The associations of daytime napping and motoric cognitive risk syndrome: Findings from the China Health and Retirement Longitudinal Study

INTRODUCTION

Motoric cognitive risk syndrome (MCR), characterized by subjective cognitive complaints and slow gait in older populations, is associated with sleep duration. However, the association between MCR and daytime nap duration has not been thoroughly explored.

METHODS

Baseline data from the China Health and Retirement Longitudinal Study (CHARLS) were used in this study. MCR was defined as the coexistence of subjective cognitive complaints and objective slow gait speed without a history of dementia or mobility disability. Daytime nap duration was categorized into four groups: no napping, short napping (<30 min), moderate napping (30-89 min) and extended napping (≥90 min). Multivariable logistic regression models were used to explore the association of daytime napping duration and MCR.

RESULTS

A total of 4230 individuals aged ≥60 were included in the current analysis, of which 463 were diagnosed with MCR. Moderate napping of 30-89 min per day was found to be significantly associated with lower odds of MCR compared with the reference group of no napping. In subgroup analysis, individuals with sleep durations of <7 h per night had lower odds of MCR in the model that adjusted for all potential confounders with ≥30 min daytime nap duration compared with no napping. Interestingly, for people with a night sleep duration of 7-8 h, only those with a moderate nap of 30-89 min had lower odds of MCR than non-nappers after adjustment for potential confounders.

CONCLUSION

A moderate nap of 30-89 min could lower the odds of MCR, especially for older adults with a night sleep duration of ≤8 h.

Association Between Changes in Sleep, Nap Duration and Bone Mineral Density in Mexican Adults

Studies have found associations between sleep, nap duration, and bone mineral density (BMD). However, the longitudinal relationship between sleep, nap duration, and BMD has not been explored. We evaluated the association between the change in sleep and nap duration and BMD in Mexican adults. Data come from 1,337 adult participants of the Health Workers Cohort Study (341 were men and 996 were women, including 450 women < 45 years old and 546 ≥ 45 years old), with two study waves. At each wave, sleep and nap duration was assessed using self-administered questionnaires and BMD in g/cm2 was determined by dual X-ray absorptiometry. We used fixed-effect regression models stratified by sex and adjusted for BMI, diet, physical activity, vitamin supplements, and hormone replacement therapy. Women who changed from < 7 to ≥ 7 h/day of sleep from baseline to follow-up were associated with increases in the total hip (β = 0.012 g/cm2; 95% CI: 0.002, 0.022) and lumbar spine BMD (β = 0.024 g/cm2; 95% CI: 0.009, 0.039). Furthermore, most of these associations were observed in women ≥ 45 years. For women, a changing from 0 to > 60 min/day of napping was associated with a significant increase in total hip BMD of 0.012 g/cm2 (95% CI: 0.004, 0.024) and lumbar spine BMD of 0.027 g/cm2 (95% CI: 0.009, 0.045). No significant associations were observed for men. Our results suggest that increased sleep and nap duration are associated with gains in BMD in Mexican women, emphasizing sleep's role in promoting bone health and supporting established recommendations.

Interaction effect of midday napping duration and depressive symptoms on subjective memory impairment among older people in China: evidence from the China health and retirement longitudinal study database

BACKGROUND

Subjective memory impairment (SMI) is common in older people. The aim of this study was to investigate the factors influencing SMI among older people in China, with specific focus on the interaction effect of midday napping duration and depressive symptoms on the risk of SMI.

METHODS

Using a dataset representative of the Chinese population from a longitudinal study of health and retirement in China, subjects with SMI were screened using the question "how do you feel about your memory now?" and the Mini-Mental State Examination. A logistic regression model was applied to explore the factors affecting SMI. Additive and multiplicative models were used to analyze the interaction effect of midday napping duration and depressive symptoms on the risk of SMI.

RESULTS

We enrolled 8,254 subjects included and the incidence of SMI was 63.9%. Depressive symptoms, nap time, and physical activity were influencing factors of SMI. Midday napping duration and depressive symptoms had positive additive interaction effects on the risk of SMI. When extended-length naps and depressive symptoms coexisted, the risk of SMI was 1.06 times greater than that for either alone (RERI, relative excess risk due to interaction = 0.27, 95% CI = 0.07-0.43; AP, attributable proportion = 0.14, 95% CI = 0.01-0.23; S, synergy index = 1.06, 95% CI = 0.57-1.62). When short naps and depressive symptoms coexisted, the risk of SMI was 1.2 times higher than that for either alone (RERI = 0.12, 95% CI=-0.14-0.39; AP = 0.13, 95% CI=-0.07-0.22; S = 1.20, 95% CI = 0.79-1.82).

LIMITATIONS

Since this was a cross-sectional study, the cause-and-effect relationships between the associated variables cannot be inferred.

CONCLUSIONS

The interaction effect that exists between nap time and depressive symptoms in older people is important for the identification and early intervention of people at risk for SMI.

Intertemporal Decision-making and Risk Decision-making Among Habitual Nappers Under Nap Sleep Restriction: A Study from ERP and Time-frequency

Sleep restriction affects people's decision-making behavior. Nap restriction is a vital subtopic within sleep restriction research. In this study, we used EEG to investigate the impact of nap sleep restriction on intertemporal decision-making (Study 1) and decision-making across risky outcomes (Study 2) from ERP and time-frequency perspectives. Study 1 found that habitual nappers restricting their naps felt more inclined to choose immediate, small rewards over delayed, large rewards in an intertemporal decision-making task. P200s, P300s, and LPP in our nap-restriction group were significantly higher than those in the normal nap group. Time-frequency results showed that the delta band (1 ~ 4 Hz) power of the restricted nap group was significantly higher than that of the normal nap group. In Study 2, the nap-restriction group was more likely to choose risky options. P200s, N2s, and P300s in the nap deprivation group were significantly higher than in the normal nap group. Time-frequency results also found that the beta band (11 ~ 15 Hz) power of the restricted nap group was significantly lower than that of the normal nap group. The habitual nappers became more impulsive after nap restriction and evinced altered perceptions of time. The time cost of the LL (larger-later) option was perceived to be too high when making intertemporal decisions, and their expectation of reward heightened when making risky decisions-believing that they had a higher probability of receiving a reward. This study provided electrophysiological evidence for the dynamic processing of intertemporal decision-making, risky decision-making, and the characteristics of nerve concussions for habitual nappers.

Daytime Napping Benefits Passing Performance and Scanning Activity in Elite Soccer Players

The present study explored the effect of a daytime napping opportunity on scanning activity, which is an essential component of successful soccer performance. Fourteen male elite collegiate soccer players performed the Trail Making Test (TMT), which was used to assess complex visual attention. In addition, a soccer passing test, modified with reference to the Loughborough Soccer Passing Test, was used to evaluate passing performance as well as scanning activity. A cross-over design was applied to examine nap and no-nap interventions. Participants (N = 14, mean age: 21.6 SD = 0.5 years, height: 1.73 ± 0.06 m, body mass: 67.1 ± 4.5 kg) were randomly allocated to a midday nap (40 minutes) or no-nap group. Subjective sleepiness was measured using the Karolinska Sleepiness Scale, and perceptive fatigue was evaluated by the visual analog scale. There were no significant differences in subjective measurements or TMT between the nap and no-nap groups. However, the performance time for the passing test and scanning activity was significantly shorter (p < 0.001) and scanning activity was significantly more frequent in the nap condition than in the no-nap condition (p < 0.00005). These results suggest that daytime napping is beneficial for soccer-related cognitive function, represented by visuospatial processing and decision-making, and particularly as a potential countermeasure to mental fatigue. Considering that inadequate sleep and residual fatigue are commonly observed in elite soccer, this finding may have practical implications for the preparation of players.

Influence of Mid-Afternoon Nap Duration and Sleep Parameters on Memory Encoding, Mood, Processing Speed and Vigilance

STUDY OBJECTIVES

To determine how mid-afternoon naps of differing durations benefit memory encoding, vigilance, speed-of-processing (SOP), mood, and sleepiness; to evaluate if these benefits extend past 3 h post-awakening and to examine how sleep macrostructure during naps modulate these benefits.

METHODS

Following short habitual sleep, 32 young adults underwent 4 experimental conditions in randomized order: wake; naps of 10min, 30min and 60min duration verified with polysomnography. A 10-min test battery was delivered at a pre-nap baseline, and at 5min, 30min, 60min and 240min post nap. Participants encoded pictures 90min post-nap and were tested for recognition 210min later.

RESULTS

Naps ranging from 10-60mins increased positive mood and alleviated subjective sleepiness up to 240min post-nap. Compared to wake, only naps of 30min improved memory encoding. Improvements for vigilance were moderate, and benefits for SOP were not observed. Sleep inertia was observed for the 30min to 60min naps but was resolved within 30mins after waking. We found no significant associations between sleep macrostructure and memory benefits.

CONCLUSIONS

With short habitual sleep, naps ranging from 10-60mins had clear and lasting benefits for positive mood and subjective sleepiness / alertness. Cognitive improvements were moderate, with only the 30min nap showing benefits for memory encoding. While there is no clear 'winning' nap duration, a 30min nap appears to have the best trade-off between practicability and benefit.

The unique contributions of day and night sleep to infant motor problem solving

The current study sought to tease apart the unique contributions of napping and nighttime sleep to infant learning, specifically in the context of motor problem solving. We challenged 54 walking infants to solve a novel locomotor problem at three time points-training, test, and follow-up the next morning. One group of infants napped during the delay between training and test. Another group did not sleep during the delay. A third group received the test immediately after training with no delay. Only the Nap group's strategy choices continued to improve through the follow-up session, suggesting that daytime sleep has an active role in strengthening otherwise fragile memory. Although group did not affect strategy maintenance, walk experience did, suggesting that task difficulty may shape the impact of sleep on learning. Thus, day sleep and night sleep make independent contributions to the consolidation of motor problem-solving strategies during infancy.

Effects and differences of sleep duration on the risk of new-onset chronic disease conditions in middle-aged and elderly populations

BACKGROUND

Few longitude cohort studies investigated the risk of the duration of nighttime sleep and naps to the new-onset common chronic disease conditions (CDCs) in middle-aged (45-60) and the elderly (age ≥ 60) populations using an age-stratified strategy.

METHODS

The 7025 participants from The China Health and Retirement Longitudinal Study were screened as eligible subjects. Established 13 cohorts with CDCs, acquired their' sleep records in 2011, and obtained new-onset incidents of CDCs during follow-up in 2011-2018. Performed risk association analyses between sleep duration and 13 new-onset CDCs respectively.

RESULTS

New-onset risk of four CDCs decreased with increasing nighttime sleep (p-nonlinear>0.05). The risk threshold was approximately 7 hours in middle-aged people and 6 hours in the elderly. For the middle-aged population, compared with 7-9hours sleep, <5hour and 5-7hours nighttime sleep were associated with 1.312∼1.675 times more risk of hypertension, kidney disease, diabetes or high blood sugar status, and multimorbidity; Compared with no nap, a 0-30 min nap was associated with 1.413(1.087∼1.837) times the heart disease risk. In the elderly, < 5 hours of night sleep was a significant risk factor for four CDCs including kidney disease and multimorbidity, etc. A long night's sleep (>9 hours) was connected with 61.2% reduction in risk of memory disease, a >90 min nap increased 62% risk of memory disease, and a 0-30 min nap was associated with higher risks of heart disease, hypertension, and a lower kidney disease risk.

CONCLUSIONS

Nighttime sleep and daytime naps may have their own implications for the new-onset CDCs' risk in the aging process.

A systematic review of effects of daytime napping strategies on sports performance in physically active individuals with and without partial-sleep deprivation

Background

Sleep is the body's natural recovery process, restoring routine metabolic and regulatory functions. Various sleep interventions have been developed to facilitate recovery, and athletic performance, and daytime napping are among them. However, due to inconsistencies in studies, it remains unclear whether daytime napping affects sports performance. This article aims to review the effects of daytime napping on various variables of sports performance in physically active individuals with and without partial-sleep deprivation.

Methods

A systematic search in three clinical databases, namely Cochrane Central Register of Controlled Trials (CENTRAL), PubMed, and Web of Science, was conducted. To be included in the current review, the study should be a randomized controlled trial that evaluated the influence of daytime napping on one or more components of sports performance in healthy adults, 18 years old or older.

Results

In the accessible data available until December 2021, 1,094 records were found, of which 12 relevant randomized controlled trials were selected for qualitative synthesis. The majority of studies reported favourable effects of daytime napping on sports performance. However, only one study reported no significant impact, possibly due to a different methodological approach and a shorter nap duration.

Conclusion

Napping strategies optimize sports performance in physically active, athletic populations, benefitting partially sleep-deprived and well-slept individuals, with longer nap durations (~90 min) having more significant advantages. Daytime naps can be considered as cost-efficient, self-administered methods promoting recovery of body functions.

Self-reported daytime napping, daytime sleepiness, and other sleep phenotypes in the development of cardiometabolic diseases: a Mendelian randomization study

AIMS

Sleep disorders are associated with an increased risk of cardiometabolic diseases in observational studies, but the causality remains unclear. In this study, we leveraged two-sample Mendelian randomization (MR) analyses to assess the causal associations of self-reported daytime napping, daytime sleepiness, and other sleep phenotypes with cardiometabolic diseases including ischaemic stroke (IS), coronary artery disease (CAD), heart failure (HF), and Type 2 diabetes mellitus (T2DM).

METHODS AND RESULTS

We selected genetic variants as instrumental variables for self-reported daytime napping, daytime sleepiness, morning person, insomnia, short sleep duration, and long sleep duration from European-descent genome-wide association studies (GWASs). Summary statistics for cardiometabolic diseases originated from four different GWASs with a total of 2 500 086 participants. We used the inverse-variance weighted method to explore the role of self-reported sleep phenotypes on the aetiology of cardiometabolic diseases in the main analyses, followed by several sensitivity analyses for robustness validation. Genetically predicted self-reported daytime napping [T2DM: OR, 1.56 (95% confidence interval, 1.21-2.02)], insomnia [IS: OR, 1.07 (1.04-1.11)]; CAD: OR, 1.13 (1.08-1.17); HF: OR, 1.10 (1.07-1.14); T2DM: OR, 1.16 (1.11-1.22); and short sleep duration [CAD: OR, 1.37 (1.21-1.55)] were causally associated with an elevated risk of cardiometabolic diseases. Moreover, genetically determined self-reported daytime sleepiness [CAD: OR, 2.05 (1.18-3.57); HF: OR, 1.82 (1.15-2.87)] and morning person [HF: 1.06 OR, (1.01-1.11)] had potential detrimental effect on cardiometabolic risks.

CONCLUSION

Self-reported daytime napping, insomnia, and short sleep duration had causal roles in the development of cardiometabolic diseases, while self-reported daytime sleepiness and morning person was the potential risk factor for cardiometabolic diseases.

Systematic review and meta-analyses on the effects of afternoon napping on cognition

Naps are increasingly considered a means to boost cognitive performance. We quantified the cognitive effects of napping in 60 samples from 54 studies. 52 samples evaluated memory. We first evaluated effect sizes for all tests together, before separately assessing their effects on memory, vigilance, speed of processing and executive function. We next examined whether nap effects were moderated by study features of age, nap length, nap start time, habituality and prior sleep restriction. Naps showed significant benefits for the total aggregate of cognitive tests (Cohen's d = 0.379, CI₉₅ = 0.296-0.462). Significant domain specific effects were present for declarative (Cohen's d = 0.376, CI₉₅ = 0.269-0.482) and procedural memory (Cohen's d = 0.494, CI₉₅ = 0.301-0.686), vigilance (Cohen's d = 0.610, CI₉₅ = 0.291-0.929) and speed of processing (Cohen's d = 0.211, CI₉₅ = 0.052-0.369). There were no significant moderation effects of any of the study features. Nap effects were of comparable magnitude across subgroups of each of the 5 moderators (Q values = 0.009 to 8.572, p values > 0.116). Afternoon naps have a small to medium benefit over multiple cognitive tests. These effects transcend age, nap duration and tentatively, habituality and prior nocturnal sleep.

Effects of an afternoon nap on sustained attention and working memory: The role of physiological arousal and sleep variables

Taking a short midday nap has been associated with higher alertness and better cognitive task performance. Yet, the mechanisms associated with nap-dependent performance enhancement are unclear. The current study was conducted to explore the impact of physiological arousal during cognitive task and sleep architecture during a pre-task nap on post-nap behavioral outcomes. A within-subjects design (N = 18) was employed, in which participants either took a nap or remained awake for 40 min during the post-lunch period. The psychomotor vigilance test (PVT) and n-back task were administered to assess sustained attention and working memory, respectively, with each task including one block of easy trials and one block of difficult trials. Results showed that a short midday nap improved sustained attention but not working memory. In addition, a midday nap induced lower physiological arousal during the performance on both cognitive tasks, with relatively higher delta and lower beta activity. The relative power of theta and alpha were positively correlated with performance on the easy PVT, whereas the alpha power was negatively correlated with performance on the difficult PVT, and the theta power was negatively correlated with reaction speed in the n-back task regardless of the task difficulty. Meanwhile, the shorter total sleep time and longer time of wake after sleep onset were associated with the faster overall reaction speed in PVT easy trials. These findings suggested that both changes in physiological arousal and sleep variables might account for changes in task performance after a short midday nap.

Daily relations between nap occurrence, duration, and timing and nocturnal sleep patterns in college students

OBJECTIVE/DESIGN

Sleep patterns change during college, and students may nap to compensate for lost sleep. Despite the increased prevalence of napping among students, few studies have investigated daily relations between napping and nocturnal sleep, as well as how timing of naps and nocturnal sleep might influence one another. The present study used daily diaries to capture the occurrence, timing, and duration of napping and relation to nocturnal sleep.

SETTING/PARTICIPANTS

Daily diary data, collected for 4-7 days, from 654 college students from a mid-sized midwestern university (81.5% female).

MEASUREMENT

Participants reported nightly sleep durations, bedtimes, and wake times as well as nap durations and nap start times.

RESULTS

Multilevel modeling (MLM) and multi-level logistic regressions revealed bidirectional relations between nocturnal sleep and napping. Regarding nocturnal sleep and its relation to next day napping, nocturnal sleep (including shorter duration and later bedtime) was associated with increased odds of napping and longer napping the following day. Shorter sleep duration was also associated with taking an earlier nap, while later bedtime was associated with a later nap the following day. Regarding napping and its association with same-night nocturnal sleep, taking a nap was associated with longer sleep duration that night, however, later nap start times and longer nap durations were associated with later bedtimes that night.

CONCLUSIONS

Findings provide evidence for bidirectional associations between napping and nocturnal sleep. Future studies are needed to explore how naps could be optimized to promote nocturnal sleep among college students, as well as for whom naps might be most beneficial.

Autonomic Central Coupling during Daytime Sleep Differs between Older and Younger People

Decreased functioning in the elderly is mirrored by independent changes in central and autonomic nervous systems. Additionally, recent work suggests that the coupling of these systems may also serve an important role. In young adults, Autonomic and Central Events (ACEs), measured in the temporal coincidence of heart rate bursts (HRBs) and increased slow-wave-activity (SWA, 0.5-1Hz) and sigma activity (12-15Hz), followed by parasympathetic surge (RR_HF) during non-rapid eye movement (NREM) sleep, predicted cognitive improvements. However, ACEs have not been examined in the elderly. Thus, the current study compared ACEs during wake and daytime sleep in older and younger adults and examined associations with working memory improvement before and after a nap. Compared to youngers, older adults showed lower amplitude of ACEs during NREM sleep, but not during wake. Furthermore, while younger adults demonstrated a parasympathetic surge after HRBs, older adults showed an earlier rise and longer maintenance of the RRHF. Taken together, our results demonstrate that autonomic-central coupling declines with age. Pathological aging implicates independent roles for decreased autonomic and central nervous system functioning, the current findings suggest that the coupling of these systems may also deserve attention.

Effect of napping on a bean bag chair on sleep stage, muscle activity, and heart rate variability

Background

Although ample evidence has demonstrated that daytime napping is beneficial for health and cognitive performance, bedding for napping has not yet been scientifically investigated.

Objectives

To explore the effect of a bean bag chair on daytime napping and physiological parameters related to sleep.

Methods

Fourteen healthy participants were enrolled within the context of a randomized, single-blind, crossover study to evaluate the effects of a bean bag chair in comparison with those of a urethane chair manufactured to have a similar shape. Electroencephalogram, electromyogram, and heart rate variability were recorded and compared between wakefulness and napping.

Results

Electroencephalogram analyses revealed no significant differences in sleep architecture or frequency components; however, a significant decrease was found in electromyogram recordings in the trapezius muscle, which represents the neck region (p = 0.019). Additionally, a significant main effect of bedding in the low-frequency/high-frequency ratio (F[1,20] = 4.314, p = 0.037) was revealed.

Conclusions

These results suggest that napping in a bean bag chair may provide a comfortable napping environment involving muscle relaxation and proper regulation of the autonomic nervous function.

Positive association of nap duration with risk of non-alcoholic fatty liver disease in an occupational population in Guangdong Province, China: a cross-sectional study

BACKGROUND

A lack of sleep or disorder in sleep-wake cycles has been associated with metabolic impairments. However, few studies have investigated the association between daytime napping duration and the risk of non-alcoholic fatty liver disease. This study aimed to investigate the association of daytime napping duration with the risk of non-alcoholic fatty liver disease in a Chinese population.

METHODS

This cross-sectional study analyzed data from the Health Management Center of Nanfang Hospital, Guangdong Province. A total of 3363 participants aged 20-79 years were recruited and admitted from January 20, 2018, to October 16, 2020. Non-alcoholic fatty liver disease was diagnosed using abdominal ultrasonography. The outcome was the association between daytime sleep duration and the risk of non-alcoholic fatty liver disease.

RESULTS

Compared with non-nappers, long daytime nappers (≥ 60 min) were associated with a higher risk of non-alcoholic fatty liver disease in the crude model (odds ratio 2.138; 95% confidence interval 1.88-2.61, P < 0.05) and in the multivariable adjustment model (odds ratio 2.211; 95% confidence interval 1.042-4.690, P < 0.05) after adjusting for demographic, educational, and metabolic risk factors. The association was moderately enhanced with additional adjustments for night sleep duration and socioeconomic or other factors (odds ratio 2.253; 95% confidence interval 1.061-4.786, P = 0.035).

CONCLUSION

In this cross-sectional study, daytime napping duration of ≥ 60 min was positively associated with the risk of non-alcoholic fatty liver disease in an occupational population of Guangdong Province after multivariable adjustment.

Nighttime sleep duration, daytime napping, and metabolic syndrome: findings from the China Health and Retirement Longitudinal Study

PURPOSE

This study aimed to assess the association between nighttime sleep, daytime napping, and metabolic syndrome (MetS) in an elderly Chinese population.

METHODS

A cross-sectional study was conducted using data from the 2011 China Health and Retirement Longitudinal Study (CHARLS) to examine the association between nighttime sleep, daytime napping, and MetS (defined according to the Chinese Diabetes Society criteria). Sleep duration was assessed by a self-reported questionnaire. Binary logistic regression models were used to estimate odds ratios and 95% confidence intervals of the associations adjusting for covariates.

RESULTS

Among 4785 elderly Chinese aged over 65 years old, there was no association between short-time sleep duration (< 7 h/day) and MetS. However, long-time sleep duration (> 8 h/day) decreased the odds of MetS by 53% (aOR= 0.47; 95% CI 0.23-0.96) compared to normal sleep duration (7-8 h/day). Compared to no daytime napping, short-time napping (≤ 30 min/day) was associated with increased odds of MetS (aOR = 1.55, 95% CI 1.02-2.36) and long-time napping (> 30 min/day) was associated with even higher odds of MetS (aOR = 1.77, 95%CI 1.24-2.53). Individuals who were over 75 years old, with elementary school education, and good health status had lower odds of MetS, while women, individuals living in rural areas, and those who reported poor health status had higher odds of MetS.

CONCLUSION

Long-time sleep duration decreased and daytime napping increased the risk of MetS among the elderly Chinese population. We speculate that increasing nighttime sleep duration and decreasing daytime napping may help reduce the risk of MetS.

Prior sleep timing and visual recognition of emotional faces in 6-month-old infants

Face recognition is an important mnemonic ability for infants when navigating the social world. While age-related changes in face processing abilities are relatively well documented, less is known about short-term intra-individual fluctuations in this ability. Given that sleep deprivation in adults leads to impairments in information processing, we assessed the role of prior sleep on 6-month-old infants' (N = 17) visual recognition of faces showing three emotional expressions (neutral, sad, angry). Visual recognition was inferred by assessing novelty preferences for unfamiliar relative to familiarized faces in a visual recognition memory paradigm. In a within-subject design, infants participated once after they had recently woken up from a nap (nap condition) and once after they had been awake for an extended period of time (awake condition). Infants failed to show visual recognition for the neutral faces in either condition. Infants showed recognition for the sad and angry faces when tested in the awake condition, but not in the nap condition. This suggests that timing of prior sleep shapes how effectively infants process emotionally relevant information in their environment.

Performance, muscle damage, and inflammatory responses to repeated high-intensity exercise following a 40-min nap

The purpose of this study was to examine the effect of a 40-min nap opportunity (N40) on performance during, markers of muscle damage and inflammation, and the perception of fatigue and recovery, in response to a 5-m shuttle run test (5msrt). Fifteen male amateur athletes performed the 5msrt under two conditions: N40 and no-nap condition (NN). Blood biomarkers were collected at rest and after the 5msrt to measure muscle damage (i.e., creatinine kinase (CK), lactate dehydrogenase (LDH), aspartate aminotransferase (ASAT), and alanine aminotransferase (ALAT)) and inflammation (i.e., C-reactive protein (CRP)). RPE was determined immediately after each repetition of the test and PRS and DOMS were determined 5 min, thereafter. Compared to NN, N40 improved the highest distance (p<0.001, Δ=+7.9%) and the total distance (p<0.001, Δ=+7.2%) attained during the 5msrt. Pre and post the 5msrt, participants presented lower muscle damage (i.e., CK, LDH, ASAT and ALAT) and inflammation (i.e., CRP) (p<0.05) values in the N40 compared to NN. Concerning RPE, DOMS, and PRS, there was a positive effect in the N40 vs. NN (p<0.01). N40 represents an effective method for improving repeated high intensity short-term maximal performance, PRS, and associated muscle damage and inflammation, and reducing RPE and DOMS.

Exploring the Effect of Long Naps on Handball Performance and Heart Rate Variability

This study explored the effect of long naps on handball-related performance and assessed the role of the cardiac autonomic nervous system in this process. Eleven male collegiate handball players performed a repeated sequential trial consisting of a 20-m consecutive turnaround run, 10-m run with a load, and shooting the ball into a target. Participants were allocated randomly and sequentially to have a short (20 minutes) nap, long (60 minutes) nap, or no nap. The Pittsburgh Sleep Quality Index was used to assess regular sleep quality. Subjective sleepiness before and after napping was measured using the Karolinska Sleepiness Scale. Heart rate variability was recorded to assess cardiac autonomic nervous function during napping. The Pittsburgh Sleep Quality Index score was correlated with shot accuracy only after long naps (ρ=0.636, r=0.048). A negative correlation was observed between the root mean square of successive differences and average load run time (ρ=−0.929, p<0.001). Long napping was associated with a significant benefit on performance in athletes with poor sleep quality, implying a role of the autonomic nervous system in this regard. Our findings indicate the effect of sleep quality on the endurance and resistance of handball players.

Chronic sleep restriction triggers inadequate napping habits in adolescents: a population-based study

BACKGROUND

The prevalence of chronic sleep restriction during adolescence is a major public health issue. Napping has been adopted to alleviate sleep pressure complaints. However, it also has the potential to amplify sleep restriction due to a vicious cycle triggered by delayed sleep times. The aim of this study was to investigate sleep and napping habits in a sample of Brazilian adolescents.

METHODS

This study enrolled 1554 high school students and included the evaluation of sleep times, daytime sleepiness, sleep quality, and circadian preference. The students were asked about their napping routine, ie its frequency and duration per week.

RESULTS

The adolescent sleep recommendation was achieved by only 27.6% of the sample. Napping habit was reported by 58.1%, with 36.2% of nappers informing naps in 1-2 times per week. Prolonged naps were reported by 44.9% of nappers. Nappers had later median bedtime (23:30) and reduced time in bed (TIB) (median = 07:00 h) compared to non-nappers. The frequency of nappers who did not achieve satisfactory TIB was higher than non-nappers. In addition, nappers reported increased daytime sleepiness and poor sleep quality. Later bedtimes and reduced TIB were associated with longer nap duration. Increased sleepiness and poor sleep quality were linked to a higher nap frequency.

CONCLUSIONS

This exploratory survey demonstrated a severe sleep restriction faced by Brazilian adolescents. Napping can be an efficient strategy to counteract sleep restriction, but it needs to be adopted with caution due to the detrimental effects of frequent and prolonged naps on nocturnal sleep.

Machine learning sleep duration classification in Preschoolers using waist-worn ActiGraphs

OBJECTIVE

To create a sleep duration classification technique for waist-worn ActiGraph accelerometers in preschool-aged children.

METHODS

Children wore ActiGraph wGT3X-BT accelerometers on their right hip for 7 days (24 h/day). Ground truth nap, sleep, and wake were estimated through visual inspection of accelerometer data, guided by sleep log-sheets and previously published visual inspection heuristics. Raw accelerometer data (30Hz) were used to generate 144 features aggregated to 1-min epochs. Machine learning classification (ie, Random Forest and Hidden Markov Modeling [HMM]) predicted nap, sleep, and wake. A simplified prediction formula was also created using features (n = 10) with the highest mean decrease in Gini index during training of Random Forests, and temporally smoothed with rolling median calculations.

RESULTS

Children (n = 89, mean age = 4.5 years, 67% boys) contributed >600,000 min of accelerometer data. Overall classification accuracy of the Random Forest and HMM classifier was 96.2% (95%CI: 96.1, 96.2%), with a Kappa score of 0.93. Additionally, overall classification accuracy for the temporally smoothed simplified formula was 93.7% (95%CI: 93.6, 93.7%) with Kappa = 0.87. Nap prediction accuracy was 99.8% for the final machine learning model, and 86.1% for the simplified formula. For participant-level daily summaries, generally small but statistically significant differences were found between machine learning and ground truth behaviour predictions, whereas non-significant differences were found between the simplified formulas and ground truth predictions.

CONCLUSIONS

Predictions for both machine learning and the simplified formula had almost perfect agreement with visual inspection ground truth measurements. Future research is needed to confirm these findings using polysomnography ground truth sleep measurements.

Alternative conformation of the C-domain of the P140 protein from Mycoplasma genitalium

The human pathogen Mycoplasma genitalium is responsible for urethritis in men, and for cervicitis and pelvic inflammatory disease in women. The adherence of M. genitalium to host target epithelial cells is mediated through an adhesion complex called Nap, which is essential for infectivity. Nap is a transmembrane dimer of heterodimers of the immunodominant proteins P110 and P140. The M. genitalium genome contains multiple copies of portions that share homology with the extracellular regions of P140 and P110 encoded by the genes mg191 and mg192, respectively. Homologous recombination between the genes and the copies allows the generation of a large diversity of P140 and P110 variants to overcome surveillance by the host immune system. Interestingly, the C-terminal domain (C-domain) of the extracellular region of P140, which is essential for the function of Nap by acting as a flexible stalk anchoring the protein to the mycoplasma membrane, presents a low degree of sequence variability. In the present work, the X-ray crystal structures of two crystal forms of a construct of the P140 C-domain are reported. In both crystal forms, the construct forms a compact octamer with D4 point-group symmetry. The structure of the C-domain determined in this work presents significant differences with respect to the structure of the C-domain found recently in intact P140. The structural plasticity of the C-domain appears to be a possible mechanism that may help in the functioning of the mycoplasma adhesion complex.

Is there an association among sleep duration, nap, and stroke? Findings from the China Health and Retirement Longitudinal Study

PURPOSE

The objective of this study was to assess the association among nighttime sleep, daytime napping, total sleep duration (nighttime sleep plus daytime napping), and stroke in an elderly Chinese population.

METHODS

Data were derived from the 2011 China Health and Retirement Longitudinal Study (CHARLS) with 4785 Chinese respondents over 65 years old. Four binary logistic regression models were used to estimate odds ratios and 95% confidence intervals of the association among total sleep duration, nighttime sleep, daytime napping, and stroke, adjusting for confounders.

RESULTS

After controlling for sociodemographic characteristics, lifestyle, health status, and comorbidity, there was no association between abnormal nighttime sleep and stroke (P values > 0.05). Compared to individuals with normal total sleep duration (7-8 h per day), short sleep duration (< 7 h per day) was approximately two times more likely to increase the risk of stroke (AOR = 1.81, 95%CI 1.10-2.97). Individuals who reported vision impairment, disability, hypertension, dyslipidemia, and mental health issues were at higher risk of stroke. In addition, physical activities with different levels were associated with a lower risk of stroke. Taking naps was not associated with stroke incidence (AOR = 1.12, 95%CI 0.77-1.64).

CONCLUSION

In this elderly Chinese population, short total sleep duration per 24 h, not merely daytime napping or nighttime sleep, was significantly associated with an increased risk of stroke. Preventive measures for stroke may require a focus on elderly, sedentary individuals who report other health problems.

Autonomic/central coupling benefits working memory in healthy young adults

Working memory (WM) is an executive function that can improve with training. However, the precise mechanism for this improvement is not known. Studies have shown greater WM gains after a period of sleep than a similar period of wake, and correlations between WM improvement and slow wave activity (SWA; 0.5-1 Hz) during slow wave sleep (SWS). A different body of literature has suggested an important role for autonomic activity during wake for WM. A recent study from our group reported that the temporal coupling of Autonomic/CentralEvents (ACEs) during sleep was associated with memory consolidation. We found that heart rate bursts (HR bursts) during non-rapid eye movement (NREM) sleep are accompanied by increases in SWA and sigma (12-15 Hz) power, as well as increases in the high-frequency (HF) component of the RR interval, reflecting vagal rebound. In addition, ACEs predict long-term, episodic memory improvement. Building on these previous results, we examined whether ACEs also contribute to gains in WM. We tested 104 young adults in an operation span task (OSPAN) in the morning and evening, with either a nap (n = 53; with electroencephalography (EEG) and electrocardiography (ECG)) or wake (n = 51) between testing sessions. We identified HR bursts in the ECG and replicated the increases in SWA and sigma prior to peak of the HR burst, as well as vagal rebound after the peak. Furthermore, we showed sleep-dependent WM improvement, which was predicted by ACE activity. Using regression analyses, we discovered that significantly more variance in WM improvement could be explained with ACE variables than with overall sleep activity not time-locked with ECG. These results provide the first evidence that coordinated autonomic and central events play a significant role in sleep-related WM improvement and implicate the potential of autonomic interventions during sleep for cognitive enhancement.

Environmental characteristics of early childhood education and care, daily movement behaviours and adiposity in toddlers: A multilevel mediation analysis from the GET UP! Study

STUDY OBJECTIVE

This study aimed to examine the direct effects of environmental characteristics of early childhood education and care (ECEC) centres on adiposity, and the indirect effects through daily movement behaviours (physical activity, sedentary time and naps).

METHODS

274 children (average age 19.73 ± 4.15 months) from 27 ECEC centres participated in this study. Environmental characteristics of ECEC centres were rated using the Infant/Toddler Environment Rating Scale-revised edition (ITERS-R). Daily movement behaviours were assessed using 24-h accelerometry. Body mass index z-scores were used to indicate adiposity.

RESULTS

There were no significant direct effects or indirect effects of environmental characteristics on toddlers' adiposity through daily movement behaviours. However, the environmental characteristics of "personal care routine" (B=0.72, p = 0.041) and "activity" (B = 0.87, p < 0.050) were positively associated with the percentage of time these toddlers spent in moderate-to-vigorous physical activity (MVPA). "Listening and talking" was also positively associated withnap(s) durations (B = 4.08 p = 0.001).

CONCLUSION

The relationships between environmental characteristics of ECEC centres and adiposity in toddlers, as well as, the mediating roles of daily movement behaviours still need confirmation by future longitudinal and experimental studies with long follow-up periods. At the same time, a broader spectrum of environmental characteristics of these settings needs to be examined with toddlers' adiposity in future studies; other potential mediators may also need to be taken into considerations.

Correlates of nocturnal sleep duration, nocturnal sleep variability, and nocturnal sleep problems in toddlers: results from the GET UP! Study

OBJECTIVE

To explore the correlates of nocturnal sleep duration, nocturnal sleep variability, and nocturnal sleep problems in a sample of Australian toddlers.

METHODS

Participants were 173 toddlers (average age 19.7 ± 4.1 months) from the GET UP!

STUDY

Nocturnal sleep duration, nocturnal sleep variability, nap(s) and physical activity were measured using 24-h accelerometry (Actigraph GT3X+) over seven consecutive days. Nocturnal sleep problems were assessed using the Tayside Children's Sleep Questionnaire. Screen time was reported by the parents. Logistic regression models were used to examine the associations between potential correlates (ie, age, sex, socio-economic status, weight status, physical activity, screen time, nap(s), bedtimes, and wake-up times) and nocturnal sleep characteristics.

RESULTS

Older children were more likely to have greater sleep variability (OR: 1.97; 95% CI: 1.08-3.61). Less physical activity (OR: 2.38; 95% CI: 1.27-4.45), shorter nap(s) (OR: 2.42, 95% CI: 1.29-4.55), and later wake-up times (OR: 4.42; 95% CI: 2.32-8.42) were associated with higher odds of having longer nocturnal sleep duration. Late bedtimes were associated with shorter nocturnal sleep duration (OR: 0.09; 95% CI: 0.04-0.18) and with greater nocturnal sleep variability (OR: 1.97; 95% CI: 1.06-3.68). None of the potential correlates were associated with nocturnal sleep problems.

CONCLUSION

The present study identifies several correlates of nocturnal sleep duration (total physical activity, nap(s), bedtime, and wake-up time) and nocturnal sleep variability (age and bedtime), whereas no correlates were identified for nocturnal sleep problems. The association between late bedtimes and shorter nocturnal sleep duration and greater nocturnal variability suggests that these may be modifiable targets for future sleep interventions in early childhood.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry: ACTRN12616000471482, 11/04/2016, retrospectively registered.

The Concept of Qailulah (Midday Napping) from Neuroscientific and Islamic Perspectives

Napping/siesta during the day is a phenomenon, which is widely practised in the world. However, the timing, frequency, and duration may vary. The basis of napping is also diverse, but it is mainly done for improvement in alertness and general well-being. Neuroscience reveals that midday napping improves memory, enhances alertness, boosts wakefulness and performance, and recovers certain qualities of lost night sleep. Interestingly, Islam, the religion of the Muslims, advocates midday napping primarily because it was a practice preferred by Prophet Muhammad (pbuh). The objectives of this review were to investigate and compare identical key points on focused topic from both neuroscientific and Islamic perspectives and make recommendations for future researches.

Phenazines Regulate Nap-Dependent Denitrification in Pseudomonas aeruginosa Biofilms

Microbes in biofilms face the challenge of substrate limitation. In particular, oxygen often becomes limited for cells in Pseudomonas aeruginosa biofilms growing in the laboratory or during host colonization. Previously we found that phenazines, antibiotics produced by P. aeruginosa, balance the intracellular redox state of cells in biofilms. Here, we show that genes involved in denitrification are induced in phenazine-null (Δphz) mutant biofilms grown under an aerobic atmosphere, even in the absence of nitrate. This finding suggests that resident cells employ a bet-hedging strategy to anticipate the potential availability of nitrate and counterbalance their highly reduced redox state. Consistent with our previous characterization of aerobically grown colonies supplemented with nitrate, we found that the pathway that is induced in Δphz mutant colonies combines the nitrate reductase activity of the periplasmic enzyme Nap with the downstream reduction of nitrite to nitrogen gas catalyzed by the enzymes Nir, Nor, and Nos. This regulatory relationship differs from the denitrification pathway that functions under anaerobic growth, with nitrate as the terminal electron acceptor, which depends on the membrane-associated nitrate reductase Nar. We identified the sequences in the promoter regions of the nap and nir operons that are required for the effects of phenazines on expression. We also show that specific phenazines have differential effects on nap gene expression. Finally, we provide evidence that individual steps of the denitrification pathway are catalyzed at different depths within aerobically grown biofilms, suggesting metabolic cross-feeding between community subpopulations.IMPORTANCE An understanding of the unique physiology of cells in biofilms is critical to our ability to treat fungal and bacterial infections. Colony biofilms of the opportunistic pathogen Pseudomonas aeruginosa grown under an aerobic atmosphere but without nitrate express a denitrification pathway that differs from that used for anaerobic growth. We report that the components of this pathway are induced by electron acceptor limitation and that they are differentially expressed over the biofilm depth. These observations suggest that (i) P. aeruginosa exhibits "bet hedging," in that it expends energy and resources to prepare for nitrate availability when other electron acceptors are absent, and (ii) cells in distinct biofilm microniches may be able to exchange substrates to catalyze full denitrification.

Exploring the nap paradox: are mid-day sleep bouts a friend or foe?

The mid-day nap, sometimes called a siesta, is a ubiquitous occurrence across the lifespan. It is well established that in addition to reducing sleepiness, mid-day naps offer a variety of benefits: memory consolidation, preparation for subsequent learning, executive functioning enhancement, and a boost in emotional stability. These benefits are present even if a sufficient amount of sleep is obtained during the night prior. However, we present a paradox: in spite of these reported benefits of naps, frequent napping has also been associated with numerous negative outcomes (eg, cognitive decline, hypertension, diabetes), particularly in older populations. This association exists even when statistically controlling for relevant health- and sleep-affecting determinants. An emerging hypothesis suggests inflammation is a mediator between mid-day naps and poor health outcomes, yet further research is necessary. Given this, it may be premature to 'prescribe' naps as a health enhancer. Herein, we aggregate findings from several branches of sleep research (eg, developmental neuroscience, cognitive neuroscience, sleep medicine) to critically examine the paradoxical role of naps in cognitive and somatic health. This review uncovers gaps in the literature to guide research opportunities in the field.

Preferential processing of emotionally and self-relevant stimuli persists in unconscious N2 sleep

Information processing has been suggested to depend on the current state of the brain as well as stimulus characteristics (e.g. salience). We compared processing of salient stimuli (subject's own names [SONs] and angry voice [AV] stimuli) to processing of unfamiliar names (UNs) and neutral voice (NV) stimuli across different vigilance stages (i.e. wakefulness as well as sleep stages N1 and N2) by means of event-related oscillatory responses during wakefulness and a subsequent afternoon nap. Our findings suggest that emotional prosody and self-relevance drew more attentional resources during wakefulness with specifically AV stimuli being processed more strongly. During N1, SONs were more arousing than UNs irrespective of prosody. Moreover, emotional and self-relevant stimuli evoked stronger responses also during N2 sleep suggesting a 'sentinel processing mode' of the brain during this state of naturally occurring unconsciousness. Finally, this initial preferential processing of salient stimuli during N2 sleep seems to be followed by an inhibitory sleep-protecting process, which is reflected by a K-complex-like response.

Sleep spindles during a nap correlate with post sleep memory performance for highly rewarded word-pairs

The consolidation of new associations is thought to depend in part on physiological processes engaged during non-REM (NREM) sleep, such as slow oscillations and sleep spindles. Moreover, NREM sleep is thought to selectively benefit associations that are adaptive for the future. In line with this, the current study investigated whether different reward cues at encoding are associated with changes in sleep physiology and memory retention. Participants' associative memory was tested after learning a list of arbitrarily paired words both before and after taking a 90-min nap. During learning, word-pairs were preceded by a cue indicating either a high or a low reward for correct memory performance at test. The motivation manipulation successfully impacted retention such that memory declined to a greater extent from pre- to post sleep for low rewarded than for high rewarded word-pairs. In line with previous studies, positive correlations between spindle density during NREM sleep and general memory performance pre- and post-sleep were found. In addition to this, however, a selective positive relationship between memory performance for highly rewarded word-pairs at posttest and spindle density during NREM sleep was also observed. These results support the view that motivationally salient memories are preferentially consolidated and that sleep spindles may be an important underlying mechanism for selective consolidation.

The experience of a Power Nap Center in the largest city of Brazil

We evaluated the frequency of naps and features of nappers who took a nap in a Power Nap Center located in downtown area of São Paulo. Company database was retrospectively analyzed and 4.625 naps were evaluated (January–December 2014). Most naps (57%) lasted 30 min. 33% of subjects took a nap more than once a week (73% male). Progressive growth in the number of naps across the months was observed (January=110 to December=505). Results suggest that the society is sleep deprived and taking a nap during the day could be an important strategy to improve quality of life and increase productivity.

Nap Interferes with Hypoxia-Inducible Factors and VEGF Expression in Retina of Diabetic Rats

The retinal microvascular damage is a complication of diabetic retinopathy (DR). Hyperglycemia and hypoxia are responsible of aberrant vessel's proliferation. The cellular response to hypoxia is mediated through activation of hypoxia-inducible factors (HIFs). Among these, HIF-1α modulates expression of its target gene, VEGF, whose upregulation controls the angiogenic event during DR development. In a previous study, we have demonstrated that a small peptide, NAP, is able to protect retina from hyperglycemic insult. Here, we have demonstrated that its intraocular administration in a rat model of diabetic retinopathy has reduced expression of HIF-1α, HIF-2α, and VEGF by increasing HIF-3α levels. These data have been also confirmed by immunolocalization study by confocal microscopy. Although these evidences need to be further deepened to understand the molecular mechanism involved in the protective NAP action, the present data suggest that this small peptide may be effective to prevent the development of this ocular pathology.

Sleep Pattern, Duration and Quality in Relation with Glycemic Control in People with Type 2 Diabetes Mellitus

Sleep disturbances have been shown to be associated with diabetes control, but the relation between planned wakings or napping with glycemic indices has not been evaluated yet. This study evaluated the relation between sleep quality, duration, and pattern, including daytime napping of people with diabetes and their glycemic control. A cross-sectional correlation research design was used for this study. We enrolled 118 people with type 2 diabetes receiving oral agents without major complications at the Shahid Bahonar Center, Kerman. The age, weight, height, serum HbA1c, as well as other glycemic indices and lipid profile were measured. BMI was also calculated. All participants were requested to fill in the Pittsburgh Sleep Quality Index (PSQI) questionnaire to evaluate their sleep quality. In addition, they were inquired about their sleep schedule during day and night. Pearson correlation and multiple regression analyses were conducted to examine the correlation between HbA1c and sleep pattern variables. The variables were also compared between participants with or without napping using t-test. All analyses were performed with the SPSS version 19 (SPSS, Chicago, IL, USA). The mean age was 58±11 years and mean HbA1c (%) was 7.8±11 (62±13 mmol/mol). Sleep duration and the number of sleep segments significantly predicted HbA1c (F (2,114)=5.232, P=0.007, R2=0.084). A one-hour increment in sleep duration was associated with a 0.174% (1.4 mmol/mol) decrement in HbA1c. PSQI score did not contribute to the regression model. Moreover, participants who napped (66%) had a lower HbA1c (7.6±1) compared to others (8.1±1.3) (P=0.04). We concluded that napping and segmented sleep are associated with a better glycemic control in type 2 diabetes and there is a linear correlation between sleep duration and better glycemic control.

Napping after complex motor learning enhances juggling performance

The present study examined whether a nap after complex motor learning enhanced the following day's physical performance. Eighteen volunteers met the inclusion criteria and were assigned to either a nap (n=9; men=5; mean age=21.0±1.5) or no-nap group (n=9; men=5; mean age=21.9±0.3). Participants practiced juggling in the morning and were tested immediately afterwards. Participants of the nap group were given a 70-minute nap opportunity after juggling practice, while the no-nap group stayed awake. Juggling performance was then tested in the evening (retest-1) and the next morning (retest-2). Two-way analysis of variance (group: nap, no-nap×time: test, retest-1, retest-2) found there was a significant effect of test time and a significant group×time interaction. The juggling performance of both groups improved from test to retest-1, respectively. However, the juggling performance level of the nap group was higher than that of the no-nap group at the retest-1. As predicted, a nap promptly after learning motor skills was associated with subsequently improved performance. Moreover, the juggling performance of the nap group showed additional significant improvements in the retest-2. In the no-nap group, however, there were no significant improvements in the juggling performance after nocturnal sleep. These results demonstrate that the benefits of a nap following learning were further enhanced after nocturnal sleep. The present results may provide justification for introducing nap periods into daily athletic training as an active method to improve performance.

Delayed benefit of naps on motor learning in preschool children

Sleep benefits memory consolidation across a variety of domains in young adults. However, while declarative memories benefit from sleep in young children, such improvements are not consistently seen for procedural skill learning. Here we examined whether performance improvements on a procedural task, although not immediately observed, are evident after a longer delay when augmented by overnight sleep (24 h after learning). We trained 47 children, aged 33-71 months, on a serial reaction time task and, using a within-subject design, evaluated performance at three time points: immediately after learning, after a daytime nap (nap condition) or equivalent wake opportunity (wake condition), and 24 h after learning. Consistent with previous studies, performance improvements following the nap did not differ from performance improvements following an equivalent interval spent awake. However, significant benefits of the nap were found when performance was assessed 24 h after learning. This research demonstrates that motor skill learning is benefited by sleep, but that this benefit is only evident after an extended period of time.

The effects of sleep, wake activity and time-on-task on offline motor sequence learning

While intervening sleep promotes the consolidation of memory, it is well established that cognitive interference from competing stimuli can impede memory retention. The current study examined changes in motor skill learning across periods of wakefulness with and without competing stimuli, and periods of sleep with and without disruption from external stimuli. A napping study design was adopted where participants (N=44) either had (1) a 30min nap composed of Non-Rapid Eye Movement (NREM) sleep, (2) 30min NREM nap fragmented by audio tone induced arousals, (3) 45min of quiet wakefulness, or (4) 45min of active wakefulness. Measures of subjective sleepiness (KSS), alertness (PVT) and motor skill learning (Sequential Finger Tapping Task, SFTT) were completed in the morning and evening to assess performance pre- and post-nap or wakefulness. Following a practice session, change in motor skill performance was measured over a 10min post training rest interval, as well as following a 7h morning to evening interval comprising one of the four study conditions. A significant offline enhancement in motor task performance (13-23%) was observed following 10min of rest in all conditions. Following the long delay with the intervening nap/wake condition, there were no further offline gains or losses in performance in any sleep (uninterrupted/fragmented) or wake (quiet/active) condition. The current findings suggest that after controlling for offline gains in performance that occur after a brief rest and likely to due to the dissipation of fatigue, the subsequent effect of an intervening sleep or wake period on motor skill consolidation is not significant. Consistent with this null result, the impact of disrupting the sleep episode or manipulating activity during intervening wake also appears to be negligible.

The Leeds food preference questionnaire after mild sleep restriction - A small feasibility study

Besides the increased sedentary lifestyle and increased caloric intake, changes in dietary composition may play an important role in the increased prevalence of obesity. Because inadequate sleep could be a risk factor in the aetiology of obesity, reliable methods for assessing food intake and food choice after sleep restriction are needed. We translated the Leeds food preference questionnaire (LFPQ), addressing preferences for sweet/savoury tastes and low-fat/high-fat foods, into Dutch, and tested it in 15 mildly sleep-restricted psychology students. The participants completed the LFPQ in our laboratory on two separate occasions, with approximately one week in between. Sleep on the preceding night was not controlled, but mild sleep-restriction was confirmed by a short sleep latency test (sSLT) or a short maintenance of wakefulness test (sMWT). Each participant completed the sSLT and sMWT once, just before the LFPQ, in a cross-over design randomised for the first test. Differences were present in preferences for food items from different categories (sweet/savoury and low-fat/high-fat; p<0.001). The choice frequencies for various food categories were comparable on both occasions (p=0.27). The choice frequencies for individual items were also comparable on both occasions (p=0.27). The LFPQ is easily implemented under mild sleep-restricted conditions, and translation is straightforward. Future studies using the LFPQ after sleep restriction could elucidate if restricting sleep or longer periods affects food choice, which could underlie increases in obesity risk.

The interactive effects of nocturnal sleep and daytime naps in relation to serum C-reactive protein

BACKGROUND AND AIM

C-reactive protein (CRP) is a general marker of inflammation that has been differentially linked with sleep. Elevated CRP (ie, high inflammation) has been associated with either short/insufficient sleep duration or long sleep duration, both, or neither. Daytime napping has also been tied to increased and decreased inflammation. We attempted to unify these findings by examining the relationship between CRP and sleep duration in conjunction with napping in a healthy young adult cohort.

PARTICIPANTS

Participants were young adults (mean age = 29.05 years, n = 2147) from the National Longitudinal Study of Adolescent Health (Add Health) cohort, a nationally representative longitudinal sample.

METHODS/RESULTS

Analysis of covariance (ANCOVA) tests examined whether self-reported sleep duration (short, medium, or long) and nap frequency (none-few days/week; most days/week; every day) interacted in relation to CRP. Standard covariates (ie, age, gender, race/ethnicity, body mass index, physical activity, depression, snoring, systolic blood pressure, clinical symptoms, and household income) were used. There was a linear increase in CRP with increased napping [contrast estimate = 0.265, 95% confidence interval (CI) (0.045-0.485), P = 0.018]. There was also an interaction between sleep duration and napping frequency in relation to CRP (F4,2128 = 2.90, P = 0.021). Inflammation differed between nap groups within the long and short sleep groups.

CONCLUSIONS

Our results suggest that increased napping is an independent predictor of inflammation in young adults. These results also provide evidence for interactive effects of inflammation, nocturnal sleep, and daytime naps. Our findings confirm that excess sleep, insufficient sleep, frequent napping, and infrequent napping can all be linked with elevated CRP, but these relationships depend on both nocturnal and daytime sleep patterns. These analyses will guide future work to more specifically examine sleep-inflammation processes and directionality.

Did a brief nap break have positive benefits on information processing among nurses working on the first 8-h night shift?

Shift workers frequently experience acute sleep deprivation on first night shift. This study compared the efficacy of 30-min nap (between 2 and 3 a.m.) on the visual attention ability of the nurses working at first 8-h night shift at the time of maximum fatigue (between 3 and 4 a.m.). In addition, we measured cognitive function (between 9 and 10 a.m.) in nurses working on daytime shift, which we defined as baseline wakefulness. The results showed that working on the night shift groups was associated with sleep loss, leading to a decrease in visual attention performance compared to the daytime shift group. There was no statistically significant difference in the visual attention performance between those taking and not taking a nap during the night shift, however the effect size was medium in the information process. It was still needed increase sample size to draw the conclusion regarding a 30-min nap break have positive benefits on perceptual speed during the first night shift.

Nap sleep preserves associative but not item memory performance

Many studies have shown that sleep improves memory performance, and that even short naps during the day are beneficial. Certain physiological components of sleep such as spindles and slow-wave-sleep are thought to be particularly important for memory consolidation. The aim of this experiment was to reveal the role of naps for hippocampus-dependent associative memory (AM) and hippocampus-independent item memory (IM) alongside their corresponding ERP old/new effects. Participants learnt single words and word-pairs before performing an IM- and an AM-test (baseline). One group was subsequently allowed to nap (∼90min) while the other watched DVDs (control group). Afterwards, both groups performed a final IM- and AM-test for the learned stimuli (posttest). IM performance decreased for both groups, while AM performance decreased for the control group but remained constant for the nap group, consistent with predictions concerning the selective impact of napping on hippocampus-dependent recognition. Putative ERP correlates of familiarity and recollection were observed in the IM posttest, whereas only the later recollection-related effect was present in the AM test. Notably, none of these effects varied with group. Positive correlations were observed between spindle density during slow-wave-sleep and AM posttest performance as well as between spindle density during non-REM sleep and AM baseline performance, showing that successful learning and retrieval both before and after sleep relates to spindle density during nap sleep. Together, these results speak for a selective beneficial impact of naps on hippocampus-dependent memories.

Cross-hemispheric Alternating Current Stimulation During a Nap Disrupts Slow Wave Activity and Associated Memory Consolidation

BACKGROUND

Slow Wave Activity (SWA), the low frequency (<4 Hz) oscillations that characterize Slow Wave Sleep (SWS) are thought to relate causally to declarative memory consolidation during nocturnal sleep. Evidence is conflicting relating SWA to memory consolidation during nap however.

OBJECTIVE/HYPOTHESIS

We applied transcranial alternating current stimulation (tACS) - which, with a cross-hemispheric electrode montage (F3 and F4 - International 10:20 EEG system), is able to disrupt brain oscillations-to determine if disruption of low frequency oscillation generation during afternoon nap is causally related to disruption in declarative memory consolidation.

METHODS

Eight human subjects each participated in stimulation and sham nap sessions. A verbal paired associate learning (PAL) task measured memory changes. During each nap period, five 5-min stimulation (0.75 Hz cross-hemispheric frontal tACS) or sham intervals were applied with 1-min post-stimulation intervals (PSI's). Spectral EEG power for Slow (0.7-0.8 Hz), Delta (1.0-4.0 Hz), Theta (4.0-8.0 Hz), Alpha (8.0-12.0 Hz), and Spindle-range (12.0-14.0) frequencies was analyzed during the 1-min preceding the onset of stimulation and the 1-min PSI's.

RESULTS

As hypothesized, power reduction due to stimulation positively correlated with reduction in word-pair recall post-nap specifically for Slow (P < 0.0022) and Delta (P < 0.037) frequency bands.

CONCLUSIONS

These results provide preliminary evidence suggesting a causal and specific role of SWA in declarative memory consolidation during nap.

To sleep or not to sleep: a repeated daily challenge for African American children

AIMS

Sleep is important for children, because of the impact on their development and well-being. Previous survey research suggested that poor sleep occurs more frequently in minorities. However, objective data characterizing their sleep patterns are lacking.

METHODS

Children enrolled in a 1-year cross-sectional sequence designed study centered on a 14-day objective sleep recording, which was repeated three times. Children lived on the South Side of Chicago and were self-defined as being African Americans.

RESULTS

Findings reflect data of 24 children with a mean age of 5.4 ± 1.7 years of which 54.2% were girls. They slept at night 6.51 h and during the day changeably 1.42 h, likely being noon naps during the week and afternoon naps on Saturday and Sunday. Variability in quality of sleep, and also nighttime sleep duration, especially on Friday and Saturday, was characteristic. The highest variability was noted in sleep onset and offset latency, and in the quality of napping. The interrelation of daytime and nighttime sleep changes was suggestive of "catch-up" daytime sleep.

CONCLUSION

At nighttime children habitually obtained few hours of sleep with diurnal sleep fluctuations likely being "a need" and "a chance." Interventions might emphasize on creating optimal opportunities to sleep.

Hazardous waste characterization among various thermal processes in South Korea: a comparative analysis

Ministry of Environment, Republic of Korea (South Korea) is in progress of converting its current hazardous waste classification system to harmonize it with the international standard and to set-up the regulatory standards for toxic substances present in the hazardous waste. In the present work, the concentrations along with the trend of 13 heavy metals, F(-), CN(-) and 19 PAH present in the hazardous waste generated among various thermal processes (11 processes) in South Korea were analyzed along with their leaching characteristics. In all thermal processes, the median concentrations of Cu (3.58-209,000 mg/kg), Ni (BDL-1560 mg/kg), Pb (7.22-5132.25mg/kg) and Zn (83.02-31419 mg/kg) were comparatively higher than the other heavy metals. Iron & Steel thermal process showed the highest median value of the heavy metals Cd (14.76 mg/kg), Cr (166.15 mg/kg) and Hg (2.38 mg/kg). Low molecular weight PAH (BDL-37.59 mg/kg) was predominant in sludge & filter cake samples present in most of the thermal processes. Comparatively flue gas dust present in most of the thermal processing units resulted in the higher leaching of the heavy metals.