Impact of sleep inertia on visual selective attention for rare targets and the influence of chronotype

Sleep inertia is affected by circadian phase, with worse performance upon awakening from sleep during the biological night than biological day. Visual search/selective visual attention performance is known to be sensitive to sleep inertia and circadian phase. Individual differences exist in the circadian timing of habitual wake time, which may contribute to individual differences in sleep inertia. Because later chronotypes awaken at an earlier circadian phase, we hypothesized that later chronotypes would have worse visual search performance during sleep inertia than earlier chronotypes if awakened at habitual wake time. We analysed performance from 18 healthy participants [five females (22.1 ± 3.7 years; mean ± SD)] at ~1, 10, 20, 30, 40 and 60 min following electroencephalogram‐verified awakening from an 8 h in‐laboratory sleep opportunity. Cognitive throughput and reaction times of correct responses were impaired by sleep inertia and took ~10–30 min to improve after awakening. Regardless whether chronotype was defined by dim light melatonin onset or mid‐sleep clock hour on free days, derived from the Munich ChronoType Questionnaire, the duration of sleep inertia for cognitive throughput and reaction times was longer for later chronotypes (n = 7) compared with earlier chronotypes (n = 7). Specifically, performance for earlier chronotypes showed significant improvement within ~10–20 min after awakening, whereas performance for later chronotypes took ~30 min or longer to show significant improvement (P < 0.05). Findings have implications for decision making immediately upon awakening from sleep, and are consistent with circadian theory suggesting that sleep inertia contributes to longer‐lasting impairments in morning performance in later chronotypes.     

Circadian cortisol profiles and psychological self-reports in shift workers with and without recent change in the shift rotation system

Cortisol profiles including the cortisol rise in the first hour after awakening (CAR) were assessed during shift work and days off (eight saliva samples per shift). Participants were 102 healthy permanent day and night shift workers (comparison groups) and former permanent day and night shift workers after implementation of a new fast-forward rota including morning, evening, and night shifts. Results show that the CAR is detectable in day as well as night shifts. In permanent night workers cortisol profiles appear to be blunted during night work and days off. However, circadian cortisol profiles are not disturbed in former night workers who recently switched to the fast rotating shift schedule. In contrast, implementation of night work in former day workers seems to lead to initially blunted cortisol profiles that normalize after a short adjustment period. Results of a psychological assessment including exhaustion, chronic stress, effort-reward imbalance, and ratings of sleep quality and sleep length are also presented.     

Yawning in morning and evening types

Yawning occurs more frequently in the early morning and in the late evening, close to sleep onset and after the awakening, and it might be linked to sleep propensity. We aimed to study yawning and its temporal distribution in morning and evening subjects who display different sleep-wake and sleepiness rhythms. Sixteen healthy young adults (8 evening-types and 8 morning-types, matched for age and gender) have been selected and instructed to keep their habitual sleep schedules and to signal every yawning occurrence for three consecutive days. Results show that evening-types yawn more frequently than morning-types, particularly during morning hours. Yawning frequency decreases across daytime in evening-types reaching its lowest level in the early evening and increases thereafter. Instead, in morning-types, yawning frequency remains quite low during daytime and increases in the evening. Moreover, both morning and evening types show a progressive increase of yawning frequency in the hours preceding sleep onset, whereas they differ after the awakening. Evening-types show a higher yawning frequency that remains quite stable in the hours following the awakening, while morning-types display a decline in yawning frequency. Our findings show that the temporal distribution of yawning frequency differs between chronotypes, supporting the hypothesis that differences in sleep-wake rhythm affect yawning, which could represent a behavioural sign of sleep propensity.     

Chronotype and sex effects on sleep architecture and quantitative sleep EEG in healthy young adults

STUDY OBJECTIVES: To evaluate the influence of chronotype (morning types and evening types) on sleep stages and quantitative sleep electroencephalograms when constraints on the sleep schedule are minimal and when sex difference is taken into account. DESIGN: A 48-hour session in the laboratory, including 2 nights of polysomnography, preceded by 7 days of ambulatory actigraphy. SETTING: Chronobiology laboratory. PARTICIPANTS: Twenty-four healthy young subjects: 12 morning types and 12 evening types selected by questionnaire. Each group included 6 men and 6 women. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: A polysomnography night of 8 hours in duration was recorded according to preferred sleep schedule. Sleep-stage analysis revealed that morning types and evening types did not differ in sleep architecture. However, morning-type men showed a higher percentage of stage 1 sleep and lower sleep efficiency than evening-type men. Electroencephalogram spectral analysis was conducted in non-rapid eye movement sleep for 6 frequency bands. Morning types had more spectral power in low sigma (12-14 Hz) compared with evening types. The most robust difference between women and men was found in high sigma (14-16 Hz) and was not present between chronotypes. The decay rate of slow-wave activity (1-5 Hz) tended to be faster in morning types compared with evening types (P = .06). This rate was almost identical for women and men. CONCLUSIONS: These results agree with the hypothesis that homeostatic sleep regulation differs between morning types and evening types, with morning types showing indications of a higher rate of dissipation of sleep pressure during the night. Morningness-eveningness seems to affect sleep in a sex-specific manner, with men being more affected by their chronotype.     

Shift work,sleep disturbances and social jetlag in healthcare workers

The aim of this study was to compare chronotype‐ and age‐dependent sleep disturbances and social jetlag between rotating shift workers and non‐shift workers, and between different types of shifts. In the Klokwerk+ cohort study, we included 120 rotating shift workers and 74 non‐shift workers who were recruited from six Dutch hospitals. Participants wore Actigraph GT3X accelerometers for 24 hr for 7 days. From the Actigraph data, we predicted the sleep duration and social jetlag (measure of circadian misalignment). Mixed models and generalized estimation equations were used to compare the sleep parameters between shift and non‐shift workers. Within shift workers, sleep on different shifts was compared with sleep on work‐free days. Differences by chronotype and age were investigated using interaction terms. On workdays, shift workers had 3.5 times (95% confidence interval: 2.2–5.4) more often a short (< 7 hr per day) and 4.1 times (95% confidence interval: 2.5–6.8) more often a long (≥ 9 hr per day) sleep duration compared with non‐shift workers. This increased odds ratio was present in morning chronotypes, but not in evening chronotypes (interaction p‐value < .05). Older shift workers (≥ 50 years) had 7.3 times (95% confidence interval: 2.5–21.8) more often shorter sleep duration between night shifts compared with work‐free days, while this was not the case in younger shift workers (< 50 years). Social jetlag due to night shifts increased with increasing age (interaction p‐value < .05), but did not differ by chronotype (interaction p‐value ≥ .05). In conclusion, shift workers, in particular older workers and morning chronotypes, experienced more sleep disturbances than non‐shift workers. Future research should elucidate whether these sleep disturbances contribute to shift work‐related health problems.     

Morningness-eveningness, habitual sleep-wake variables and cortisol level

The free cortisol rise immediately after awakening is a distinctive part of the cortisol circadian rhythm. Few studies have focused on the relationship between morningness and cortisol awakening response (CAR). As the suprachiasmatic nucleus may be of major importance for both, one may hypothesise that the CAR should also be associated with morningness. We used saliva samplings and applied questionnaires in adolescents and young adults. Saliva samplings were made at awakening (t1) and 30 min later (t2). Chronotype was measured using the Composite Scale of Morningness (CSM), and habitual time in bed was calculated from habitual rise times and bed times. In both, the adolescent sample and the young adults, positive correlations existed between cortisol measures at t1 immediately after awakening and CSM scores. Using a multivariate model controlling for age group, smoking status and time of t1, we identified CSM scores and bed times as the most relevant variables for CAR. When comparing extreme chronotypes, morning types had higher cortisol levels immediately after awakening than evening types. These results strongly suggest an association between morningness-eveningness and CAR.     

Burnout, perceived stress, and cortisol responses to awakening

OBJECTIVE: The effects of burnout and perceived stress on early morning free cortisol levels after awakening were investigated in a group of teachers. Previous studies revealed that cortisol levels show a significant increase after awakening, with high intraindividual stability. METHODS: Sixty-six teachers from local public schools (42 women and 24 men, mean age 42+/-5 years) were asked to sample saliva for cortisol analysis on 3 consecutive days. On each day, cortisol levels were measured at the time of awakening and 15, 30, and 60 minutes thereafter. On the night before the third day, subjects took 0.5 mg dexamethasone orally for testing glucocorticoid feedback inhibition. Burnout and perceived stress were measured by three different questionnaires. RESULTS: Perceived stress correlated with increases of cortisol levels during the first hour after awakening after dexamethasone pretreatment. In addition, teachers scoring high on burnout showed lower overall cortisol secretion on all sampling days, and a higher suppression of cortisol secretion after dexamethasone administration. In the subgroup of teachers with both high levels of perceived stress and high levels of burnout, a lower overall cortisol secretion was observed on the first 2 days, with stronger increases during the first hour after awakening after dexamethasone suppression. This subgroup also showed the lowest self-esteem, the highest external locus of control, and the highest number of somatic complaints. CONCLUSIONS: These results demonstrate differential effects of burnout and perceived stress on hypothalamic-pituitary-adrenal axis regulation.     

Actigraph measures of sleep among female hospital employees working day or alternating day and night shifts

Sleep disturbance is common among shift workers, and may be an important factor in the effect of shift work on chronic disease development. In this cross‐sectional study, we described sleep patterns of 294 female hospital workers (142 alternating day–night shift workers, 152 day workers) and determined associations between shift work and sleep duration. Rest–activity cycles were recorded with the ActiGraph GT3X+ for 1 week. Analyses were stratified by chronotype of shift workers. Using all study days to calculate average sleep duration, shift workers slept approximately 13 min less than day workers during main sleep periods, while 24‐h sleep duration did not differ between day workers and shift workers. Results from age‐adjusted models demonstrated that all shift workers, regardless of chronotype, slept 20–30 min less than day workers on day shifts during main and total sleep. Early and intermediate chronotypes working night shifts slept between 114 and 125 min less than day workers, both with regard to the main sleep episode and 24‐h sleep duration, while the difference was less pronounced among late chronotypes. When sleep duration on free days was compared between shift workers and day workers, only shift workers with late chronotypes slept less, by approximately 50 min, than day workers during main sleep. Results from this study demonstrate how an alternating day–night shift work schedule impacts sleep negatively among female hospital workers, and the importance of considering chronotype in sleep research among shift workers.     

Chronotype and time-of-day influences on the alerting,orienting, and executive components of attention

Recent research on attention has identified three separable components, known as alerting, orienting, and executive functioning, which are thought to be subserved by distinct neural networks. Despite systematic investigation into their relatedness to each other and to psychopathology, little is known about how these three networks might be modulated by such factors as time-of-day and chronotype. The present study administered the Attentional Network Test (ANT) and a self-report measure of alertness to 80 participants at 0800, 1200, 1600, and 2000 hours on the same day. Participants were also chronotyped with a morningness/eveningness questionnaire and divided into evening versus morning/neither-type groups; morning chronotypes tend to perform better early in the day, while evening chronotypes show enhanced performance later in the day. The results replicated the lack of any correlations between alerting, orienting, and executive functioning, supporting the independence of these three networks. There was an effect of time-of-day on executive functioning with higher conflict scores at 1200 and 1600 hours for both chronotypes. The efficiency of the orienting system did not change as a function of time-of-day or chronotype. The alerting measure, however, showed an interaction between time-of-day and chronotype such that alerting scores increased only for the morning/neither-type participants in the latter half of the day. There was also an interaction between time-of-day and chronotype for self-reported alertness, such that it increased during the first half of the day for all participants, but then decreased for morning/neither types (only) toward evening. This is the first report to examine changes in the trinity of attentional networks measured by the ANT throughout a normal day in a large group of normal participants, and it encourages more integration between chronobiology and cognitive neuroscience for both theoretical and practical reasons. An erratum to this article can be found at     

A prospective study of diurnal cortisol responses to the social experience of school transition in four-year-old children: anticipation, exposure, and adaptation

This study examined psychosocial influences on hypothalamic-pituitary-adrenal axis activity in 105 4-year-old children transitioning to primary school. Measuring before, during, and after school transition over a period of up to 12 months, salivary cortisol was assessed on awakening and early evening. Parents reported child temperament and teachers recorded adaptive behavior. Whilst cortisol at awakening and early evening increased from baseline to school transition, effects were not significant. A significant decrease occurred between transition and follow-up and from baseline to follow-up for both awakening and evening cortisol. Poorer effortful control was associated with high morning and steeper diurnal slope of cortisol at transition whilst surgency/extroversion was associated individually with greater morning and evening cortisol at transition and adaptation. Greater increase in internalizing social isolation during the first 6 months of school in more surgent/extrovert children predicted higher morning and evening cortisol at follow-up. This study is the first to explore these adaptive relationships over a 12-month period and supports social isolation over time as a key element in developmental endocrine activation.     

Chronotype Differences in Health Behaviors and Health-Related Quality of Life: A Population-Based Study Among Aged and Older Adults

This study investigates health behaviors, health-related quality of life (HRQOL) and sleep among chronotypes in a community-based sample (n = 2,976). Analysis of covariance indicated evening types (E-types) had a significantly higher percentage of current smokers and more sleep-interfering behaviors compared to intermediate and morning types (M-type), and also lower physical activity and more sleep disturbance compared to M-types. E-types also had worse mental HRQOL compared to both chronotypes, and worse physical HRQOL compared to M-types. Exploratory analyses indicated E-types consumed more caffeinated beverages at night, smoked or ate heavy meals before bedtime, kept irregular sleep-wake schedules, and took more naps. Mediational analyses indicated that sleep-interfering behavior partially mediated the relationship between chronotype and sleep disturbance, and physical activity partially mediated the relationship between chronotype and mental HRQOL. E-types had more unhealthy behaviors, which may subsequently place them at higher risk for health problems.     

Impact of acute sleep restriction on cortisol and leptin levels in young women

Sleep restriction alters hormone patterns and appetite in men, but less is known about effects on women. We assessed effects of overnight sleep restriction on cortisol and leptin levels and on appetite in young women. Participants' baseline sleep duration and eating habits were monitored for a week before the study. Salivary cortisol and leptin were sampled from fifteen healthy women (aged 18-25) during two consecutive days: first after a 10 h overnight sleep opportunity (Baseline day) and then after a night including only 3 h sleep (Post sleep-restriction day). Participants also completed appetite questionnaires on both days. Sleep restriction significantly reduced morning cortisol levels (p = 0.02), elevated morning leptin levels (p = 0.04), elevated afternoon/evening cortisol area under the curve values (p = 0.008), and slowed the decline in cortisol concentration during the day (p = 0.04). Hunger and craving scores did not differ significantly between days. A single night of restricted sleep affected cortisol rhythms and morning leptin levels in young women.     

Circadian and homeostatic sleep regulation in morningness-eveningness

Morningness-eveningness has been associated with the entrained circadian phase. However, we recently identified morning and evening types having similar circadian phases. In this paper, we compared parameters of slow-wave activity (SWA) decay in non-rapid-eye-movement (NREM) sleep between these two subgroups to test the hypothesis that differences in the dynamics of nocturnal homeostatic sleep pressure could explain differences in sleep timing preference. Twelve morning-type subjects and 12 evening-type subjects with evening types (aged 19-34 years) selected using the Morningness-Eveningness Questionnaire were further classified according to the phase of their dim light melatonin onset (DLMO). The six morning types with the earliest DLMO were compared to the six evening types with the latest DLMO ('extreme' phases), and the six morning types with the latest DLMO were compared to the six evening types with the earliest DLMO ('intermediate' phases). Subjects slept according to their preferred sleep schedule. Spectral activity in four midline derivations (Fz, Cz, Pz, Oz) was calculated in NREM sleep and an exponential decay function was applied on SWA data averaged per sleep cycle. In the subjects with intermediate circadian phases, both initial level and decay rate of SWA in Fz were significantly higher in morning than in evening types. No difference appeared between chronotypes of extreme circadian phases. There was no correlation between individual estimates of SWA decay and DLMO. These results support the hypothesis that chronotype can originate from differences in the dissipation of sleep pressure and that homeostatic and circadian processes influence the sleep schedule preference independently.     

The spinal precerebellar nuclei: calcium binding proteins and gene expression profile in the mouse

Sleep restriction is a widespread phenomenon, specifically in adolescents. This study investigated the impact of increasing sleep restriction in adolescents on cortisol levels and daytime sleepiness. Eighty-eight healthy adolescents were randomized to five sleep restriction protocols (four consecutive nights with 9, 8, 7, 6, or 5 h time in bed). Polysomnography (baseline and last experimental night) and multiple sleep latency test (day 6) data were obtained. Saliva cortisol levels were assessed half-hourly in the evening before and in the morning after the baseline and the last experimental night. Four nights of sleep restriction in healthy adolescents lead to a linear increase of objective sleepiness, but had no significant effect on evening or morning cortisol levels. The lack of detrimental effects of sleep restriction on cortisol levels might be due to compensation mechanisms during sleep.     

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.     

Morningness-eveningness and early-morning salivary cortisol levels.

The purposes of this exploratory study were: (1) to describe a 2-h segment of the early-morning salivary cortisol levels of morning (M) and evening (E) types of healthy, day-active adults on one morning; and (2) to compare selected demographic and sleep characteristics. The sample consisted of 20 subjects, aged 23-39 years, 10 of each type. Measures included: morningness-eveningness questionnaire score, demographic information, self-report sleep characteristics, and self-report of well-being. Beginning with time of arising, seven salivary samples were collected at approximately 20-min intervals. Among the sleep variables, bedtime (p = 0.005), time of mid-sleep (p = 0.002), and arising time (p = 0.043) were later in the E group as compared to the M group. Six M and one E subject awoke spontaneously on the morning of sampling without an awakening aid (p = 0.018). Even though total hours of sleep were comparable between groups, E subjects reported feeling less rested in the morning (p = 0.019). Although mean M group salivary cortisol levels were greater than mean E group levels for each sampling time, there were no significant group differences. Eight M subjects reached a sampling period salivary cortisol peak by 50 min after arising, contrasted with six E subjects who reached their peak at that time. These preliminary findings suggest that E types demonstrate lower morning arousal and a delay in their early-morning peak of salivary cortisol relative to M types. Further study is needed to explore the relationship between M and E types, their sleep-wake patterns, and cortisol secretion patterns.     

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.     

Day-to-day variation in saliva cortisol—Relation with sleep, stress and self-rated health

The objective was to examine the day-to-day variation in cortisol among healthy individuals and its relation to the time of saliva sampling, work, stress and fatigue. During 4 consecutive weeks, 14 office workers provided saliva samples (at awakening, 15 min after awakening and at bedtime) and made diary ratings for each day. Results showed a variation in cortisol values between participants but also within individuals. After controlling for the individual differences, results showed that low cortisol levels in the morning were associated with sleepiness at awakening and anxiety, exhaustion, and poor health the day before. High evening levels of cortisol were associated with symptoms of stress and poor self-rated health. Further analysis of the cortisol awakening response (CAR) showed that all participants had a mixture of both a positive and negative responses. During mornings with a negative response participants stayed in bed for a longer time after the initial awakening, which might be a sign of snoozing, thus missing the awakening response.     

Anticipated next‐day demand affects the magnitude of the cortisol awakening response,but not subjective or objective sleep

Whilst the association between sleep and stress is well established, few studies have examined the effects of an anticipated stressor upon sleep and relevant physiological markers. The aim of the present study was to examine whether an anticipated stressor in the form of next‐day demand affects subjective and objective sleep, and multiple indices of the cortisol awakening response. Subjective and objective sleep and the cortisol awakening response were measured over three consecutive nights in 40 healthy adults in a sleep laboratory. During their second night, participants were informed that they would either be required to complete a series of demanding cognitive tasks, in a competition format, during the next day (anticipation condition; n = 22), or were given no instruction (sedentary condition; n = 18). Sleep was measured subjectively using sleep diaries, objectively using polysomnography, and saliva was measured at awakening, +15, +30, +45 and +60 min each morning, from which cortisol awakening response measurement indices were derived: awakening cortisol levels, the mean increase in cortisol levels and total cortisol secretion. There were no between‐group differences in subjective or objective sleep in the night preceding the anticipated demand; however, compared with the sedentary condition, those in the anticipation group displayed a larger mean increase in cortisol levels, representing the cortisol awakening response magnitude, on the morning of the anticipated demand. Overall, the results suggest that whilst anticipated stress affected the subsequent cortisol awakening response, subjective and objective sleep remained undisturbed. It is possible that the timing of an anticipated stressor, rather than its expected duration, may influence subsequent sleep disruption.     

Increased homeostatic response to behavioral sleep fragmentation in morning types compared to evening types

STUDY OBJECTIVES: To evaluate the influence of chronotype on sleep stages and quantitative sleep EEG when sleep pressure is increased and sleep schedule remains constant. DESIGN: A 5-day session comprising an adaptation night, a baseline night, two nights of sleep fragmentation, and a recovery night. SETTING: Chronobiology laboratory. PARTICIPANTS: Twenty-four healthy subjects aged 19-34 years: 12 morning types and 12 evening types selected by questionnaire. Each group included 6 men and 6 women with a habitual sleep duration of 7 to 9 hours. Interventions: Two nights of behavioral sleep fragmentation induced by forced 5-min awakenings every half-hour. MEASUREMENTS AND RESULTS: Each night of polysomnography recording lasted 8 hours and was based on each subject's preferred sleep schedule. On both nights of sleep fragmentation, stage 1 sleep increased, while both total sleep time and minutes of slow wave sleep decreased. No difference was observed in sleep architecture between morning types and evening types during sleep fragmentation nights or during recovery night. Spectral analysis of all-night NREM sleep EEG showed that during the recovery night, morning types had a larger fronto-central increase in low frequency activities and a larger centro-parietal decrease in 14-15 Hz activity than evening types. The largest group difference was for slow wave activity in the fronto-central area during the first part of the sleep episode. CONCLUSIONS: These results add further support to a postulated difference in homeostatic sleep regulation between morning types and evening types, with morning types showing indications of a higher homeostatic response to sleep disruption.