Sleep inertia

The effects of napping on cognitive functioning

Naps (brief sleeps) are a global and highly prevalent phenomenon, thus warranting consideration for their effects on cognitive functioning. Naps can reduce sleepiness and improve cognitive performance. The benefits of brief (5-15 min) naps are almost immediate after the nap and last a limited period (1-3h). Longer naps (> 30 min) can produce impairment from sleep inertia for a short period after waking but then produce improved cognitive performance for a longer period (up to many hours). Other factors that affect the benefits from the nap are the circadian timing of the nap with early afternoon being the most favourable time. Longer periods of prior wakefulness favour longer naps over brief naps. Those who regularly nap seem to show greater benefits than those who rarely nap. These conclusions, however, need to be accepted cautiously until more comprehensive research programmes are conducted in which all these parameters are varied. Research is also needed to test the benefits of brief naps taken more naturalistically at the time when sleepiness becomes intrusive. The significant benefits of a brief nap, containing virtually no slow wave EEG activity, are not predicted by the present theory of homeostatic sleep drive (Process S). A new biological process (Process O) suggests that sleep onset followed by only 7-10 min of sleep can result in a substantial increase of alertness because it allows the rapid dissipation of inhibition in the 'wake-active' cells associated with the 'sleep-switch' mechanism rather than the dissipation of Process S.

Hangover Predicts Residual Alcohol Effects on Psychomotor Vigilance the Morning After Intoxication

OBJECTIVES: Both hangover and performance deficits have been documented the day after drinking to intoxication after breath alcohol concentration (BrAC) has returned to near zero. But few studies have examined the relationship between hangover and post-intoxication performance. METHOD: We performed secondary analyses of data from a previously reported controlled cross-over laboratory study to assess the relationship of hangover incidence and severity to sustained attention/reaction time the morning after drinking to about 0.11 g% BrAC. Relationships were investigated while controlling for gender, type of alcoholic beverage (bourbon or vodka), and neurocognitive performance after placebo. RESULTS: Hangover severity and neurocognitive performance were significantly correlated. Participants reporting stronger hangover were more impaired than those reporting little or no hangover. Comparing any to no hangover showed a trend in the same direction of effect. CONCLUSIONS: More intense hangover may indicate less fitness for duty in workers in certain safety-sensitive occupations, with implications for occupational alcohol policies.

The effect of self-awakening from nocturnal sleep on sleep inertia

The present study examined the effects of self-awakening on sleep inertia after nocturnal sleep. Ten undergraduate and graduate students participated in the study. Their polysomnograms were recorded for five consecutive nights; the first, second, and third to fifth nights were adaptation, forced-awakening, and self-awakening nights, respectively. Participants rated sleepiness, fatigue, comfort, and work motivation, and these ratings were followed by switching (7 min) and auditory reaction time tasks (6 min), both before bedtime (15 min) and immediately after awakening (4 min x 15 min). Although reaction times on the auditory were task prolonged, and participants complained of feeling uncomfortable immediately after forced-awakening, reaction times were shortened after self-awakening, and the participants did not complain of feeling uncomfortable on these nights. The results of this study suggest that sleep inertia occurs after forced-awakening and that it can be prevented by self-awakening.

The intensity of downbeat nystagmus during daytime

On the basis of reports by patients with downbeat nystagmus (DBN) that their symptoms were worse during the morning but better during the daytime, we investigated whether the intensity of DBN changes during the daytime. DBN was measured at 9 am, 11 am, and 1 pm. The mean peak slow phase velocity (MPSPV) of DBN was determined in different eye positions, with and without fixation, as well as in three different body positions: sitting upright, lying supine with the nose up, and lying prone with the nose down. Twelve patients with DBN either due to cerebellar degeneration or of idiopathic etiology were examined. The major findings of this study were as follows. First, the intensity of DBN significantly decreased during the daytime. When measured in the sitting upright position and primary eye position, MPSPV decreased from 4.32 deg/sec (+/-SEM 1.02) at 9 am to 2.12 deg/sec (+/- 0.5) at 11 am (P < 0.01) and stayed constant around 1.93 deg/sec (+/- 0.57) at 1 pm (P < 0.01 from 9 am to 1 pm) and 2.08 deg/sec (+/- 0.75) at 3 pm (P < 0.01 from 9 am to 3 pm). Second, this change did not depend on fixation during the measurements. Third, this effect was not influenced by the eye position during the measurements (upward, downward, or straight ahead). Our data show that the intensity of DBN decreases during the daytime. This decrease correlates with the symptoms of the patients. This change during daytime did not depend on visual fixation. Another possible mechanism is the modulation of DBN by head position relative to gravity, that is, by otolith input. This should be evaluated in further studies.

Gender Differences in Polysomnographic Sleep in Young Healthy Sleepers

Middle-aged and elderly populations exhibit gender differences in polysomnographic (PSG) sleep; however, whether young men and women also show such differences remains unclear. Thirty-one young healthy sleepers (16 men and 15 women, aged 18 to 30 yr, mean+/-SD, 20.5+/-2.4 yr) completed 3 consecutive overnight sessions in a sleep laboratory, after maintaining a stable sleep-wake cycle for 1 wk before study entry. Standard PSG sleep and self-rated sleepiness data were collected each night. Across nights, women showed better sleep quality than men: they fell asleep faster (shorter sleep onset latency) and had better sleep efficiency, with more time asleep and less time awake (all differences showed large effect sizes, d=0.98 to 1.12). By contrast, men were sleepier than women across nights. Both men and women demonstrated poorer overall sleep quality on the first night compared with the subsequent 2 nights of study. We conclude young adult healthy sleepers show robust gender differences in PSG sleep, like older populations, with better sleep quality in women than in men. These results highlight the importance of gender in sleep and circadian rhythm research studies employing young subjects and have broader implications for women's health issues relating to these topics.

Approaches to measuring the effects of wake-promoting drugs: a focus on cognitive function

OBJECTIVES

In clinical drug development, wakefulness and wake-promotion may be assessed by a large number of scales and questionnaires. Objective assessment of wakefulness is most commonly made using sleep latency/maintenance of wakefulness tests, polysomnography and/or behavioral measures. The purpose of the present review is to highlight the degree of overlap in the assessment of wakefulness and cognition, with consideration of assessment techniques and the underlying neurobiology of both concepts.

DESIGN

Reviews of four key areas were conducted: commonly used techniques in the assessment of wakefulness; neurobiology of sleep/wake and cognition; targets of wake promoting and/or cognition enhancing drugs; and ongoing clinical trials investigating wake promoting effects.

RESULTS

There is clear overlap between the assessment of wakefulness and cognition. There are common techniques which may be used to assess both concepts; aspects of the neurobiology of both concepts may be closely related; and wake-promoting drugs may have nootropic properties (and vice versa). Clinical trials of wake-promoting drugs often, though not routinely, assess aspects of cognition.

CONCLUSIONS

Routine and broad assessment of cognition in the development of wake-promoting drugs may reveal important nootropic effects, which are not secondary to alertness/wakefulness, whilst existing cognitive enhancers may have underexplored or unknown wake promoting properties.

Effects of waking time and breakfast intake prior to evaluation of psychomotor performance in the early morning

Many studies conducted in the field of chronobiology report diurnal fluctuation in cognitive and physical performance that occurs in phase with the body temperature circadian rhythm. Waking time and whether or not breakfast is consumed are currently considered to influence the diurnal fluctuation in data collected in the morning at 06:00 h and evening at 18:00 h. Nineteen male subjects participated in four test sessions to examine if wake-up time (04:00 h or 05:00 h) and eating or not eating breakfast influence psychomotor performance capacity at 06:00 h. All four sessions were separated by >/=36 h and were completed in a counterbalanced order. Each test session comprised sign cancellation, Epworth Sleepiness Scale, simple reaction time, and manual dexterity tests. Most of the results indicate that psychomotor performance when evaluated at 06:00 h under each of the four different study situations (two waking times and two breakfast conditions) is not statistically significantly different. Consequently, previous results that documented diurnal fluctuations in morning and evening performance capacities, with test sessions at 06:00 h, are confirmed. Being less efficient in the early morning than in the afternoon potentially exposes people to elevated risk of accident and injury at this time of the day. Prior waking time and/or consumption of a light meal, plus other countermeasures mentioned in the literature, are insufficient to prevent this risk.

Sleep and behavioral correlates of napping among young adults: a survey of first-year university students in Madrid, Spain

OBJECTIVE

Between November 2002 and March 2003, the authors assessed the prevalence and correlates of napping among Spanish university students.

PARTICIPANTS

The sample comprised 1,276 first-year university students; the mean age was 18.74 +/- 1.24 years, and 35.45% were men.

METHODS

The study was cross-sectional, and the students completed self-report, anonymous questionnaires provided during an in-class survey.

RESULTS

Almost half (44%) of the sample reported napping (90% did so after lunch for longer than 1 hour). Multiple logistic regression analysis showed that experiencing an irregular sleep-wakefulness pattern, having a morning school schedule, and being male were significant predictor variables of napping. Further significant outcome variables related to napping were having excessive daytime sleepiness, missing classes because of tiredness, better ability to concentrate later in the afternoon, and a perception of deeper nighttime sleep.

CONCLUSIONS

Habitual napping is common among Spanish university students and associated with an irregular sleep-wakefulness pattern. Taking long postlunch naps seems to be used by students to cope with insufficient sleep and daytime sleepiness.

An endogenous circadian rhythm in sleep inertia results in greatest cognitive impairment upon awakening during the biological night

Sleep inertia is the impaired cognitive performance immediately upon awakening, which decays over tens of minutes. This phenomenon has relevance to people who need to make important decisions soon after awakening, such as on-call emergency workers. Such awakenings can occur at varied times of day or night, so the objective of the study was to determine whether or not the magnitude of sleep inertia varies according to the phase of the endogenous circadian cycle. Twelve adults (mean, 24 years; 7 men) with no medical disorders other than mild asthma were studied. Following 2 baseline days and nights, subjects underwent a forced desynchrony protocol composed of seven 28-h sleep/wake cycles, while maintaining a sleep/wakefulness ratio of 1:2 throughout. Subjects were awakened by a standardized auditory stimulus 3 times each sleep period for sleep inertia assessments. The magnitude of sleep inertia was quantified as the change in cognitive performance (number of correct additions in a 2-min serial addition test) across the first 20 min of wakefulness. Circadian phase was estimated from core body temperature (fitted temperature minimum assigned 0 degrees ). Data were segregated according to: (1) circadian phase (60 degrees bins); (2) sleep stage; and (3) 3rd of the night after which awakenings occurred (i.e., tertiary 1, 2, or 3). To control for any effect of sleep stage, the circadian rhythm of sleep inertia was initially assessed following awakenings from Stage 2 (62% of awakening occurred from this stage; n = 110). This revealed a significant circadian rhythm in the sleep inertia of cognitive performance (p = 0.007), which was 3.6 times larger during the biological night (circadian bin 300 degrees , approximately 2300-0300 h in these subjects) than during the biological day (bin 180 degrees , approximately 1500-1900 h). The circadian rhythm in sleep inertia was still present when awakenings from all sleep stages were included (p = 0.004), and this rhythm could not be explained by changes in underlying sleep drive prior to awakening (changes in sleep efficiency across circadian phase or across the tertiaries), or by the proportion of the varied sleep stages prior to awakenings. This robust endogenous circadian rhythm in sleep inertia may have important implications for people who need to be alert soon after awakening.

The incidence and severity of hangover the morning after moderate alcohol intoxication

AIMS

To determine the incidence and covariates of hangover following a night of moderate alcohol consumption at a targeted breath alcohol level.

DESIGN

Data were combined from three randomized cross-over trials investigating the effects of heavy drinking on next-day performance. A total of 172 participants received either alcoholic beverage (mean=0.115 g% breath alcohol concentration) or placebo on one night and the other beverage a week later. The next day, participants completed a hangover scale.

PARTICIPANTS

Participants were 54 professional merchant mariners attending a recertification course at Kalmar Maritime Academy (Kalmar, Sweden) and 118 university students or recent graduates recruited from greater Boston.

SETTING

One trial was conducted at Kalmar Maritime Academy (Sweden); the other two were conducted at the General Clinical Research Center at Boston Medical Center.

MEASUREMENTS

A nine-item scale assessed hangover.

FINDINGS

Hangover was reported by 76% of participants. Neither alcoholic beverage type nor participant characteristics was associated with incidence of hangover.

CONCLUSIONS

Our findings on the propensity of hangover suggest that 25-30% of drinkers may be resistant to hangover.

Factors involved in sleep satisfaction in the elderly

BACKGROUND

In healthy aged subjects, subjective complaints of poor sleep are not as frequent as one would expect from the notable objective age-related sleep impairments. This discrepancy could depend on the sleep characteristics they require to feel satisfied about their sleep, which could be different from younger subjects. In order to verify this hypothesis, our study aims to identify changes in sleep satisfaction predictors as a function of age.

METHODS

Sleep features, both quantitative (sleep latency, sleep duration, frequency and duration of night-time awakenings) and qualitative (calmness of sleep, ease of falling asleep, satisfaction with sleep, ease of awakening, freshness after awakening and sufficient sleep), as well as afternoon nap habits were investigated throughout a pre-arranged interview in healthy individuals: 117 elderly subjects (47 men, 70 women, 65-99 years) and 120 young adults (48 men, 72 women, 19-28 years).

RESULTS

Quantitative sleep features worsen with age, whereas qualitative ones are equivalent or even improved in the aged group; only "calmness of sleep" decreases with age. Afternoon nap habits increase in elderly subjects, but they do not appear to be linked to sleep satisfaction. Predictors of sleep satisfaction differ between age groups: freshness after awakening but not frequency of night-time awakenings were relevant for elderly subjects, whereas the opposite was observed in young adults.

CONCLUSIONS

These findings point out that sleep satisfaction is preserved in healthy elderly individuals despite the worsening of quantitative night-time sleep features, reflected by the increase of afternoon naps. This discrepancy could be explained by changes in sleep satisfaction determinants, towards which a spontaneous adaptive adjustment is likely to occur in aged subjects. In contrast with young adults, elderly subjects heed the freshness perceived after the awakening and pay little attention to frequent night-time awakenings.

Impact of nap length, nap timing and sleep quality on sustaining early morning performance

The study examined how nap length, nap timing and sleep quality affect early morning performance (6:00 to 8:00). Twelve students participated in a simulated nightshift schedule (22:00 to 8:00) where the length and timing of nocturnal naps were manipulated (0:00-1:00, 0:00-2:00, 4:00-5:00 and 4:00-6:00). A performance test battery was administered consisting of a psychomotor vigilance test, a logical reasoning test, and a visual analogue scale for subjective fatigue and sleepiness. The results showed that a 120-min nap sustained early morning performance better than a 60-min nap. Taking a nap earlier or later did not affect the neurobehavioral performance tests, although participants slept more efficiently during naps later in the night shift. A negative effect of a nocturnal nap during the night shift on subsequent daytime and nocturnal sleep was not observed in the sleep architecture. It still remains unclear whether slow wave sleep plays an important role in sustaining early morning performance. In terms of work safety and sleep health, the results suggest that a longer and later nap is beneficial during night shifts.

Circadian rhythms in cognitive performance: Methodological constraints, protocols, theoretical underpinnings

The investigation of time-of-day effects on cognitive performance began in the early days of psychophysiological performance assessments. Since then, standardised, highly controlled protocols (constant routine and forced desynchrony) and a standard performance task (psychomotor vigilance task) have been developed to quantify sleep-wake homeostatic and internal circadian time-dependent effects on human cognitive performance. However, performance assessment in this field depends on a plethora of factors. The roles of task difficulty, task duration and complexity, the performance measure per se, practice effects, inter-individual differences, and ageing are all relevant aspects. Therefore, well-defined theoretical approaches and standard procedures are needed for tasks pinpointing higher cortical functions along with more information about time-dependent changes in the neural basis of task performance. This promises a fascinating challenge for future research on sleep-wake related and circadian aspects of different cognitive domains.

Automatic detection of slow wave sleep using two channel electro-oculography

An automatic method was developed for detecting slow wave sleep (SWS). The automatic method is based on a two-channel electro-oculography (EOG) with left mastoid (M1) as reference. Synchronous electroencephalographic (EEG) activity was detected by calculating cross-correlation between the two EOG channels by using 0.5-6 Hz band. An amplitude criterion was used for detecting slow waves and beta power 18-30 Hz was used to exclude artefacts. The automatic scoring was compared to a standard visual sleep scoring based on EOG, central EEG and submental EMG. Sleep EEG and EOG were recorded from 265 subjects. The optimal cross-correlation, amplitude and beta thresholds were derived using data from 133 training subjects and then applied to the data from different 132 validation subjects. Results were most sensitive to the changes in the amplitude criteria. Cohen's Kappa between the visual and the new developed automatic scoring in separating non-SWS and SWS was substantial (0.70) with epoch-by-epoch agreement of 93%. SWS epoch detection sensitivity was 75% and specificity was 96%. Also the total amount of slow waves, slow wave time (SWT), was estimated. The advantage of the automatic method is that it could be applied during online recordings using only four disposable self-adhesive electrodes.

Good sleep, bad sleep! The role of daytime naps in healthy adults

PURPOSE OF REVIEW

Millions of people all over the world take a nap during the day. People nap out of habit, because they are sleep-deprived as a result of a sleep disorder, or after a long work shift. Individuals of all age groups, from infants to the elderly, indulge in an afternoon nap. This review examines the benefits and drawbacks of daytime naps in healthy adults.

RECENT FINDINGS

A nap during the afternoon restores wakefulness and promotes performance and learning. Several investigators have shown that napping for as short as 10 min improves performance. Naps of less than 30 min duration confer several benefits, whereas longer naps are associated with a loss of productivity and sleep inertia. Recent epidemiological studies indicate that frequent and longer naps may lead to adverse long-term health effects.

SUMMARY

A nap of less than 30 min duration during the day promotes wakefulness and enhances performance and learning ability. In contrast, the habit of taking frequent and long naps may be associated with higher morbidity and mortality, especially among the elderly. The benefits of napping could be best obtained by training the body and mind to awaken after a short nap.

Parasomnias

Parasomnias are undesirable behaviors that arise from sleep but are not fully under voluntary control. Parasomnias are grouped broadly according to whether they arise from non-rapid eye movement (NREM) or rapid eye movement (REM) sleep. NREM parasomnias are disorders of arousal that occur along a continuum of behavioral, affective, and autonomic activation. REM-related parasomnias include REM sleep behavior disorder, sleep paralysis, and nightmare disorder. Parasomnias can often be managed successfully using behavioral and pharmacologic therapies.

Semantic priming effect during REM-sleep inertia in patients with narcolepsy

Patients with narcolepsy-cataplexy (NC) present excessive daytime sleepiness (EDS), cataplexy and an altered architecture of nocturnal sleep, with frequent episodes of REM-sleep at sleep onset (SOREM-sleep). This altered organization of nocturnal sleep may be accompanied by some differences in the functioning of the cognitive processes involved in the access, organization and consolidation of information during sleep. This study attempts to ascertain whether the activation of semantic memory during REM-sleep, as measured using a technique of semantic priming (namely, the facilitation of the activation of strongly-related rather than weakly-related and, overall, unrelated pairs of prime-target words) is different in NC patients compared to normal subjects. A lexical decision task (LDT) was carried out twice in wakefulness (at 10a.m. and after a 24h interval) and twice in the period of sleep inertia following awakening from SOREM and 4th-cycle REM-sleep on 12 NC patients and from 1st- and 4th-cycle REM-sleep on 12 matched controls. Reaction time (RT) to target words, taken as a measure of the semantic priming effect, proved to be longer (a) in NC patients than in control subjects; (b) in the period of REM-sleep inertia than in wakefulness; (c) in the first rather than the second session; and (d) for unrelated compared to weakly-related and, overall, strongly-related prime-target pairs. RT in post-REM-sleep sessions was less impaired, compared to waking sessions, and less dependent on the associative strength of prime-target pairs in NC patients than in normal subjects. Finally, RT of NC patients, although longer than that of normal subjects in waking sessions, significantly improved in the second session, as a consequence of either the amount of exercise or the consolidation advantage provided by REM-sleep for the procedural components of the task. The whole picture suggests a greater effectiveness of the activation of semantic memory during (SO)REM-sleep in NC patients rather than in normal subjects, and overall for the organization of new and unexpected relationships (such as those between unrelated pairs) between items of information.

Sleep and circadian rhythms in children and adolescents with bipolar disorder

The aim of this paper is to highlight the importance of the sleep-wake cycle in children and adolescents with bipolar disorder. After presenting an overview of the measurement and function of human sleep, we describe changes in sleep and circadian functioning across the life cycle. We then review evidence that, in adults, sleep and/or circadian rhythms are of considerable influence in the multifactorial causal chain implicated in relapse in bipolar disorder, discussing relevant mechanisms. The latter include abnormalities in the amount and timing of sleep, the role of social zeitgebers, and the importance of sleep in regulating emotional responses and mood. We next present preliminary data indicating considerable sleep disturbance among children and adolescents with bipolar disorder. Given the considerable sleep disturbance evident among children and adolescents with bipolar disorder along with a key role for sleep in emotion regulation and learning, we conclude that sleep among children and adolescents with bipolar disorder is a critical domain for future research. An agenda for future research is presented that includes descriptive studies, investigations of causality, and treatment development research.

Visual attention, reaction time, and self-reported alertness upon awakening from sleep bouts of varying lengths

The aim of the present study was to examine visual attention, especially the executive control functions that deal with conflict, when participants were in a low arousal state shortly after a nighttime awakening. Fifteen participants spent four consecutive nights at a laboratory and performed a flankers task using two levels of target-distractor spacing (0.75 degrees and 1.50 degrees) and three trial types (compatible, incompatible, and neutral). The first night was a habituation night. For the next three nights, participants went to sleep at 2300 hours and were then awakened at either 2400 hours (1-h sleep bout), 0300 hours (4-h sleep bout), or 0600 hours (7-h sleep bout) and were administered a flankers task and a self-report questionnaire that measured arousal level. These testing times were counter-balanced across participants, and a 2100 hours (pre-sleep) flankers task was also randomly assigned to be completed on one of the testing nights. Response time on neutral-flanker trials was increased if participants were awakened from a sleep bout and was slowest at 0300 hours, appearing to parallel circadian body temperature. In contrast, failures of selective attention, as indexed by the difference between compatible and incompatible trials, increased linearly as a function of the length of the sleep bout. Compared to the 2100 hours pre-sleep condition, self-reported energy was lower and Tiredness was higher after awakening from a sleep bout. Taken together, the current data suggest a dissociation between the processes that perform a non-conflict task and the executive control of attention. Specifically, longer sleep bouts seem to be associated with greater difficulty in inhibiting task-irrelevant information, perhaps due to a sleep inertia effect affecting the anterior cingulate cortex.

Functional EEG topography in sleep and waking: State-dependent and state-independent features

Power spectra in the non-rapid eye movement sleep (NREMS) electroencephalogram (EEG) have been shown to exhibit frequency-specific topographic features that may point to functional differences in brain regions. Here, we extend the analysis to rapid eye movement sleep (REMS) and waking (W) to determine the extent to which EEG topography is determined by state under two different levels of sleep pressure. Multichannel EEG recordings were obtained from young men during a baseline night, a 40-h waking period, and a recovery night. Sleep deprivation enhanced EEG power in the low-frequency range (1-8 Hz) in all three vigilance states. In NREMS, the effect was largest in the delta band, in W, in the theta band, while in REMS, there was a peak in both the delta and the theta band. The response of REMS to prolonged waking and its pattern of EEG topography was intermediate between NREMS and W. Cluster analysis revealed a major topographic segregation into three frequency bands (1-8 Hz, 9-15 Hz, 16-24 Hz), which was largely independent of state and sleep pressure. To assess individual topographic traits within each state, the differences between pairs of power maps were compared within (i.e., for baseline and recovery) and between individuals (i.e., separately for baseline and recovery). A high degree of intraindividual correspondence of the power maps was observed. The frequency-specific clustering of power maps suggests that distinct generators underlie EEG frequency bands. Although EEG power is modulated by state and sleep pressure, basic topographic features appear to be state-independent.

Alerting effects of light are sensitive to very short wavelengths

In humans a range of non-image-forming (NIF) light responses (melatonin suppression, phase shifting and alertness) are short wavelength sensitive (440-480 nm). The aim of the current study was to assess the acute effect of three different short wavelength light pulses (420, 440 and 470 nm) and 600 nm light on subjective alertness. Healthy male subjects (n = 12, aged 27 +/- 4 years, mean +/- S.D.) were studied in 39, 4-day laboratory study sessions. The subjects were maintained in dim light (<8 lx) and on day 3 they were exposed to a single 4-h light pulse (07:15-11:15 h). Four monochromatic wavelengths were administered at two photon densities: 420 and 440 nm at 2.3 x 10(13)photons/cm(2)/s and 440, 470 and 600 nm at 6.2 x 10(13)photons/cm(2)/s. Subjective mood and alertness were assessed at 30 min intervals during the light exposure, using four 9-point VAS scales. Mixed model regression analysis was used to compare alertness and mood ratings during the 470 nm light to those recorded with the other four light conditions. There was a significant effect of duration of light exposure (p < 0.001) on alertness but no significant effect of subject. Compared to 470 nm light, alertness levels were significantly higher in 420 nm light and significantly lower in the 600 nm light (p < 0.05). These data (420 nm>470 nm>600 nm) suggest that subjective alertness may be maximally sensitive to very short wavelength light.

Diurnal variation in cycling performance: influence of warm-up

We examined the effects of time of day on a cycling time trial with and without a prolonged warm-up, among cyclists who tended towards being high in "morningness". Eight male cyclists (mean +/- s: age = 24.9 +/- 3.5 years, peak power output = 319 +/- 34 W, chronotype = 39 +/- 6 units) completed a 16.1-km time trial without a substantial warm-up at both 07:30 and 17:30 h. The time trial was also completed at both times of day after a 25-min warm-up at 60% of peak power. Power output, heart rate, intra-aural temperature and category ratings of perceived exertion (CR-10) were measured throughout the time trial. Post-test blood lactate concentration was also recorded. Warm-up generally improved time trial performance at both times of day (95% CI for improvement = 0 to 30 s), but mean cycling time was still significantly slower at 07:30 h than at 17:30 h after the warm-up (95% CI for difference = 33 to 66 s). Intra-aural temperature increased as the time trial progressed (P < 0.0005) and was significantly higher throughout the time trials at 17:30 h (P = 0.001), irrespective of whether the cyclists performed a warm-up or not. Blood lactate concentration after the time trial was lowest at 07:30 h without a warm-up (P = 0.02). No effects of time of day or warm-up were found for CR-10 or heart rate responses during the time trial. These results suggest that 16.1-km cycling performance is worse in the morning than in the afternoon, even with athletes who tend towards 'morningness', and who perform a vigorous 25-min warm-up. Diurnal variation in cycling performance is, therefore, relatively robust to some external and behavioural factors.

Effects of sleep reduction on spatial attention

To investigate the effects exerted by sleep loss on specific attentive components the performance to a simple reaction time task and to a cued reaction time task were recorded at regular intervals during days following either 8 or 3 h of uninterrupted sleep. Eleven subjects took part in the experiment. The results show that, notwithstanding a general reduction of alertness produced by sleep curtailment (as indicated by the increase of reaction times in the simple reaction time task), in the cued reaction time task only the reaction times to invalidly cued targets significantly increase, while no difference is observed when attention is summoned by a valid cue. This result suggests that the mechanisms underlying orienting of attention are differentially affected by the reduction of alertness level.

How sleep affects the developmental learning of bird song

Sleep affects learning and development in humans and other animals, but the role of sleep in developmental learning has never been examined. Here we show the effects of night-sleep on song development in the zebra finch by recording and analysing the entire song ontogeny. During periods of rapid learning we observed a pronounced deterioration in song structure after night-sleep. The song regained structure after intense morning singing. Daily improvement in similarity to the tutored song occurred during the late phase of this morning recovery; little further improvement occurred thereafter. Furthermore, birds that showed stronger post-sleep deterioration during development achieved a better final imitation. The effect diminished with age. Our experiments showed that these oscillations were not a result of sleep inertia or lack of practice, indicating the possible involvement of an active process, perhaps neural song-replay during sleep. We suggest that these oscillations correspond to competing demands of plasticity and consolidation during learning, creating repeated opportunities to reshape previously learned motor skills.

Sleep inertia: performance changes after sleep, rest and active waking

Napping benefits and sustains subsequent performance. Prophylactic naps have been recommended as a means to maintain performance during extended wakefulness, as required during shiftwork. However, napping may cause short-term performance impairments, because awakening from sleep is followed by sleep inertia, a period of hypovigilance and impaired cognitive and behavioral performance. We investigated sleep inertia after an afternoon nap. Healthy 18-28 year-olds (n=50, not sleep deprived) were assigned to sleep, active wake or rest groups for a 2-h experimental phase with polysomnography starting either at 14:00 or 16:00 for half of each group. Before (baseline, 12:30 or 14:30) and in five sessions during the hour after the experimental phase (16:00-17:00 or 18:00-19:00), subjects completed an addition task, an auditory reaction time task, and the Stanford Sleepiness Scale. In session one, addition speed in the sleep group was reduced compared with baseline and with active wake controls, whereas calculation accuracy did not change. Addition speed in the sleep and rest groups increased substantially from session one to session two and reached a level similar to that of the active wake group by the fifth session. In the first session, auditory reaction speed of the sleep group was reduced compared with baseline and with rest controls but did not differ from the active wake group. The slowest reaction times showed significant recovery after 20 min. The groups reported similar increases in subjective sleepiness after the experimental period. These findings provide evidence for performance slowing and recovery during the hour following a 2-h nap opportunity. They highlight the importance of employing multiple control groups and various objective and subjective measures to assess sleep inertia.

Short nap versus short rest: recuperative effects during VDT work

The effects of a 20-min nap during 2 h of visual display terminal (VDT) work were examined. Ten young healthy adults took a 20-min nap or a 20-min rest I h after VDT work, followed by another 1 h of VDT work. A 20-min rest temporarily restored subjective sleepiness, but it deteriorated during the additional 1 h of work. In contrast, a 20-min nap maintained subjective alertness and performance level at a higher level and mental fatigue at a lower level for the additional 1 h of work. These results suggest that a short nap would be useful to both fatigue recovery and fatigue prevention during continuous VDT work. The present findings may provide a new work/rest strategy.

Post-lunch nap as a worksite intervention to promote alertness on the job

A worksite study was conducted to examine whether a 15-min nap during a post-lunch rest period would affect subsequent alertness, performance, and nocturnal sleep in eight factory workers under a 3-week protocol. Subjects were asked to take the nap at 12:30 h on a reclining chair during the nap week, and to remain awake during the no-nap week. The order of these 2 weeks was counterbalanced between the subjects. During the third, follow-up week, each subject determined whether or not she/he would nap. Alertness on the job and nocturnal sleep were assessed using a sleep diary. Wrist activity was also recorded during sleep at night. Choice reaction time task (RT) was performed at 10:00 and 15:00 h every day of the nap week and every other day of the no-nap and follow-up weeks. Perceived alertness was significantly higher in the afternoon after nap than after no nap at the end of the week. Similar effects were observed during the follow-up week where almost half of the subjects napped. No significant differences between the three weeks were found for RT performance or nocturnal sleep. Workers' attitudes toward the nap were favourable. Although further intervention research is required, our results suggest that post-lunch napping may have the potential to promote daytime alertness at work.

Intracortical inhibition and facilitation upon awakening from different sleep stages: a transcranial magnetic stimulation study

Intracortical facilitation and inhibition, as assessed by the paired-pulse transcranial magnetic stimulation technique with a subthreshold conditioning pulse followed by a suprathreshold test pulse, was studied upon awakening from REM and slow-wave sleep (SWS). Ten normal subjects were studied for four consecutive nights. Intracortical facilitation and inhibition were assessed upon awakening from SWS and REM sleep, and during a presleep baseline. Independently of sleep stage at awakening, intracortical inhibition was found at 1-3-ms interstimulus intervals and facilitation at 7-15-ms interstimulus intervals. Motor thresholds were higher in SWS awakenings, with no differences between REM awakenings and wakefulness, while motor evoked potential amplitude to unconditioned stimuli decreased upon REM awakening as compared to the other conditions. REM sleep awakenings showed a significant increase of intracortical facilitation at 10 and 15 ms, while intracortical inhibition was not affected by sleep stage at awakening. While the dissociation between motor thresholds and motor evoked potential amplitudes could be explained by the different excitability of the corticospinal system during SWS and REM sleep, the heightened cortical facilitation upon awakening from REM sleep points to a cortical motor activation during this stage.

The alerting effects of caffeine, bright light and face washing after a short daytime nap

OBJECTIVE

The present study examined whether the combination of a short daytime nap with caffeine, bright light and face washing was effective against mid-afternoon sleepiness.

METHODS

Ten young healthy adults participated in 5 experimental conditions; those experiments were-Nap only: taking a 20 min nap; Caffeine+Nap: taking 200 mg of caffeine followed by a nap; Nap+Bright-light: being exposed to 2000 lx of bright light for 1 min immediately after napping; Nap+Face-washing: washing their faces immediately after napping; and No-Nap: taking a rest without sleep. These naps were taken at 12:40 hours. The subjects engaged in computer tasks for 15 min before napping and for 1 h after napping.

RESULTS

Caffeine+Nap was the most effective for subjective sleepiness and performance level; its effects lasted throughout 1 h after napping. Nap+Bright-light was comparable with Caffeine+Nap, except for performance level. Nap+Face-washing showed mild and transient effects, however, it suppressed subjective sleepiness immediately after napping.

CONCLUSIONS

The effects of a short nap against mid-afternoon sleepiness could be enhanced by combining caffeine intake, exposure to bright light, or face washing.

SIGNIFICANCE

The present study would provide effective countermeasures against mid-afternoon sleepiness and sleepiness related accidents.

The circadian and homeostatic modulation of sleep pressure during wakefulness differs between morning and evening chronotypes

The purpose of this study was to evaluate homeostatic and circadian sleep process in 'larks' and 'owls' under daily life conditions. Core body temperature, subjective sleepiness and waking electroencephalogram (EEG) theta-alpha activity (6.25-9 Hz) were assessed in 18 healthy men (nine morning and nine evening chronotypes, 21.4 +/- 1.9 years) during a 36-h constant routine that followed a week of a normal 'working' sleep-wake schedule (bedtime: 23.30 h, wake time: 07.30 h). The phase of the circadian rhythm of temperature and sleepiness occurred respectively, 1.5 h (P = 0.01) and 2 h (P = 0.009) later in evening- than in morning-type subjects. Only morning-type subjects showed a bimodal rhythm of sleep-wake propensity. The buildup of subjective sleepiness, as quantified by linear regression, was slower in evening than in morning types (P = 0.04). The time course of EEG theta-alpha activity of both chronotypes could be closely fitted by an exponential curve. The time constant of evening types was longer than that of morning types (P = 0.03), indicating a slower increase in sleep pressure during extended wakefulness. These results suggest that both the circadian signal and the kinetics of sleep pressure buildup differ between the two chronotypes even under prior naturalistic conditions mimicking the usual working day.

The role of prescribed napping in sleep medicine

Napping, when its timing and duration are designed properly, has the potential to improve our daily lives. Laboratory findings indicate that scheduled napping promotes waking function after normal sleep at night, and also counteracts decreased alertness and performance under conditions of sleep deprivation. Since these effects are evident even with naps shorter than 30 min, shiftwork problems may be alleviated by the short nap at the workplace. Multiple short naps are effective in managing excessive daytime sleepiness in narcoleptic patients under medication. The therapeutic usefulness of napping in other sleep disorders, however, remains to be established. Epidemiological studies suggest a decrease in the risk of cardiovascular and cognitive dysfunction by the practice of taking short naps several times a week. Sleep inertia occurs immediately after napping, but its severity can be minimized by avoiding long naps that may result in awakening from deep non-rapid eye movement sleep. Activities during the post-nap period should also be undertaken carefully. To allow the maximum advantage to be gained from napping, more efforts are needed to identify the strategies of napping that are compatible with individual cases including aging, work schedules, and sleep disorders, and to examine their efficacy in real-life settings.

Defining the states of consciousness

Consciousness remains an elusive concept due to the difficulty to define what has been regarded for many years as a subjective experience, therefore irrelevant for scientific study. Recent development in this field of research has allowed to provide some new insight to a possible way to define consciousness. Going through the extensive literature in this domain, several perspectives are proposed to define this concept. (1) Consciousness and Attention may not reflect the same process. (2) Consciousness during wake and sleep may not involve the same mechanisms. (3) Besides physiological states of consciousness, human beings can experience modified states of consciousness either by self-training (transcendental meditation, hypnosis, etc.) or by drug intake (hallucinogens, anaesthetics, etc.). Altogether, we address the question of a more precise terminology, given the theoretical weight words can convey. To this respect, we propose different definitions for concepts like consciousness, vigilance, arousal and alertness as candidates to separate functional entities.