood during the COVID-19 pandemic: a stratified randomised controlled trial

STUDY OBJECTIVES

Stressful life events, such as the COVID-19 pandemic, can cause acute insomnia. Cognitive behavioural therapy for acute insomnia is effective but is both time and resource-intensive. This study investigated if an online behavioural self-help intervention, which has been successfully used alongside sleep restriction for acute insomnia, reduced insomnia severity and improved mood in acute insomnia. This study also assessed good sleepers to explore if a "sleep vaccination" approach was feasible.

METHODS

In this online stratified randomised controlled trial, 344 participants (103 good sleepers and 241 participants with DSM-5 acute insomnia) were randomised to receive the intervention/no intervention (good sleepers) or intervention/intervention after 28 days (poor sleepers). Insomnia severity was assessed using the ISI (primary outcome), and anxiety and depression using the GAD-7/PHQ-9 (secondary outcomes) at baseline, one week, one month and three-month follow-up.

RESULTS

In people with acute insomnia, relative to baseline, there were significant reductions in ISI (dz = 1.17), GAD-7 (dz = .70) and PHQ-9 (dz = .60) scores at one week follow-up. ISI, GAD-7 and PHQ-9 scores were significantly lower at all follow-up time points, relative to baseline. Subjective diary-derived sleep continuity was unaffected. No beneficial effects upon sleep or mood were observed in good sleepers.

CONCLUSIONS

An online behavioural self-help intervention rapidly reduces acute insomnia severity (within one week), and benefits mood in people with acute insomnia. These beneficial effects are maintained up to three months later. Although the use of the intervention is feasible in good sleepers, their subjective sleep was unaffected.

Nutritional interventions in treating menopause-related sleep disturbances: a systematic review

CONTEXT

Sleep disturbances are a core symptom of menopause, which refers to the permanent cessation of menstrual periods. Nutritional interventions may alleviate menopause-related sleep disturbances, as studies have shown that certain interventions (eg, tart cherry juice, or tryptophan-rich foods) can improve relevant aspects of sleep.

OBJECTIVE

The aim of this systematic review was to examine the effect of nutritional interventions for menopause-related sleep disturbances, in order to inform the subsequent development of specific interventional trials and assess their potential as a treatment for menopause-related sleep disturbances.

DATA SOURCES

Published studies in English were located by searching PubMed and PsycArticles databases (until September 15, 2022).

DATA EXTRACTION

Following full-text review, a final total of 59 articles were included. The search protocol was performed in accordance with PRISMA guidelines.

DATA ANALYSIS

A total of 37 studies reported that a nutritional intervention improved some aspect of sleep, and 22 studies observed no benefit. Most (n = 24) studies recruited postmenopausal women, 18 recruited menopausal women, 3 recruited perimenopausal women, and 14 recruited women from multiple groups. The majority of the studies were of low methodological quality. Due to the heterogeneity of the studies, a narrative synthesis without meta-analysis is reported.

CONCLUSION

Despite the large heterogeneity in the studies and choice of intervention, the majority of the identified studies reported that a nutritional intervention did benefit sleep, and that it is mainly subjective sleep that is improved. More high-quality, adequately powered, randomized controlled trials of the identified nutritional interventions are necessary.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42021262367.

A review study on early detection of pancreatic ductal adenocarcinoma using artificial intelligence assisted diagnostic methods

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive, chemo-refractory and recalcitrant cancer and increases the number of deaths. With just around 1 in 4 individuals having respectable tumours, PDAC is frequently discovered when it is in an advanced stage. Accordingly, ED of PDAC improves patient survival. Subsequently, this paper reviews the early detection of PDAC, initially, the work presented an overview of PDAC. Subsequently, it reviews the molecular biology of pancreatic cancer and the development of molecular biomarkers are represented. This article illustrates the importance of identifying PDCA, the Immune Microenvironment of Pancreatic Cancer. Consequently, in this review, traditional and non-traditional imaging techniques are elucidated, traditional and non-traditional methods like endoscopic ultrasound, Multidetector CT, CT texture analysis, PET-CT, magnetic resonance imaging, diffusion-weighted imaging, secondary signs of pancreatic cancer, and molecular imaging. The use of artificial intelligence in pancreatic cancer, novel MRI techniques, and the future directions of AI for PDAC detection and prognosis is then described. Additionally, the research problem definition and motivation, current trends and developments, state of art of survey, and objective of the research are demonstrated in the review. Consequently, this review concluded that Artificial Intelligence Assisted Diagnostic Methods with MRI images can be proposed in future to improve the specificity and the sensitivity of the work, and to classify malignant PDAC with greater accuracy.

Habitual Subjective Sleep Continuity is Not Associated With Fluid Intelligence: An Exploratory Study

The link between sleep and cognition is well-established, but the link between subjective sleep and fluid intelligence is poorly understood. The aim of this exploratory study was to examine the relationship between habitual subjective sleep continuity and fluid intelligence. In this study, a total of 56 healthy sleepers (M_age = 30.91 years; SD_age = 12.93 years) completed two fluid intelligence (abstract reasoning and two-dimensional mental rotation) tasks after completing seven consecutive days of sleep diaries. Relationships between subjective sleep continuity (total sleep time [TST]; sleep efficiency [SE%]); wake after sleep onset (WASO) and sleep onset latency (SOL), and task accuracy and speed were assessed using Pearson correlations. Overall, there were no associations between subjective sleep continuity (TST, SE%, WASO, SOL) and either task accuracy or speed (adjusted p-values > 0.0125). Overall, habitual subjective sleep continuity and fluid intelligence may not be associated. These results should be replicated in larger samples.

Contrasting Effects of Sleep Restriction, Total Sleep Deprivation, and Sleep Timing on Positive and Negative Affect

Laboratory-based sleep manipulations show asymmetries between positive and negative affect, but say little about how more specific moods might change. We report extensive analyzes of items from the Positive and Negative Affect Scale (PANAS) during days following nights of chronic sleep restriction (6 h sleep opportunity), during 40 h of acute sleep deprivation under constant routine conditions, and during a week-long forced desynchrony protocol in which participants lived on a 28-h day. Living in the laboratory resulted in medium effects sizes on all positive moods (Attentiveness, General Positive Affect, Joviality, Assuredness), with a general deterioration as the days wore on. These effects were not found with negative moods. Sleep restriction reduced some positive moods, particularly Attentiveness (also General Positive), and increased Hostility. A burden of chronic sleep loss also led to lower positive moods when participants confronted the acute sleep loss challenge, and all positive moods, as well as Fearfulness, General Negative Affect and Hostility were affected. Sleeping at atypical circadian phases resulted in mood changes: all positive moods reduced, Hostility and General Negative Affect increased. Deteriorations increased the further participants slept from their typical nocturnal sleep. In most cases the changes induced by chronic or acute sleep loss or mistimed sleep waxed or waned across the waking day, with linear or various non-linear trends best fitting these time-awake-based changes. While extended laboratory stays do not emulate the fluctuating emotional demands of everyday living, these findings demonstrate that even in controlled settings mood changes systematically as sleep is shortened or mistimed.

Science Forum: Sex differences and sex bias in human circadian and sleep physiology research

Growing evidence shows that sex differences impact many facets of human biology. Here we review and discuss the impact of sex on human circadian and sleep physiology, and we uncover a data gap in the field investigating the non-visual effects of light in humans. A virtual workshop on the biomedical implications of sex differences in sleep and circadian physiology then led to the following imperatives for future research: (1) design research to be inclusive and accessible, (2) implement recruitment strategies that lead to a sex-balanced sample, (3) use data visualization to grasp the effect of sex, (4) implement statistical analyses that include sex as a factor and/or perform group analyses by sex, where possible, (5) make participant-level data open and available to facilitate future meta-analytic efforts.

Individual differences and diversity in human physiological responses to light

Exposure to light affects our physiology and behaviour through a pathway connecting the retina to the circadian pacemaker in the hypothalamus - the suprachiasmatic nucleus (SCN). Recent research has identified significant individual differences in the non-visual effects of light,mediated by this pathway. Here, we discuss the fundamentals and individual differences in the non-visual effects of light. We propose a set of actions to improve our evidence database to be more diverse: understanding systematic bias in the evidence base, dedicated efforts to recruit more diverse participants, routine deposition and sharing of data, and development of data standards and reporting guidelines.

Molecular docking analysis of selected pyrimidine derivatives with human cyclin-dependent kinase 2

A series of pyrimidine were synthesized, characterized and evaluated for their antioxidant properties using the human cyclin-dependent kinase-2 protein model. Data shows that the pyrimidine derivatives (compound ID 4G) with para fluoro groups substitution at phenyl ring attached to the 4th position (IC50: 98.5µg/ml), compound 4B bearing hydroxy group at para position of phenyl ring (IC50: 117.8 µg/ml) have significant antioxidant activity. Docking data infer that compounds 4c, 4a, 4h and 4b possess binding energy (-7.9, -7.7, -7.5 and -7.4 kcal.mol-1) with 1HCK (PDB ID) receptor.

Sleepiness is a signal to go to bed: data and model simulations

Study Objectives

Assess the validity of a subjective measure of sleepiness as an indicator of sleep drive by quantifying associations between intraindividual variation in evening sleepiness and bedtime, sleep duration, and next morning and subsequent evening sleepiness, in young adults.

Methods

Sleep timing and sleepiness were assessed in 19 students in late autumn and late spring on a total of 771 days. Karolinska Sleepiness Scales (KSS) were completed at half-hourly intervals at fixed clock times starting 4 h prior to participants’ habitual bedtime, and in the morning. Associations between sleepiness and sleep timing were evaluated by mixed model and nonparametric approaches and simulated with a mathematical model for the homeostatic and circadian regulation of sleepiness.

Results

Intraindividual variation in evening sleepiness was very large, covering four or five points on the 9-point KSS scale, and was significantly associated with subsequent sleep timing. On average, a one point higher KSS value was followed by 20 min earlier bedtime, which led to 11 min longer sleep, which correlated with lower sleepiness next morning and the following evening. Associations between sleepiness and sleep timing were stronger in early compared to late sleepers. Model simulations indicated that the directions of associations between sleepiness and sleep timing are in accordance with their homeostatic and circadian regulation, even though much of the variance in evening sleepiness and details of its time course remain unexplained by the model.

Conclusion

Subjective sleepiness is a valid indicator of the drive for sleep which, if acted upon, can reduce insufficient sleep.

In vitro and molecular docking studies of an anti-inflammatory scaffold with human peroxiredoxin 5 and tyrosine kinase receptor

A new series of 4-(3-(2-amino-3,5-dibromophenyl)-1-(4-substitutedbenzoyl)-4,5-dihydro-1H-pyrazol-5-yl)benzonitrile (4a-h) compounds were synthesized and evaluated for in-vitro anti-inflammatory activities. The spectral (IR, NMR) and elemental analyses data of the product indicated the formation of new pyrazoles 4a-h. Compound 4e exhibited potent anti-inflammatory property with 85.45 % inhibitions. This value was compared with standard diclofenac sodium. This data is explained using molecular docking analysis of receptor- ligand binding. These results demonstrated that pyrazole derivatives are potential inhibitors of Human Peroxiredoxin 5 and Tyrosine kinase receptor in the treatment of inflammation related illness.

Testing an early online intervention for the treatment of disturbed sleep during the COVID-19 pandemic (Sleep COVID-19): structured summary of a study protocol for a randomised controlled trial

OBJECTIVES

The primary aim of the present study is to examine the efficacy of an online intervention for poor sleep in the context of an ongoing stressful major life event, by assessing if this intervention can reduce insomnia severity at short-term (one week post-intervention) and long-term (one and three months post-intervention) follow-up time points. It is hypothesised that the intervention will: 1) reduce insomnia severity in poor sleepers, compared to wait-list control poor sleepers, and good sleepers; 2) reduce subjective symptoms of anxiety and depression in all groups, and 3) prevent the transition to acute insomnia in good sleepers.

TRIAL DESIGN

This study is a cluster randomised controlled trial.

PARTICIPANTS

Both healthy good sleepers, who do not report having any current sleep problems, and individuals who report having sleep problems, will be recruited for the present study. This is a single-site study (Northumbria University). This study will be delivered using the internet and there are no geographic restrictions. Individuals who self-report as poor sleepers will meet DSM-5 criteria for acute insomnia, which is where individuals: 1) have difficulties in falling asleep, staying asleep, or awakening too early for at least three nights per week, for a time period of between two weeks and three months; and 2) report experiencing distress or impairment caused by sleep loss. Both 1) and 2) must have occurred despite the individual having had an adequate opportunity for sleep during this time period. Good sleepers will be individuals who do not have current sleep problems. All participants must have a sufficient level of English comprehension to understand and complete study measures. Individuals cannot participate if they report having chronic sleep problems (where they have existed for more than three months immediately prior to providing consent), nor will individuals who are actively seeking treatment for their sleep problems irrespective of how long they have had the sleep problem. Individuals also cannot participate if they have a self-reported history of head injuries, or if they have a self-reported diagnosis of schizophrenia, epilepsy or personality disorder, as the distraction techniques involved in the insomnia intervention may increase rumination in individuals with these conditions, and influence the effectiveness of the intervention.

INTERVENTION AND COMPARATOR

Participants who receive the intervention will be provided with an online version of a self-help leaflet. A printed version of this leaflet has been successfully used in previous treatment studies, which have been conducted by our research group. Participants will be encouraged to download, save or print out this leaflet, which will be provided in PDF format. There will be no restrictions on use and participants will be encouraged to refer to this leaflet as often as they wish to. Briefly, this self-help leaflet aims to improve sleep by identifying and addressing sleep-related dysfunctional thinking by providing education about sleep, providing techniques to distract from intrusive worrisome thoughts at night, and providing guidelines for sleep-related stimulus control. The comparator is a wait-list control (i.e. where they will receive the intervention after a one month delay) group.

MAIN OUTCOMES

The primary outcome measure will be insomnia severity, as measured using the Insomnia Severity Index (Bastien, Vallières, & Morin, 2001), assessed immediately prior to the intervention and at one week, one month and three months post-intervention, compared to baseline. Secondary outcome measures will include subjective mood, measured using the 7-item Generalised Anxiety Disorder Questionnaire (GAD-7; Spitzer, Kroenke, Williams, & Lowe, 2006)) and 9-item Patient Health Questionnaire (PHQ-9; Kroenke, Spitzer, & Williams, 2001), assessed immediately prior to the intervention, and one week, one month and three months post-intervention, compared to baseline. Additionally, subjective sleep continuity, derived from sleep diaries (Carney et al., 2012), will be compared pre and post-intervention.

RANDOMISATION

This study will operate as a cluster randomised controlled trial. Good sleepers will be randomised into an intervention or a no-intervention group, with a 1:1 allocation. Poor sleepers will be randomised into an intervention or wait-list control group, with a 1:1 allocation. Randomisation will be conducted automatically using Qualtrics study software, where block sizes will be equal and randomisation will be computer-generated.

BLINDING (MASKING)

Participants will not be blinded to group assignment. The outcomes will be assessed by a blinded investigator.

NUMBERS TO BE RANDOMISED (SAMPLE SIZE)

The minimum sample size is 60. A total of 30 poor sleepers will be randomised to the intervention or wait-list control group. A total of 30 good sleepers will be randomised to the intervention or no intervention group.

TRIAL STATUS

Recruitment for this study has yet to start. It is anticipated that recruitment will begin in August 2020 and end in April 2022. The current study protocol is version 1.0 (20 July 2020) TRIAL REGISTRATION: This study was prospectively registered in the ISRCTN registry (registration number ISRCTN43900695 , date of registration: 8 April 2020).

FULL PROTOCOL

The full protocol is attached as an additional file, accessible from the Trials website (Additional file 1). In the interest in expediting dissemination of this material, the familiar formatting has been eliminated; this Letter serves as a summary of the key elements of the full protocol. The study protocol has been reported in accordance with the Standard Protocol Items: Recommendations for Clinical Interventional Trials (SPIRIT) guidelines (Additional file 2).

Applications in sleep: How light affects sleep

Sleep is an active physiological state that plays a critical role in our physical and mental health and well-being. It is generated by a complex interplay between two oscillators, namely, the circadian oscillator and the sleep-wake homeostat. Sleep propensity is a function of wakefulness, that is, the longer one is awake the greater the homeostatic sleep pressure. Sleep onset occurs as a wake promoting circadian signal subsides, coinciding with an evening rise in melatonin and drop in core temperature. Light is one of the strongest time signals for the circadian oscillator. Poor sleep is a prevalent complaint today, attributable, in part, to our easy access to artificial light, especially after dusk. This non-visual effect of light is mediated by a multi-component photoreceptive system, consisting of rods, cones and melanopsin-expressing intrinsically-photosensitive retinal ganglion cells (ipRGC). Perhaps, with this available biological knowledge we can engineer artificial light to minimize its disruptive effect on sleep. We will highlight this by discussing circadian photoreception and its effect on sleep, in the blind population.

Sleep Timing in Late Autumn and Late Spring Associates With Light Exposure Rather Than Sun Time in College Students

Timing of the human sleep-wake cycle is determined by social constraints, biological processes (sleep homeostasis and circadian rhythmicity) and environmental factors, particularly natural and electrical light exposure. To what extent seasonal changes in the light-dark cycle affect sleep timing and how this varies between weekdays and weekends has not been firmly established. We examined sleep and activity patterns during weekdays and weekends in late autumn (standard time, ST) and late spring (daylight saving time, DST), and expressed their timing in relation to three environmental reference points: clock-time, solar noon (SN) which occurs one clock hour later during DST than ST, and the midpoint of accumulated light exposure (50% LE). Observed sleep timing data were compared to simulated data from a mathematical model for the effects of light on the circadian and homeostatic regulation of sleep. A total of 715 days of sleep timing and light exposure were recorded in 19 undergraduates in a repeated-measures observational study. During each three-week assessment, light and activity were monitored, and self-reported bed and wake times were collected. Light exposure was higher in spring than in autumn. 50% LE did not vary across season, but occurred later on weekends compared to weekdays. Relative to clock-time, bedtime, wake-time, mid-sleep, and midpoint of activity were later on weekends but did not differ across seasons. Relative to SN, sleep and activity measures were earlier in spring than in autumn. Relative to 50% LE, only wake-time and mid-sleep were later on weekends, with no seasonal differences. Individual differences in mid-sleep did not correlate with SN but correlated with 50% LE. Individuals with different habitual bedtimes responded similarly to seasonal changes. Model simulations showed that light exposure patterns are sufficient to explain sleep timing in spring but less so in autumn. The findings indicate that during autumn and spring, the timing of sleep associates with actual light exposure rather than sun time as indexed by SN.

Machine-learning-derived sleep-wake staging from around-the-ear electroencephalogram outperforms manual scoring and actigraphy

Quantification of sleep is important for the diagnosis of sleep disorders and sleep research. However, the only widely accepted method to obtain sleep staging is by visual analysis of polysomnography (PSG), which is expensive and time consuming. Here, we investigate automated sleep scoring based on a low-cost, mobile electroencephalogram (EEG) platform consisting of a lightweight EEG amplifier combined with flex-printed cEEGrid electrodes placed around the ear, which can be implemented as a fully self-applicable sleep system. However, cEEGrid signals have different amplitude characteristics to normal scalp PSG signals, which might be challenging for visual scoring. Therefore, this study evaluates the potential of automatic scoring of cEEGrid signals using a machine learning classifier ("random forests") and compares its performance with manual scoring of standard PSG. In addition, the automatic scoring of cEEGrid signals is compared with manual annotation of the cEEGrid recording and with simultaneous actigraphy. Acceptable recordings were obtained in 15 healthy volunteers (aged 35 ± 14.3 years) during an extended nocturnal sleep opportunity, which induced disrupted sleep with a large inter-individual variation in sleep parameters. The results demonstrate that machine-learning-based scoring of around-the-ear EEG outperforms actigraphy with respect to sleep onset and total sleep time assessments. The automated scoring outperforms human scoring of cEEGrid by standard criteria. The accuracy of machine-learning-based automated scoring of cEEGrid sleep recordings compared with manual scoring of standard PSG was satisfactory. The findings show that cEEGrid recordings combined with machine-learning-based scoring holds promise for large-scale sleep studies.

Chronotype Genetic Variant in PER2 is Associated with Intrinsic Circadian Period in Humans

The PERIOD2 (PER2) gene is a core molecular component of the circadian clock and plays an important role in the generation and maintenance of daily rhythms. Rs35333999, a missense variant of PER2 common in European populations, has been shown to associate with later chronotype. Chronotype relates to the timing of biological and behavioral activities, including when we sleep, eat, and exercise, and later chronotype is associated with longer intrinsic circadian period (cycle length), a fundamental property of the circadian system. Thus, we tested whether this PER2 variant was associated with circadian period and found significant associations with longer intrinsic circadian period as measured under forced desynchrony protocols, the 'gold standard' for intrinsic circadian period assessment. Minor allele (T) carriers exhibited significantly longer circadian periods when determinations were based on either core body temperature or plasma melatonin measurements, as compared to non-carriers (by 12 and 11 min, respectively; accounting for ~7% of inter-individual variance). These findings provide a possible underlying biological mechanism for inter-individual differences in chronotype, and support the central role of PER2 in the human circadian timing system.

Healthier rhythm, healthier brain? Integrity of circadian melatonin and temperature rhythms relates to the clinical state of brain-injured patients

Background

Healthy circadian rhythmicity has been suggested to relate to a better state of brain‐injured patients and to support the emergence of consciousness in patient groups characterized by a relative instability thereof such as patients with disorders of consciousness (DOC).

Methods

Going beyond earlier studies, a systems‐level perspective was adopted and, using multilevel modelling, the joint predictive value of three indices of circadian rhythm integrity derived from skin temperature variations, melatoninsulfate secretion, and physical activity (wrist actigraphy) patterns was evaluated for the behaviourally assessed state [Coma Recovery Scale ‐ Revised (CRS‐R) score] of DOC patients [13 unresponsive wakefulness syndrome; seven minimally conscious (exit) state]. Additionally, it was assessed in a subset of 16 patients whether patients’ behavioural repertoire (CRS‐R score) varied (i) with time of day or (ii) offset from the body temperature maximum (BT_max), i.e. when cognitive performance is expected to peak.

Results

The results reveal that better integrity of circadian melatoninsulfate and temperature rhythms relate to a richer behavioural repertoire. Moreover, higher CRS‐R scores are, by trend, related to assessments taking place at a later daytime or deviating less from the pre‐specified time of occurrence of BT_max.

Conclusions

In conclusion, the results suggest that therapeutic approaches aimed at improving circadian rhythms in brain‐injured patients are promising and should be implemented in hospitals or nursing homes. Beyond this, it might be helpful to schedule diagnostic procedures and therapies around the (pre‐assessed) BT_max (≈4 pm in healthy individuals) as this is when patients should be most responsive.

Sleep EEG Derived From Behind-the-Ear Electrodes (cEEGrid) Compared to Standard Polysomnography: A Proof of Concept Study

Electroencephalography (EEG) recordings represent a vital component of the assessment of sleep physiology, but the methodology presently used is costly, intrusive to participants, and laborious in application. There is a recognized need to develop more easily applicable yet reliable EEG systems that allow unobtrusive long-term recording of sleep-wake EEG ideally away from the laboratory setting. cEEGrid is a recently developed flex-printed around-the-ear electrode array, which holds great potential for sleep-wake monitoring research. It is comfortable to wear, simple to apply, and minimally intrusive during sleep. Moreover, it can be combined with a smartphone-controlled miniaturized amplifier and is fully portable. Evaluation of cEEGrid as a motion-tolerant device is ongoing, but initial findings clearly indicate that it is very well suited for cognitive research. The present study aimed to explore the suitability of cEEGrid for sleep research, by testing whether cEEGrid data affords the signal quality and characteristics necessary for sleep stage scoring. In an accredited sleep laboratory, sleep data from cEEGrid and a standard PSG system were acquired simultaneously. Twenty participants were recorded for one extended nocturnal sleep opportunity. Fifteen data sets were scored manually. Sleep parameters relating to sleep maintenance and sleep architecture were then extracted and statistically assessed for signal quality and concordance. The findings suggest that the cEEGrid system is a viable and robust recording tool to capture sleep and wake EEG. Further research is needed to fully determine the suitability of cEEGrid for basic and applied research as well as sleep medicine.

Functional decoupling of melatonin suppression and circadian phase resetting in humans

KEY POINTS

There is assumed to be a monotonic association between melatonin suppression and circadian phase resetting induced by light exposure. We tested the association between melatonin suppression and phase resetting in humans. Sixteen young healthy participants received nocturnal bright light (∼9500 lux) exposure of continuous or intermittent patterns, and different durations ranging from 12 min to 6.5 h. Intermittent exposure patterns showed significant phase shifts with disproportionately less melatonin suppression. Each and every bright light stimulus in an intermittent exposure pattern induced a similar degree of melatonin suppression, but did not appear to cause an equal magnitude of phase shift. These results suggest that phase shifts and melatonin suppression are functionally independent such that one cannot be used as a proxy measure of the other.

ABSTRACT

Continuous experimental light exposures show that, in general, the conditions that produce greater melatonin suppression also produce greater phase shift, leading to the assumption that one can be used as a proxy for the other. We tested this association in 16 healthy individuals who participated in a 9-day inpatient protocol by assessing melatonin suppression and phase resetting in response to a nocturnal light exposure (LE) of different patterns: (i) dim-light control (<3 lux; n = 6) or (ii) two 12-min intermittent bright light pulses (IBL) separated by 36 min of darkness (∼9500 lux; n = 10). We compared these results with historical data from additional LE patterns: (i) dim-light control (<3 lux; n = 11); (ii) single continuous bright light exposure of 12 min (n = 9), 1.0 h (n = 10) or 6.5 h (n = 6); or (iii) an IBL light pattern consisting of six 15-min pulses with 1.0 h dim-light recovery intervals between them during a total of 6.5 h (n = 7). All light exposure groups had significantly greater phase-delay shifts than the dim-light control condition (P < 0.0001). While a monotonic association between melatonin suppression and circadian phase shift was observed, intermittent exposure patterns showed significant phase shifts with disproportionately less melatonin suppression. Each and every IBL stimulus induced a similar degree of melatonin suppression, but did not appear to cause an equal magnitude of phase shift. These results suggest unique specificities in how light-induced phase shifts and melatonin suppression are mediated such that one cannot be used as a proxy measure of the other.

Combined experimental and theoretical studies on molecular structures, spectroscopy of 4-(3-(2-amino-3,5-dibromophenyl)-1-(benzoyl)-4,5-dihydro-1H-pyrazol-5-yl)benzonitriles through NBO, FT-IR, HOMO-LUMO and NLO analyzes

The pyrazole compounds 4-(3-(2-amino-3,5-dibromophenyl)-1-(4-substitutedbenzoyl)-4,5-dihydro-1H-pyrazol-5-yl) benzonitriles (4–6) have been synthesized and characterized by elemental, IR, 1HNMR spectral methods. In addition, the synthesized compounds were subjected to density functional theory for further understanding of the molecular architecture and optoelectronic properties. The optimized geometric parameters were in support of the corresponding experimental values. The FT-IR spectra of 4–6 have been investigated extensively using DFT employing B3LYP/6-31G (d,p) level theory. The molecular electrostatic potential analysis has been utilized to identify reactive sites of title compounds. Natural bonding orbital analysis proved the inter- and intra-molecular delocalization and acceptor–donor interactions based on the second-order perturbation interactions. The calculated band gap energies revealed that charge transfer occurs within the molecule. The polarizability and hyperpolarizability were calculated which show that compounds posses nonlinear optical nature.

Significance of circadian rhythms in severely brain-injured patients: A clue to consciousness?

Objective:

To investigate the relationship between the presence of a circadian body temperature rhythm and behaviorally assessed consciousness levels in patients with disorders of consciousness (DOC; i.e., vegetative state/unresponsive wakefulness syndrome or minimally conscious state).

Methods:

In a cross-sectional study, we investigated the presence of circadian temperature rhythms across 6 to 7 days using external skin temperature sensors in 18 patients with DOC. Beyond this, we examined the relationship between behaviorally assessed consciousness levels and circadian rhythmicity.

Results:

Analyses with Lomb-Scargle periodograms revealed significant circadian rhythmicity in all patients (range 23.5–26.3 hours). We found that especially scores on the arousal subscale of the Coma Recovery Scale–Revised were closely linked to the integrity of circadian variations in body temperature. Finally, we piloted whether bright light stimulation could boost circadian rhythmicity and found positive evidence in 2 out of 8 patients.

Conclusion:

The study provides evidence for an association between circadian body temperature rhythms and arousal as a necessary precondition for consciousness. Our findings also make a case for circadian rhythms as a target for treatment as well as the application of diagnostic and therapeutic means at times when cognitive performance is expected to peak.

Circadian phase resetting by a single short-duration light exposure

BACKGROUND. In humans, a single light exposure of 12 minutes and multiple-millisecond light exposures can shift the phase of the circadian pacemaker. We investigated the response of the human circadian pacemaker to a single 15-second or 2-minute light pulse administered during the biological night. METHODS. Twenty-six healthy individuals participated in a 9-day inpatient protocol that included assessment of dim light melatonin onset time (DLMO time) before and after exposure to a single 15-second (n = 8) or 2-minute (n = 12) pulse of bright light (9,500 lux; 4,100 K fluorescent) or control background dim light (<3 lux; n = 6). Phase shifts were calculated as the difference in clock time between the two phase estimates. RESULTS. Both 15-second and 2-minute exposures induced phase delay shifts [median (± SD)] of -34.8 ± 47.2 minutes and -45.4 ± 28.4 minutes, respectively, that were significantly (P = 0.04) greater than the control condition (advance shift: +22.3 ± 51.3 minutes) but were not significantly different from each other. Comparisons with historic data collected under the same conditions confirmed a nonlinear relationship between exposure duration and the magnitude of phase shift. CONCLUSIONS. Our results underscore the exquisite sensitivity of the human pacemaker to even short-duration single exposures to light. These findings may have real-world implications for circadian disruption induced by exposure to brief light stimuli at night. TRIAL REGISTRATION. The study was registered as a clinical trial on www.clinicaltrials.org, NCT #01330992. FUNDING. Funding for this study was provided by NSBRI HFP02802 and NIH P01-AG09975, R01-HL114088 (EBK), RC2-HL101340-0 (EBK, SWL, SAR, REK), K02-HD045459 (EBK), K24-HL105664 (EBK), T32-HL07901 (MSH, SAR), HL094654 (CAC), and AG044416 (JFD). The project described was supported by NIH grant 1UL1 TR001102-01, 8UL1TR000170-05, UL1 RR 025758, Harvard Clinical and Translational Science Center, from the National Center for Advancing Translational Science.

Blood transcriptome based biomarkers for human circadian phase

Diagnosis and treatment of circadian rhythm sleep-wake disorders both require assessment of circadian phase of the brain’s circadian pacemaker. The gold-standard univariate method is based on collection of a 24-hr time series of plasma melatonin, a suprachiasmatic nucleus-driven pineal hormone. We developed and validated a multivariate whole-blood mRNA-based predictor of melatonin phase which requires few samples. Transcriptome data were collected under normal, sleep-deprivation and abnormal sleep-timing conditions to assess robustness of the predictor. Partial least square regression (PLSR), applied to the transcriptome, identified a set of 100 biomarkers primarily related to glucocorticoid signaling and immune function. Validation showed that PLSR-based predictors outperform published blood-derived circadian phase predictors. When given one sample as input, the R² of predicted vs observed phase was 0.74, whereas for two samples taken 12 hr apart, R² was 0.90. This blood transcriptome-based model enables assessment of circadian phase from a few samples.

DOI:http://dx.doi.org/10.7554/eLife.20214.001

Impact of Common Diabetes Risk Variant in MTNR1B on Sleep, Circadian, and Melatonin Physiology

The risk of type 2 diabetes (T2D) is increased by abnormalities in sleep quantity and quality, circadian alignment, and melatonin regulation. A common genetic variant in a receptor for the circadian-regulated hormone melatonin (MTNR1B) is associated with increased fasting blood glucose and risk of T2D, but whether sleep or circadian disruption mediates this risk is unknown. We aimed to test if MTNR1B diabetes risk variant rs10830963 associates with measures of sleep or circadian physiology in intensive in-laboratory protocols (n = 58-96) or cross-sectional studies with sleep quantity and quality and timing measures from self-report (n = 4,307-10,332), actigraphy (n = 1,513), or polysomnography (n = 3,021). In the in-laboratory studies, we found a significant association with a substantially longer duration of elevated melatonin levels (41 min) and delayed circadian phase of dim-light melatonin offset (1.37 h), partially mediated through delayed offset of melatonin synthesis. Furthermore, increased T2D risk in MTNR1B risk allele carriers was more pronounced in early risers versus late risers as determined by 7 days of actigraphy. Our results provide the surprising insight that the MTNR1B risk allele influences dynamics of melatonin secretion, generating a novel hypothesis that the MTNR1B risk allele may extend the duration of endogenous melatonin production later into the morning and that early waking may magnify the diabetes risk conferred by the risk allele.

'nparACT' package for R: A free software tool for the non-parametric analysis of actigraphy data

For many studies, participants’ sleep-wake patterns are monitored and recorded prior to, during and following an experimental or clinical intervention using actigraphy, i.e. the recording of data generated by movements. Often, these data are merely inspected visually without computation of descriptive parameters, in part due to the lack of user-friendly software. To address this deficit, we developed a package for R Core Team [6], that allows computing several non-parametric measures from actigraphy data. Specifically, it computes the interdaily stability (IS), intradaily variability (IV) and relative amplitude (RA) of activity and gives the start times and average activity values of M10 (i.e. the ten hours with maximal activity) and L5 (i.e. the five hours with least activity). Two functions compute these ‘classical’ parameters and handle either single or multiple files. Two other functions additionally allow computing an L-value (i.e. the least activity value) for a user-defined time span termed ‘Lflex’ value. A plotting option is included in all functions. The package can be downloaded from the Comprehensive R Archives Network (CRAN).

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The package ‘nparACT’ for R serves the non-parametric analysis of actigraphy data.

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Computed parameters include interdaily stability (IS), intradaily variability (IV) and relative amplitude (RA) as well as start times and average activity during the 10 h with maximal and the 5 h with minimal activity (i.e. M10 and L5).

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.

Synthesis and Characterization of 1,3,5-Trisubstituted Pyrazoline Derivatives by Ultrasonic Irradiation Method and Evaluation of its Antibacterial Activity

A series of novel 1,3,5-trisubstituted pyrazoline derivatives (P1-P10) have been synthesized by the reaction of substituted chalcones (C1-C10) with 4-hydroxybenzhydrazide. The starting material, chalcones were prepared by claisen Schmidt condensation of 4-methylacetophenone with substituted aldehydes in the presence of sodium hydroxide in ethanol. 4-hydroxybenzhydrazide was synthesized by condensing methyl 4-hydroxybenzoate with hydrazine hydrate. The cycloaddition of chalcones with 4-hydroxybenzhydrazide gives 1, 3, 5-trisubstituted pyrazoline derivatives. The structures of synthesized derivatives were confirmed by IR, 1HNMR and 13C NMR spectrum. The synthesized compounds were screened for their antibacterial and antifungal activity.

Morning sleep inertia in alertness and performance: effect of cognitive domain and white light conditions

The transition from sleep to wakefulness entails a temporary period of reduced alertness and impaired performance known as sleep inertia. The extent to which its severity varies with task and cognitive processes remains unclear. We examined sleep inertia in alertness, attention, working memory and cognitive throughput with the Karolinska Sleepiness Scale (KSS), the Psychomotor Vigilance Task (PVT), n-back and add tasks, respectively. The tasks were administered 2 hours before bedtime and at regular intervals for four hours, starting immediately after awakening in the morning, in eleven participants, in a four-way cross-over laboratory design. We also investigated whether exposure to Blue-Enhanced or Bright Blue-Enhanced white light would reduce sleep inertia. Alertness and all cognitive processes were impaired immediately upon awakening (p<0.01). However, alertness and sustained attention were more affected than cognitive throughput and working memory. Moreover, speed was more affected than accuracy of responses. The light conditions had no differential effect on performance except in the 3-back task (p<0.01), where response times (RT) at the end of four hours in the two Blue-Enhanced white light conditions were faster (200 ms) than at wake time. We conclude that the effect of sleep inertia varies with cognitive domain and that it’s spectral/intensity response to light is different from that of sleepiness. That is, just increasing blue-wavelength in light may not be sufficient to reduce sleep inertia. These findings have implications for critical professions like medicine, law-enforcement etc., in which, personnel routinely wake up from night-time sleep to respond to emergency situations.

Synthesis, Characterization and Anti-Diabetic Activity of 1,3,5-Triaryl-2-Pyrazolines in Acetic Acid Solution under Ultrasound Irradiation

A chalcone was prepared by the reaction of 4-methylbenzaldehyde with 4-methylacetophenone in dilute methanolic sodium hydroxide solution under ultrasonic irradiationin the water bath of an ultrasonic cleaner at room temperature. Treatment of this chalcone with thiosemicarbazide/semicarbazide hydrochloride/benzhydrazide/benzenesulphonyl hydrazide/phenylhydrazine hydrochloride afforded the corresponding 2-pyrazoline in good yields. All the new compounds have been characterized by IR, 1H-NMR, 13CNMR spectral data. All the target compounds were evaluated for their In Vivo anti-diabetic activity in rates in comparison with as reference drug.

Circadian period and the timing of melatonin onset in men and women: predictors of sleep during the weekend and in the laboratory

Sleep complaints and irregular sleep patterns, such as curtailed sleep during workdays and longer and later sleep during weekends, are common. It is often implied that differences in circadian period and in entrained phase contribute to these patterns, but few data are available. We assessed parameters of the circadian rhythm of melatonin at baseline and in a forced desynchrony protocol in 35 participants (18 women) with no sleep disorders. Circadian period varied between 23 h 50 min and 24 h 31 min, and correlated positively (n = 31, rs  = 0.43, P = 0.017) with the timing of the melatonin rhythm relative to habitual bedtime. The phase of the melatonin rhythm correlated with the Insomnia Severity Index (n = 35, rs  = 0.47, P = 0.004). Self-reported time in bed during free days also correlated with the timing of the melatonin rhythm (n = 35, rs  = 0.43, P = 0.01) as well as with the circadian period (n = 31, rs  = 0.47, P = 0.007), such that individuals with a more delayed melatonin rhythm or a longer circadian period reported longer sleep during the weekend. The increase in time in bed during the free days correlated positively with circadian period (n = 31, rs  = 0.54, P = 0.002). Polysomnographically assessed latency to persistent sleep (n = 34, rs  = 0.48, P = 0.004) correlated with the timing of the melatonin rhythm when participants were sleeping at their habitual bedtimes in the laboratory. This correlation was significantly stronger in women than in men (Z = 2.38, P = 0.017). The findings show that individual differences in circadian period and phase of the melatonin rhythm associate with differences in sleep, and suggest that individuals with a long circadian period may be at risk of developing sleep problems.

Effects of partial and acute total sleep deprivation on performance across cognitive domains, individuals and circadian phase

Background

Cognitive performance deteriorates during extended wakefulness and circadian phase misalignment, and some individuals are more affected than others. Whether performance is affected similarly across cognitive domains, or whether cognitive processes involving Executive Functions are more sensitive to sleep and circadian misalignment than Alertness and Sustained Attention, is a matter of debate.

Methodology/Principal Findings

We conducted a 2 × 12-day laboratory protocol to characterize the interaction of repeated partial and acute total sleep deprivation and circadian phase on performance across seven cognitive domains in 36 individuals (18 males; mean ± SD of age = 27.6±4.0 years). The sample was stratified for the rs57875989 polymorphism in PER3, which confers cognitive susceptibility to total sleep deprivation. We observed a deterioration of performance during both repeated partial and acute total sleep deprivation. Furthermore, prior partial sleep deprivation led to poorer cognitive performance in a subsequent total sleep deprivation period, but its effect was modulated by circadian phase such that it was virtually absent in the evening wake maintenance zone, and most prominent during early morning hours. A significant effect of PER3 genotype was observed for Subjective Alertness during partial sleep deprivation and on n-back tasks with a high executive load when assessed in the morning hours during total sleep deprivation after partial sleep loss. Overall, however, Subjective Alertness and Sustained Attention were more affected by both partial and total sleep deprivation than other cognitive domains and tasks including n-back tasks of Working Memory, even when implemented with a high executive load.

Conclusions/Significance

Sleep loss has a primary effect on Sleepiness and Sustained Attention with much smaller effects on challenging Working Memory tasks. These findings have implications for understanding how sleep debt and circadian rhythmicity interact to determine waking performance across cognitive domains and individuals.

The spectral composition of evening light and individual differences in the suppression of melatonin and delay of sleep in humans

The effect of light on circadian rhythms and sleep is mediated by a multi-component photoreceptive system of rods, cones and melanopsin-expressing intrinsically photosensitive retinal ganglion cells. The intensity and spectral sensitivity characteristics of this system are to be fully determined. Whether the intensity and spectral composition of light exposure at home in the evening is such that it delays circadian rhythms and sleep also remains to be established. We monitored light exposure at home during 6-8wk and assessed light effects on sleep and circadian rhythms in the laboratory. Twenty-two women and men (23.1±4.7yr) participated in a six-way, cross-over design using polychromatic light conditions relevant to the light exposure at home, but with reduced, intermediate or enhanced efficacy with respect to the photopic and melanopsin systems. The evening rise of melatonin, sleepiness and EEG-assessed sleep onset varied significantly (P<0.01) across the light conditions, and these effects appeared to be largely mediated by the melanopsin, rather than the photopic system. Moreover, there were individual differences in the sensitivity to the disruptive effect of light on melatonin, which were robust against experimental manipulations (intra-class correlation=0.44). The data show that light at home in the evening affects circadian physiology and imply that the spectral composition of artificial light can be modified to minimize this disruptive effect on sleep and circadian rhythms. These findings have implications for our understanding of the contribution of artificial light exposure to sleep and circadian rhythm disorders such as delayed sleep phase disorder.

Assessment of circadian rhythms in humans: comparison of real-time fibroblast reporter imaging with plasma melatonin

We compared the period of the rhythm of plasma melatonin, driven by the hypothalamic circadian pacemaker, to in vitro periodicity in cultured peripheral fibroblasts to assess the effects on these rhythms of a polymorphism of PER3 (rs57875989), which is associated with sleep timing. In vitro circadian period was determined using luminometry of cultured fibroblasts, in which the expression of firefly luciferase was driven by the promoter of the circadian gene Arntl (Bmal1). The period of the melatonin rhythm was assessed in a 9-d forced desynchrony protocol, minimizing confounding effects of sleep-wake and light-dark cycles on circadian rhythmicity. In vitro periods (32 participants, 24.61±0.33 h, mean±SD) were longer than in vivo periods (31 participants, 24.16±0.17 h; P<0.0001) but did not differ between PER3 genotypes (P>0.4). Analyses of replicate in vitro assessments demonstrated that circadian period was reproducible within individuals (intraclass correlation=0.62), but in vivo and in vitro period assessments did not correlate (P>0.9). In accordance with circadian entrainment theory, in vivo period correlated with the timing of melatonin (P<0.05) at baseline and with diurnal preference (P<0.05). Individual circadian rhythms can be reliably assessed in fibroblasts but may not correlate with physiological rhythms driven by the central circadian pacemaker.

Human responses to bright light of different durations

Light exposure in the early night induces phase delays of the circadian rhythm in melatonin in humans. Previous studies have investigated the effect of timing, intensity, wavelength, history and pattern of light stimuli on the human circadian timing system. We present results from a study of the duration–response relationship to phase-delaying bright light. Thirty-nine young healthy participants (16 female; 22.18±3.62 years) completed a 9-day inpatient study. Following three baseline days, participants underwent an initial circadian phase assessment procedure in dim light (<3 lux), and were then randomized for exposure to a bright light pulse (∼10,000 lux) of 0.2 h, 1.0 h, 2.5 h or 4.0 h duration during a 4.5 h controlled-posture episode centred in a 16 h wake episode. After another 8 h sleep episode, participants completed a second circadian phase assessment. Phase shifts were calculated from the difference in the clock time of the dim light melatonin onset (DLMO) between the initial and final phase assessments. Exposure to varying durations of bright light reset the circadian pacemaker in a dose-dependent, non-linear manner. Per minute of exposure, the 0.2 h duration was over 5 times more effective at phase delaying the circadian pacemaker (1.07±0.36 h) as compared with the 4.0 h duration (2.65±0.24 h). Acute melatonin suppression and subjective sleepiness also had a dose-dependent response to light exposure duration. These results provide strong evidence for a non-linear resetting response of the human circadian pacemaker to light duration.

Analysis method and experimental conditions affect computed circadian phase from melatonin data

Accurate determination of circadian phase is necessary for research and clinical purposes because of the influence of the master circadian pacemaker on multiple physiologic functions. Melatonin is presently the most accurate marker of the activity of the human circadian pacemaker. Current methods of analyzing the plasma melatonin rhythm can be grouped into three categories: curve-fitting, threshold-based and physiologically-based linear differential equations. To determine which method provides the most accurate assessment of circadian phase, we compared the ability to fit the data and the variability of phase estimates for seventeen different markers of melatonin phase derived from these methodological categories. We used data from three experimental conditions under which circadian rhythms - and therefore calculated melatonin phase - were expected to remain constant or progress uniformly. Melatonin profiles from older subjects and subjects with lower melatonin amplitude were less likely to be fit by all analysis methods. When circadian drift over multiple study days was algebraically removed, there were no significant differences between analysis methods of melatonin onsets (P = 0.57), but there were significant differences between those of melatonin offsets (P<0.0001). For a subset of phase assessment methods, we also examined the effects of data loss on variability of phase estimates by systematically removing data in 2-hour segments. Data loss near onset of melatonin secretion differentially affected phase estimates from the methods, with some methods incorrectly assigning phases too early while other methods assigning phases too late; missing data at other times did not affect analyses of the melatonin profile. We conclude that melatonin data set characteristics, including amplitude and completeness of data collection, differentially affect the results depending on the melatonin analysis method used.

Sex differences in phase angle of entrainment and melatonin amplitude in humans

Studies of sex differences in the timing of human circadian rhythms have reported conflicting results. This may be because the studies conducted to date have not controlled for the masking effects of the rest activity cycle on the circadian rhythms being assessed. In the present analysis of data collected under controlled conditions, we examined sex differences in the timing of circadian rhythms while minimizing masking from behavioral and environmental factors using a constant routine (CR) protocol. All participants (28 women and 28 men paired by habitual wake time; age range, 18 30 years) maintained a regular self selected sleep wake schedule at home prior to the study. After 3 baseline days in the laboratory, participants began a CR. Women were found to have a significantly higher melatonin amplitude and lower temperature amplitude than men. While sleep timing was the same between the 2 groups, the timing of the circadian rhythms of core body temperature and pineal melatonin secretion was earlier relative to sleep time in women as compared to men. Sleep therefore occurred at a later biological time for women than men, despite being at the same clock time. Given that sleep propensity and structure vary with circadian phase and are impacted by circulating melatonin, these findings may have important implications for understanding sex differences in sleep timing and duration, diurnal preference, and the prevalence of sleep disorders such as insomnia.

The impact of sleep timing and bright light exposure on attentional impairment during night work

The prevalence of hazardous incidents induced by attentional impairment during night work and ensuing commute times is attributable to circadian misalignment and increased sleep pressure. In a 10-day shift work simulation protocol (4 day shifts and 3 night shifts), the efficacies of 2 countermeasures against nighttime (2300 to 0700 h) attentional impairment were compared: (1) Morning Sleep (0800 to 1600 h; n = 18) in conjunction with a phase-delaying light exposure (2300 to 0300 h), and (2) Evening Sleep (1400 to 2200 h; n = 17) in conjunction with a phase-advancing light exposure (0300 to 0700 h). Analysis of the dim light salivary melatonin onset indicated a modest but significant circadian realignment in both sleep groups (evening sleep: 2.27 +/- 0.6 h phase advance, p < 0.01; morning sleep: 4.98 +/- 0.43 h phase delay, p < 0.01). Daytime sleep efficiency and total sleep time did not differ between them or from their respective baseline sleep (2200 to 0600 h; p > 0.05). However, on the final night shift, the evening sleep subjects had 37% fewer episodes of attentional impairment (long response times: 22 +/- 4 vs. 35 +/- 4; p = 0.02) and quicker responses (p < 0.01) on the Psychomotor Vigilance Task than their morning sleep counterparts. Their response speed recovered to near daytime levels (p = 0.47), whereas those of the morning sleep subjects continued to be slower than their daytime levels (p = 0.008). It is concluded that partial circadian realignment to night work in combination with reduced homeostatic pressure contributed to the greater efficacy of a schedule of Evening Sleep with a phase-advancing light exposure as a countermeasure against attentional impairment, over a schedule of Morning Sleep with a phase-delaying light exposure. These results have important implications for managing patients with shift work disorder.

Acute sleep deprivation and circadian misalignment associated with transition onto the first night of work impairs visual selective attention

Background

Overnight operations pose a challenge because our circadian biology promotes sleepiness and dissipates wakefulness at night. Since the circadian effect on cognitive functions magnifies with increasing sleep pressure, cognitive deficits associated with night work are likely to be most acute with extended wakefulness, such as during the transition from a day shift to night shift.

Methodology/Principal Findings

To test this hypothesis we measured selective attention (with visual search), vigilance (with Psychomotor Vigilance Task [PVT]) and alertness (with a visual analog scale) in a shift work simulation protocol, which included four day shifts followed by three night shifts. There was a nocturnal decline in cognitive processes, some of which were most pronounced on the first night shift. The nighttime decrease in visual search sensitivity was most pronounced on the first night compared with subsequent nights (p = .04), and this was accompanied by a trend towards selective attention becoming ‘fast and sloppy’. The nighttime increase in attentional lapses on the PVT was significantly greater on the first night compared to subsequent nights (p<.05) indicating an impaired ability to sustain focus. The nighttime decrease in subjective alertness was also greatest on the first night compared with subsequent nights (p<.05).

Conclusions/Significance

These nocturnal deficits in attention and alertness offer some insight into why occupational errors, accidents, and injuries are pronounced during night work compared to day work. Examination of the nighttime vulnerabilities underlying the deployment of attention can be informative for the design of optimal work schedules and the implementation of effective countermeasures for performance deficits during night work.

Scheduling of sleep/darkness affects the circadian phase of night shift workers

Shift work results in a misalignment between circadian timing and the sleep/wake schedule, leading to irregular and poor quality sleep. Inconsistent input from the daily light cycle further interferes with circadian entrainment. It has been hypothesized that scheduling the sleep/dark cycle on the night shift could aid in promoting adaptation to night shift work by facilitating appropriate phase shifts. In a simulated shift-work study, we compared the ability of two sleep/dark schedules to shift circadian phase. Our results indicate that scheduled sleep/darkness can aid in adaptation to night shift work by inducing both advance and delay phase shifts, depending on the timing of the sleep schedule, although the size of the phase shifts are not sufficient to produce complete adaptation to the night shift. These results have applications to night shift workers, particularly in occupations in which alterations in the timing of light exposure cannot be achieved during working hours.

A random-ray model for speed and accuracy in perceptual experiments

We present a 'random ray' model to describe Yes/No reaction times (RTs) and errors in perceptual experiments. The ray model is analogous to a random walk, but it is computationally simpler, requiring only elementary geometry. Ray parameters control the drift rates to the Yes and No decision boundaries, bias, and a termination or 'time-out' rule. Rays are normally distributed, but predicted RT distributions are skewed by projection onto the boundaries. Model parameters can be estimated directly from the 16th, 50th, and 84th percentiles of the RT distributions on hit, correct rejection, false alarm, and miss trials, if the data satisfy three easily testable constraints. Examples are given from visual search and object recognition.