A time to think: Circadian rhythms in human cognition

Time of day is associated with paradoxical reductions in global signal fluctuation and functional connectivity

The brain exhibits substantial diurnal variation in physiology and function, but neuroscience studies rarely report or consider the effects of time of day. Here, we examined variation in resting-state functional MRI (fMRI) in around 900 individuals scanned between 8 AM and 10 PM on two different days. Multiple studies across animals and humans have demonstrated that the brain’s global signal (GS) amplitude (henceforth referred to as “fluctuation”) increases with decreased arousal. Thus, in accord with known circadian variation in arousal, we hypothesised that GS fluctuation would be lowest in the morning, increase in the midafternoon, and dip in the early evening. Instead, we observed a cumulative decrease in GS fluctuation as the day progressed. Although respiratory variation also decreased with time of day, control analyses suggested that this did not account for the reduction in GS fluctuation. Finally, time of day was associated with marked decreases in resting-state functional connectivity across the whole brain. The magnitude of decrease was significantly stronger than associations between functional connectivity and behaviour (e.g., fluid intelligence). These findings reveal time of day effects on global brain activity that are not easily explained by expected arousal state or physiological artefacts. We conclude by discussing potential mechanisms for the observed diurnal variation in resting brain activity and the importance of accounting for time of day in future studies.

The brain exhibits substantial diurnal variation in physiology and function. A large-scale fMRI study reveals that the brain’s global signal amplitude, typically elevated during drowsy states, unexpectedly reduces steadily as the day progresses.

Living Without Temporal Cues: A Case Study

Isolation from external time cues allows endogenous circadian rhythmicity to be demonstrated. In this study, also filmed as a television documentary, we assessed rhythmic changes in a healthy man time isolated in a bunker for 9 days/nights. During this period the lighting conditions were varied between: (1) self-selected light/dark cycle, (2) constant dim light, and (3) light/dark cycle with early wake up. A range of variables was assessed and related to the sleep-wake cycle, psychomotor and physical performance and clock-time estimation. This case study using modern non-invasive monitoring techniques emphasizes how different physiological circadian rhythms persist in temporal isolation under constant dim light conditions with different waveforms, free-running with a period (τ) between 24 and 25 h. In addition, a significant correlation between time estimation and mid-sleep time, a proxy for circadian phase, was demonstrated.

The impact of social jetlag and chronotype on attention, inhibition and decision making in healthy adults

Sleep and circadian clock disruption are associated with neuropsychiatric disorders, such as attention deficit hyperactivity disorder, but the impact on neurocognitive performance is unclear. We assessed whether chronotype and everyday circadian misalignment manifested as social jetlag were associated with inter-individual neurocognitive performance across domains of attention, inhibitory control and decision making. One hundred and eighty-eight healthy young adults were assessed for sleep and circadian properties and performed two neurocognitive tasks, the Continuous Performance Test and the Iowa Gambling Task. Social jetlag was associated with significantly faster and less variable reaction times and commission errors on the Continuous Performance Test. Poorer subjective sleep quality was associated with poorer decision making on the Iowa Gambling Task. No effects were present for polymorphisms in the circadian clock genes CLOCK and PER3. We conclude that circadian disruption shaped by everyday environmental factors may impact on attentional/inhibitory performance but not on a measure of risky decision making.

Ideal Time of Day for Risky Decision Making: Evidence from the Balloon Analogue Risk Task

BACKGROUND

Previous studies have demonstrated that individuals showed higher risk preference in the afternoon than in the morning. However, few studies aimed to explore the alteration of feedback learning effect during risky decision making, which is one of the important psychological processes of real risk behaviors. Moreover, cognitive function altered at the off-peak time due to impaired inhibitory control. The present study is to investigate the time-of-day effect on risky decision making and inhibitory control and whether the alteration of inhibitory control causes the differences in risky decision making across one day.

PARTICIPANTS AND METHODS

We adopted a within-participants design without extremely chronotype individuals to measure the time-of-day (9 am vs 3 pm) effect on risky decision making by using the Balloon Analogue Risk Task. At the same time, we measured the inhibitory control by using the Go/no-go task.

RESULTS

Our results confirmed that individuals showed higher risk preference in the afternoon than in the morning. In addition, we found that individuals were insensitive to loss and the previous negative feedback in the afternoon. Critically, the results did not reveal any significant correlation between risky decision making and inhibitory control under the regulation of the time-of-day effects, although individuals performed worse on inhibitory control in the afternoon.

CONCLUSION

The current findings revealed that the time-of-day effect regulated risky decision making and inhibitory control. Individuals act with higher risk preference, less sensitivity to loss as negative feedback, and lower inhibitory control in the afternoon than in the morning. This may reflect the effects of time-of-day on risk propensity and inhibitory control is relatively independent.

A systematic review of cognitive assessment in physical activity research involving children and adolescents

OBJECTIVES

To summarise the reporting, administrative requirements and psychometric properties of cognitive measures used in experimental physical activity research conducted with school-aged youth.

DESIGN

Systematic review.

METHODS

Five databases (CINAHL, SPORTDiscus, Medline, Embase, and Psychinfo) were searched from inception to October, 2018. Studies meeting the following criteria were eligible for inclusion: experimental study design; apparently healthy youth aged 5-18 years; use of physical activity; and use of a performance-based cognitive test. Reporting, administration requirements, reliability, and validity of the included cognitive measures was extracted.

RESULTS

Included studies (n=109) used 60 unique cognitive tests. Across the 109 included studies, a total of 181 tests were reported on. Test format (e.g. pen and paper, computer) was specified for 166 (91.7%); administration type (individual or group) for 108 (59.7%); and administration time for 49 (27.1%) of the tests. Of the 181 tests reported on, 72 (39.8%) provided information on either test-retest reliability or internal consistency, and 82 (45.3%) provided at least one form of test validation.

CONCLUSIONS

A lack of reporting of test administration time, as well as information on the reliability and validity of included cognitive tasks are notable limitations of studies included in this review. Agreement on a smaller number of tests should be sought to improve the interpretability of future research. The summary provided by this systematic review can be used to inform the selection of performance-based cognitive measures in future physical activity research.

Effects of time of day on radiological interpretation

Accurate interpretation of radiological images involves a complex visual search that relies on several cognitive processes, including selective attention, working memory, and decision-making. Patient outcomes often depend on the accuracy of image interpretations, and yet research has revealed that conclusions vary significantly from one radiologist to another. A myriad of factors has been shown to contribute to the likelihood of interpretative errors and discrepancies, including the radiologist's level of experience and fatigue, and these factors are well reported elsewhere; however, a potentially important factor that has been given little previous consideration is how radiologists' interpretations might be impacted by the time of day at which the reading takes place, a factor that other disciplines have shown to be a determinant of competency. The available literature shows that while the time of day is known to significantly impact some cognitive functions that likely relate to reading competence, including selective visual attention and visual working memory, little is known about the impact of the time of day on radiology interpretation performance. This review explores the evidence regarding the relationship between time of day and performance, with a particular emphasis on radiological activities.

Evening preference and poor sleep independently affect attentional-executive functions in patients with depression

Cognitive impairments are well documented in major depressive disorder (MDD), however, they cannot be fully explained by depressive symptom severity. We investigated how diurnal preference and sleep quality affect cognitive function in MDD. In 34 inpatients with current MDD and 29 healthy controls (HC), we obtained diurnal preference (Morningness-Eveningness Questionnaire, MEQ) and subjective sleep quality (Pittsburgh Sleep Quality Index, PSQI). Further, current mood and neuropsychological performance (Trail Making Test, TMT, part A and B) were assessed in the evening and in the following morning. Patients with MDD performed worse than HC on the TMT-B (particularly requiring executive function), but not on the TMT-A (assessing foremost visuomotor processing speed). In general, participants with evening preference (MEQ-score median split) performed poorer on the TMT than participants with morning preference. Subgroup analyses within MDD confirmed the negative effect of evening preference on the TMT. In addition, patients with severely impaired sleep quality (PSQI > 10) performed cognitively worse than patients with normal to moderately impaired sleep quality (PSQI ≤ 10). The results were largely independent of current mood state. Our findings suggest that evening preference and severely impaired sleep quality independently contribute to cognitive impairment in MDD.

Work by day and sleep by night, do not sleep too little or too much: Effects of sleep duration, time of day and circadian synchrony on flanker-task performance in internet brain-game users from teens to advanced age

Research elucidating the effects of sleep and circadian rhythm on cognitive performance is advancing, yet many important questions remain. Using flanker-task performance scores from a large internet sample (N = 48,881) with repeated measures of cognitive performance and linked prior-night self-reported sleep duration, we analysed the relationship between sleep duration, time of day of task performance, and chronotype synchrony with performance in participants aged 15-80 years. Results indicate a performance peak at 7 hr habitual sleep duration, and point to a variable effect of deviation from habitual sleep duration depending on users' habitual sleep duration and age. Time-of-day effects were notable for a steady decline in performance up until 01:00 hours-02:00 hours for the group as a whole, which was accounted for by nighttime deterioration on trials requiring inhibitory executive functioning, particularly in older subjects. Analyses did not demonstrate an advantage for playing in synchrony with self-identified chronotype. Results strengthen findings indicating an inverted U-shaped relationship between sleep duration and cognitive performance across a broad spectrum of age groups. These findings underscore the importance of daytime task performance for tasks requiring inhibitory function, especially in elderly people. Findings highlight the utility of large-scale internet data in contributing to sleep and circadian science.

Circadian misalignment impairs ability to suppress visual distractions

Evening-type individuals often perform poorly in the morning because of a mismatch between internal circadian time and external social time, a condition recognized as social jet lag. Performance impairments near the morning circadian (~24 hr) trough have been attributed to deficits in attention, but the nature of the impairment is unknown. Using electrophysiological indices of attentional selection (N2pc) and suppression (P_D ), we show that evening-type individuals have a specific disability in suppressing irrelevant visual distractions. More specifically, evening-type individuals managed to suppress a salient distractor in an afternoon testing session, as evidenced by a P_D , but were less able to suppress the distractor in a morning testing session, as evidenced by an attenuated P_D and a concomitant distractor-elicited N2pc. Morning chronotypes, who would be well past their circadian trough at the time of testing, did not show this deficit at either test time. These results indicate that failure to filter out irrelevant stimuli at an early stage of perceptual processing contributes to impaired cognitive functioning at nonoptimal times of day and may underlie real-world performance impairments, such as distracted driving, that have been associated with circadian mismatch.

How Do Nurses Cope with Shift Work? A Qualitative Analysis of Open-Ended Responses from a Survey of Nurses

Nurses are frequently required to engage in shift work given the 24/7 nature of modern healthcare provision. Despite the health and wellbeing costs associated with shift work, little is known about the types of coping strategies employed by nurses. It may be important for nurses to adopt strategies to cope with shift work in order to prevent burnout, maintain wellbeing, and ensure high quality care to patients. This paper explores common strategies employed by nurses to cope with shift work. A workforce survey was completed by 449 shift working nurses that were recruited from a major metropolitan health service in Melbourne, Australia. Responses to open-ended questions about coping strategies were analysed using the framework approach to thematic analysis. Four interconnected main themes emerged from the data: (i) health practices, (ii) social and leisure, (iii) cognitive coping strategies, and (iv) work-related coping strategies. Although a range of coping strategies were identified, sleep difficulties often hindered the effective use of coping strategies, potentially exacerbating poor health outcomes. Findings suggest that in addition to improving nurses' abilities to employ effective coping strategies on an individual level, workplaces also play an important role in facilitating nurses' wellbeing.

Inhibition of casein kinase 1δ/εimproves cognitive-affective behavior and reduces amyloid load in the APP-PS1 mouse model of Alzheimer's disease

Circadian rhythm disruption is one of the earliest biomarkers of Alzheimer’s disease (AD), and there exists a bidirectional relationship by which dysfunctions in the circadian clock drive AD pathology and AD pathology drives circadian dysfunction. Casein kinase 1 (CK1) isoforms ε and δ, key circadian regulators, are significantly upregulated in AD and may contribute to AD pathogenesis. In the current studies, we have examined how inhibition of CK1ε/δ with PF-670462 (at 10 mg/kg, δ isoform selective, or 30 mg/kg, δ and ε selective) impacts regional Aβ and circadian gene expression in 10–13 month old APP-PS1 mice and nontransgenic controls. We have also assessed circadian, cognitive, and affective behavioral correlates of these neural changes. At baseline, APP-PS1 mice showed a short period, as well as impaired cognitive performance in both prefrontal cortex and hippocampus-dependent tasks. Both doses of PF-670462 lengthened the period and improved affect, whereas only the higher dose improved cognition. Further, PF-670462 treatment produced a dose-dependent reduction in amyloid burden – overall Aβ signal decreased in all three areas; in the prefrontal cortex and hippocampus, PF-670462 also reduced plaque size. Together, these findings support chronotherapy as a potential tool to improve behavior in AD.

Eveningness is associated with greater subjective cognitive impairment in individuals with self-reported symptoms of unipolar depression

BACKGROUND

Eveningness is associated with depression diagnosis and increased depressive symptom severity. Time-of-day preference has been linked with differences in cognitive function in the general population, with cognitive difficulties being a major factor in psychosocial impairment in depression. We therefore investigated the impact of time-of-day preference and self-reported depressed state on subjective cognitive function.

METHODS

Participants over the age of 18 with a self-reported history of depression completed an online questionnaire. They provided demographic and mental health information, and completed self-report scales assessing depression symptoms, time-of-day preference, and cognition. Participants were classified as "currently" or "previously depressed" based on self-reported symptoms, and as having a morning, neither, or evening time-of-day preference.

RESULTS

A total of 804 participants reporting a history of unipolar depression were included. Currently-depressed participants reported more cognitive difficulties in all areas measured. Evening types reported more complex attentional and retrospective memory difficulties than neither types, and reported more executive and prospective memory difficulties than both neither and morning types. There was an additive effect of mood state and time-of-day preference, with self-reported depressed evening types reporting the most cognitive problems.

LIMITATIONS

Depression history, time-of-day preference, and cognitive function were assessed using unsupervised self-report measures. Time-of-day preference does not necessarily reflect the physiological circadian system.

CONCLUSIONS

Both depressed state and evening preference were individually associated with subjective cognitive complaints in people with a self-reported history of unipolar depression. The additive effect of poor mood and eveningness is important given the high prevalence of eveningness in depression. Assessment of time-of-day preference could help to identify those susceptible to cognitive symptoms, and inform treatment.

The road ahead in clinical network neuroscience

Clinical network neuroscience, the study of brain network topology in neurological and psychiatric diseases, has become a mainstay field within clinical neuroscience. Being a multidisciplinary group of clinical network neuroscience experts based in The Netherlands, we often discuss the current state of the art and possible avenues for future investigations. These discussions revolve around questions like "How do dynamic processes alter the underlying structural network?" and "Can we use network neuroscience for disease classification?" This opinion paper is an incomplete overview of these discussions and expands on ten questions that may potentially advance the field. By no means intended as a review of the current state of the field, it is instead meant as a conversation starter and source of inspiration to others.

Beyond the Low Frequency Fluctuations: Morning and Evening Differences in Human Brain

Human performance, alertness, and most biological functions express rhythmic fluctuations across a 24-h-period. This phenomenon is believed to originate from differences in both circadian and homeostatic sleep-wake regulatory processes. Interactions between these processes result in time-of-day modulations of behavioral performance as well as brain activity patterns. Although the basic mechanism of the 24-h clock is conserved across evolution, there are interindividual differences in the timing of sleep-wake cycles, subjective alertness and functioning throughout the day. The study of circadian typology differences has increased during the last few years, especially research on extreme chronotypes, which provide a unique way to investigate the effects of sleep-wake regulation on cerebral mechanisms. Using functional magnetic resonance imaging (fMRI), we assessed the influence of chronotype and time-of-day on resting-state functional connectivity. Twenty-nine extreme morning- and 34 evening-type participants underwent two fMRI sessions: about 1 h after wake-up time (morning) and about 10 h after wake-up time (evening), scheduled according to their declared habitual sleep-wake pattern on a regular working day. Analysis of obtained neuroimaging data disclosed only an effect of time of day on resting-state functional connectivity; there were different patterns of functional connectivity between morning (MS) and evening (ES) sessions. The results of our study showed no differences between extreme morning-type and evening-type individuals. We demonstrate that circadian and homeostatic influences on the resting-state functional connectivity have a universal character, unaffected by circadian typology.

Yin and Yang: Why did evolution implement and preserve the circadian rhythmicity?

Yin and Yang concept emphasizes the reciprocal and interrelated nature; neither is sufficient, both are needed to sustain the overall balance of the living system. Changing the balance, by implementing deficiency or excess of one of them, upsets the equilibrium (homeostasis) of the whole system.

PURPOSE

In this opinion article intermittent exposure is presented as the stimulus for development and evolutionary conservation of circadian rhythm, an endogenous, entrainable oscillation of approximately 24 h, to counteract/balance the cells' natural tendency to attenuate their response during long-term exposure to different endogenous substances.

RESULTS

The concept of Yin and Yang duality is an allegory on which the avoidance of attenuation of the cells' responses hypothesis is presented as an explanation for the circadian rhythmicity, which is integrated in all human cells, with the exception of stem and cancer cells.

CONCLUSIONS

We hypothesize, that circadian rhythmicity has evolved, during evolution, into a mechanism that prevents disruption of the organism's negative-feedback-loop homeostasis.

Time-of-day effects on prospective memory

Cognitive performance fluctuates during the course of a day. Different cognitive functions show optimal performance at different times of the day, known as the 'time-of-day effect'. While this effect has been observed for a number of cognitive domains including declarative memory, it is presently unclear whether performance fluctuations are also seen in prospective memory, i.e. memory for intentions to be realized in the future. The present study examined time-of-day effects in four different prospective memory tasks with varying degrees of complexity, taking into account circadian preference (i.e. morningness-eveningness/chronotype) and attentional resources (in one of the tasks). In a pilot study (n = 48) and a main experiment (n = 39), prospective memory was compared between morning groups (˜09:00) and evening groups (˜21:00) of young adults. We found time-of-day effects, with better performance in the evening than in the morning, in a simple one-item prospective memory task (Red Pencil Task, p = .02), a classical event-based prospective memory task including the detection of cue syllables in a lexical decision ongoing task (Syllable Detection Task, p < .048), and a rather naturalistic complex planning task for breakfast preparation (Dresden Breakfast Task, including time-based prospective memory (p = .026) and event-based prospective memory (p = .054)). These time-of-day effects were neither modulated by circadian preference nor by attentional resources. Another simple one-item prospective memory task was not affected by time of day (Color Task, p = .14). Ongoing task performance in the Syllable Detection Task and the Dresden Breakfast Task, overall, did not differ significantly between morning and evening groups. These findings provide tentative evidence for time-of-day effects in prospective memory of young adults, with better performance in the evening hours.

Weak Associations of Morningness-Eveningness and Stability with Skin Temperature and Cortisol Levels

Differences in daytime preferences can be described on the dimension of morningness-eveningness (continuous) or circadian typology (categorical) and are associated with our physiological functioning, which is reflected in body temperature and cortisol levels in the morning. The purpose of the present study was to explore the relationship between morningness-eveningness, stability and physiological markers (body temperature and cortisol) based on a three-dimensional conceptualization of morningness-eveningness using the Morningness-Eveningness-Stability Scale improved (MESSi). In contrast to previously used unidimensional measures, the MESSi determines circadian typology and its amplitude in three dimensions: Morning affect (MA), Eveningness (EV) and Stability/Distinctness (DI). Furthermore, the differences of the cortisol levels between weekday and weekend were examined. The sample (N = 42) consisted of extreme chronotypes (age 18–54 years; M = 24.8 years, SD = 5.83; 22 morning types [5 men and 17 women] and 20 evening types [8 men and 12 women]). The participants were asked to measure their skin temperature for one week and sample four saliva probes for cortisol determination. Morning types showed a better fit in the actual temperature data to the approximating data as compared to Evening types and showed a higher overall temperature. The Stability/Distinctness (DI) component of the MESSi was negatively correlated with the nadir. Morning types also showed higher cortisol levels than Evening types immediately after awakening. The cortisol levels were higher on a weekday compared to the weekend. To conclude, the present findings demonstrate that the skin temperature is weakly associated with morningness-eveningness and the stability of the circadian phase.

A Cross-Syndrome Comparison of Sleep-Dependent Learning on a Cognitive Procedural Task

Sleep plays a key role in the consolidation of newly acquired information and skills into long term memory. Children with Down syndrome (DS) and Williams syndrome (WS) frequently experience sleep problems, abnormal sleep architecture, and difficulties with learning; thus, we predicted that children from these clinical populations would demonstrate impairments in sleep-dependent memory consolidation relative to children with typical development (TD) on a cognitive procedural task: The Tower of Hanoi. Children with DS (n = 17), WS (n = 22) and TD (n = 34) completed the Tower of Hanoi task. They were trained on the task either in the morning or evening, then completed it again following counterbalanced retention intervals of daytime wake and night time sleep. Children with TD and with WS benefitted from sleep for enhanced memory consolidation and improved their performance on the task by reducing the number of moves taken to completion, and by making fewer rule violations. We did not find any large effects of sleep on learning in children with DS, suggesting that these children are not only delayed, but atypical in their learning strategies. Importantly, our findings have implications for educational strategies for all children, specifically considering circadian influences on new learning and the role of children's night time sleep as an aid to learning.

Nap Opportunity During the Daytime Affects Performance and Perceived Exertion in 5-m Shuttle Run Test

Purpose

To compare the effect of different durations of nap opportunity during the daytime on repeated high-intensity short-duration performance and rating of perceived exertion (RPE).

Methods

Seventeen physically active men (age: 21.3 ± 3.4 years, height: 176.7 ± 5.9 cm, body mass: 71.8 ± 10.2 kg) performed a 5 m shuttle run test [to determine best distance (BD), total distance (TD), and fatigue index (FI)] under four conditions: a 25 min nap opportunity (N25), a 35 min nap opportunity (N35), a 45 min nap opportunity (N45), and control condition (no-nap) (N0). The sleep quality of each nap opportunity was evaluated using a scale ranging from 0 "no sleep" to 10 "uninterrupted, deep sleep throughout." The four conditions were performed in a random order. RPE was recorded after each repetition of the 5 m shuttle run test and the mean score was calculated.

Results

BD increased after N25 (+6%) and N45 (+9%) compared to N0 (p < 0.05) and was significantly higher after N45 compared to N35 (p < 0.05). Compared to N0, the three nap opportunity durations enhanced TD (p < 0.05) with greater enhancement after N45 compared to N25 (+8% vs. +3%) and N35 (+8% vs. +3%). For FI, no-significant differences were observed between the three nap opportunity durations and N0. The mean RPE score was significantly higher after N25 (+20%) and N0 (+19%) compared to N45 (p < 0.05). All participants were able to fall asleep during each nap condition with a sleep quality score of 6.9 ± 1.0, 7.0 ± 0.7, and 7.1 ± 0.8 for N25, N35, and N45.

Conclusion

A nap opportunity during the daytime was beneficial for physical performance and perceived exertion with the N45 being the most effective for improving performance and reducing fatigue during the 5 m shuttle run test. The implication of the present study is that athletes might benefit from a nap opportunity of 25, 35 or 45 min before practice or before a competition.

Subclinical Scores in Self-Report Based Screening Tools for Attention Deficits Correlate With Cognitive Traits in Typical Evening-Type Adults Tested in the Morning

Previous studies suggest that in adolescents and young adults, evening chronotype is a subclinical factor in physical, cognitive, and psychiatric fitness; poor sleep habits and larger misalignment with the social schedule constraints may exacerbate symptoms of inattention, impulsivity and the risks for detrimental behaviors. The influence of chronotype on neurocognitive performance during morning hours and scores in self-reports about attention deficit symptoms (ADS) and executive functioning, was explored in 42 healthy young university students (29 women), divided to evening type (ET) and combined morning/intermediate type (MT/IT) groups. Evening chronotypes scored significantly higher in the questionnaires of inattention Adult ADHD Self-Report Scale (ASRS-6) (MT/IT: 1.62 ± 1.59; ET: 2.71 ± 1.62, p < 0.05) and day-time sleepiness Epworth scale (MT/IT: 7.19 ± 5.17; ET: 11.48 ± 5.26, p < 0.01), reported lower subjective alertness (MT/IT: 63.02 ± 21.40; ET: 40.76 ± 17.43, p < 0.001), and had slower reaction times (MT/IT: 321.47 ± 76.81; ET: 358.94 ± 75.16, p < 0.05) during tests, compared to non-evening chronotypes. Nevertheless, ETs did not significantly differ in self-reports of executive functioning in the Behavioral Rating Inventory of Executive Functions-A (BRIEF-A) from non-ETs. The scores on standard self-report screening tools for ADS and executive functioning (ASRS-6, BRIEF-A-Metacognition) correlated with eveningness. We conclude that eveningness, subjective sleepiness and low arousal levels during morning can present as subclinical Attention Deficit and Hyperactivity Disorder (ADHD) symptoms in typical young adults with no evident sleep problems. Self-report based screening tools for ADS and executive functioning reflect chronotype-related traits in healthy young adults. Strong eveningness may bias the results of neurocognitive performance screening for ADHD when administered at morning hours.

An oculometrics-based biofeedback system to impede fatigue development during computer work: A proof-of-concept study

A biofeedback system may objectively identify fatigue and provide an individualized timing plan for micro-breaks. We developed and implemented a biofeedback system based on oculometrics using continuous recordings of eye movements and pupil dilations to moderate fatigue development in its early stages. Twenty healthy young participants (10 males and 10 females) performed a cyclic computer task for 31–35 min over two sessions: 1) self-triggered micro-breaks (manual sessions), and 2) biofeedback-triggered micro-breaks (automatic sessions). The sessions were held with one-week inter-session interval and in a counterbalanced order across participants. Each session involved 180 cycles of the computer task and after each 20 cycles (a segment), the task paused for 5-s to acquire perceived fatigue using Karolinska Sleepiness Scale (KSS). Following the pause, a 25-s micro-break involving seated exercises was carried out whether it was triggered by the biofeedback system following the detection of fatigue (KSS≥5) in the automatic sessions or by the participants in the manual sessions. National Aeronautics and Space Administration Task Load Index (NASA-TLX) was administered after sessions. The functioning core of the biofeedback system was based on a Decision Tree Ensemble model for fatigue classification, which was developed using an oculometrics dataset previously collected during the same computer task. The biofeedback system identified fatigue with a mean accuracy of approx. 70%. Perceived workload obtained from NASA-TLX was significantly lower in the automatic sessions compared with the manual sessions, p = 0.01 Cohen’s d_z = 0.89. The results give support to the effectiveness of integrating oculometrics-based biofeedback in timing plan of micro-breaks to impede fatigue development during computer work.

Sunset time and the economic effects of social jetlag: evidence from US time zone borders

The rapid evolution into a 24 h society challenges individuals' ability to conciliate work schedules and biological needs. Epidemiological research suggests that social and biological time are increasingly drifting apart ("social jetlag"). This study uses a spatial regression discontinuity design to estimate the economic cost of the misalignment between social and biological rhythms arising at the border of a time-zone in the presence of relatively rigid social schedules (e.g., work and school schedules). Exploiting the discontinuity in the timing of natural light at a time-zone boundary, we find that an extra hour of natural light in the evening reduces sleep duration by an average of 19 minutes and increases the likelihood of reporting insufficient sleep. Using data drawn from the Centers for Disease Control and Prevention and the US Census, we find that the discontinuity in the timing of natural light has significant effects on health outcomes typically associated with circadian rhythms disruptions (e.g., obesity, diabetes, cardiovascular diseases, and breast cancer) and economic performance (per capita income). We provide a lower bound estimate of the health care costs and productivity losses associated with these effects.

Neural correlates of dynamic changes in working memory performance during one night of sleep deprivation

Total sleep deprivation (TSD) is common in modern society leading to deterioration of multiple aspects of cognition. Dynamic interaction effect of circadian rhythmicity and homeostatic sleep pressure on sustained attention have been intensively investigated, while how this effect was represented on performance and cerebral responses to working memory, another important element of many neurobehavioral tasks, was not well elucidated. Thirty-six healthy subjects with intermediate chronotype performed the Sternberg working-memory task (SWMT) while undergoing functional magnetic resonance imaging every 2 hr from 10:00 p.m. on the first day to 6:00 a.m. on the second day. Using data from three imaging sessions (10:00 p.m., 04:00 a.m., and 06:00 a.m.), we found that the slowest SWMT reaction time and weakest cerebral responses were not at the end of TSD (06:00 a.m.) but during the early morning (04:00 a.m.) hours of the TSD. In addition, during this worst period of TSD, reaction time for the SWMT were found to be negatively correlated with task-related activation in the angular gyrus and positively correlated with the degree of negative correlation between the control and default networks. Our results revealed a rebound of SWMT reaction time and cerebral responses after the mid-time point of regular biological sleep night and provided more evidence that different cognitive tasks are differentially affected by sleep loss and circadian rhythmicity.

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.

The reliability of estimating visual working memory capacity

The reliability of estimations of working memory capacity has not been thoroughly examined. The present study examined the test-retest reliability for working memory capacity as estimated in a lateralized change detection task, which is frequently used in studies involving electroencephalography. The test-retest correlations between K values for each set size in the two tests varied from 0.502 to 0.757, with test-retest correlations rising as set size increased. The results indicate that individual visual working memory capacity can be reliably estimated in a change detection task. Furthermore, test-retest reliability was higher when the two tests occurred at the same time of day than at different times of day.

Factorial Structure of the Morningness-Eveningness-Stability-Scale (MESSi) and Sex and Age Invariance

Assessing morningness-eveningness preferences (chronotype), an individual characteristic that is mirrored in daily mental and physiological fluctuations, is crucial given their overarching influence in a variety of domains. The current work aimed to investigate the best factor structure of an instrument recently presented to asses this characteristic: the Morningness-Eveningness-Stability-Scale improved (MESSi). For the first time, the originally proposed three-factor structure was pitched against a uni- and a two-factor solution. Another novelty was to establish that the best-fitting model would be invariant in relation to sex and age, two variables that influence chronotype. A Confirmatory Factor Analyses on the data obtained from a sample of 2096 German adults (age: 18–76; M = 25.5, SD = 7.64) revealed that the originally proposed three-factor structure of the MESSi – Morning Affect, Eveningness, and Distinctness – was the only one to achieve acceptable fit indicators. Furthermore, each scale obtained good internal consistency. In order to assess age invariance, following the literature on development and chronotype, our sample was divided into three age groups: 18–21 years, 22–31 years, and 32 years or older. Full measurement invariance of the three-factor model was found for sex and age. Regarding differences between sexes, females did not differ significantly from males in Morning Affect, but scored significantly lower on Eveningness and higher on Distinctness; this last result has been consistent across validation studies of the MESSi. With respect to age differences, the oldest group scored lower on Eveningness and Distinctness in comparison with the other two age-groups; the intermediate group (age: 22–31) scored lower on Morning Affect when compared to both the younger and older age groups. Additionally, both Eveningness and Distinctness were negatively correlated with age. This latter relation has been consistently reported in other validation studies. Our results reinforce the idea that the MESSi assesses three different components of chronotype in a reliable manner and that this instrument can be used to explore sex and age differences.

Effects of Illuminance and Correlated Color Temperature on Daytime Cognitive Performance, Subjective Mood, and Alertness in Healthy Adults

This study investigated the impact of indoor illuminance and correlated color temperature (CCT) on healthy adults’ cognitive performance, subjective mood, and alertness during daytime office hours and differences in time-of-day effects. A 2(illuminance) × 2(CCT) × 2(morning vs. afternoon) mixed design ( N = 60) was employed. Participants felt less sleepy in the bright light exposure. The low “cool” lighting induced the least positive mood. The effects of illuminance and CCT on subjective feelings were not time-of-day dependent. The results demonstrated the slowest responses in inhibition, working memory, and recognition of facial expression tasks in the low “warm” lighting. The effect on long-term memory was most pronounced under the high “cool” light exposure, but only in the afternoon for recognition of neutral words. The findings suggest that future research on good indoor lighting should consider illuminance levels and CCT as well as other variables to optimize lighting effects during regular daytime hours.

Effects of circadian misalignment on cognition in chronic shift workers

Shift work is associated with increased human operational errors, presumably due to the circadian timing system that inhibits optimal cognitive function during the night. Circadian misalignment, which is the misalignment between the circadian pacemaker and behavioral/environmental cycles, impairs cognitive performance in non-shift workers. However, it remains uncertain whether the adverse cognitive consequences of circadian misalignment are also observed in chronic shift workers. Thus, we investigated the effects of circadian misalignment on cognitive performance in chronic shift workers. Using a randomized, cross-over design that simulated day shift work (circadian alignment) and night shift work (circadian misalignment), we show that circadian misalignment increases cognitive vulnerability on sustained attention, information processing and visual-motor performance, particularly after more than 10 hours of scheduled wakefulness. Furthermore, their increased levels of subjective sleepiness and their decreased sleep efficiency were significantly associated with impaired sustained attention and visual-motor performance. Our data suggest that circadian misalignment dramatically deteriorates cognitive performance in chronic shift workers under circadian misalignment. This increased cognitive vulnerability may have important safety consequences, given the increasing number of nighttime jobs that crucially rely on the availability of cognitive resources.

Three Reasons to Consider the Role of Tiredness in Sexual Risk-Taking Among Gay and Bisexual Men

Numerous factors have been shown to increase sexual risk-taking-especially among gay and bisexual men (GBM), who remain disproportionately affected by HIV and STIs. We present three lines of evidence that highlight the need to consider a previously under-explored situational factor in sexual risk-taking: tiredness. While tiredness has been shown, in sleep science literature, to impair cognition, emotional functioning, and decision-making in a wide range of behaviors, it has yet to be considered in-depth as a risk factor in sexual behavior. Counter to the common-sense assumption that being tired should impede the performance of active, effortful behaviors such as sex, we propose that tiredness may actually increase sexual risk-taking. Analyzing data from an online survey of 1113 HIV-negative GBM, we found that sex with casual partners most commonly occurred at night, especially among younger GBM and those with an evening chronotype, and that sex without condoms more often occurred at or later than one's usual time of feeling tired (as was reported by 44.2% of men) than did sex with condoms (reported by 36.6%). We also found that tiredness can increase sexual desire in many GBM (endorsed by 29.9%), and increases the likelihood of engaging in receptive positioning in anal sex (endorsed by almost 40% of men with a versatile sexual positioning identity). These findings highlight the importance of considering tiredness as a situational risk factor in sexual health-especially among younger GBM-and of counting sex among the behaviors that can be adversely impacted by poor or overdue sleep.

Can chronotype function as predictor of a persistent course of depressive and anxiety disorder?

BACKGROUND

The role of chronotype, the individual timing of sleep/activity, has been studied in relation to depressive and anxiety disorders. A cross-sectional association between a depressive episode and evening-type has been identified. However, until now the predicting capacity of chronotype concerning persistence of psychiatric disorders remains unclear. Our aim is to examine whether a later chronotype in patients with a depressive and/or anxiety disorder can serve as a predictor of a persistent course.

METHODS

A subsample of patients with a depressive and/or anxiety disorder diagnosis and chronotype data of the longitudinal Netherlands Study of Depression and Anxiety (NESDA) was used. Diagnosis of depressive and anxiety disorders (1-month DSM-IV based diagnosis) were determined at baseline (n = 505). From this group persistence was determined at 2-year (FU2) (persistent course: n = 248, non-persistent course: n = 208) and 4-year follow-up (FU4) (persistent course: n = 151, non-persistent course: n = 264). Chronotype was assessed at baseline with the Munich Chronotype Questionnaire.

RESULTS

A later chronotype did not predict a persistent course of depressive and/or anxiety disorder at FU2 (OR (95% CI) = 0.99 (0.83-1.19), P = 0.92) or at FU4 (OR (95% CI) = 0.94 (0.77-1.15), P = 0.57).

LIMITATIONS

Persistence was defined as having a diagnosis of depressive and/or anxiety disorder at the two-year and four-year follow-up, patients may have remitted and relapsed between assessments.

CONCLUSION

Chronotype, measured as actual sleep timing, of patients with a depressive or anxiety disorder did not predict a persistent course which suggests it might be unsuitable as predictive tool in clinical settings.

Sleep- and Wake-Promoting Drugs: Where Are They Being Sourced, and What Is Their Impact?

Background: Recent decades have seen both an increased number of shift workers in order to deliver services 24/7, and increased potential for social interactions at all hours of the day. People have sought to engage in strategies, which either promote vigilance or facilitate sleep, with the use of sleep- and wake-promoting drugs representing one strategy. Methods: We investigated use of sleep- and wake-promoting drugs in participants (n = 377) who completed a survey investigating the type and source of sleep- and wake-promoting drugs, and their impact on sleep and performance outcomes. Results: The most commonly reported wake-promoting drugs were amphetamine and dextroamphetamin salts, modafinil, and illicit substances including methamphetamine and cocaine, while the most commonly reported sleep-promoting drugs were benzodiazepines and antihistamines. Use of a sleep-promoting drug in the past month was associated with higher odds of having poorer sleep quality (OR = 3.15) and moderate-high insomnia (OR = 3.30), while use of a wake-promoting drug was associated with poor sleep quality (OR = 3.76), or making a fatigue-related error (OR = 2.65). Conclusions: These findings represent novel data on the use and source of sleep- and wake-promoting- drugs, and suggest that despite their use, poor sleep and performance outcomes persist, likely representing individuals struggling to keep up with the 24/7 world.

Diurnal changes in differential sensitivity and temporal resolution in morning-type and evening-type individuals with normal hearing

The present study attempts to determine diurnal changes by testing the differential sensitivity and temporal resolution in morning-type, evening-type, and intermediate-type individuals with normal hearing. Thirty participants with normal hearing were divided into morning-type, evening-type, and intermediate-type using “Morningness–Eveningness Questionnaire”. The tests of differential sensitivity and temporal resolution were administered to all the participants in the morning and evening, respectively. The differences in the test results between different timing across all the three groups were analyzed. The results of the study showed that there was a significant diurnal effect on psychoacoustic tests as morning-type individuals performed better when tested in morning and evening-type performed better when they were tested in evening. However, there was no diurnal effect found in intermediate group. The lack of inhibitory control and poor cognitive load in off peak time could have lead to poor scores. Thus, the variable of diurnal effects should be considered in further studies on psychoacoustic tests, especially in young adults. Furthermore, studies could be performed to explore diurnal effects on objective audiological tests in a larger group of population in the future.

Subjectively-defined optimal/non-optimal time of day modulates controlled but not automatic retrieval processes in verbal memory

Performance for controlled, resource-demanding retrieval in episodic memory has been consistently found to be better at an optimal compared with non-optimal time of the day, evidencing a synchrony effect. However, performance in memory tasks in which retrieval is mostly based on automatic processes was inconclusively found either to be better at a non-optimal time of day or independent of synchrony effects. A caveat in most prior studies is that optimal/non-optimal time of day is based on morningness-eveningness composite scores derived from chronotype questionnaires, which might not efficiently predict subjectively-defined cognitive efficiency periods. An additional caveat is that separate tasks are used to assess explicit and implicit retrieval in verbal memory. Indeed, no task is process-pure, and both controlled and automatic retrieval processes may potentially contribute to retrieval scores in different types of memory tasks. In the present study, we investigated the impact of individually defined subjective optimal/non-optimal time of day on verbal memory retrieval, using an adaptation of the Process-Dissociation Procedure that allows estimating the respective contributions of automatic and controlled memory retrieval processes within the same memory task. Our results disclose a higher involvement of controlled processes at subjectively optimal compared with non-optimal time of day, but no differences for automatic processes. Synchrony effects and subjectively-defined peaks and troughs of performance for controlled components of memory retrieval should be considered in the evaluation of episodic memory.

The role of chronotype, circadian misalignment, and tiredness in the substance use behaviors of gay and bisexual men

Although the potential of alcohol and drugs to detrimentally affect sleep has been established, the potential of tiredness to in turn influence substance use has received less attention. We contend that tiredness increases risk for substance use because tiredness impairs self-regulation and heightens the utility of substances to combat tiredness, albeit temporarily-and that these links are especially important because decision-making regarding use often occurs late at night when people are tired. Accordingly, we investigated chronotype, circadian misalignment, and perceived tiredness as risk factors in substance use among gay and bisexual men (GBM). We analyzed two online survey datasets-one of 3,696 GBM and one of 1,113 GBM-asking participants about their time for most frequently using alcohol or club/party drugs, their chronotype, whether they use substances to stay awake, and use severity. Alcohol use and club/party drug use most often occurred from 9pm onwards (for 51.3% and 75.1% of men, respectively), especially among younger men and evening types. Further, many men with a morning chronotype reported most often using alcohol (33.2%) and drugs (64.7%) from 9pm onwards, implicating circadian misalignment. Additionally, feeling tired was a motivator of alcohol use and drug use (for 53.1% and 26.9% of men, respectively), especially among younger men. Finally, those endorsing this motivation had greater use severity. These findings highlight the importance of chronotype, circadian misalignment, and tiredness in substance use, especially among younger men. We therefore recommend including substance use among the behaviors adversely affected by tiredness from circadian misalignment and inadequate/overdue sleep.

A Mobile App Delivering a Gamified Battery of Cognitive Tests Designed for Repeated Play (OU Brainwave): App Design and Cohort Study

BACKGROUND

Mobile phone and tablet apps are an increasingly common platform for collecting data. A key challenge for researchers has been participant "buy-in" and attrition for designs requiring repeated testing.

OBJECTIVE

The objective of this study was to develop and assess the utility of 1-2 minute versions of both classic and novel cognitive tasks using a user-focused and user-driven mobile phone and tablet app designed to encourage repeated play.

METHODS

A large sample of app users (N=13,979 at first data collection) participated in multiple, self-paced sessions of classic working memory (N-back), spatial cognition (mental rotation), sustained attentional focus (persistent vigilance task), and split attention (multiple object tracking) tasks, along with the implementation of a comparatively novel action-learning task. The "OU Brainwave" app was designed to measure time-of-day variation in cognitive performance and did not offer any training program or promise any cognitive enhancement. To record participants' chronotype, a full Morningness-Eveningness questionnaire was also included, which measures whether a person's circadian rhythm produces peak alertness in the morning, in the evening, or in between. Data were collected during an 18-month period. While the app prompted re-engagement at set intervals, participants were free to complete each task as many times as they wished.

RESULTS

We found a significant relationship between morningness and age (r=.298, n=12,755, P<.001), with no effect of gender (t_13,539=-1.036, P=.30). We report good task adherence, with ~4000 participants repeatedly playing each game >4 times each-our minimum engagement level for analysis. Repeated plays of these games allowed us to replicate commonly reported gender effects in gamified spatial cognition (F_1,4216=154.861, P<.001, η²_ρ=.035), split attention (F_1,4185=11.047, P=.001, η²_ρ=.003), and sustained attentional focus (F_1,4238=15.993, P<.001, η²_ρ=.004) tasks. We also report evidence of a small gender effect in an action-learning task (F_1,3988=90.59, P<.001, η²_ρ=.022). Finally, we found a strong negative effect of self-reported age on performance, when controlling for number of plays, in sustained attentional focus (n=1596, F_6,1595=30.23, P<.001, η²=.102), working memory (n=1627, F_6,1626=19.78, P<.001, η²=.068), spatial cognition (n=1640, F_6,1639=23.74, P<.001, η²=.080), and split attention tasks (n=1616, F_6,1615=2.48, P=.02, η²=.009).

CONCLUSIONS

Using extremely short testing periods and permitting participants to decide their level of engagement-both in terms of which gamified task they played and how many sessions they completed-we were able to collect a substantial and valid dataset. We suggest that the success of OU Brainwave should inform future research oriented apps-particularly in issues of balancing participant engagement with data fidelity.

Unraveling the Biopsychosocial Factors of Fatigue and Sleep Problems After Traumatic Brain Injury: Protocol for a Multicenter Longitudinal Cohort Study

Background

Fatigue and sleep problems are common after a traumatic brain injury (TBI) and are experienced as highly distressing symptoms, playing a significant role in the recovery trajectory, and they can drastically impact the quality of life and societal participation of the patient and their family and friends. However, the etiology and development of these symptoms are still uncertain.

Objective

The aim of this study is to examine the development of fatigue and sleep problems following moderate to severe TBI and to explore the changes in underlying biological (pain, brain damage), psychological (emotional state), and social (support family, participation) factors across time.

Methods

This study is a longitudinal multicenter observational cohort study with 4 measurement points (3, 6, 12, and 18 months postinjury) including subjective questionnaires and cognitive tasks, preceded by 7 nights of actigraphy combined with a sleep diary. Recruitment of 137 moderate to severe TBI patients presenting at emergency and neurology departments or rehabilitation centers across the Netherlands is anticipated. The evolution of fatigue and sleep problems following TBI and their association with possible underlying biological (pain, brain damage), psychological (emotional state), and social (support family, participation) factors will be examined.

Results

Recruitment of participants for this longitudinal cohort study started in October 2017, and the enrollment of participants is ongoing. The first results are expected at the end of 2020.

Conclusions

To the authors’ knowledge, this is the first study that examines the development of both post-TBI fatigue and sleep longitudinally within a biopsychosocial model in moderate to severe TBI using both subjective and objective measures. Identification of modifiable factors such as mood and psychosocial stressors may give direction to the development of interventions for fatigue and sleep problems post-TBI.

Trial Registration

Netherlands Trial Register NTR7162; http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=7162 (Archived by WebCite at http://www.webcitation.org/6z3mvNLuy)

International Registered Report Identifier (IRRID)

RR1-10.2196/11295

Does the Improvement of Position Sense Following Motor Imagery Practice Vary as a Function of Age and Time of Day?

The effectiveness of motor imagery practice is known to depend on age and on the ability to form motor images. In the same individual, motor imagery quality changes during the day, being better late in the morning for older adults and in the afternoon for younger adults. Does this mean that motor imagery practice should be done at specific time of the day depending on the age of participants to maximize motor learning? To examine whether the effect of motor imagery practice varies as a function of time of day and age, the authors used an arm configuration reproduction task and measured position sense accuracy before and after 135 kinesthetic motor imagery trials. Younger and older participants were randomly assigned to either a morning or an afternoon session. Data showed that the accuracy for reproducing arm configurations improved following imagery practice regardless of time of day for both younger and older adults. Moreover, the authors observed that the position sense was less accurate in the afternoon than in the morning in older participants (before and after motor imagery practice), while performance did not change during the day in younger participants. These results may have practical implications in motor learning and functional rehabilitation programs. They highlight the effectiveness of motor imagery practice for movement accuracy in both younger and older adults regardless of time of day. By contrast, they reveal that the assessment of position sense requires that the time of day be taken into account when practitioners want to report on the older patients' progress without making any mistakes.

Comprehensive Neuropsychological Assessment of Cognitive Functioning of Adults With Lower Limb Amputation in Rehabilitation

OBJECTIVE

To establish a comprehensive profile of cognitive functioning in people engaged in lower limb amputation (LLA) rehabilitation.

DESIGN

Cross-sectional study as part of a longitudinal prospective cohort.

SETTING

A national tertiary rehabilitation hospital.

PARTICIPANTS

Adult volunteer participants (N=87) referred for comprehensive rehabilitation for major LLA were sampled from 207 consecutive admissions. Participants with both vascular (n=69) and nonvascular (n=18) LLA etiologies were included.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Demographic and health information and a battery of standardized neuropsychological assessments.

RESULTS

Compared to normative data, impairment was evident in overall cognitive functioning (P≤.003). Impairment was also evident in particular areas, including reasoning, psychomotor function, information processing, attention, memory, language/naming, visuospatial functions, and executive functions (all P≤.003 Holm-corrected). There were also higher frequencies of impaired functions across most aspects of functioning in this group compared with expected frequencies in normative data (P≤.003 Holm-corrected). There were no significant differences in cognitive functioning between participants of vascular and nonvascular LLA etiology.

CONCLUSIONS

Findings support the need for cognitive screening at rehabilitation admission regardless of etiology. Administration of comprehensive neuropsychological assessment with a battery sensitive to vascular cognitive impairment is recommended in some cases to generate an accurate and precise understanding of relative strengths and weaknesses in cognitive functioning. Cognitive functioning is a potential intervention point for improvement of rehabilitation outcomes for those with LLA, and further research is warranted in this area.

Cognitive performance in DSWPD patients upon awakening from habitual sleep compared with forced conventional sleep

Difficult early morning awakening is one of the defining symptoms of delayed sleep-wake phase disorder. It is accompanied by low cognitive arousal and drowsiness resulting in difficulty concentrating and focusing attention upon awakening. We designed the current study to quantitate cognitive performance (i.e. omissions, commissions, reaction time [average and variability]) and cognitive domains (i.e. focused attention, sustained attention, impulsivity and vigilance) with Conners' Continuous Performance Test II during both habitual and conventional (00:00-07:00 hr) sleep-wake schedule in young adult patients with delayed sleep-wake phase disorder (n = 20, mean age = 24.8 years, SD = 3.0) and controls (n = 16, mean age = 24.4 years, SD = 3.4). Conners' Continuous Performance Test II was administered after awakening and in the afternoon during both habitual and conventional conditions. In-laboratory polysomnography was performed for 2 nights. We assessed sleep, tiredness, chronotype and depression using questionnaires. Saliva was sampled for dim light melatonin onset measurements. Repeated-measures ANOVAs were applied for the Conners' Continuous Performance Test II measures with group (patient/control), time (afternoon/morning) and condition (habitual/conventional schedule) as fixed factors. Patients with delayed sleep-wake phase disorder had reduced reaction times, especially in the morning, greater response speed variability, and made more omission and commission errors compared with controls. Patients with delayed sleep-wake phase disorder also had reduced focused attention, especially upon forced early awakening. The short total sleep time of patients with delayed sleep-wake phase disorder could not statistically explain this outcome. In conclusion, we observed a state-dependent reduced ability to focus attention upon early morning awakening in patients with delayed sleep-wake phase disorder. Patients also had more omissions, longer reaction time and increased RT variability after habitual sleep, suggesting a possible small cognitive trait dysfunction in delayed sleep-wake phase disorder.

The role of sleep in emotional memory processing in middle age

Sleep benefits memory in young adults, and this effect may be particularly strong for representations associated with negative emotion. Many aspects of sleep important for memory consolidation change with aging, particularly by middle age, suggesting that sleep-related consolidation may be reduced. However, the influence of sleep on memory has rarely been investigated in a middle-aged population. In the current study, young and middle-aged adults viewed negative and neutral pictures and underwent a recognition test after sleep or wake. Subjective emotional reactivity was also measured. Compared to waking, sleep benefited memory in young adults. Performance did not differ between sleep and wake groups in middle-aged adults, and it matched the level of young adults who slept. The effect of sleep versus wake was not influenced by memory valence in either age group. These results suggest the relative influence of sleep compared to wake on memory declines with aging, specifically by middle age, and that this decline extends to negative memory.

Subjective time expansion with increased stimulation of intrinsically photosensitive retinal ganglion cells

Intrinsically photosensitive retinal ganglion cells (ipRGCs) contain photoreceptors that are especially sensitive to blue light. Nevertheless, how blue light and ipRGCs affect time perception remains unsolved. We used the oddball paradigm and manipulated the background light to examine whether and how blue light and ipRGCs affect perceived duration. In the oddball paradigm, participants were asked to judge the duration of the target (oddball), compared to that of the standard, with a two alternative-forced-choice procedure. When the background light was controlled to be either blue or red in Experiment 1, results showed that blue light led to longer subjective duration compared to red light. Experiment 2 further clarified the contribution of the ipRGCs. A set of multi-primary projector system that could manipulate the ipRGC stimulation were used, while the color and luminance of the background lights were kept constant throughout. Results showed that increased stimulation of ipRGCs under metameric background expanded subjective time. These results suggest that ipRGC stimulation increases arousal/attention so as to expand subjective duration.