Manifest sleepiness and the spectral content of the EEG during shift work

Twenty-five three-shift workers in a process industry were subjected to ambulatory polysomnography during one afternoon and one night shift. The electroencephalographic (EEG) recordings were analyzed with spectral analysis. Subjective sleepiness increased during the night work but did not reach an extreme level. Five subjects fell asleep during night work and the involuntary naps were preceded by a few minutes of increased alpha (8-11.9 Hz) power density. Alpha and theta activity occurred in very short bursts. The hourly mean EEG alpha power density increased significantly but moderately during the night shift and correlated with subjective ratings of sleepiness. Theta power density (4-7.9 Hz) did not increase during the night shift, nor did it correlate with subjective sleepiness. It was suggested that the shift workers could prevent much of the polysomnographic manifestations of sleepiness by various types of activity (including succumbing to sleep). It was also suggested that averaging power density values across long time periods might not be an optimal strategy for detection of sleepiness, but rather some method of emphasizing the occurrence of alpha or theta bursts.     

Adjustment of Circadian Rhythms and EEG Sleep Functions to Day and Night Sleep Among Permanent Nightworkers and Rotating Shiftworkers

Six workers on a permanent night work schedule and 6 workers on a weekly rotating day-night shift schedule were compared with regard to the quantity and quality of sleep as measured by EEG recordings, sleep diaries, and subjective ratings of sleep. They were also compared regarding the degree of adjustment of the body temperature rhythm and self-rated activation. The observations for all variables were made at the beginning, end, and after the end of the night shift period, and also in connection with free days. It was shown that compared to rotating shiftworkers the permanent nightworkers exhibited a better adjustment of the body temperature rhythm to night work and day sleep and also had fewer disturbances in sleep functions during day sleep. The rotating shiftworkers showed the poorest adjustment of the body temperature rhythm and sleep functions during day sleep at the beginning of the night shift week, whereas for permanent nightworkers corresponding, albeit less pronounced, disturbances were present in connection with night sleep. It was concluded that there was a close relationship between the degree of adjustment of the body temperature rhythm and EEG sleep functions, with a permanent night work schedule facilitating the adjustment to night work.     

Effects of Night Duty on Sleep Patterns of Nurses

The diurnal sleep patterns of female nurses working night duty were compared to their nocturnal sleep patterns while they were working regular hours during the day. Continuous EEG, EOG, and EMG recordings were made at the end of 2 month periods of night and day duty respectively. Day and night sleep differed with respect to both duration and pattern. Despite an earlier onset, the major sleep period was shorter during the day than the night and seemed to be more interrupted later in the session. This finding is in keeping with the increased amount of Stage 1 and decreased amount of slow wave sleep during the day than the night. Although no differences were evident with respect to overall percent REM, differences in the distribution of REM did occur. REM sleep occurred sooner during day than night sleep and there was more of it during the first part of day sleep. Thus night duty seemed to affect the pattern of sleep stage distribution as well as the absolute amount of, not only total sleep, but also some sleep stages, such as Stage SS. It is an open question how the naps of extended duration taken while on night duty influence the pattern of sleep during the day.     

Stability of day and night sleep--a two-year follow-up of EEG parameters in three-shift workers.

Twenty rotating three-shift workers participated. Night and day sleep in connection with work on afternoon and night shifts, respectively, were recorded using 24-hour polysomnographic recording techniques. The procedure was repeated 2 years later. Both day and night sleep showed high significant correlations between years for rapid eye movement (REM) sleep, slow wave sleep (SWS-stages 3 + 4), total sleep time, slow wave energy, in the delta band (obtained via spectral analysis) and subjective sleep quality. Stage 2, stage 1, percent waking, sleep latency, SWS latency and REM latency were not correlated across years. None of the variables showed a significant difference between years. It was concluded that core variables of sleep show considerable interindividual stability across time and that a 2-year exposure to rotating shift work does not affect sleep in experienced shift workers.     

Sleep in the domestic hen (Gallus domesticus)

Electrophysiological recordings were made of five closely observed hens, all permanently implanted with both EEG and EMG electrodes. Five behavioural postures were distinguished and percentages of wakefulness, sleep and presumably paradoxical sleep (PS) were determined during the third and sixth hour of the dark period. Substantial agreement was generally found between behaviour and sleep with the exception of sitting or standing motionless with at least one eye open. During two thirds of this behavioural posture, the EEG showed large amplitude slow waves undistinguishable from slow wave sleep. Characteristics of PS were determined: periods were short, whereas its percentage increased during the night. Furthermore, EMG atonia was never found. An all night recording was made, and delta activity (2-5 Hz) was filtered and plotted against time for three of the hens. A significant decrease in delta activity across the night was found. Differences and similarities between sleep in hens and in mammals are discussed. Although large similarities exist it is concluded that some properties of birds' sleep make it unique and are a challenge for further study.     

Consolidated and distributed nap schedules and performance

This study compared alertness and psychomotor performance over an extended work period in which participants received either a 4-h afternoon nap or four 1-h naps during the night. It was hypothesized that alertness and performance would be superior during the night following the 4-h afternoon nap and that the overall level of performance would be related to the amount of sleep obtained. It was found that when a series of 1-h naps was taken during the normal night period, oral temperature and psychomotor performance also declined. However, performance was relatively improved on the following evening. In contrast, with an effective 4-h prophylactic nap, performance remained near baseline levels across the night. It was concluded that the placement of sleep periods during extended work be based on knowledge of when maximal performance would be required.     

The effect of daytime napping and full‐night sleep on the consolidation of declarative and procedural information

Many studies investigating sleep and memory consolidation have evaluated full‐night sleep rather than alternative sleep periods such as daytime naps. This multi‐centre study followed up on, and was compared with, an earlier full‐night study (Schabus et al., 2004) investigating the relevance of daytime naps for the consolidation of declarative and procedural memory. Seventy‐six participants were randomly assigned to a nap or wake group, and performed a declarative word‐pair association or procedural mirror‐tracing task. Performance changes from before to after a 90‐min retention interval filled with sleep or quiet wakefulness were evaluated between groups. Associations between performance changes, sleep architecture, spindles, and slow oscillations were investigated. For the declarative task we observed a trend towards stronger forgetting across a wake period compared with a nap period, and a trend towards memory increase over the full‐night. For the procedural task, accuracy was significantly decreased following daytime wakefulness, showed a trend to increase with a daytime nap, and significantly increased across full‐night sleep. For the nap protocol, neither sleep stages, spindles, nor slow oscillations predicted performance changes. A direct comparison of day and nighttime sleep revealed that daytime naps are characterized by significantly lower spindle density, but higher spindle activity and amplitude compared with full‐night sleep. In summary, data indicate that daytime naps protect procedural memories from deterioration, whereas full‐night sleep improves performance. Given behavioural and physiological differences between day and nighttime sleep, future studies should try to characterize potential differential effects of full‐night and daytime sleep with regard to sleep‐dependent memory consolidation.     

Promoting alertness with a short nap during a night shift

The use of a short (< 1 h) nap in improving alertness during the early morning hours in the first night shift was examined under laboratory conditions. The study contained four experimental, non-consecutive night shifts with a nap of either 50 or 30 min at 01.00 or 04.00 hours. An experimental night shift without a nap served as a control condition. Each experimental shift was followed by daytime sleep. Fourteen experienced male shift workers went through all of the experimental conditions. The results showed that the naps improved the ability to respond to visual signals during the second half of the night shift. Physiological sleepiness was alleviated by the early naps, as measured 50 min after awakening, but not at the end of the shift. Subjective sleepiness was somewhat decreased by the naps. The naps produced sleep inertia which lasted for about 10–15 min. Daytime sleep was somewhat impaired by the 50 min naps. The study shows that a nap shorter than 1 h is able to improve alertness to a certain extent during the first night shift.     

Sleep patterns in the parakeet Melopsittacus undulatus

Electrophysiological and behavioral studies of vigilance states were performed on adult specimens of the parakeet Melopsittacus undulatus. Four states of vigilance were identified: Wakefulness, drownsiness, slow wave sleep and paradoxical sleep. During wakefulness, a low voltage fast EEG pattern was observed. This pattern was progressively increasing in amplitude and decreasing in frequency when passing from drowsiness to slow wave sleep. Sleep spindles were not present. Slow wave sleep was frequently interrupted by paradoxical sleep episodes of short duration (6.4 +/- 3.2 sec), characterized by an EEG pattern similar to that of waking state. During wakefulness there were body and eye movements. This motor activity decreased when animals went into drowsiness and slow wave sleep. Paradoxical sleep was characterized by slight motor automatisms, including sometimes ocular movements.     

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.

Citation:

Münch M; Silva EJ; Ronda JM; Czeisler CA; Duffy JF. EEG sleep spectra in older adults across all circadian phases during NREM sleep. SLEEP 2010;33(3):389-401.     

Effects of sleep inertia after daytime naps vary with executive load and time of day

The effects of executive load on working memory performance during sleep inertia after morning or afternoon naps were assessed using a mixed design with nap/wake as a between-subjects factor and morning/afternoon condition as a within-subject factor. Thirty-two healthy adults (mean 22.5 ± 3.0 years) attended two laboratory sessions after a night of restricted sleep (6 hrs), and at first visit, were randomly assigned to the Nap or Wake group. Working memory (n-back) and subjective workload were assessed approximately 5 and 25 minutes after 90-minute morning and afternoon nap opportunities and at the corresponding times in the Wake condition. Actigraphically assessed nocturnal sleep duration, subjective sleepiness, and psychomotor vigilance performance before daytime assessments did not vary across conditions. Afternoon naps showed shorter EEG assessed sleep latencies, longer sleep duration, and more Slow Wave Sleep than morning naps. Working memory performance deteriorated, and subjective mental workload increased at higher executive loadings. After afternoon naps, participants performed less well on more executive-function intensive working memory tasks (i.e., 3-back), but waking and napping participants performed equally well on simpler tasks. After some 30 minutes of cognitive activity, there were no longer performance differences between the waking and napping groups. Subjective Task Difficulty and Mental Effort requirements were less affected by sleep inertia and dissociated from objective measures when participants had napped in the afternoon. We conclude that executive functions take longer to return to asymptotic performance after sleep than does performance of simpler tasks which are less reliant on executive functions.     

A controlled intervention study on the effects of a very rapidly forward rotating shift system on sleep-wakefulness and well-being among young and elderly shift workers.

Shift work is related to problems in sleep/wakefulness and social life. The effects of a very rapidly forward rotating shift system on sleep, health and well-being of young (-45) and elderly (45+) maintenance workers were studied by a controlled intervention study. In the beginning, all the workers had a continuous backward rotating three-shift system. A very quickly forward rotating shift system was developed, avoiding consecutive night shifts and with more free-time between the individual shifts. The effect of the new shift system on sleep/wakefulness and general well-being was studied by questionnaire and field studies including on-site registration of sleep (actigraphy), subjective sleepiness (KSS) and psychomotor performance (PVT). Based on a linear mixed model for repeated measurements, the new shift system increased the main sleep length after the night shift and improved alertness and PVT performance during the night shift among the older workers. Alertness also improved during free-time after the night shift and sleep complaints decreased after all shifts. The workers on the new shift schedule perceived the effects of the new shift system on sleep, alertness, general health, well-being at work, social and family life more positively than the workers in the old shift system. At the end of the study, all subjects voted for the new shift system. It is concluded that although the new shift system increased the operating hours at night, the very rapidly forward rotating shift system had positive effects on the sleep, alertness and well-being of especially the older shift workers.     

Development of nap neurophysiology: preliminary insights into sleep regulation in early childhood

Although all young children nap, the neurophysiological features and associated developmental trajectories of daytime sleep remain largely unknown. Longitudinal studies of napping physiology are fundamental to understanding sleep regulation during early childhood, a sensitive period in brain and behaviour development and a time when children transition from a biphasic to a monophasic sleep–wakefulness pattern. We investigated daytime sleep in eight healthy children with sleep electroencephalography (EEG) assessments at three longitudinal points: 2 years (2.5–3.0 years), 3 years (3.5–4.0 years) and 5 years (5.5–6.0 years). At each age, we measured nap EEG during three randomized conditions: after 4 h (morning nap), 7 h (afternoon nap) and 10 h (evening nap) duration of prior wakefulness. Developmental changes in sleep were most prevalent in the afternoon nap (e.g. decrease in sleep duration by 30 min from 2 to 3 years and by 20 min from 3 to 5 years). In contrast, nap sleep architecture (% of sleep stages) remained unchanged across age. Maturational changes in non‐rapid eye movement sleep EEG power were pronounced in the slow wave activity (SWA, 0.75–4.5 Hz), theta (4.75–7.75 Hz) and sigma (10–15 Hz) frequency ranges. These findings indicate that the primary marker of sleep depth, SWA, is less apparent in daytime naps as children mature. Moreover, our fundamental data provide insight into associations between sleep regulation and functional modifications in the central nervous system during early childhood.     

The effect of sleep on item recognition and source memory recollection among shift‐workers and permanent day‐workers

We studied the effect of sleep versus wakefulness on item recognition and source memory recollection in a sample of shift‐workers and permanent day‐workers. Recognition of words that were previously viewed arrayed in quadrants of a page, and recollection of the original source location of the words on the page were assessed after a 12‐h retention interval that was filled with wakefulness incorporating the subjects' work‐shift, or an equal period that included sleep. Both shift‐workers and permanent day‐workers had poorer item recognition and source memory recollection when the retention interval was spent awake rather than including sleep. Shift‐workers expressed larger deficits in performance than day‐workers after wakefulness. This effect was not mediated by whether the shift‐workers were on a day‐ or night‐shift at the time of the study. These results indicate that sleep is an important contributor to successful item recognition and source recollection, and that mnemonic processing in shift‐workers may be especially sensitive across their work‐shift.     

The cortisol awakening response (CAR) in 2- to 4-year-old children: effects of acute nighttime sleep restriction, wake time, and daytime napping

The cortisol awakening response (CAR) is presumed critically important for healthy adaptation. The current literature, however, is hampered by systematic measurement difficulties relative to awakening, especially with young children. While reports suggest the CAR is smaller in children than adults, well‐controlled research in early childhood is scarce. We examined whether robust CARs exist in 2‐ to 4‐year‐old children and if sleep restriction, wake timing, and napping influence the CAR (n = 7). During a 25‐day in‐home protocol, researchers collected four salivary cortisol samples (0, 15, 30, 45 min post‐wake) following five polysomnographic sleep recordings on nonconsecutive days after 4 hr (morning nap), 7 hr (afternoon nap), 10 hr (evening nap), 13 hr (baseline night), and 16 hr (sleep restriction night) of wakefulness (20 samples/child). The CAR was robust after nighttime sleep, diminished after sleep restriction, and smaller but distinct after morning and afternoon (not evening) naps. Cortisol remained elevated 45 min after morning and afternoon naps. © 2011 Wiley Periodicals, Inc. Dev Psychobiol 54:412–422, 2012.     

Facilitated Recall Following RFM And NREM Naps

A novel procedure was used to assess (a) the differential effects of REM and SWS on retention and (b) whether these sleep stages enhanced recall for different types of information. In a 2 × 2 factorial design, subjects were given non-meaningful and meaningful verbal learning tasks. Learning took place either early in the morning or late in the afternoon. Following learning subjects either slept or remained awake for a 2-hr retention interval, after which recall was assessed. Sleep for morning subjects was composed of stages 1, 2 and rapid eye movement sleep while sleep for afternoon subjects was composed of stages 1, 2 and slow wave sleep. Retention for both tasks was better following periods of sleep than following periods of wakefulness but no differences in recall were observed after REM vs. NREM naps.     

Sleep and EEG profile in neonatal hippocampal lesion model of schizophrenia

Sleep architecture, EEG power pattern and locomotor activity were investigated in a putative animal model of schizophrenia. The model was prepared by excitotoxic damage of the ventral hippocampus on postnatal day 7 (PD 7), after which locomotor activity and electroencephalographic (EEG) sleep profile were compared between lesioned and sham operated animals respectively, at prepuberty (postnatal day PD 35) and postpuberty (PD 56). An enhancement of locomotor activity was observed in lesioned adult PD 56, but not in juvenile PD 35 rats. Spontaneous EEG/EMG recordings during 24 h showed no major differences between both groups at PD 35 and at PD 56. However, quantitative analysis of the EEG revealed an enhancement of power in delta (delta), theta (theta) and alpha (alpha) activities in lesioned animals at PD 35 during wakefulness in both light and dark phases. At PD 56, the power in the delta and theta bands was increased during the light and dark periods in both wakefulness and non-REM sleep. These findings suggest that ventral hippocampus lesion is not associated with disturbance of sleep architecture in rats, while consistent changes were observed in the dynamic of EEG slow wave frequency domain. Thus, the data indicate that neonatal lesion of ventral hippocampus did not mimic sleep abnormalities observed in schizophrenia, however this rodent model may model some EEG features seen in schizophrenia such as a frontally pronounced slowing of the slow EEG activity in delta and theta frequency bands.     

The Effect of Afternoon Body Heating on Body Temperature and Slow Wave Sleep

Recent evidence suggests that body temperature at sleep onset affects the subsequent level of slow wave sleep. According to one hypothesis, the actual temperature is the critical factor determining the relationship. An alternative proposal is that it is the rate of fall of body temperature following sleep onset. These hypotheses were tested by measuring rectal temperature and sleep, following late afternoon passive heating in a warm bath and during a control condition. Passive heating increased rectal temperature, which then returned rapidly toward the control level. However, immediately before lights out rectal temperature was still higher in the passive heating condition, a difference that continued throughout the night. Following passive heating the amount of slow wave sleep was higher in the early part of the night. These results support the hypothesis that body temperature at sleep onset and the amount of slow wave sleep are positively related.     

Scheduled napping as a countermeasure to sleepiness in air traffic controllers

The aims of this study were to measure sleep during a planned nap on the night shift; and to use objective measures of performance and alertness to compare the effects of the nap opportunity versus staying awake. Twenty-eight air traffic controllers (mean age 36 years, nine women) completed four night shifts (two with early starts and two with late starts). Each type of night shift (early/late start) included a 40-min planned nap opportunity on one occasion and no nap on the other. Polysomnographic data were used to measure sleep and waking alertness [spectral power in the electroencephalogram (EEG) during the last hour of the night shift and the occurrence of slow rolling eye movements (SEMs) subsequent to the nap]. Psychomotor performance task [Psychomotor Vigilance Task (PVT)] was completed at the beginning and end of the shift, and after the nap (or an equivalent time if no nap was taken). Nap sleep latencies were relatively long (mean = 19 min) and total sleep time short (mean = 18 min), with minimal slow wave sleep (SWS, mean = 0%), and no rapid eye movement sleep. Nap sleep resulted in improved PVT performance (mean and slowest 10% of reaction time events), decreased spectral power in the EEG and reduced the likelihood of SEMs. The occurrence of SWS in the nap decreased spectral power in the EEG. This study indicates that although sleep taken at work is likely to be short and of poor quality it still results in an improvement in objective measures of alertness and performance.     

Sleep patterns in a chelonian reptile (Gopherus flavomarginatus)

Individuals of Gopherus flavomarginatus, previously adapted to experimental conditions were chronically implanted for polygraphic recordings. Four different states of vigilance were observed:. Active wakefulness, quiet wakefulness, quiet sleep and active sleep. EEG was polymorphic and irregular showing a decreasing tendency in frequency and amplitude when passing from wakefulness to quiet sleep. Heart rate decreased with sleep but it was slightly higher during active sleep than quiet sleep. Motor automatisms were present during active sleep being sometimes accompanied by ocular movements. This sleep always appeared after long periods of quiet sleep. Its average duration from animal to animal varied between 9.15 and 13.62 sec. Reaction threshold increased during sleep. The conclusion is that Gopherus flavomarginatus shows two phases of sleep similar to slow and paradoxical sleep in mammals.