Circadian determinants of the postlunch dip in performance

Diurnal variation in anxiety and activity is influenced by chronotype and probable anxiety-related disorder status

Anxiety symptoms vary moment-to-moment within a day. One factor that may influence these variations is chronotype. Evening chronotypes prefer to engage in activities (e.g., sleep, physical and social activity) later in the day, and evening chronotype is implicated in psychopathology, including anxiety-related disorders. However, it is unknown whether chronotype influences diurnal variation in anxiety symptoms and whether these effects are amplified in individuals with a probable anxiety-related disorder. We examined the diurnal variation in anxiety symptoms and daily activities in morning and evening chronotypes with and without probable generalized anxiety disorder (GAD) or obsessive-compulsive disorder (OCD) in a community sample of adults (N = 410). Evening chronotypes reported higher anxiety symptoms, particularly in the evening hours, and lower engagement in daily activities, predominantly in the morning hours. Evening chronotypes with probable GAD or OCD reported worse anxiety symptoms in the evening. Our findings indicate that anxiety symptoms and engagement in daily activities fluctuate considerably across the day, and these patterns differ depending on chronotype. Evening chronotypes have more anxiety symptoms in the evening, despite preferring this time of day. Personalized treatment approaches that consider chronotype and target certain times of day may be efficient in alleviating peaks in anxiety symptoms.

The EEG correlates and dangerous behavioral consequences of drowsy driving after a single night of mild sleep deprivation

OBJECTIVE

Here, we investigated the behavioral, cognitive, and electrophysiological impact of mild, acute sleep loss via simultaneously recorded behavioral and electrophysiological measures of vigilance during a "real-world", simulated driving task.

METHODS

Participants (N = 34) visited the lab for two testing days where their brain activity and vigilance were simultaneously recorded during a driving simulator task. The driving task lasted approximately 70 mins and consisted of tailgating the lead car at high speed, which braked randomly, requiring participants to react quickly to avoid crashing. The night before testing, participants either slept from 12am-9am (Normally Rested), or 1am-6am (Sleep Restriction).

RESULTS

After a single night of mild sleep restriction, sleepiness was increased, participants took longer to brake, missed more braking events, and crashed more often. Brain activity showed more intense alpha burst activity and significant changes in EEG spectral power frequencies related to arousal (e.g., delta, theta, alpha). Importantly, increases in amplitude and number of alpha bursts predicted delays in reaction time when braking.

CONCLUSIONS

The findings of this study suggest that a single night of mild sleep loss has significant, negative consequences on driving performance and vigilance, and a clear impact on the physiology of the brain in ways that reflect reduced arousal.

SIGNIFICANCE

Understanding neural and cognitive changes associated with sleep loss may lead to important advancements in identifying and preventing potentially dangerous sleep-related lapses in vigilance.

Revealing the hidden reality of the mammalian 12-h ultradian rhythms

Biological oscillations often cycle at different harmonics of the 24-h circadian rhythms, a phenomenon we coined "Musica Universalis" in 2017. Like the circadian rhythm, the 12-h oscillation is also evolutionarily conserved, robust, and has recently gained new traction in the field of chronobiology. Originally thought to be regulated by the circadian clock and/or environmental cues, recent new evidences support the notion that the majority of 12-h rhythms are regulated by a distinct and cell-autonomous pacemaker that includes the unfolded protein response (UPR) transcription factor spliced form of XBP1 (XBP1s). 12-h cycle of XBP1s level in turn transcriptionally generates robust 12-h rhythms of gene expression enriched in the central dogma information flow (CEDIF) pathway. Given the regulatory and functional separation of the 12-h and circadian clocks, in this review, we will focus our attention on the mammalian 12-h pacemaker, and discuss our current understanding of its prevalence, evolutionary origin, regulation, and functional roles in both physiological and pathological processes.

Effects of time of day on radiological interpretation

Accurate interpretation of radiological images involves a complex visual search that relies on several cognitive processes, including selective attention, working memory, and decision-making. Patient outcomes often depend on the accuracy of image interpretations, and yet research has revealed that conclusions vary significantly from one radiologist to another. A myriad of factors has been shown to contribute to the likelihood of interpretative errors and discrepancies, including the radiologist's level of experience and fatigue, and these factors are well reported elsewhere; however, a potentially important factor that has been given little previous consideration is how radiologists' interpretations might be impacted by the time of day at which the reading takes place, a factor that other disciplines have shown to be a determinant of competency. The available literature shows that while the time of day is known to significantly impact some cognitive functions that likely relate to reading competence, including selective visual attention and visual working memory, little is known about the impact of the time of day on radiology interpretation performance. This review explores the evidence regarding the relationship between time of day and performance, with a particular emphasis on radiological activities.

Trained-feature-specific offline learning by sleep in an orientation detection task

Training-induced performance gains in a visual perceptual learning (VPL) task that take place during sleep are termed "offline performance gains." Offline performance gains of VPL so far have been reported in the texture discrimination task and other discrimination tasks. This raises the question as to whether offline performance gains on VPL occur exclusively in discrimination tasks. The present study examined whether offline performance gains occur in detection tasks. In Experiment 1, subjects were trained on a Gabor orientation detection task. They were retested after a 12-hr interval, which included either nightly sleep or only wakefulness. Offline performance gains occurred only after sleep on the trained orientation, not on an untrained orientation. In Experiment 2, we tested whether offline performance gains in the detection task occur over a nap using polysomnography. Moreover, we tested whether sigma activity during non-rapid eye movement (NREM) sleep recorded from occipital electrodes, previously implicated in offline performance gains of the texture discrimination task, was associated with the degree of offline performance gains of the Gabor orientation detection task. We replicated offline performance gains on the trained orientation in the detection task over the nap. Sigma activity during NREM sleep was significantly larger in the occipital electrodes relative to control electrodes in correlation with offline performance gains. The results suggest that offline performance gains occur over the sleep period generally in VPL. Moreover, sigma activity in the occipital region during NREM sleep may play an important role in offline performance gains of VPL.

Effects of binge alcohol consumption on sleep and inflammation in healthy volunteers

Objective

Alcohol is a hypnotic that modifies immune function, specifically the cytokines interferon gamma (IFN-γ) and interleukin 2 (IL-2). We evaluated the association between unscheduled napping and acute alcohol-induced augmentation of IFN-γ and IL-2 expression.

Methods

In this prospective, observational pilot study, volunteers completed questionnaires on sleep quality, alcohol use, and hangover characteristics. Actigraph recordings began three nights before and continued for four nights after study initiation. Napping was recorded by actigraphy and self-reporting. A weight-based dose of 100-proof vodka was consumed, and the blood alcohol content (BAC) and phytohemagglutinin-M stimulated cytokine level were measured before and 20 minutes, 2 hours, and 5 hours after binge consumption.

Results

Ten healthy volunteers participated (mean age, 34.4 ± 2.3 years; mean body mass index, 23.9 ± 4.6 kg/m²; 60% female). The mean 20-minute BAC was 137.7 ± 40.7 mg/dL. Seven participants took an unscheduled nap. The ex vivo IFN-γ and IL-2 levels significantly increased at all time points after binge consumption in the nappers, but not in the non-nappers.

Conclusion

Augmented IFN-γ and IL-2 levels are associated with unscheduled napping after binge alcohol consumption. Further studies are needed to clarify the associations among alcohol consumption, sleep disruption, and inflammatory mediators.

Unveiling "Musica Universalis" of the Cell: A Brief History of Biological 12-Hour Rhythms

"Musica universalis" is an ancient philosophical concept claiming the movements of celestial bodies follow mathematical equations and resonate to produce an inaudible harmony of music, and the harmonious sounds that humans make were an approximation of this larger harmony of the universe. Besides music, electromagnetic waves such as light and electric signals also are presented as harmonic resonances. Despite the seemingly universal theme of harmonic resonance in various disciplines, it was not until recently that the same harmonic resonance was discovered also to exist in biological systems. Contrary to traditional belief that a biological system is either at stead-state or cycles with a single frequency, it is now appreciated that most biological systems have no homeostatic "set point," but rather oscillate as composite rhythms consisting of superimposed oscillations. These oscillations often cycle at different harmonics of the circadian rhythm, and among these, the ~12-hour oscillation is most prevalent. In this review, we focus on these 12-hour oscillations, with special attention to their evolutionary origin, regulation, and functions in mammals, as well as their relationship to the circadian rhythm. We further discuss the potential roles of the 12-hour clock in regulating hepatic steatosis, aging, and the possibility of 12-hour clock-based chronotherapy. Finally, we posit that biological rhythms are also musica universalis: whereas the circadian rhythm is synchronized to the 24-hour light/dark cycle coinciding with the Earth's rotation, the mammalian 12-hour clock may have evolved from the circatidal clock, which is entrained by the 12-hour tidal cues orchestrated by the moon.

Circadian rhythm abnormalities and autonomic dysfunction in patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) patients frequently show autonomic symptoms which may be associated with a hypothalamic dysfunction. This study aimed to explore circadian rhythm patterns in rest and activity and distal skin temperature (DST) and their association with self-reported outcome measures, in CFS/ME patients and healthy controls at two different times of year. Ten women who met both the 1994 CDC/Fukuda definition and 2003 Canadian criteria for CFS/ME were included in the study, along with ten healthy controls matched for age, sex and body mass index. Self-reported measures were used to assess fatigue, sleep quality, anxiety and depression, autonomic function and health-related quality of life. The ActTrust actigraph was used to record activity, DST and light intensity, with data intervals of one minute over seven consecutive days. Sleep variables were obtained through actigraphic analysis and from subjective sleep diary. The circadian variables and the spectral analysis of the rhythms were calculated. Linear regression analysis was used to evaluate the relationship between the rhythmic variables and clinical features. Recordings were taken in the same subjects in winter and summer. Results showed no differences in rhythm stability, sleep latency or number of awakenings between groups as measured with the actigraph. However, daily activity, the relative amplitude and the stability of the activity rhythm were lower in CFS/ME patients than in controls. DST was sensitive to environmental temperature and showed lower nocturnal values in CFS/ME patients than controls only in winter. A spectral analysis showed no differences in phase or amplitude of the 24h rhythm, but the power of the second harmonic (12h), revealed differences between groups (controls showed a post-lunch dip in activity and peak in DST, while CFS/ME patients did not) and correlated with clinical features. These findings suggest that circadian regulation and skin vasodilator responses may play a role in CFS/ME.

Mobile Manifestations of Alertness: Connecting Biological Rhythms with Patterns of Smartphone App Use

Our body clock causes considerable variations in our behavioral, mental, and physical processes, including alertness, throughout the day. While much research has studied technology usage patterns, the potential impact of underlying biological processes on these patterns is under-explored. Using data from 20 participants over 40 days, this paper presents the first study to connect patterns of mobile application usage with these contributing biological factors. Among other results, we find that usage patterns vary for individuals with different body clock types, that usage correlates with rhythms of alertness, that app use features such as duration and switching can distinguish periods of low and high alertness, and that app use reflects sleep interruptions as well as sleep duration. We conclude by discussing how our findings inform the design of biologically-friendly technology that can better support personal rhythms of performance.

Timing of examinations affects school performance differently in early and late chronotypes

Circadian clocks of adolescents typically run late-including sleep times-yet adolescents generally are expected at school early in the morning. Due to this mismatch between internal (circadian) and external (social) times, adolescents suffer from chronic sleep deficiency, which, in turn, affects academic performance negatively. This constellation affects students' future career prospects. Our study correlates chronotype and examination performance. In total, 4734 grades were collected from 741 Dutch high school students (ages 11-18 years) who had completed the Munich ChronoType Questionnaire to estimate their internal time. Overall, the lowest grades were obtained by students who were very late chronotypes (MSFsc > 5.31 h) or slept very short on schooldays (SDw < 7.03 h). The effect of chronotype on examination performance depended on the time of day that examinations were taken. Opposed to late types, early chronotypes obtained significantly higher grades during the early (0815-0945 h) and late (1000-1215 h) morning. This group difference in grades disappeared in the early afternoon (1245-1500 h). Late types also obtained lower grades than early types when tested at the same internal time (hours after MSFsc), which may reflect general attention and learning disadvantages of late chronotypes during the early morning. Our results support delaying high school starting times as well as scheduling examinations in the early afternoon to avoid discrimination of late chronotypes and to give all high school students equal academic opportunities.

Time-of-day differences and short-term stability of the neural response to monetary reward: a pilot study

Human and animal studies indicate that reward function is modulated by the circadian clock that governs our daily sleep/wake rhythm. For example, a robust circadian rhythm exists in positive affect, which is lower in the morning hours and peaks in the afternoon. A handful of functional neuroimaging studies suggest that systematic diurnal variation exists in brain activity related to other functions, but no published human studies have examined daily variation in the neural processing of reward. In the present study, we attempt to advance this literature by using functional neuroimaging methods to examine time-of-day changes in the responsivity of the reward circuit. Using a within-person design and a functional magnetic resonance imaging (fMRI) monetary reward task, we compared morning and afternoon reward-related brain activation in a sample of healthy young adults within 24h. Region of interest analyses focused on the striatum, and we hypothesized greater reward activation in the afternoon, concordant with the circadian peak in positive affect. Results were consistent with our hypothesis. In addition, we counterbalanced the order of morning and afternoon scans in order to explore the short-term stability of the neural response. Whole-brain analyses showed a markedly higher reactivity to reward throughout the brain in the first scan relative to the second scan, consistent with habituation to the monetary reward stimuli. However, these effects did not appear to explain the time-of-day findings. In summary, we report the first preliminary evidence of circadian variation in the neural processing of reward. These findings have both methodological and theoretical implications.

Half of the family members of critically ill patients experience excessive daytime sleepiness

BACKGROUND

Sleepiness and fatigue are commonly reported by family members of intensive care unit (ICU) patients. Sleep deprivation may result in cognitive deficits. Sleep deprivation and cognitive blunting have not been quantitatively assessed in this population. We sought to determine the proportion of family members of ICU patients that experience excessive daytime sleepiness, sleep-associated functional impairment, and cognitive blunting.

METHODS

Multicenter, cross-sectional survey of family members of patients admitted to ICUs at the University of Maryland Medical Center, Johns Hopkins University Hospital, and Christiana Hospital. Family members of ICU patients were evaluated using the Epworth Sleepiness Scale, a validated survey assessing sleepiness in everyday situations (normal, less than 10); the Functional Outcomes of Sleep Questionnaire-10 (FOSQ-10), a questionnaire quantifying the impact of sleepiness on daily activities (normal, at least 17.9); and psychomotor vigilance testing, a test of cognitive function, in relation to sleep deprivation (normal mean reaction time less than 500 ms).

RESULTS

A total of 225 family members were assessed. Of these, 50.2 % (113/225) had Epworth scores consistent with excessive daytime sleepiness. Those with sleepiness experienced greater impairment in performing daily activities by FOSQ-10 (15.6 ± 3.0 vs 17.4 ± 2.2, p < 0.001). Cognitive blunting was found in 13.3 % (30/225) of family members and 15.1 % (14/93) of surrogate decision-makers. Similar rates of cognitive blunting as reported by mean reaction time of at least 500 ms were found among family members whether or not they reported sleepiness (15.0 % (17/113) vs. 11.6 % (13/112), p = 0.45).

CONCLUSIONS

Half of the family members of ICU patients suffer from excessive daytime sleepiness. This sleepiness is associated with functional impairment, but not cognitive blunting.

Diurnal fatigue patterns, sleep timing, and mental health outcomes among healthy postpartum women

Postpartum women have frequently interrupted sleep, report high levels of fatigue, and may experience circadian rhythm disruptions. They are also susceptible to mood impairments, anxiety, and stress. The current study explored associations between maternal postpartum daily fatigue patterns, which should vary according to circadian influences and mental health. Seventy-one primiparous, healthy mothers completed multiple daily self-reports of fatigue during postpartum Weeks 2 and 12 and were categorized at each week as having either a rhythmic or random fatigue pattern during the daytime. Wrist actigraphy data were used to calculate sleep midpoints. Surveys assessed chronotype, mood, anxiety, and stress. At postpartum Week 2, there were no differences in mental health measures between fatigue groups. At postpartum Week 12, higher overall fatigue levels were associated with increased anxiety, stress, and mood disruption. However, overall fatigue levels did not differ between fatigue groups. Women with a rhythmic fatigue pattern reported significantly less stress and more vigor than women with a random fatigue pattern. An earlier sleep midpoint was associated with a rhythmic fatigue pattern during postpartum Week 12. These data suggest that, despite similar average daily fatigue levels, having a rhythmic daily pattern of fatigue may be advantageous for mental health outcomes among postpartum women.

Sleep ability mediates individual differences in the vulnerability to sleep loss: evidence from a PER3 polymorphism

Sleep deprivation is highly prevalent in our 24/7 society with harmful consequences on daytime functioning on the individual level. Genetically determined, trait-like vulnerability contributes to prominent inter-individual variability in the behavioral responses to sleep loss and adverse circadian phase. We aimed at investigating the effects of differential sleep pressure levels (high vs low) on the circadian modulation of neurobehavioral performance, sleepiness correlates, and nap sleep in individuals genotyped for a polymorphism in the clock gene PERIOD3. Fourteen homozygous long (PER3(5/5)) and 15 homozygous short (PER3(4/4)) allele carriers underwent both a 40-h sleep deprivation and multiple nap protocol under controlled laboratory conditions. We compared genotypes regarding subjective and ocular correlates of sleepiness, unintentional sleep episodes as well as psychomotor vigilance during both protocols. Nap sleep was monitored by polysomnography and visually scored according to standard criteria. The detrimental effects of high sleep pressure on sleepiness correlates and psychomotor vigilance were more pronounced in PER3(5/5) than PER3(4/4) carriers. Under low sleep pressure, both groups showed similar circadian time courses. Concomitantly, nap sleep efficiency and subjective sleep quality across all naps tended to be higher in the more vulnerable PER3(5/5) carriers. In addition, PER3-dependent sleep-loss-related attentional lapses were mediated by sleep efficiency across the circadian cycle. Our data corroborate a greater detrimental impact of sleep deprivation in PER3(5/5) compared to PER3(4/4) carriers. They further suggest that the group with greater attentional performance impairment due to sleep deprivation (PER3(5/5) carriers) is superior at initiating sleep over the 24-h cycle. This higher sleep ability may mirror a faster sleep pressure build-up between the multiple sleep opportunities and thus a greater flexibility in sleep initiation. Finally, our data show that this higher nap sleep efficiency is positively related to attentional failures under sleep loss conditions and might thus be used as a marker for inter-individual vulnerability to elevated sleep pressure.

Neural decoding of visual imagery during sleep

Visual imagery during sleep has long been a topic of persistent speculation, but its private nature has hampered objective analysis. Here we present a neural decoding approach in which machine-learning models predict the contents of visual imagery during the sleep-onset period, given measured brain activity, by discovering links between human functional magnetic resonance imaging patterns and verbal reports with the assistance of lexical and image databases. Decoding models trained on stimulus-induced brain activity in visual cortical areas showed accurate classification, detection, and identification of contents. Our findings demonstrate that specific visual experience during sleep is represented by brain activity patterns shared by stimulus perception, providing a means to uncover subjective contents of dreaming using objective neural measurement.

Circadian rhythms as a basis for work organization: a study with live line electricians

OBJECTIVE

With the assumption that circadian rhythms influence human performance, the work of live line electricians was reorganized and evaluated. The hypothesis was that in highly physical and attention-demanding work, the organization of tasks, according to the ideal period of day and day of week, should diminish stress and consequent work risks.

BACKGROUND

There are only a few studies reporting the work of electricians and even fewer approaching work organization. Moreover, these investigations often do not consider human physiological limitations and capabilities as well as task demands.

METHOD

A new work system was proposed with consideration of (a) the circadian cycles and homeostatic processes; (b) the effect of heat, which is a zeitgeber (synchronizer) for the biological clocks; and (c) the degree of physical and mental demands of the different performed tasks, which was assessed on the basis of opinions of the electricians and physiological markers of stress that are controlled by circadian rhythms. The traditional and new systems were compared on the basis of two cognitive indices (the arrangement of matchsticks and the perception of a minute) and three physiological markers of mental-to-physical loads (heart frequency and the level of adrenaline and noradrenaline).

RESULTS

Both physical and mental loads were reduced in the new system.

CONCLUSION

Work organization should include consideration of human circadian rhythms, mainly when stressful and high-risk tasks are involved.

APPLICATION

The findings can be applied in any work design, but they are especially suited for highly demanding work carried out outdoors.

Modulation of attention-deficit/hyperactivity disorder symptoms by short- and long-acting methylphenidate over the course of a day

The purpose of this study was to investigate whether a long-acting methylphenidate formulation (MPH-ret) is as effective as two doses of immediate-release methylphenidate (MPH-IR) in reducing attention-deficit/hyperactivity disorder (ADHD) symptoms including inattention, impulsivity, and hyperactivity during the course of the day. Two groups of children (n=18 each) with ADHD aged between 8 and 12 years completed a continuous performance test in combination with a motion-tracking system four times a day within 8 hours. Inattention (standard deviation of reaction time), impulsivity (commission error rate), and hyperactivity (path length of the headband) were simultaneously measured. We included a control group (n=20) to rule out circadian fluctuations of attentional performance and motor activity. We observed a postlunch dip in attentional performance and an increasing trend of motor activity throughout the day whereas impulsivity remained stable in controls. The MPH-ret and MPH-IR groups had comparable treatment effects on measures of hyperactivity and inattention and normalized participant performance to control levels. In contrast, MPH-IR seems to have an advantage over MPH-ret in impulsivity treatments. Thus, our data suggest that it is crucial to assess the different domains of ADHD symptoms precisely over the course of a day to determine the optimal titration and stimulant formulation for a person with ADHD.

Induced hyperammonemia may compromise the ability to generate restful sleep in patients with cirrhosis

In patients with cirrhosis, hyperammonemia and hepatic encephalopathy are common after gastrointestinal bleeding and can be simulated by an amino acid challenge (AAC), or the administration of a mixture of amino acids mimicking the composition of hemoglobin. The aim of this study was to investigate the clinical, psychometric, and wake-/sleep-electroencephalogram (EEG) correlates of induced hyperammonemia. Ten patients with cirrhosis and 10 matched healthy volunteers underwent: (1) 8-day sleep quality/timing monitoring; (2) neuropsychiatric assessment at baseline/after AAC; (3) hourly ammonia/subjective sleepiness assessment for 8 hours after AAC; (4) sleep EEG recordings (nap opportunity: 17:00-19:00) at baseline/after AAC. Neuropsychiatric performance was scored according to age-/education-adjusted Italian norms. Sleep stages were scored visually for 20-second epochs; power density spectra were calculated for consecutive 20-second epochs and average spectra determined for consolidated episodes of non-rapid eye movement (non-REM) sleep of minimal common length. The AAC resulted in: (i) an increase in ammonia concentrations/subjective sleepiness in both patients and healthy volunteers; (ii) a worsening of neuropsychiatric performance (wake EEG slowing) in two (20%) patients and none of the healthy volunteers; (iii) an increase in the length of non-REM sleep in healthy volunteers [49.3 (26.6) versus 30.4 (15.6) min; P = 0.08]; (iv) a decrease in the sleep EEG beta power (fast activity) in the healthy volunteers; (v) a decrease in the sleep EEG delta power in patients.

CONCLUSION

AAC led to a significant increase in daytime subjective sleepiness and changes in the EEG architecture of a subsequent sleep episode in patients with cirrhosis, pointing to a reduced ability to produce restorative sleep.

Aspectos do regime de embarque, turnos e gestão do trabalho em plataformas offshore da Bacia de Campos (RJ) e sua relação com a saúde e a segurança dos trabalhadores

O artigo aborda pesquisa desenvolvida na indústria petrolífera offshore da Bacia de Campos (Rio de Janeiro, Brasil), campo empírico que acompanhamos de forma sistemática desde 2003 e que se situa no rol dos sistemas sociotécnicos complexos. Nosso objetivo é destacar os riscos potenciais associados à organização do trabalho, em especial o regime de embarque e o sistema de turnos adotados nas plataformas de petróleo por algumas das empresas atuantes na região. Isto porque entendemos que, no contexto investigado, os problemas relacionados à saúde - aí inclusos os que se situam na esfera mental - e à segurança dos trabalhadores possuem relação importante com aspectos da organização do trabalho, como aqueles que aqui se encontram em foco. Indicam-se proposições de mudança com o intuito de reduzir os impactos deletérios de tais fatores sobre a saúde e a segurança dos trabalhadores. A base teórico-metodológica utilizada na pesquisa se fundamenta, principalmente, no instrumental da Ergonomia da Atividade e da Psicodinâmica do Trabalho, numa perspectiva ergológica.

Circadian rhythm in force tracking and in dual task costs

The present study determined a circadian rhythm in force control during a visually guided tracking task under single task conditions (i.e., tracking task presented alone) and dual task conditions (i.e., tracking task together with a memory task). Nine healthy young male subjects participated in a Constant Routine protocol involving a week of regular bedtimes, a baseline night of 8 h sleep, and subsequent wakefulness of 40 h. Subjects performed an eye-hand coordination task that required tracking an unpredictable target (presented on a computer screen) by using grip force to adjust a visual feedback to the changing target. Tracking performance (both in precision and delay) were time-of-day-specific with worst performance at around 04:00 h. The dual task costs, as an index of interference of two tasks performed simultaneously, only showed a significant effect of the memory task on tracking precision during the circadian minimum. In contrast, dual task costs were close to zero during midday and absent in tracking delay. Tracking precision descriptively revealed inter-individual differences: half of the subjects maintained fairly stable performance during the 40 h of wakefulness, whereas the other half showed a clear circadian rhythmicity in tracking precision. Thus, tracking precision seems to be a sensitive parameter for conditions of divided attention and inter-individual variability during the circadian minimum, whereas tracking delay revealed neither a dichotomy of task conditions nor inter-individual differences in performance-amplitude over sessions. Nonetheless, both tracking precision and delay showed a comparable circadian rhythmicity.

Cognitive status changes based on time of day in nursing home patients with and without dementia

BACKGROUND

Changes in behavior and cognition have been observed with disruption of the circadian rhythm.

METHODS

This study examined the effects of time of day (TOD) on administration of Mini-Mental State Examinations (MMSEs) in nursing home patients with dementia (patients) or functional psychiatric disorders (control), using repeated measures analyses of covariance (ANCOVAs).

RESULTS

Controls (n = 34) scored significantly higher than patients (n = 38) on total MMSE and all subscales. Within the patients, men and women performed equally in the morning, but women performed marginally worse in the afternoon on total MMSE scores, orientation, and immediate recall and men performed significantly better in the afternoon. Within the control, no gender or time effects were detected.

CONCLUSION

Results indicate that TOD had no significant impact on cognitive status in patients with dementia or patients with other psychiatric illnesses. No changes in activity timings are recommended in nursing home patients with dementia.

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.

Self-awakening, sleep inertia, and P3 amplitude in elderly people

It is well known that sleepiness is sometimes experienced in the afternoon. A short afternoon nap is thought to be effective in reducing sleepiness. However, sleep inertia occurs even after a short nap, and this could be a major risk factor for injuries from falling by the elderly. In the present study, the effect of self-awakening on sleep inertia after a 20-min. nap was examined. Nine participants (M=74.1 yr., SD=5.0 yr.) took part in the three experimental conditions: the self-awakened nap, the forced-awakened nap, and the control (no-nap) conditon. Analysis showed sleepiness and performance after the nap significantly improved compared with the control condition. P3 amplitude tended to be larger after self-awakening than after forced-awakening. The present study indicates a 20-min. nap reduces afternoon sleepiness, and the application of self-awakening may contribute to higher arousal after a nap taken by this elderly group.

Effectiveness of Aroma on Work Efficiency: Lavender Aroma during Recesses Prevents Deterioration of Work Performance

The present study investigated whether exposure to aromas during recess periods affects work performance. Subjects comprised 36 healthy male students (mean age, 24.2 +/- 2.2 years) who were randomly divided into three groups: (1) control group, not exposed to aroma during recesses; (2) jasmine group, exposed to jasmine aroma during recesses; and (3) lavender group, exposed to lavender aroma during recesses. All participants completed five work sessions performing a task requiring concentration on a computer monitor, with each session lasting 60 min. Recess periods of 30 min were provided between each session. To clarify the time at which work concentration was lowest, work performance for the control group was analyzed. Concentration was lowest in the afternoon period, where afternoon drowsiness is strongest. Comparison of the three groups for this time period indicated significantly higher concentration levels for the lavender group than for the control group. No such effect was noted for the jasmine group. Although lavender is a sedative-type aroma, use during recess periods after accumulation of fatigue seems to prevent deterioration of performance in subsequent work sessions.

The effects of self-awakening on heart rate activity in a short afternoon nap

OBJECTIVES

This study examined whether anticipatory changes exist in heart rate prior to awakening from a nap by means of self-awakening. The effects of self-awakening on sleepiness after the short nap were also studied.

METHOD

Nine students participated in 3 experimental conditions: (1) the control condition, in which participants watched television instead of taking a short nap; (2) the self-awakening condition, in which participants tried to wake up approximately 15 min after 'lights off' (criterion range: 15+/-5 min) and (3) the forced-awakening condition, in which participants were instructed to sleep for 30 min, but were awoken by the experimenter after 15 min.

RESULTS

In the self-awakening condition, heart rate gradually increased approximately 3 min before awakening. The error response ratio of the auditory-oddball task and the duration of doze time during the task were less after both types of nap conditions than in the control condition. Subjective sleepiness, which is measured after awakening, was lowest in the self-awakening condition.

CONCLUSIONS

The results of this experiment suggest that self-awakening prepares autonomic activation that facilitates a more smooth transition from sleep to awakening, and reduces sleepiness after naps.

Circasemidian 12 h cycle of slow wave sleep under constant darkness

OBJECTIVES

Afternoon sleepiness is a widespread phenomenon. The present study aimed to test Broughton's hypothesis (Sleep and alertness: chronobiological, behavioral, and medical aspects of napping. New York, NY: Raven Press, 1989. p. 71-98) that afternoon sleep propensity might reflect the circasemidian 12h cycle of slow wave sleep (SWS).

METHODS

Nine subjects (21-27 year) stayed alone under constant darkness (0 lux) without social contact for 72 h. They were allowed to sleep and eat freely. Their polysomnograms during 72 h of constant darkness were analyzed.

RESULTS

The total sleep time (TST) accounted for 41.6h (57.9%) of the 72 h and decreased progressively as a function of time. The reduction in TST was dependent on the decrease in sleep stage 2 and rapid eye movement (REM) sleep. The amount of SWS did not significantly change among the days. The circadian (1 cycle/day) and circasemidian (2cycles/day) cycles were observed in SWS. Those accounted for 13.9 and 11.1% of the total variance, respectively. SWS during the time corresponding to daytime occurred 9-10h before and 15-16 h after the nocturnal sleep gate. In addition, weak but significant correlations were observed between the amounts of SWS and the waking time before the sleep episodes (r=0.332) and prior REM sleep (r=-0.236).

CONCLUSIONS

The present findings suggest that SWS might occur not only always in a homeostatic manner as a function of prior wakefulness, but also as a circasemidian rhythmic function.

Sleep-wake as a biological rhythm

Evidence that the sleep-wake rhythm is generated endogenously has been provided by studies employing a variety of experimental paradigms such as sleep deprivation, sleep displacement, isolating subjects in environments free of time cues, or imposing on subjects sleep-wake schedules widely deviating from 24 hours. The initial observations obtained in isolated subjects revealed that the period of the endogenous circadian pacemaker regulating sleep is of approximately 25 hours. More recent studies, however, in which a more rigorous control of subjects' behavior was exerted, particularly over lighting conditions, have shown that the true periodicity of the endogenous pacemaker deviates from 24 hours by a few minutes only. Besides sleep propensity, the circadian pacemaker has been shown to regulate sleep consolidation, sleep stage structure, and electroencephalographic activities. The pattern of light exposure throughout the 24 hours appears to participate in the entrainment of the circadian pacemaker to the geophysical day-night cycle. Melatonin, the pineal hormone produced during the dark hours, participates in communicating both between the environmental light-dark cycle and the circadian pacemaker, and between the circadian pacemaker and the sleep-wake-generating mechanism. In contrast to prevailing views that have placed great emphasis on homeostatic sleep drive, recent data have revealed a potent circadian cycle in the drive for wakefulness, which is generated by the suprachiasmatic nucleus. This drive reaches a peak during the evening hours just before habitual bedtime.

Gender differences in diurnal variations of subjective activation and mood

This article evaluates the influence of gender on diurnal and postlunch period variations in subjective activation and mood. This topic is not often addressed in the literature; particularly, little attention has been paid to how biological rhythms might bias research results. We studied 40 university student volunteers (20 men, 20 women) aged 18 to 23 years old (X = 20.23, SD = 1.03); they responded to questions on eight unipolar visual analog scales every hour from 08:00 to 21:00. Gender differences were observed in both diurnal and postlunch variations for scales of positive activation (alertness, vigor); sleepiness, however, was only sensitive to diurnal variation, and weariness was sensitive only to a postlunch effect. Women displayed a morning-type pattern, with their optimal moment (11:00) coming 2h earlier than for men, and their activation ratings ranged more widely. The only mood scale that showed differences related to gender was that of happiness, for which women had a higher diurnal mean, a diurnal peak 2h earlier, and a less-intense postlunch effect. Endogenous control of rhythmic pattern appears to be less intense in women, probably due to the coexistence of circamensual rhythmicity, although environmental or sociocultural influences may play a modulating role. Chronopsychological gender differences in affective states should be studied further given the implication they have for the prevention and treatment of mood disorders.

Steroid hormones, memory and mood in a healthy elderly population

Men (n = 31), women estrogen-users (n = 14), and women estrogen non-users (n = 41), whose average age was 72.1 +/- 5.6 years, were tested with a battery of psychological tests measuring verbal memory, visual memory, concentration and attention, language fluency and semantic memory, and mood. Plasma levels of testosterone (T), estradiol (E2), cortisol (CRT) and dehydroepiandrosterone-sulfate (DHEAS) were assessed by radioimmunoassay. The ratio of DHEAS to CRT was calculated to determine it's relationship to memory functioning. The men had higher T and DHEAS levels than both groups of women. Women estrogen-users had higher E2 levels than both men and estrogen non-users and the men had higher E2 levels and a higher DHEAS/CRT ratio than the estrogen non-users. There were no group differences in CRT levels. Men and estrogen-users had higher total (p < .01) and forward (p < .001) digit span scores compared with non-users. Women estrogen-users also had higher backward digit span scores than non-users (p < .05), while both groups of women performed better than men on category retrieval (p < .01). The implications of these findings with respect to hormonal influences on memory in elderly men and women are discussed.