Comparing Sleep‐Loss Sleepiness and Sleep Inertia: Lapses Make the Difference

To compare the behavioral effects of sleep‐loss sleepiness (performance impairment due to sleep loss) and sleep inertia (period of impaired performance that follows awakening), mean response latencies and number of lapses from a visual simple reaction‐time task were analyzed. Three experimental conditions were designed to manipulate sleepiness and sleep‐inertia levels: uninterrupted sleep, partial sleep reduction, and total sleep deprivation. Each condition included two consecutive nights (the first always a night of uninterrupted sleep, and the second either a night of uninterrupted sleep, a night when sleep was reduced to 3 h, or a night of total sleep deprivation), as well as two days in which performance was assessed at 10 different time points (08:00, 08:30, 09:00, 09:30, 10:00, 11:00, 14:00, 17:00, 20:00, and 23:00 h). From 08:00 to 09:00 h, reaction times in the partial sleep‐reduction and total sleep‐deprivation conditions were at a similar level and were slower than those observed in the uninterrupted sleep condition. In the same time period, the frequency of lapses in the total sleep‐deprivation condition was higher than in the partial sleep‐reduction condition, while this latter condition never differed from the uninterrupted sleep condition. The results indicate that both sleep inertia and sleep‐loss sleepiness lead to an increase in response latencies, but only extreme sleepiness leads to an increase in lapse frequency. We conclude that while reaction times slow as a result of both sleep inertia and sleep‐loss sleepiness, lapses appear to be a specific feature of sleep‐loss sleepiness.     

The effects of extended nap periods on cognitive,physiological and subjective responses under simulated night shift conditions

Extended nap opportunities have been effective in maintaining alertness in the context of extended night shifts (+12?h). However, there is limited evidence of their efficacy during 8-h shifts. Thus, this study explored the effects of extended naps on cognitive, physiological and perceptual responses during four simulated, 8-h night shifts. In a laboratory setting, 32 participants were allocated to one of three conditions. All participants completed four consecutive, 8-h night shifts, with the arrangements differing by condition. The fixed night condition worked from 22h00 to 06h00, while the nap early group worked from 20h00 to 08h00 and napped between 00h00 and 03h20. The nap late group worked from 00h00 to 12h00 and napped between 04h00 and 07h20. Nap length was limited to 3 hours and 20 minutes. Participants performed a simple beading task during each shift, while also completing six to eight test batteries roughly every 2?h. During each shift, six test batteries were completed, in which the following measures were taken. Performance indicators included beading output, eye accommodation time, choice reaction time, visual vigilance, simple reaction time, processing speed and object recognition, working memory, motor response time and tracking performance. Physiological measures included heart rate and tympanic temperature, whereas subjective sleepiness and reported sleep length and quality while outside the laboratory constituted the self reported measures. Both naps reduced subjective sleepiness but did not alter the circadian and homeostatic-related changes in cognitive and physiological measures, relative to the fixed night condition. Additionally, there was evidence of sleep inertia following each nap, which resulted in transient reductions in certain perceptual cognitive performance measures. The present study suggested that there were some benefits associated with including an extended nap during 8-h night shifts. However, the effects of sleep inertia need to be effectively managed to ensure that post-nap alertness and performance is maintained.     

Sleepiness and performance in response to repeated sleep restriction and subsequent recovery during semi-laboratory conditions

There is an ongoing debate of how best to measure the effects of sleep loss in a reliable and feasible way, partly because well controlled laboratory studies and field studies have come to different conclusions. The aims of the present study were to investigate both sleepiness and performance in response to long-term sleep restriction and recovery in a semi-laboratory environment, investigate order effects (i.e., whether levels return to baseline) in a study with seven days of recovery, and characterize individual differences in tolerance to restricted sleep. Nine healthy men (age 23-28 yrs) participated in the protocol, which included one habituation day (sleep 23:00-07:00 h), two baseline days (23:00-07:00 h), five days with restricted sleep (03:00-07:00 h), and seven recovery days (23:00-07:00 h). Participants went outdoors at least twice each day. Reaction-time tests were performed at 08:00, 14:00, and 20:00 h each day in the laboratory. Sleepiness was self-rated by the Karolinska Sleepiness Scale (KSS)after each test. The mixed-effect regression models showed that each day of restricted sleep resulted in an increase of sleepiness by 0.64+/- .05 KSS units (a nine-step scale, p < .001), increase of median reaction times of 6.6+/- 1.6 ms ( p = .003), and increase of lapses/test of 0.69 +/- .16 ms ( p < .001). Seven days of recovery allowed participants to return to the baseline for sleepiness and median reaction time, but not for lapses. The individual differences were larger for performance measures than for sleepiness; the between-subject standard deviation for the random intercept was in the magnitude of the effects of 1.1 days of restricted sleep for sleepiness, 6.6 days of restricted sleep for median reaction time, and 3.2 days for lapses. In conclusion, the present study shows that sleepiness is closely related to sleep pressure, while performance measures, to a larger extent, appear determined by specific individual traits. Moreover, it is suggested to measure sleepiness in a standardized situation so as to minimize the influences of contextual factors.     

Sleepiness and Performance in Response to Repeated Sleep Restriction and Subsequent Recovery during Semi‐Laboratory Conditions

There is an ongoing debate of how best to measure the effects of sleep loss in a reliable and feasible way, partly because well controlled laboratory studies and field studies have come to different conclusions. The aims of the present study were to investigate both sleepiness and performance in response to long‐term sleep restriction and recovery in a semi‐laboratory environment, investigate order effects (i.e., whether levels return to baseline) in a study with seven days of recovery, and characterize individual differences in tolerance to restricted sleep. Nine healthy men (age 23–28 yrs) participated in the protocol, which included one habituation day (sleep 23:00–07:00 h), two baseline days (23:00–07:00 h), five days with restricted sleep (03:00–07:00 h), and seven recovery days (23:00–07:00 h). Participants went outdoors at least twice each day. Reaction‐time tests were performed at 08:00, 14:00, and 20:00 h each day in the laboratory. Sleepiness was self‐rated by the Karolinska Sleepiness Scale (KSS) after each test. The mixed‐effect regression models showed that each day of restricted sleep resulted in an increase of sleepiness by 0.64±.05 KSS units (a nine‐step scale, p<.001), increase of median reaction times of 6.6±1.6 ms (p=.003), and increase of lapses/test of 0.69±.16 ms (p<.001). Seven days of recovery allowed participants to return to the baseline for sleepiness and median reaction time, but not for lapses. The individual differences were larger for performance measures than for sleepiness; the between‐subject standard deviation for the random intercept was in the magnitude of the effects of 1.1 days of restricted sleep for sleepiness, 6.6 days of restricted sleep for median reaction time, and 3.2 days for lapses. In conclusion, the present study shows that sleepiness is closely related to sleep pressure, while performance measures, to a larger extent, appear determined by specific individual traits. Moreover, it is suggested to measure sleepiness in a standardized situation so as to minimize the influences of contextual factors.     

Effect of Time of Day and Partial Sleep Deprivation on Short‐Term,High‐Power Output

The purpose of this study was to determine whether delaying bedtime or advancing rising time by 4 h affects anaerobic performance of individuals the following day in the morning and afternoon. Eleven subjects participated in the study, during which we measured the maximal, peak, and mean powers (i.e., P_max [force‐velocity test], P_peak, and P_mean [Wingate test], respectively). Measurements were performed twice daily, at 07∶00 and 18∶00 h, following a reference normal sleep night (RN), a partial sleep deprivation timed at the beginning of the night (SDB), and a partial sleep deprivation timed at the end of the night (SDE), and oral temperature was measured every 4 h. Each of the three experimental conditions was separated by a one‐week period. Our results showed a circadian rhythm in oral temperature, and analysis of variance revealed a significant sleep×test‐time effect on peak power (P_peak), mean power (P_mean), and maximal power (P_max). These variables improved significantly from the morning to the afternoon for all three experimental conditions. Whereas the morning‐afternoon improvement in the measures was similar after the RN and SDB conditions, it was smaller following the SDE condition. There was no significant difference in the effect of the two sleep‐deprivation conditions on anaerobic performances at 07∶00 and at 18∶00 h under the SDB condition in comparison with the post‐reference night. However, the performance variables were significantly lower at 18∶00 h after the SDE condition. In conclusion, a 4 h partial sleep deprivation at the end of the night appears to be more disturbing than partial sleep deprivation at the beginning of the night.     

Effect of one night of sleep loss on changes in tumor necrosis factor alpha (TNF-α) levels in healthy men

Total sleep deprivation in humans is associated with increased daytime sleepiness, decreased performance, elevations in inflammatory cytokines, and hormonal/metabolic disturbances.To assess the effects of 40 h of total sleep deprivation (TSD) under constant and well controlled conditions, on plasma levels of TNF-α and its receptor (TNFR1), interleukin-6 (IL-6), cortisol and C-reactive protein (CRP), sleepiness and performance, 12 healthy men (29 ± 3 years) participated in a 5-days sleep deprivation experiment (two control nights followed by a night of sleep loss and one recovery night). Between 0800 and 2300 (i.e. between 25 and 40 h of sleep deprivation), a serial of blood sampling, multiple sleep latency, subjective levels of sleepiness and reaction time tests were completed before (day 2: D2) and after (day 4: D4) one night of sleep loss. We showed that an acute sleep deprivation (i.e. after 34 and 37 h of sleep deprivation) induced a significant increase in TNF-α (P < 0.01), but there were no significant changes in TNFR1, IL-6, cortisol and CRP. In conclusion, our study in which constant and controlled experimental conditions were realized with healthy subjects and in absence of psychological or physical stressors, an acute total sleep deprivation (from 34 h) was sufficient to induce secretion of pro-inflammatory cytokine such as TNF-α, a marker more described in chronic sleep restriction or deprivation and as mediators of excessive sleepiness in humans in pathological conditions.     

The Effect of One Night's Sleep Deprivation on Temperature,Mood, and Physical Performance in Subjects with Different Amounts of Habitual Physical Activity

Eleven healthy males were studied twice. On one occasion (control, C), they slept (night 1) and then underwent a battery of tests at 4h intervals from 06: 00 day 1 to 02: 00 day 2; then, after a normal sleep (night 2), they were tested from 10: 00 to 22: 00 on day 2. On the second occasion (sleep deprivation, SD), the subjects remained awake during night 1. Each battery of tests consisted of measurements of tympanic membrane temperature, profile of mood states (POMS), muscle strength, self-chosen work rate (SCWR), perceived exertion, and heart rate (HR) while exercising on a stationary cycle ergometer. Subjects also kept a diary of their activities during the two days and answered a questionnaire about their habitual physical activity. Results showed a significant negative effect of sleep deprivation on most mood states on day 1, but no effect on the other variables. By day 2, mood had tended to recover, though muscle strength tended to be worse in both control and sleep-deprivation experiments. There was also a more general tendency for negative effects to be present at the end of day 1 (02: 00) or at the beginning of day 2 (10: 00). There was limited support for the view that subjects who were habitually more active showed less negative effects after sleep deprivation and responded less adversely to the poor sleep achieved on the university premises (night 2). These results stress the considerable interindividual variation in the responses to sleep loss and, therefore, the difficulty associated with giving general advice to individuals about work or training capability after sleep loss.     

Recovery of cognitive performance from sleep debt: do a short rest pause and a single recovery night help?

We studied the recovery of multitask performance and sleepiness from acute partial sleep deprivation through rest pauses embedded in performance sessions and an 8 h recovery sleep opportunity the following night. Sixteen healthy men, aged 19-22 yrs, participated in normal sleep (two successive nights with 8 h sleep) and sleep debt (one 2 h night sleep followed by an 8 h sleep the following night) conditions. In both conditions, the participants performed four 70 min multitask sessions, with every other one containing a 10 min rest pause with light neck-shoulder exercise. The multitask consisted of four simultaneously active subtasks, with the level of difficulty set in relation to each participant's ability. Physiological sleepiness was assessed with continuous electroencephalography/electro-oculography recordings during themultitask sessions, and subjective sleepiness was self-rated with the Karolinska Sleepiness Scale. Results showed that multitask performance and physiological and subjective sleepiness were impaired by the sleep debt ( p > .001). The rest pause improved performance and subjective sleepiness for about 15 min, regardless of the amount of prior sleep ( p > .01-.05). Following recovery sleep, all outcome measures showed marked improvement ( p < .001), but they failed to reach the levels observed in the control condition ( p < .001-.05). A correlation analysis showed the participants whose multitask performance deteriorated the most following the night of sleep loss tended to be the same persons whose performance was most impaired following the night of the recovery sleep ( p < .001). Taken together, our results suggest that a short rest pause with light exercise is not an effective countermeasure in itself for sleep debt-induced impairments when long-term effects are sought. In addition, it seems that shift arrangements that lead to at least a moderate sleep debt should be followed by more than one recovery night to ensure full recovery. Persons whose cognitive performance is most affected by sleep debt are likely to require the most sleep to recover.     

Effects of two nights partial sleep deprivation on an evening submaximal weightlifting performance; are 1 h powernaps useful on the day of competition?

We have investigated the effects that sleep restriction (3-h sleep during two consecutive nights) have on an evening (17:00 h) submaximal weightlifting session; and whether this performance improves following a 1-h post-lunch powernap. Fifteen resistance-trained males participated in this study. Before the experimental protocol commenced, 1RM bench press and inclined leg press and normative habitual sleep were recorded. Participants were familiarised with the testing protocol, then completed three experimental conditions with two nights of prescribed sleep: (i) Normal (N): retire at 23:00 h and wake at 06:30 h, (ii) partial sleep-deprivation (SD): retire at 03:30 h and wake at 06:30 h and (iii) partial sleep-deprivation with nap (SD_N): retire at 03:30 h and wake at 06:30 h with a 1-h nap at 13:00 h. Each condition was separated by at least 7 days and the order of administration was randomised and counterbalanced. Rectal (T_rec) and mean skin (T_s) temperatures, Profile of Mood Scores, subjective tiredness, alertness and sleepiness values were measured at 08:00, 11:00, 14:00 and 17:00 h on the day of the weightlifting session. Following the final temperature measurements at 17:00 h, participants completed a 5-min active warm-up before a ‘strength’ protocol. Participants performed three repetitions of right-hand grip strength, then three repetitions at each incremental load (40%, 60% and 80% of 1RM) for bench press and inclined leg press, with a 5-min recovery in between each repetition. A linear encoder was attached perpendicular to the movement, to the bar used for the exercises. Average power (AP), average force (AF), peak velocity (PV), distance (D) and time-to-peak velocity (tPV) were measured (MuscleLab software) during the concentric phase of the movements for each lift. Data were analysed using general linear models with repeated measures. The main findings were that SD reduced maximal grip (2.7%), bench press (11.2% AP, 3.3% AF and 9.4% PV) and leg press submaximal values (5.7% AP) with a trend for a reduction in AF (3.3% P = 0.06). Furthermore, RPE increased for measures of grip strength, leg and bench press during SD. Following a 1-h powernap (SD_N), values of grip and bench press improved to values similar in N, as did tiredness, alertness and sleepiness. There was a main effect for “load” on the bar for both bench and leg press where AP, AF, tPV values increased with load (P < 0.05) and PV decreased from the lightest to the heaviest load for both bench and leg press. An interaction of “load and condition” was present in leg press only, where the rate of change of AP is greater in the N than SD and SD_N conditions. In addition, for PV and tPV the rate of change was greater for SD_N than N or SD condition values. In summary, SD had a negative effect on grip strength and some components of bench and inclined leg press. The use of a 1-h power nap that ended 3 h before the “strength” assessment had a positive effect on weightlifting performance, subjective mood and ratings of tiredness.     

Recovery of Cognitive Performance from Sleep Debt: Do a Short Rest Pause and a Single Recovery Night Help?

We studied the recovery of multitask performance and sleepiness from acute partial sleep deprivation through rest pauses embedded in performance sessions and an 8 h recovery sleep opportunity the following night. Sixteen healthy men, aged 19–22 yrs, participated in normal sleep (two successive nights with 8 h sleep) and sleep debt (one 2 h night sleep followed by an 8 h sleep the following night) conditions. In both conditions, the participants performed four 70 min multitask sessions, with every other one containing a 10 min rest pause with light neck‐shoulder exercise. The multitask consisted of four simultaneously active subtasks, with the level of difficulty set in relation to each participant's ability. Physiological sleepiness was assessed with continuous electroencephalography/electro‐oculography recordings during the multitask sessions, and subjective sleepiness was self‐rated with the Karolinska Sleepiness Scale. Results showed that multitask performance and physiological and subjective sleepiness were impaired by the sleep debt (p>.001). The rest pause improved performance and subjective sleepiness for about 15 min, regardless of the amount of prior sleep (p>.01–.05). Following recovery sleep, all outcome measures showed marked improvement (p<.001), but they failed to reach the levels observed in the control condition (p<.001–.05). A correlation analysis showed the participants whose multitask performance deteriorated the most following the night of sleep loss tended to be the same persons whose performance was most impaired following the night of the recovery sleep (p<.001). Taken together, our results suggest that a short rest pause with light exercise is not an effective countermeasure in itself for sleep debt‐induced impairments when long‐term effects are sought. In addition, it seems that shift arrangements that lead to at least a moderate sleep debt should be followed by more than one recovery night to ensure full recovery. Persons whose cognitive performance is most affected by sleep debt are likely to require the most sleep to recover.     

Effect of bright light on EEG activities and subjective sleepiness to mental task during nocturnal sleep deprivation

The purpose of this study was to investigate the effect of the exposure to bright light on EEG activity and subjective sleepiness at rest and at the mental task during nocturnal sleep deprivation. Eight male subjects lay awake in semi-supine in a reclining seat from 21:00 to 04:30 under the bright (BL; >2500 lux) or the dim (DL; <150 lux) light conditions. During the sleep deprivation, the mental task (Stroop color-word conflict test: CWT) was performed each 15 min in one hour. EEG, subjective sleepiness, rectal and mean skin temperatures and urinary melatonin concentrations were measured. The subjective sleepiness increased with time of sleep deprivation during both rest and CWT under the DL condition. The exposure to bright light delayed for 2 hours the increase in subjective sleepiness at rest and suppressed the increase in that during CWT. The bright light exposure also delayed the increase in the theta and alpha wave activities in EEG at rest. In contrast, the effect of the bright light exposure on the theta and alpha wave activities disappeared by CWT. Additionally, under the BL condition, the entire theta activity during CWT throughout nocturnal sleep deprivation increased significantly from that in a rest condition. Our results suggest that the exposure to bright light throughout nocturnal sleep deprivation influences the subjective sleepiness during the mental task and the EEG activity, as well as the subjective sleepiness at rest. However, the effect of the bright light exposure on the EEG activity at the mental task diminishes throughout nocturnal sleep deprivation.     

Sleep Deprivation Influences Diurnal Variation of Human Time Perception with Prefrontal Activity Change: A Functional Near-Infrared Spectroscopy Study

Human short-time perception shows diurnal variation. In general, short-time perception fluctuates in parallel with circadian clock parameters, while diurnal variation seems to be modulated by sleep deprivation per se. Functional imaging studies have reported that short-time perception recruits a neural network that includes subcortical structures, as well as cortical areas involving the prefrontal cortex (PFC). It has also been reported that the PFC is vulnerable to sleep deprivation, which has an influence on various cognitive functions. The present study is aimed at elucidating the influence of PFC vulnerability to sleep deprivation on short-time perception, using the optical imaging technique of functional near-infrared spectroscopy. Eighteen participants performed 10-s time production tasks before (at 21:00) and after (at 09:00) experimental nights both in sleep-controlled and sleep-deprived conditions in a 4-day laboratory-based crossover study. Compared to the sleep-controlled condition, one-night sleep deprivation induced a significant reduction in the produced time simultaneous with an increased hemodynamic response in the left PFC at 09:00. These results suggest that activation of the left PFC, which possibly reflects functional compensation under a sleep-deprived condition, is associated with alteration of short-time perception.     

Duration of Sleep Inertia after Napping during Simulated Night Work and in Extended Operations

Due to the mixed findings of previous studies, it is still difficult to provide guidance on how to best manage sleep inertia after waking from naps in operational settings. One of the few factors that can be manipulated is the duration of the nap opportunity. The aim of the present study was to investigate the magnitude and time course of sleep inertia after waking from short (20-, 40- or 60-min) naps during simulated night work and extended operations. In addition, the effect of sleep stage on awakening and duration of slow wave sleep (SWS) on sleep inertia was assessed. Two within-subject protocols were conducted in a controlled laboratory setting. Twenty-four healthy young men (Protocol 1: n?=?12, mean age?=?25.1 yrs; Protocol 2: n?=?12, mean age?=?23.2 yrs) were provided with nap opportunities of 20-, 40-, and 60-min (and a control condition of no nap) ending at 02:00?h after ～20?h of wakefulness (Protocol 1 [P1]: simulated night work) or ending at 12:00?h after ～30?h of wakefulness (Protocol 2 [P2]: simulated extended operations). A 6-min test battery, including the Karolinska Sleepiness Scale (KSS) and the 4-min 2-Back Working Memory Task (WMT), was repeated every 15?min the first hour after waking. Nap sleep was recorded polysomnographically, and in all nap opportunities sleep onset latency was short and sleep efficiency high. Mixed-model analyses of variance (ANOVA) for repeated measures were calculated and included the factors time (time post-nap), nap opportunity (duration of nap provided), order (order in which the four protocols were completed), and the interaction of these terms. Results showed no test x nap opportunity effect (i.e., no effect of sleep inertia) on KSS. However, WMT performance was impaired (slower reaction time, fewer correct responses, and increased omissions) on the first test post-nap, primarily after a 40- or 60-min nap. In P2 only, performance improvement was evident 45?min post-awakening for naps of 40?min or more. In ANOVAs where sleep stage on awakening was included, the test x nap opportunity interaction was significant, but differences were between wake and non-REM Stage 1/Stage 2 or wake and SWS. A further series of ANOVAs showed no effect of the duration of SWS on sleep inertia. The results of this study demonstrate that no more than 15?min is required for performance decrements due to sleep inertia to dissipate after nap opportunities of 60?min or less, but subjective sleepiness is not a reliable indicator of this effect. Under conditions where sleep is short, these findings also suggest that SWS, per se, does not contribute to more severe sleep inertia. When wakefulness is extended and napping occurs at midday (i.e., P2), nap opportunities of 40- and 60-min have the advantage over shorter duration sleep periods, as they result in performance benefits ～45?min after waking.     

Morning caffeine ingestion increases cognitive function and short-term maximal performance in footballer players after partial sleep deprivation

The aim of the present study was to evaluate the effects of caffeine ingestion and partial sleep deprivation at the end of night on cognitive and physical performance. In randomised order, fourteen football players (age: 23.57 ± 1.98 years; body weight: 59.57 ± 4.29 kg; height: 174.35 ± 5.07 cm) completed four test sessions at 08:00 h: after placebo or 3 mg·kg^?1 of caffeine ingestion during a reference night, RN (bed time: from 22:30 h to 07:00 h) or a night of partial sleep deprivation, PSD (bed time: from 22:30 h to 03:00 h). During each test session, participants assessed vigilance and reaction times and performed a series of tests: cancelation test, squat jumps (SJ), and the 30-s Wingate test (for the measurement of peak power, PP, and mean power, PM). During RN, results showed that PP, PM, SJ, and vigilance increased after caffeine ingestion in comparison with placebo (p < 0.001). Moreover, both simple and choice reactions were significantly better after caffeine ingestion in comparison with placebo ingestion (p < 0.05 and p < 0.001, respectively). Results showed that reaction time, vigilance, and SJ were affected by PSD, even though PP, PM, and SJ were not affected, the following day at 08:00 h. During the PSD condition, PP, PM, SJ, and vigilance were significantly higher after caffeine ingestion in comparison with placebo ingestion (p < 0.001). However, both simple and choice reaction times were significantly poorer during PSD in comparison with RN (p < 0.05 and p < 0.001, respectively). Therefore, ingesting caffeine is an effective strategy to maintain physical and cognitive performances after PSD.     

Duration of sleep inertia after napping during simulated night work and in extended operations

Due to the mixed findings of previous studies, it is still difficult to provide guidance on how to best manage sleep inertia after waking from naps in operational settings. One of the few factors that can be manipulated is the duration of the nap opportunity. The aim of the present study was to investigate the magnitude and time course of sleep inertia after waking from short (20-, 40- or 60-min) naps during simulated night work and extended operations. In addition, the effect of sleep stage on awakening and duration of slow wave sleep (SWS) on sleep inertia was assessed. Two within-subject protocols were conducted in a controlled laboratory setting. Twenty-four healthy young men (Protocol 1: n = 12, mean age = 25.1 yrs; Protocol 2: n = 12, mean age = 23.2 yrs) were provided with nap opportunities of 20-, 40-, and 60-min (and a control condition of no nap) ending at 02:00 h after ～20 h of wakefulness (Protocol 1 [P1]: simulated night work) or ending at 12:00 h after ～30 h of wakefulness (Protocol 2 [P2]: simulated extended operations). A 6-min test battery, including the Karolinska Sleepiness Scale (KSS) and the 4-min 2-Back Working Memory Task (WMT), was repeated every 15 min the first hour after waking. Nap sleep was recorded polysomnographically, and in all nap opportunities sleep onset latency was short and sleep efficiency high. Mixed-model analyses of variance (ANOVA) for repeated measures were calculated and included the factors time (time post-nap), nap opportunity (duration of nap provided), order (order in which the four protocols were completed), and the interaction of these terms. Results showed no test x nap opportunity effect (i.e., no effect of sleep inertia) on KSS. However, WMT performance was impaired (slower reaction time, fewer correct responses, and increased omissions) on the first test post-nap, primarily after a 40- or 60-min nap. In P2 only, performance improvement was evident 45 min post-awakening for naps of 40 min or more. In ANOVAs where sleep stage on awakening was included, the test x nap opportunity interaction was significant, but differences were between wake and non-REM Stage 1/Stage 2 or wake and SWS. A further series of ANOVAs showed no effect of the duration of SWS on sleep inertia. The results of this study demonstrate that no more than 15 min is required for performance decrements due to sleep inertia to dissipate after nap opportunities of 60 min or less, but subjective sleepiness is not a reliable indicator of this effect. Under conditions where sleep is short, these findings also suggest that SWS, per se, does not contribute to more severe sleep inertia. When wakefulness is extended and napping occurs at midday (i.e., P2), nap opportunities of 40- and 60-min have the advantage over shorter duration sleep periods, as they result in performance benefits ～45 min after waking.     

Challenging the sleep homeostat does not influence the thermoregulatory system in men: evidence from a nap vs. sleep-deprivation study

The purpose of our study was to understand the relationship between the components of the three-process model of sleepiness regulation (homeostatic, circadian, and sleep inertia) and the thermoregulatory system. This was achieved by comparing the impact of a 40-h sleep deprivation vs. a 40-h multiple nap paradigm (10 cycles with 150/75 min wakefulness/sleep episodes) on distal and proximal skin temperatures, core body temperature (CBT), melatonin secretion, subjective sleepiness, and nocturnal sleep EEG slow-wave activity in eight healthy young men in a "controlled posture" protocol. The main finding of the study was that accumulation of sleep pressure increased subjective sleepiness and slow-wave activity during the succeeding recovery night but did not influence the thermoregulatory system as measured by distal, proximal, and CBT. The circadian rhythm of sleepiness (and proximal temperature) was significantly correlated and phase locked with CBT, whereas distal temperature and melatonin secretion were phase advanced (by 113 +/- 28 and 130 +/- 30 min, respectively; both P < 0.005). This provides evidence for a primary role of distal vasodilatation in the circadian regulation of CBT and its relationship with sleepiness. Specific thermoregulatory changes occur at lights off and on. After lights off, skin temperatures increased and were most pronounced for distal; after lights on, the converse occurred. The decay in distal temperature (vasoconstriction) was significantly correlated with the disappearance of sleep inertia. These effects showed minor and nonsignificant circadian modulation. In summary, the thermoregulatory system seems to be independent of the sleep homeostat, but the circadian modulation of sleepiness and sleep inertia is clearly associated with thermoregulatory changes.     

Light exposure among adolescents with delayed sleep phase disorder: a prospective cohort study

The objective of this study was to compare light exposure and sleep parameters between adolescents with delayed sleep phase disorder (DSPD; n=16, 15.3±1.8 yrs) and unaffected controls (n=22, 13.7±2.4 yrs) using a prospective cohort design. Participants wore wrist actigraphs with photosensors for 14 days. Mean hourly lux levels from 20:00 to 05:00 h and 05:00 to 14:00 h were examined, in addition to the 9-h intervals prior to sleep onset and after sleep offset. Sleep parameters were compared separately, and were also included as covariates within models that analyzed associations with specified light intervals. Additional covariates included group and school night status. Adolescent delayed sleep phase subjects received more evening (p< .02, 22:00-02:00 h) and less morning (p .05, 08:00-09:00 h and 10:00-12:00 h) light than controls, but had less pre-sleep exposure with adjustments for the time of sleep onset (p< .03, 5-7 h prior to onset hour). No differences were identified with respect to the sleep offset interval. Increased total sleep time and later sleep offset times were associated with decreased evening (p< .001 and p= .02, respectively) and morning (p= .01 and p< .001, respectively) light exposure, and later sleep onset times were associated with increased evening exposure (p< .001). Increased total sleep time also correlated with increased exposure during the 9 h before sleep onset (p= .01), and a later sleep onset time corresponded with decreased light exposure during the same interval (p< .001). Outcomes persisted regardless of school night status. In conclusion, light exposure interpretation requires adjustments for sleep timing among adolescents with DSPD. Pre- and post-sleep light exposures do not appear to contribute directly to phase delays. Sensitivity to morning light may be reduced among adolescents with DSPD.     

Effects of time of day and sleep deprivation on motorcycle-driving performance

The aim of this study was to investigate whether motorcycle handling capabilities--measured by means of the efficiency of emergency manoeuvres--were dependent on prior sleep deprivation and time of day. Twelve male participants voluntarily took part in four test sessions, starting at 6 a.m., 10 a.m., 2 p.m., and 6 p.m., following a night either with or without sleep. Each test session comprised temperature and sleepiness measurements, before three different types of motorcycling tests were initiated: (1) stability in straight ahead riding at low speed (in "slow motion" mode and in "brakes and clutch" mode), (2) emergency braking and (3) crash avoidance tasks performed at 20 kph and 40 kph. The results indicate that motorcycle control at low speed depends on time of day, with an improvement in performance throughout the day. Emergency braking performance is affected at both speeds by time of day, with poorer performance (longer total stopping distance, reaction time and braking distance) in the morning, and also by sleep deprivation, from measurements obtained at 40 kph (incorrect initial speed). Except for a tendency observed after the sleepless night to deviate from the initial speed, it seems that crash avoidance capabilities are quite unaffected by the two disturbance factors. Consequently, some motorcycle handling capabilities (stability at low speed and emergency braking) change in the same way as the diurnal fluctuation observed in body temperature and sleepiness, whereas for others (crash avoidance) the participants were able to maintain their initial performance level despite the high levels of sleepiness recorded after a sleepless night. Motorcycle riders have to be aware that their handling capabilities are limited in the early morning and/or after sleep deprivation. Both these situations can increase the risk of falls and of being involved in a road accident.     

Mood, alertness, and performance in response to sleep deprivation and recovery sleep in experienced shiftworkers versus non-shiftworkers

Previous studies have shown increased sleepiness and mood changes in shiftworkers, which may be due to sleep deprivation or circadian disruption. Few studies, however, have compared responses of experienced shiftworkers and non-shiftworkers to sleep deprivation in an identical laboratory setting. The aim of this laboratory study, therefore, was to compare long-term shiftworkers and non-shiftworkers and to investigate the effects of one night of total sleep deprivation (30.5 h of continuous wakefulness) and recovery sleep on psychomotor vigilance, self-rated alertness, and mood. Eleven experienced male shiftworkers (shiftwork ≥5 yrs) were matched with 14 non-shiftworkers for age (mean ± SD: 35.7 ± 7.2 and 32.5 ± 6.2 yrs, respectively) and body mass index (BMI) (28.7 ± 3.8 and 26.6 ± 3.4 kg/m(2), respectively). After keeping a 7-d self-selected sleep/wake cycle (7.5/8 h nocturnal sleep), both groups entered a laboratory session consisting of a night of adaptation sleep and a baseline sleep (each 7.5/8 h), a sleep deprivation night, and recovery sleep (4-h nap plus 7.5/8 h nighttime sleep). Subjective alertness and mood were assessed with the Karolinska Sleepiness Scale (KSS) and 9-digit rating scales, and vigilance was measured by the visual psychomotor vigilance test (PVT). A mixed-model regression analysis was carried out on data collected every hour during the sleep deprivation night and on all days (except for the adaptation day), at .25, 4.25, 5.25, 11.5, 12.5, and 13.5 h after habitual wake-up time. Despite similar circadian phase (melatonin onset), demographics, food intake, body posture, and environmental light, shiftworkers felt significantly more alert, more cheerful, more elated, and calmer than non-shiftworkers throughout the laboratory study. In addition, shiftworkers showed a faster median reaction time (RT) compared to non-shiftworkers, although four other PVT parameters did not differ between the groups. As expected, both groups showed a decrease in subjective alertness and PVT performance during and following the sleep deprivation night. Subjective sleepiness and most aspects of PVT performance returned to baseline levels after a nap and recovery sleep. The mechanisms underlying the observed differences between shiftworkers and non-shiftworkers require further study, but may be related to the absence of shiftwork the week prior to and during the laboratory study as well as selection into and out of shiftwork.