Evaluation of sleep strategies between night shifts in actual shift workers.

OBJECTIVES: The aim of this observational study was to examine sleep obtained between consecutive night shifts from shift workers in their natural environment. The goal was to identify the various sleep strategies and the timing, duration, regularity, and quality of sleep associated with the strategies. METHODS: Participants (N = 33, 23 women, aged 40 ± 15years) reported their sleep information in daily diaries over 2weeks while working at least one series of consecutive night shifts. Sleep timing, duration, quality, and regularity were calculated for each sleep episode between consecutive night shifts. RESULTS: Based on the reported sleep behavior, shift workers were categorized as either morning, delayed, split- or mixed sleepers. We found significant differences between the groups in timing of sleep, feeling refreshed, and regularity of sleep between consecutive night shifts, whereas duration and subjective soundness of sleep did not show significant differences. CONCLUSIONS: In this sample, four sleep strategies were observed between consecutive night shifts in actual shift workers. These observations may help design future interventions to improve sleep that are individualized to the worker.

Entrainment to gradual vs. immediate 8-hour phase advance shifts with and without short-wavelength enriched polychromatic green light.

OBJECTIVES: For optimal health and well-being the sleep episode and the circadian timing system should be properly aligned. We evaluated the effectiveness of different dynamic light and sleep/wake shift schedules for rapid circadian entrainment following an 8-hour advance of sleep. METHODS: Forty-three healthy participants completed an 8-day inpatient protocol in which the 8-hour sleep episode was advanced by 8 hours. Participants were assigned to one of five conditions: (1) dim ambient WHITE light and GRADUAL shift in which the sleep episode was incrementally advanced over 5days; (2) dim GREEN, short-wavelength (∼504 nm) polychromatic light and GRADUAL shift; (3) dim WHITE light and SLAM shift, including an abrupt 8-hour advance on day 3 following an extended 32-hour wake episode; (4) GREEN light and SLAM shift; or (5) COMBINED (higher illuminance WHITE plus GREEN) light and modified SLAM shift with 2 short naps scheduled on the day prior to the abrupt advance. Phase shifts of the plasma dim light melatonin onset and sleep measures were compared to examine effects of protocol condition. RESULTS: After 5days, the COMBINED light/modified SLAM shift condition showed larger phase advances of dim light melatonin onset (4.02 ± 1.13 hours) compared to the other 4 conditions (range 1.50 ± 0.96-2.83 ± 2.23 hours; p < .05) and resulted in increased REM sleep duration and fewer sleep disruptions. CONCLUSIONS: Consideration of the type of shift and the illuminance and wavelength of light may assist in designing lighting countermeasures to sleep and circadian disruption, which has implications for jetlag, shiftwork, and circadian rhythm sleep disorders.

Influence of circadian phase and extended wakefulness on glucose levels during forced desynchrony.

OBJECTIVES: Circadian misalignment and sleep deprivation often occur in tandem, and both negatively impact glucose homeostasis and metabolic health. The present study employed a forced desynchrony protocol to examine the influence of extended wakefulness and circadian misalignment on hourly glucose levels. METHODS: Nine healthy adults (4F/5M; 26 ± 4years) completed a 31-day in-laboratory protocol. After three 24 hour baseline days with 8 hours scheduled sleep opportunities, participants were scheduled to 14 consecutive 42.85 hour sleep-wake cycles, with 28.57 hours extended wakefulness and 14.28 hours sleep opportunities each cycle. Blood was sampled hourly across the forced desynchrony and over 600 plasma samples per participant were analyzed for glucose levels. RESULTS: Both hours into the 42.85 hours forced desynchrony day and circadian phase modulated glucose levels (p < .0001). Glucose peaked after each meal during scheduled wakefulness and decreased during scheduled sleep/fasting. Glucose levels were, on average, lowest during the biological daytime and rose throughout the biological night, peaking in the biological morning. When analyzed separately for scheduled sleep vs. wakefulness, the peak timing of the circadian rhythm in glucose was later during sleep (p < .05). Glucose area under the curve levels increased rapidly from the beginning of the forced desynchrony protocol and were highest on the second forced desynchrony day (p < .01), returning towards forced desynchrony day 1 levels thereafter. CONCLUSIONS: These findings have important implications for understanding factors contributing to altered glucose metabolism during sleep loss and circadian misalignment, and for potential physiological adaptation of metabolism in healthy adults, who are increasingly exposed to such conditions in our society.

Circadian- and wake-dependent influences on face-name memory in healthy men and women over 3weeks of chronic sleep restriction.

OBJECTIVES: Facial recognition is one of the key functions of the human brain, and linking a face to a name is critical in many social and occupational settings. This study assessed circadian- and wake-dependent effects on face-name recognition in healthy adults. METHODS: Thirteen healthy adults (20-70years; 7 F) were studied in a 39-day inpatient protocol that included 3weeks of 28 hours forced desynchrony with sleep restriction (6.5:21.5 hours sleep:wake). Starting 3 hours after scheduled wake, 6 novel face-name pairs were presented every 4 waking hours; recognition was tested 2 hours later. Performance data were averaged across ∼4 hours circadian phase or time-awake bins. RESULTS: Face-name recognition deteriorated with increased time awake (p < .0001) and exhibited significant circadian variation (p < .0001), with worst performance shortly after the core temperature nadir. There was a significant interaction between sex and circadian phase (p = .0177), with women performing significantly better than men at all circadian phases except 60° and 120°. Women exhibited a significantly higher amplitude than men during the third week of forced desynchrony (p < .01). CONCLUSIONS: Like many other aspects of neurobehavioral performance, recalling face-name associations is impacted by both duration of time awake and circadian phase. These results have implications for face recognition testing in medical contexts, such as in testing for dementia, because performance may be impacted by sleep deficiency and the time of testing.

Desynchronizing the sleep---wake cycle from circadian timing to assess their separate contributions to physiology and behaviour and to estimate intrinsic circadian period.

Circadian clocks drive cyclic variations in many aspects of physiology, but some daily variations are evoked by periodic changes in the environment or sleep-wake state and associated behaviors, such as changes in posture, light levels, fasting or eating, rest or activity and social interactions; thus, it is often important to quantify the relative contributions of these factors. Yet, circadian rhythms and these evoked effects cannot be separated under typical 24-h day conditions, because circadian phase and the length of time awake or asleep co-vary. Nathaniel Kleitman's forced desynchrony (FD) protocol was designed to assess endogenous circadian rhythmicity and to separate circadian from evoked components of daily rhythms in multiple parameters. Under FD protocol conditions, light intensity is kept low to minimize its impact on the circadian pacemaker, and participants have sleep-wake state and associated behaviors scheduled to an imposed non-24-h cycle. The period of this imposed cycle, Τ, is chosen so that the circadian pacemaker cannot entrain to it and therefore continues to oscillate at its intrinsic period (τ, ~24.15 h), ensuring circadian components are separated from evoked components of daily rhythms. Here we provide detailed instructions and troubleshooting techniques on how to design, implement and analyze the data from an FD protocol. We provide two procedures: one with general guidance for designing an FD study and another with more precise instructions for replicating one of our previous FD studies. We discuss estimating circadian parameters and quantifying the separate contributions of circadian rhythmicity and the sleep-wake cycle, including statistical analysis procedures and an R package for conducting the non-orthogonal spectral analysis method that enables an accurate estimation of period, amplitude and phase.

High dose melatonin increases sleep duration during nighttime and daytime sleep episodes in older adults.

Aging is associated with changes in sleep, and improving sleep may have important consequences for the health, cognition, and quality of life of older adults. Many prescription sleep aids increase the risk of nighttime falls, have adverse effects on next-day cognition, and are associated with increased mortality. Melatonin, a hormone secreted at night, increases sleep duration in young adults but only when administered during the day when endogenous levels are low. In a month-long cross-over study, we randomized 24 healthy older (age >55, mean 64.2 ± 6.3 years) participants to receive 2 weeks of placebo and 2 weeks of either a low (0.3 mg) or high (5.0 mg) dose of melatonin 30 min before lights out. Sleep was polysomnographically recorded and was scheduled during both the biological day and night using a forced desynchrony design. Although 0.3 mg melatonin had a trend towards increasing sleep efficiency (SE) overall, this was due to its effects on sleep during the biological day. In contrast, 5 mg melatonin significantly increased SE during both biological day and night, mainly by increasing the duration of Stage 2 non-rapid eye movement sleep and slightly shortening awakenings. Melatonin should be further explored as a sleep aid for older adults.

Impact of chronic sleep restriction on sleep continuity, sleep structure, and neurobehavioral performance.

Chronic sleep restriction (CSR) has been associated with adverse effects including cognitive impairment and increased risk of diabetes and cardiovascular disease. Yet, sleep restriction therapy is an essential component of most behavioral treatments for insomnia. Moreover, little is known about the impact of CSR on sleep continuity and structure in healthy people whose need for sleep is satiated. We investigated the impact of CSR on sleep continuity and structure in nine healthy participants. They had 4 nights of sleep extension, 2 nights of post-extension sleep, 21 nights of CSR (5/5.6-hour time-in-bed), and 9 nights of recovery sleep. Compared to postextension sleep, during CSR sleep duration was reduced by 95.4 ±â€…21.2 min per night, Slow-Wave Activity was significantly increased, and sleep was more consolidated. During recovery, sleep duration was increased by 103.3 ±â€…23.8 min compared to CSR, and the CSR-induced increase in Slow-Wave Activity persisted, particularly after the 5-hour exposure. Yet, we found that sustained vigilant attention was not fully recovered even after nine nights of recovery sleep. Our results suggest that CSR improves traditional metrics of sleep quality and may have a persistent impact on sleep depth, which is consistent with the reported benefits on sleep continuity and structure of sleep restriction therapy. However, these improvements in traditional metrics of sleep quality were associated with deterioration rather than improvement in neurobehavioral performance, demonstrating that sleep duration should be included in assessments of sleep quality. These results have implications for the long-term use of sleep restriction in the behavioral treatment of insomnia. Clinical Trial Registration: Impact of Chronic Circadian Disruption vs. Chronic Sleep Restriction on Metabolism (https://clinicaltrials.gov/ct2/show/; #NCT02171273).

Efficacy of intermittent exposure to bright light for treating maladaptation to night work on a counterclockwise shift work rotation.

OBJECTIVES: Rotating shift work is associated with adverse outcomes due to circadian misalignment, sleep curtailment, work-family conflicts, and other factors. We tested a bright light countermeasure to enhance circadian adaptation on a counterclockwise rotation schedule. METHODS: Twenty-nine adults (aged 20-40 years; 15 women) participated in a 4-week laboratory simulation with weekly counterclockwise transitions from day, to night, to evening, to day shifts. Each week consisted of five 8-hour workdays including psychomotor vigilance tests, two days off, designated 8-hour sleep episodes every day, and an assessment of circadian melatonin secretion. Participants were randomized to a treatment group (N=14), receiving intermittent bright light during work designed to facilitate circadian adaptation, or a control group (N=15) working in indoor light. Adaptation was measured by how much of the melatonin secretion episode overlapped with scheduled sleep timing. RESULTS: On the last night shift, there was a greater overlap between melatonin secretion and scheduled sleep time in the treatment group [mean 4.90, standard deviation (SD) 2.8 hours] compared to the control group (2.62, SD 2.8 hours; P=0.002), with night shift adaptation strongly influenced by baseline melatonin timing (r2=-0.71, P=0.01). While the control group exhibited cognitive deficits on the last night shift, the treatment group's cognitive deficits on the last night and evening shifts were minimized. CONCLUSIONS: In this laboratory setting, intermittent bright light during work hours enhanced adaptation to night work and subsequent readaptation to evening and day work. Light regimens scheduled to shift circadian timing should be tested in actual shift workers on counterclockwise schedules as a workplace intervention.

Young adults are more vulnerable to chronic sleep deficiency and recurrent circadian disruption than older adults.

More than a third of US adults report fewer than 6 hours of sleep a night, making chronic sleep restriction a growing public health concern. Sleep curtailment is associated with an increase in industrial accidents, motor vehicle accidents, medical and other occupational errors. Young adults are more vulnerable to acute sleep deprivation than older adults, but less is known about how young vs. older adults respond to the more commonly experienced chronic sleep restriction. To test the hypothesis that young adults are more vulnerable to chronic sleep loss than older adults, we compared data from young and older adults who underwent three weeks of chronic sleep restriction (equivalent to 5.6 hours/24 hours) combined with recurrent circadian disruption in an experiment that enabled us to separate the influences of the sleep-wake homeostatic process, the circadian timing system, and the chronic sleep deficit. We found that while young and older adults reported similar levels of subjective sleepiness, objective measures of sleepiness revealed that young adults were more vulnerable and had more attentional failures than the older adults. These results have important public health implications, particularly related to prevention of sleep-related motor vehicle crashes in young drivers. Further research is needed to understand the neurobiological basis of these age-related differences.

Improved cognitive morning performance in healthy older adults following blue-enriched light exposure on the previous evening.

OBJECTIVES: Exposure to light can have acute alerting and circadian phase-shifting effects. This study investigated the effects of evening exposure to blue-enriched polychromatic white (BEL) vs. polychromatic white light (WL) on sleep inertia dissipation the following morning in older adults. METHODS: Ten healthy older adults (average age = 63.3 yrs; 6F) participated in a 13-day study comprising three baseline days, an initial circadian phase assessment, four days with 2-h evening light exposures, a post light exposure circadian phase assessment and three recovery days. Participants were randomized to either BEL or WL of the same irradiance for the four evening light exposures. On the next mornings at 2, 12, 22 and 32 min after each wake time, the participants completed a 90-s digit-symbol substitution test (DSST) to assess working memory, and objective alertness was assessed using a wake EEG recording. DSST and power density from the wake EEG recordings were compared between the two groups. RESULTS: DSST performance improved with time awake (p < 0.0001) and across study days in both light exposure groups (p < 0.0001). There was no main effect of group, although we observed a significant day x group interaction (p = 0.0004), whereby participants exposed to BEL performed significantly better on the first two mornings after light exposures than participants in WL (post-hoc, p < 0.05). On those days, the BEL group showed higher EEG activity in some of the frequency bins in the sigma and beta range (p < 0.05) on the wake EEG. CONCLUSION: Exposure to blue-enriched white light in the evening significantly improved DSST performance the following morning when compared to polychromatic white light. This was associated with a higher level of objective alertness on the wake EEG, but not with changes in sleep or circadian timing.

Self-reported Drowsiness and Safety Outcomes While Driving After an Extended Duration Work Shift in Trainee Physicians.

STUDY OBJECTIVES: Extended duration (≥24 hours) work shifts (EDWSs) are associated with increased risk of motor vehicle crashes, and awareness of any impairment has important implications on legal accountability for any adverse driving outcome. The extent to which adverse driving events were preceded by predrive self-reported sleepiness was evaluated in medical residents after an EDWS. METHODS: Sixteen resident physicians (10 females; 29.2 ± 2.0 years) working EDWS were monitored when driving on their commute to and from the hospital (438 drives). Sleep and work hours were obtained from daily logs, and adverse driving outcomes were captured from a driving log completed at the end of each drive. Self-reported sleepiness (Karolinska Sleepiness Scale; KSS) and objective drowsiness were captured using a time-stamped, hand-held device and infra-red reflectance oculography. RESULTS: Self-reported sleepiness and objective indices of drowsiness were positively correlated, and both were elevated following EDWSs. Compared with the commute to work, EDWSs were associated with more than double the self-reported adverse outcomes when driving home, significantly higher than drives to or from the day shift at comparable times of day. EDWSs more than tripled the odds of reporting sleep-related, inattentive, hazardous, or violation-driving events. The number and type of adverse event was predicted by the predrive KSS level and in a dose-dependent manner. CONCLUSIONS: Driving after an EDWS puts resident physicians/drivers and other road users at avoidable and unnecessary risk. Demonstrating self-reported sleepiness at the beginning of the drive is associated with adverse outcomes has serious implications on the legal accountability for driving when drowsy.

A new face of sleep: The impact of post-learning sleep on recognition memory for face-name associations.

Sleep has been demonstrated to improve consolidation of many types of new memories. However, few prior studies have examined how sleep impacts learning of face-name associations. The recognition of a new face along with the associated name is an important human cognitive skill. Here we investigated whether post-presentation sleep impacts recognition memory of new face-name associations in healthy adults. Fourteen participants were tested twice. Each time, they were presented 20 photos of faces with a corresponding name. Twelve hours later, they were shown each face twice, once with the correct and once with an incorrect name, and asked if each face-name combination was correct and to rate their confidence. In one condition the 12-h interval between presentation and recall included an 8-h nighttime sleep opportunity ("Sleep"), while in the other condition they remained awake ("Wake"). There were more correct and highly confident correct responses when the interval between presentation and recall included a sleep opportunity, although improvement between the "Wake" and "Sleep" conditions was not related to duration of sleep or any sleep stage. These data suggest that a nighttime sleep opportunity improves the ability to correctly recognize face-name associations. Further studies investigating the mechanism of this improvement are important, as this finding has implications for individuals with sleep disturbances and/or memory impairments.

Sleep inertia, sleep homeostatic and circadian influences on higher-order cognitive functions.

Sleep inertia, sleep homeostatic and circadian processes modulate cognition, including reaction time, memory, mood and alertness. How these processes influence higher-order cognitive functions is not well known. Six participants completed a 73-day-long study that included two 14-day-long 28-h forced desynchrony protocols to examine separate and interacting influences of sleep inertia, sleep homeostasis and circadian phase on higher-order cognitive functions of inhibitory control and selective visual attention. Cognitive performance for most measures was impaired immediately after scheduled awakening and improved during the first ~2-4 h of wakefulness (decreasing sleep inertia); worsened thereafter until scheduled bedtime (increasing sleep homeostasis); and was worst at ~60° and best at ~240° (circadian modulation, with worst and best phases corresponding to ~09:00 and ~21:00 hours, respectively, in individuals with a habitual wake time of 07:00 hours). The relative influences of sleep inertia, sleep homeostasis and circadian phase depended on the specific higher-order cognitive function task examined. Inhibitory control appeared to be modulated most strongly by circadian phase, whereas selective visual attention for a spatial-configuration search task was modulated most strongly by sleep inertia. These findings demonstrate that some higher-order cognitive processes are differentially sensitive to different sleep-wake regulatory processes. Differential modulation of cognitive functions by different sleep-wake regulatory processes has important implications for understanding mechanisms contributing to performance impairments during adverse circadian phases, sleep deprivation and/or upon awakening from sleep.

Prevalence of sleep deficiency and use of hypnotic drugs in astronauts before, during, and after spaceflight: an observational study.

BACKGROUND: Sleep deprivation and fatigue are common subjective complaints among astronauts. Previous studies of sleep and hypnotic drug use in space have been limited to post-flight subjective survey data or in-flight objective data collection from a small number of crew members. We aimed to characterise representative sleep patterns of astronauts on both short-duration and long-duration spaceflight missions. METHODS: For this observational study, we recruited crew members assigned to Space Transportation System shuttle flights with in-flight experiments between July 12, 2001, and July 21, 2011, or assigned to International Space Station (ISS) expeditions between Sept 18, 2006, and March 16, 2011. We assessed sleep-wake timing objectively via wrist actigraphy, and subjective sleep characteristics and hypnotic drug use via daily logs, in-flight and during Earth-based data-collection intervals: for 2 weeks scheduled about 3 months before launch, 11 days before launch until launch day, and for 7 days upon return to Earth. FINDINGS: We collected data from 64 astronauts on 80 space shuttle missions (26 flights, 1063 in-flight days) and 21 astronauts on 13 ISS missions (3248 in-flight days), with ground-based data from all astronauts (4014 days). Crew members attempted and obtained significantly less sleep per night as estimated by actigraphy during space shuttle missions (7·35 h [SD 0·47] attempted, 5·96 h [0·56] obtained), in the 11 days before spaceflight (7·35 h [0·51], 6·04 h [0·72]), and about 3 months before spaceflight (7·40 h [0·59], 6·29 h [0·67]) compared with the first week post-mission (8·01 h [0·78], 6·74 h [0·91]; p<0·0001 for both measures). Crew members on ISS missions obtained significantly less sleep during spaceflight (6·09 h [0·67]), in the 11 days before spaceflight (5·86 h [0·94]), and during the 2-week interval scheduled about 3 months before spaceflight (6·41 h [SD 0·65]) compared with in the first week post-mission (6·95 h [1·04]; p<0·0001). 61 (78%) of 78 shuttle-mission crew members reported taking a dose of sleep-promoting drug on 500 (52%) of 963 nights; 12 (75%) of 16 ISS crew members reported using sleep-promoting drugs. INTERPRETATION: Sleep deficiency in astronauts was prevalent not only during space shuttle and ISS missions, but also throughout a 3 month preflight training interval. Despite chronic sleep curtailment, use of sleep-promoting drugs was pervasive during spaceflight. Because chronic sleep loss leads to performance decrements, our findings emphasise the need for development of effective countermeasures to promote sleep. FUNDING: The National Aeronautics and Space Administration.

Assessment of drowsiness based on ocular parameters detected by infrared reflectance oculography.

STUDY OBJECTIVES: Numerous ocular parameters have been proposed as reliable physiological markers of drowsiness. A device that measures many of these parameters and then combines them into a single metric (the Johns Drowsiness Scale [JDS]) is being used commercially to assess drowsiness in professional drivers. Here, we examine how these parameters reflect changes in drowsiness, and how they relate to objective and subjective indices of the drowsy state in a controlled laboratory setting. DESIGN: A within subject prospective study. PARTICIPANTS: 29 healthy adults (18 males; mean age 23.3 ± 4.6 years; range 18-34 years). INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Over the course of a 30-h extended wake vigil under constant routine (CR) conditions, participants were monitored using infrared reflectance oculography (Optalert) and completed bi-hourly neurobehavioral tests, including the Karolinska Sleepiness Scale (KSS) and Psychomotor Vigilance Task (PVT). Ocular-defined increases in drowsiness were evident with extended time awake and during the biological night for all ocular parameters; JDS being the most sensitive marker of drowsiness induced by sleep regulatory processes (p < 0.0001). In addition, the associations between JDS in the preceding 10-min period and subsequent PVT lapses and KSS were stronger (AUC 0.74/0.80, respectively) than any other ocular metric, such that PVT lapses, mean response time (RT), and KSS increased in a dose-response manner as a function of prior JDS score (p < 0.0001). CONCLUSIONS: Ocular parameters captured by infrared reflectance oculography detected fluctuations in drowsiness due to time awake and during the biological night. The JDS outcome was the strongest predictor of drowsiness among those tested, and showed a clear association to objective and subjective measures of drowsiness. Our findings indicate this real-time objective drowsiness monitoring system is an effective tool for monitoring changes in alertness and performance along the alert-drowsy continuum in a controlled laboratory setting.

The effects of circadian phase, time awake, and imposed sleep restriction on performing complex visual tasks: evidence from comparative visual search.

Cognitive performance not only differs between individuals, but also varies within them, influenced by factors that include sleep-wakefulness and biological time of day (circadian phase). Previous studies have shown that both factors influence accuracy rather than the speed of performing a visual search task, which can be hazardous in safety-critical tasks such as air-traffic control or baggage screening. However, prior investigations used simple, brief search tasks requiring little use of working memory. In order to study the effects of circadian phase, time awake, and chronic sleep restriction on the more realistic scenario of longer tasks requiring the sustained interaction of visual working memory and attentional control, the present study employed two comparative visual search tasks. In these tasks, participants had to detect a mismatch between two otherwise identical object distributions, with one of the tasks (mirror task) requiring an additional mental image transformation. Time awake and circadian phase both had significant influences on the speed, but not the accuracy of task performance. Over the course of three weeks of chronic sleep restriction, speed but not accuracy of task performance was impacted. The results suggest measures for safer performance of important tasks and point out the importance of minimizing the impact of circadian phase and sleep-wake history in laboratory vision experiments.

One night of sleep deprivation affects reaction time, but not interference or facilitation in a Stroop task.

The Stroop color-naming task is one of the most widely studied tasks involving the inhibition of a prepotent response, regarded as an executive function. Several studies have examined performance on versions of the Stroop task under conditions of acute sleep deprivation. Though these studies revealed effects on Stroop performance, the results often do not differentiate between general effects of sleep deprivation on performance and effects specifically on interference in the Stroop task. To examine the effect of prolonged wakefulness on performance on the Stroop task, we studied participants in a 40-h "constant routine" protocol during which they remained awake in constant conditions and performed a Stroop color-naming task every two hours. We found that reaction time was slowest when the color and word did not match (incongruent), fastest when the color and word did match (congruent), and intermediate when participants named the color of the non-word stimulus (neutral). Performance on all three trial types degraded significantly as a function of time awake. Extended wakefulness did not significantly change the additional time needed to respond when the color and word did not match (Stroop interference), nor did it change the amount of facilitation when color and word matched. These results indicate that one night of sleep deprivation influences performance on the Stroop task by an overall increase in response time, but does not appear to impact the underlying processes of interference or facilitation. The results suggest that the degree to which an "executive function" is affected by sleep deprivation may depend on the particular executive function studied and the degree to which it is subserved by the prefrontal cortex.

Comparison of sustained attention assessed by auditory and visual psychomotor vigilance tasks prior to and during sleep deprivation.

To date, no detailed examination of the pattern of change in reaction time performance for different sensory modalities has been conducted across the circadian cycle during sleep deprivation. Therefore, we compared sustained auditory and visual attention performance during 40h of sleep deprivation assessing multiple metrics of auditory and visual psychomotor vigilance tasks (PVT). Forty healthy participants (14 women) aged 30.8±8.6years were studied. Subjects were scheduled for an ∼8h sleep schedule at home prior to three-six laboratory baseline days with an 8 h sleep schedule followed by 40h sleep deprivation. Visual and auditory PVTs were 10min in duration, and were administered every 2h during sleep deprivation. Data were analysed with mixed-model anova. Sleep deprivation and circadian phase increased response time, lapses, anticipations, standard deviation of response times and time on task decrements for visual and auditory PVTs. In general, auditory vigilance was faster and less variable than visual vigilance, with larger differences between auditory and visual PVT during sleep deprivation versus baseline. Failures to respond to stimuli within 10s were four times more likely to occur to visual versus auditory stimuli. Our findings highlight that lapses during sleep deprivation are more than just long responses due to eye closure or visual distraction. Furthermore, our findings imply that the general pattern of change in attention during sleep deprivation (e.g. circadian variation, response slowing, lapsing and anticipations, time on task decrements and state instability) is similar among sensory-motor behavioral response modalities.

Circadian and wake-dependent influences on subjective sleepiness, cognitive throughput, and reaction time performance in older and young adults.

STUDY OBJECTIVES: To assess circadian and homeostatic influences on subjective sleepiness and cognitive performance in older adults when sleep and waking are scheduled at different times of day; to assess changes in subjective sleepiness and cognitive performance across several weeks of an inpatient study; and to compare these findings with results from younger adults. DESIGN: Three 24-h baseline days consisting of 16 h of wakefulness and an 8-h sleep opportunity followed by 3-beat cycles of a 20-h forced desynchrony (FD) condition; 18 20-h "days," each consisting of 13.33 h of scheduled wakefulness and 6.67 h of scheduled sleep opportunity. SETTING: Intensive Physiological Monitoring Unit of the Brigham and Women's Hospital General Clinical Research Center. PARTICIPANTS: 10 healthy older adults (age 64.00 +/- 5.98 y, 5 females) and 10 healthy younger adults (age 24.50 +/- 3.54 y, 5 females). INTERVENTIONS: Wake episodes during FD scheduled to begin 4 h earlier each day allowing for data collection at a full range of circadian phases. MEASUREMENTS AND RESULTS: Subjective sleepiness, cognitive throughput, and psychomotor vigilance assessed every 2 h throughout the study. Core body temperature (CBT) data collected throughout to assess circadian phase. Older subjects were less sleepy and performed significantly better on reaction time (RT) measures than younger subjects. Decrements among younger subjects increased in magnitude further into the experiment, while the performance of older subjects remained stable. CONCLUSIONS: Our findings demonstrate that the waking performance and alertness of healthy older subjects are less impacted by the cumulative effects of repeated exposure to adverse circadian phase than that of young adults. This suggests that there are age-related changes in the circadian promotion of alertness, in the wake-dependent decline of alertness, and/or in how these 2 regulatory systems interact in healthy aging.

EEG sleep spectra in older adults across all circadian phases during NREM sleep.

STUDY OBJECTIVES: Healthy aging is associated with changes in sleep-wake regulation, and those changes often lead to problems sleeping, both during the night and during daytime. We aimed to examine the electroencephalographic (EEG) sleep spectra during non-rapid eye movement (NREM) sleep when sleep was scheduled at all times of day. DESIGN/INTERVENTIONS: After three 24-h baseline (BL) days, participants were scheduled to live on 20-hour "days" consisting of 6.7 hours of bed rest and 13.3 hours of wakefulness for 12 consecutive days (forced desynchrony, FD). The EEG was recorded from a central derivation during all scheduled sleep episodes, with subsequent visual scoring and spectral analysis. SETTING: Intensive Physiological Monitoring Unit of the Brigham & Women's Hospital General Clinical Research Center. PARTICIPANTS: Twenty-four healthy older subjects (64.2 +/- 6.3 yr; 13 women, 11 men) MEASUREMENTS AND RESULTS: Compared with BL nights, EEG activity in the slow wave (0.5 to 5.25 Hz), theta (6 to 6.25 and 7 Hz), alpha (10 to 11.25 Hz), and high spindle range (14.5 to 15.5 Hz) was significantly greater during FD, when subjects slept across many times of day and night. During FD, there was a significant interaction between homeostatic and circadian factors, such that EEG delta activity (0.5 to 1.5 Hz) was higher in the biological morning/early afternoon than at other times. EEG activity was significantly increased in almost all frequency ranges (0.5 to 21 Hz) during the biological day, as compared with the biological night, except for the lower EEG spindle range (12.25 to 14 Hz). Overall, EEG beta activity was positively correlated with wakefulness and negatively correlated with total sleep time. CONCLUSION: Our findings provide some new evidence for the underlying mechanisms that contribute to age-related difficulties in sleep consolidation, especially when sleep occurs during the daytime.