The effect of a daytime nap on priming and recognition tasks in preschool children

Children extract a new linguistic rule more quickly than adults

Children achieve better long-term language outcomes than adults. However, it remains unclear whether children actually learn language more quickly than adults during real-time exposure to input-indicative of true superior language learning abilities-or whether this advantage stems from other factors. To examine this issue, we compared the rate at which children (8-10 years) and adults extracted a novel, hidden linguistic rule, in which novel articles probabilistically predicted the animacy of associated nouns (e.g., "gi lion"). Participants categorized these two-word phrases according to a second, explicitly instructed rule over two sessions, separated by an overnight delay. Both children and adults successfully learned the hidden animacy rule through mere exposure to the phrases, showing slower response times and decreased accuracy to occasional phrases that violated the rule. Critically, sensitivity to the hidden rule emerged much more quickly in children than adults; children showed a processing cost for violation trials from very early on in learning, whereas adults did not show reliable sensitivity to the rule until the second session. Children also showed superior generalization of the hidden animacy rule when asked to classify nonword trials (e.g., "gi badupi") according to the hidden animacy rule. Children and adults showed similar retention of the hidden rule over the delay period. These results provide insight into the nature of the critical period for language, suggesting that children have a true advantage over adults in the rate of implicit language learning. Relative to adults, children more rapidly extract hidden linguistic structures during real-time language exposure. RESEARCH HIGHLIGHTS: Children and adults both succeeded in implicitly learning a novel, uninstructed linguistic rule, based solely on exposure to input. Children learned the novel linguistic rules much more quickly than adults. Children showed better generalization performance than adults when asked to apply the novel rule to nonsense words without semantic content. Results provide insight into the nature of critical period effects in language, indicating that children have an advantage over adults in real-time language learning.

Consensus statement on Singapore integrated 24-hour activity guide for early childhood

Introduction

Early childhood is a critical period for growth and development. Adopting healthy lifestyle behaviours during this period forms the foundation for future well-being and offers the best protection against non-communicable diseases. Singapore studies have shown that many young children are not achieving the recommendations on physical activity, sedentary behaviour and sleep. A workgroup was set up to develop recommendations for caregivers of infants, toddlers and preschoolers (aged <7 years) on how to integrate beneficial activities within a daily 24-hour period for optimal development and metabolic health.

Method

The Grading of Recommendations Assessment, Development and Evaluation (GRADE)- ADOLOPMENT approach was employed for adoption, adaption or de novo development of recommendations. International and national guidelines were used as references, and an update of the literature reviews up to September 2021 was conducted through an electronic search of PubMed, Embase and Cochrane Central Register of Controlled Trials (CENTRAL) databases.

Results

Four consensus statements were developed for each age group: infants, toddlers and preschoolers. The statements focus on achieving good metabolic health through regular physical activity, limiting sedentary behaviour, achieving adequate sleep and positive eating habits. The 13th consensus statement recognises that integration of these activities within a 24-hour period can help obtain the best results.

Conclusion

This set of recommendations guides and encourages caregivers of Singapore infants, toddlers and preschoolers to adopt beneficial lifestyle activities within each 24-hour period.

Do naps benefit novel word learning? Developmental differences and white matter correlates

Memory representations of newly learned words undergo changes during nocturnal sleep, as evidenced by improvements in explicit recall and lexical integration (i.e., after sleep, novel words compete with existing words during online word recognition). Some studies have revealed larger sleep-benefits in children relative to adults. However, whether daytime naps play a similar facilitatory role is unclear. We investigated the effect of a daytime nap (relative to wake) on explicit memory (recall/recognition) and lexical integration (lexical competition) of newly learned novel words in young adults and children aged 10-12 years, also exploring white matter correlates of the pre- and post-nap effects of word learning in the child group with diffusion weighted MRI. In both age groups, a nap maintained explicit memory of novel words and wake led to forgetting. However, there was an age group interaction when comparing change in recall over the nap: children showed a slight improvement whereas adults showed a slight decline. There was no evidence of lexical integration at any point. Although children spent proportionally more time in slow-wave sleep (SWS) than adults, neither SWS nor spindle parameters correlated with over-nap changes in word learning. For children, increased fractional anisotropy (FA) in the uncinate fasciculus and arcuate fasciculus were associated with the recognition of novel words immediately after learning, and FA in the right arcuate fasciculus was further associated with changes in recall of novel words over a nap, supporting the importance of these tracts in the word learning and consolidation process. These findings point to a protective role of naps in word learning (at least under the present conditions), and emphasize the need to better understand both the active and passive roles that sleep plays in supporting vocabulary consolidation over development.

Asia-Pacific consensus statement on integrated 24-hour activity guidelines for the early years

Background

Early childhood is a vital period for development and growth. Promoting beneficial lifestyle behaviours in early childhood can help optimise children's health, development and learning, shape their behaviours in adulthood and offer the best protection against future non-communicable diseases (NCDs). In the Asia-Pacific region, NCDs are significant causes of healthcare burden and mortality. Furthermore, there is also a high prevalence of adverse metabolic risk factors and unhealthy lifestyle behaviours among these children.

Method

Representatives from 19 Asia-Pacific nations and/or jurisdictions developed a consensus statement on integrated 24-hour activity guidelines for the early years using the GRADE-ADOLOPMENT framework.

Findings

These guidelines apply to all infants, toddlers and pre-schoolers below 5 years of age. The guidelines aim to provide a holistic and practical approach to lifestyle activities by framing physical activity, sedentary behaviour and sleep within a 24-hour period. Dietary patterns were included as they play an integral role in metabolic health and energy balance.

Interpretation

Aligned with the World Health Organization's Global Action Plan for the Prevention and Control of NCDs through health promotion interventions in early life, through cultivating healthy lifestyle behaviours in the children's early years, we aim to provide children with the best start in life and reduce the burden of future NCDs in the Asia-Pacific region.

Funding

Funded by Integrated platform for research in advancing metabolic health outcomes of women and children.

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.

Sleep Deficiency in Young Children

There is growing public health concern about the high prevalence of sleep deficiency in early childhood and the associated risk for sleep-associated poor health outcomes, including metabolic, cardiovascular, and mental health. The recent shift to conceptualize sleep health as a multidimensional construct, influenced by socioecological factors, highlights the potential role of sleep in health disparities. Understanding the development of sleep health and the emergence of sleep disorders in early life is a current priority in pediatric sleep research. Future behavioral sleep interventions should consider the multiple socioecological influences on children's sleep health and be tested using inclusive sampling methods.

Nap effects on preschool children’s learning of letter‐sound mappings

This study explored whether a daytime nap aids children's acquisition of letter‐sound knowledge, which is a fundamental component for learning to read. Thirty‐two preschool children in Sydney, Australia (M_age = 4 years;3 months) were taught letter‐sound mappings in two sessions: one followed by a nap and the other by a wakeful period. Learning was assessed by explicit letter‐sound mappings (“Which sound does this letter make?”) and knowledge generalization tasks (“Here's Tav and Cav, which one is /kav/?”). Results from the knowledge generalization task showed better performance after a nap than after wake. However, no nap benefit was found for explicit letter‐sound knowledge. This study provides initial evidence that naps could be beneficial for preschool children's learning of letter‐sound mappings.

Sleep Characteristics in the Italian Pediatric Population: A Systematic Review

OBJECTIVE

During childhood sleep duration, quality and patterns evolve and change greatly and relate strongly to healthy development. This systematic review aims to summarize the literature on sleep characteristics in the Italian pediatric population, adopting a cultural perspective.

METHOD

Pubmed, PsycINFO and Medline databases were systematically searched. Eligible studies had to: include Italian children and adolescents; report data for one or more sleep-related variables; be published in English or Italian.

RESULTS

Twenty-nine studies were selected including 18551 Italian children or adolescents. Studies were categorized by age group: infancy and toddlerhood (0-3 years); preschool and school age (3-12 years); adolescence (12-18 years) and mixed age groups. Overall, studies showed that the Italian pediatric population present shorter sleep duration and longer sleep onset latency compared to international recommendations. Furthermore, data indicate high prevalence of dysfunctional sleep habits, such as late bed-time (all age groups), involvement of parents during bed-time (infancy and toddlerhood), and high variability between sleep times on week-days vs. weekends (adolescence). Nevertheless, most studies lacked comprehensive data on sleep patterns, focusing instead on isolated variables.

CONCLUSION

These results suggest a strong trend among Italian children and adolescents towards unhealthy sleep patterns. Comprehensive data are still lacking and large studies evaluating a broad range of sleep characteristics in Italian pediatric populations are needed. Data strongly suggest that Italian Pediatric Primary Care should place higher focus on sleep problems and implement clinical protocols directed towards improving sleep patterns in children and adolescents.

The role of naps in memory and executive functioning in early childhood

While sleep, including naps, has been shown to benefit many cognitive functions in adults, understanding whether naps are beneficial in early childhood has important translational implications. Here we review recent studies which, collectively, suggest that naps indeed benefit cognition at this age. Specifically, declarative, motor, and emotional memory are better if a nap follows learning. Executive functions such as attention and emotion processing are likewise better following sleep. However, a better understanding of the mechanism supporting these benefits and the generalizability to other forms of learning and executive functions is necessary. It is important for future research to extend such findings, which may promote the use of naps to support early education, particularly for learning-impaired children.

Longitudinal correlates of sleep duration in young children

OBJECTIVE

The primary aim of this study was to longitudinally examine potential demographic and screen time correlates of nap duration, nighttime sleep duration, and total sleep duration in young children over two time points.

METHODS

Data from the supporting Healthy physical AcTive Childcare setting (HATCH) study were analyzed. Participants were 206 toddlers (19-35 months) and preschoolers (36-60 months) in Alberta and Ontario, Canada. Child age, screen time (television, video games), and sleep duration (nap, nighttime) were measured at baseline and six-month follow-up, while other demographic variables were assessed at baseline only using the HATCH parental questionnaire. Mixed models were performed to examine the associations between potential correlates and sleep duration over time.

RESULTS

In the multiple regression models, significant correlates of total sleep duration (min/d) were child age (months; B = -3.03; 95%CI:-3.88,-2.19) and parental education (bachelor's degree vs. below bachelor level; B = 29.74, 95%CI:7.43,52.06). Significant correlates of nighttime sleep duration (min/d) included child age (B = -0.81; 95CI%:-1.53,-0.10), child race/ethnicity (Caucasian vs. non-Caucasian; B = 15.31; 95%CI:0.38,30.25), household income (>$150,000 vs. <$50,000; B = 32.93, 95%CI:9.80,56.06), television time (B = -0.19, 95%CI:-0.32,-0.05), video games time (B = -0.19, 95%CI: -0.38, -0.01) and total screen time (B = -0.19; 95%CI:-0.29,-0.08). Significant correlates of nap duration (min/d) were child age (B = -2.10; 95%CI:-2.68,-1.51) and race/ethnicity (Caucasian vs. non-Caucasian; B = -13.73; 95%CI:-25.78,-1.68).

CONCLUSION

Young children who were non-Caucasian, from lower income families, who had less-educated parents, or who had more screen time tended to have shorter sleep duration. Targeting these demographic groups and screen time appears important for promoting adequate sleep duration in early childhood.

Actigraphy in sleep research with infants and young children: Current practices and future benefits of standardized reporting

Actigraphy is a cost‐efficient method to estimate sleep–wake patterns over long periods in natural settings. However, the lack of methodological standards in actigraphy research complicates the generalization of outcomes. A rapidly growing methodological diversity is visible in the field, which increasingly necessitates the detailed reporting of methodology. We address this problem and evaluate the current state of the art and recent methodological developments in actigraphy reporting with a special focus on infants and young children. Through a systematic literature search on PubMed (keywords: sleep, actigraphy, child *, preschool, children, infant), we identified 126 recent articles (published since 2012), which were classified and evaluated for reporting of actigraphy. Results show that all studies report on the number of days/nights the actigraph was worn. Reporting was good with respect to device model, placement and sleep diary, whereas reporting was worse for epoch length, algorithm, artefact identification, data loss and definition of variables. In the studies with infants only (n = 58), the majority of articles (62.1%) reported a recording of actigraphy that was continuous across 24 hr. Of these, 23 articles (63.9%) analysed the continuous 24‐hr data and merely a fifth used actigraphy to quantify daytime sleep. In comparison with an evaluation in 2012, we observed small improvements in reporting of actigraphy methodology. We propose stricter adherence to standards in reporting methodology in order to streamline actigraphy research with infants and young children, to improve comparability and to facilitate big data ventures in the sleep community.

Sleep and Early Brain Development

The early years of life are characterized by dramatic developmental changes. Within this important time period lies the transition from newborn to childhood. Sleep is one of the primary activities of the brain during early development and plays an important role in healthy cognitive and psychosocial development in early life. This paper will first review the normal sleep characteristics and their development in neonates and children, including architecture of sleep, development of a healthy sleep rhythm in early childhood, sleep recommendations and cultural disparity, as well as important factors for establishing a healthy sleep pattern during the first years of life, such as regular and consistent bedtime routine, safe and comfortable sleep environment, and appropriate sleep onset associations. This paper then provides recent updates of evidence of the effects of sleep on early brain development, particularly on learning and memory, emotional regulation, and general cognitive development through behavioral and neurophysiological studies. As regards the mechanism, many experimental sleep deprivation studies in animals and adults have attempted to explain the underlying mechanisms of sleep on cognition and the emotional brain. Future studies are expected to delineate the effects of sleep on brain structural and functional networks in the developing brain with the marked development of image acquisition approaches and the novel analysis tools for infants and young children in recent years.

The cross-sectional and prospective associations between sleep characteristics and adiposity in toddlers: Results from the GET UP! Study

BACKGROUND

The associations between sleep characteristics and adiposity in children under three years are not fully understood yet.

OBJECTIVE

The objective of the study is to examine the cross-sectional and prospective associations between sleep characteristics and adiposity in toddlers over a 12-month period.

METHODS

Participants were 202 toddlers from the GET-UP!

STUDY

Sleep duration, sleep timing, and sleep variability were assessed using 24-hour accelerometry for seven consecutive days. Height and weight were measured, and BMI z scores were calculated. Linear mixed models were performed to examine the cross-sectional and prospective associations between sleep characteristics and adiposity, with adjustments for clustering effects and demographic factors.

RESULTS

Total sleep duration was negatively associated with higher adiposity cross-sectionally (B = -0.12; 95% CI: -0.23, -0.01; .033) but not prospectively (B = 0.01; 95% CI: -0.13, 0.10; .843). Nap duration was prospectively associated with higher levels of adiposity (B = 0.41; 95% CI: 0.14, 0.68; .003). Sleep variability and sleep timing were not associated with concurrent or subsequent adiposity.

CONCLUSION

Although sleep duration is an important factor associated with obesity in toddlerhood, the potential effects of different types of sleep duration may vary. While longer total sleep duration may protect children from increasing adiposity, longer nap duration seems to be risk factor. As evidence in this age group is scarce, more research is needed to confirm this finding.

Does splitting sleep improve long-term memory in chronically sleep deprived adolescents?

Sleep aids the encoding and consolidation of declarative memories, but many adolescents do not obtain the recommended amount of sleep each night. After a normal night of sleep, there is abundant evidence that a daytime nap enhances the consolidation of material learned before sleep and also improves the encoding of new information upon waking. However, it remains unclear how learning is affected when sleep is split between nocturnal and daytime nap periods during a typical school week of restricted sleep. We compared long-term memory in 58 adolescents who underwent two simulated school weeks of suboptimal continuous (6.5 h nocturnal sleep opportunity) or split sleep (5 h nocturnal sleep +1.5 h daytime nap at 14:00). In the first week, participants encoded pictures in the late afternoon on Day 5 and were tested after 2-nights of recovery sleep. On 3 consecutive days in the second week, participants learned about six species of amphibians in the morning, and six different amphibians in the late afternoon. Testing was performed in the evening following a night of recovery sleep. In the first week, the split sleep group recognized more pictures. In the second week, they remembered more facts about species learned in the afternoon. Groups did not differ for species learned in the morning. This suggests that under conditions of sleep restriction, a split sleep schedule benefits learning after a nap opportunity without impairing morning learning, despite less preceding nocturnal sleep. While not replacing adequate nocturnal sleep, a split sleep schedule may be beneficial for chronically sleep restricted learners.

Priming effect in children with Type 1 Diabetes Mellitus

Previous studies have evidenced cognitive difficulties across various domains in Type 1 Diabetes Mellitus (T1DM) children, but the implicit memory system has not yet been systematically explored.Taking into account that the interplay between memory and perception may be modulated by the semantic category of the stimuli and their salience, we explored explicit and implicit memory using both object and food stimuli to verify whether for T1DM children there is a feebleness in performing the function of memory as a function of the stimuli used.Eighteen T1DM children and 47 healthy children performed an explicit recognition task in which they were requested to judge whether the presented image had already been shown ("old") or not ("new") and an identification priming task in which they were asked to name new and old pictures presented at nine ascending levels of spatial filtering.Results did not reveal any differences between controls and T1DM children in the explicit memory recognition task, whereas some differences between the two groups were found in the identification priming task. In T1DM children, the priming effect was observed only for food images.The dissociation between implicit and explicit memory observed in children with diabetes seems to be modulated by the category of the stimuli, and these results underscore the relevance of taking into account this variable when exploring cognitive functions.

Early polysomnographic characteristics associated with neurocognitive development at 36 months of age

BACKGROUND

Few studies on the relationship between sleep quantity and/or quality and cognition have been conducted among preschoolers from the healthy general population. We aimed to identify, among 3-year-old children, early polysomnography (PSG) sleep factors associated with estimated intelligence quotient (IQ) using the Weschler Preschool and Primary Scale Intelligence-III test (WPPSI-III) and its indicators: full-scale (FISQ), verbal (VIQ), and performance (PIQ) intelligence quotients.

METHODS

We included full-term children from the French birth-cohort AuBE with PSG recording at term (M0) and/or six months (M6), and available WPPSI-III scores at three years. Sleep and arousal characteristics of these infants were evaluated during day and night sleep periods. Relationships between IQ scores and sleep parameters were estimated using models with the child as a repeated effect adjusted for time (night/day), maturation (M0/M6), tobacco exposure (yes/no), anxiety-depressive scores during pregnancy, maternal age, duration of breastfeeding and child's gender.

RESULTS

A total of 118 PSG recordings were obtained, representing a total of 78 unique children (38 with one PSG and 40 with two PSG). No correlations were found between night and day sleep durations at M0 or M6. Mean VIQ, PIQ, and FSIQ scores were within normal ranges. In multivariate models, longer sleep duration and higher sleep efficiency during the day were negatively associated with all IQ scores. More frequent arousals during the night were associated with lower VIQ scores.

CONCLUSION

Early sleep characteristics such as night sleep fragmentation or longer naps could be associated with impaired cognitive function at three years of age.

Differential effects of sleep on explicit and implicit memory for potential trauma reminders: findings from an analogue study

Background: Recent findings suggest that disruptions of sleep-related memory processing are involved in the development of posttraumatic stress symptoms. More specifically, exposure to an analogue traumatic event resulted in fewer intrusive memories, when it was followed by sleep instead of continued wakefulness. However, competing evidence suggests that sleep deprivation may reduce intrusive re-experiencing. To address these conflicting accounts, we examined how sleep - as opposed to partial sleep deprivation - modulates explicit and implicit trauma memory using an analogue procedure. Methods: Healthy participants (N = 41) were assigned to a Sleep or Partial sleep deprivation group. Prior to nocturnal sleep, both groups were exposed to "traumatic" picture stories. After sleep or partial sleep deprivation, participants were subjected to tests of explicit and implicit memory for potential trauma reminders. Thereafter, participants completed an intrusion triggering task that was embedded in a distractor task. Results: Analyses revealed higher explicit memory for potential trauma reminders after sleep as compared to partial sleep deprivation. No group differences were found for implicit memory. Participants responded with fewer intrusions after sleep than following partial sleep deprivation. Conclusions: The current findings support a protective role of sleep in trauma memory processing, which may be evident after the first night of sleep post-trauma. Although more research is needed, our results corroborate the importance of promoting restful sleep in trauma-exposed individuals.

Post-class naps boost declarative learning in a naturalistic school setting

Laboratory evidence of a positive effect of sleep on declarative memory consolidation suggests that naps can be used to boost school learning in a scalable, low-cost manner. The few direct investigations of this hypothesis have so far upheld it, but departed from the naturalistic setting by testing non-curricular contents presented by experimenters instead of teachers. Furthermore, nap and non-nap groups were composed of different children. Here we assessed the effect of post-class naps on the retention of Science and History curricular contents presented by the regular class teacher to 24 students from 5th grade. Retention was repeatedly measured 3-4 days after content learning, with weekly group randomization over 6 consecutive weeks. Contents followed by long naps (>30 min), but not short naps (<30 min), were significantly more retained than contents followed by waking (Cohen's d = 0.7962). The results support the use of post-class morning naps to enhance formal education.

Spotlight on daytime napping during early childhood

Daytime napping undergoes a remarkable change in early childhood, and research regarding its relationship to cognitive development has recently accelerated. In this review, we summarize our current understanding of this relationship focusing on children aged <5 years. First, we evaluate different studies on the basis of the experimental design used and the specific cognitive processes they investigate. Second, we analyze how the napping status of children may modulate the relationship between learning and napping. Third, the possible role of sleep spindles, ie, specific electroencephalographic components during sleep, in cognitive development is explored. We conclude that daytime napping is crucial in early memory development.

Systematic review of the relationships between sleep duration and health indicators in the early years (0-4 years)

Background

The objective of this systematic review was to examine for the first time the associations between sleep duration and a broad range of health indicators in children aged 0 to 4 years.

Methods

Electronic databases were searched with no limits on date or study design. Included studies (published in English or French) were peer-reviewed and met the a priori determined population (apparently healthy children aged 1 month to 4.99 years), intervention/exposure/comparator (various sleep durations), and outcome criteria (adiposity, emotional regulation, cognitive development, motor development, growth, cardiometabolic health, sedentary behaviour, physical activity, quality of life/well-being, and risks/injuries). The quality of evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework. Due to high levels of heterogeneity across studies, narrative syntheses were employed.

Results

A total of 69 articles/studies (62 unique samples) met inclusion criteria. Data across studies included 148,524 unique participants from 23 countries. The study designs were randomized trials (n = 3), non-randomized interventions (n = 1), longitudinal studies (n = 16), cross-sectional studies (n = 42), or longitudinal studies that also reported cross-sectional analyses (n = 7). Sleep duration was assessed by parental report in 70% of studies (n = 48) and was measured objectively (or both objectively and subjectively) in 30% of studies (n = 21). Overall, shorter sleep duration was associated with higher adiposity (20/31 studies), poorer emotional regulation (13/25 studies), impaired growth (2/2 studies), more screen time (5/5 studies), and higher risk of injuries (2/3 studies). The evidence related to cognitive development, motor development, physical activity, and quality of life/well-being was less clear, with no indicator showing consistent associations. No studies examined the association between sleep duration and cardiometabolic biomarkers in children aged 0 to 4 years. The quality of evidence ranged from “very low” to “high” across study designs and health indicators.

Conclusions

Despite important limitations in the available evidence, longer sleep duration was generally associated with better body composition, emotional regulation, and growth in children aged 0 to 4 years. Shorter sleep duration was also associated with longer screen time use and more injuries. Better-quality studies with stronger research designs that can provide information on dose-response relationships are needed to inform contemporary sleep duration recommendations.

Electronic supplementary material

The online version of this article (10.1186/s12889-017-4850-2) contains supplementary material, which is available to authorized users.

Priming recognition in good sleepers and in insomniacs

Insomniacs often report memory and concentration problems, but these complaints have not been consistently supported by performance measurements. Furthermore, while the majority of studies have addressed explicit memory, few have investigated the implicit domain, and very little is known concerning other types of implicit memory besides procedural memory, such as priming. Thus, the purpose of the study was to investigate priming effect for visual stimuli in insomniacs and good sleepers. Twenty-three insomniacs and 20 good sleepers performed a visual priming task in which they were asked to name new and old pictures presented at nine ascending levels of spatial filtering. Both neutral and sleep-related stimuli were used, as previous research evidenced an attentional bias for sleep-related stimuli. Visual priming effect was observed in both groups, suggesting that poor sleep quality does not affect this type of implicit memory. However, the identification process in insomniacs is influenced by the nature of the stimulus to identify: insomniacs recognized both new and old sleep-related stimuli at lower spatial frequencies compared with good sleepers. The tendency to selectively attend to sleep-related stimuli may influence top-down processes occurring during identification of filtering stimuli, by determining a pre-allocation of attentional resources and facilitating identification processes even when sensorial information is scant. Differences in the identification processes of sleep-related stimuli compared with neutral ones should be carefully taken into account as possible pre-clinical markers of insomnia in poor sleepers.

Napping: A public health issue. From epidemiological to laboratory studies

Sleep specialists have proposed measures to counteract the negative short- and long-term consequences of sleep debt, and some have suggested the nap as a potential and powerful "public health tool". Here, we address this countermeasure aspect of napping viewed as an action against sleep deprivation rather than an action associated with poor health. We review the physiological functions that have been associated positively with napping in both public health and clinical settings (sleep-related accidents, work and school, and cardiovascular risk) and in laboratory-based studies with potential public health issues (cognitive performance, stress, immune function and pain sensitivity). We also discuss the circumstances in which napping-depending on several factors, including nap duration, frequency, and age-could be a potential public health tool and a countermeasure for sleep loss in terms of reducing accidents and cardiovascular events and improving sleep-restriction-sensitive working performance. However, the impact of napping and the nature of the sleep stage(s) involved still need to be evaluated, especially from the perspective of coping strategies in populations with chronic sleep debt, such as night and shift workers.

Sleep Physiology in Toddlers: Effects of Missing a Nap on Subsequent Night Sleep

The shift from a biphasic to a monophasic sleep schedule is a fundamental milestone in early childhood. This transition, however, may result in periods of acute sleep loss as children may nap on some but not all days. Although data indicating the behavioral consequences of nap deprivation in young children are accumulating, little is known about changes to sleep neurophysiology following daytime sleep loss. This study addresses this gap in knowledge by examining the effects of acute nap deprivation on subsequent nighttime sleep electroencephalographic (EEG) parameters in toddlers. Healthy children (n=25; 11 males; ages 30–36 months) followed a strict sleep schedule for ≥5 days before sleep EEG recordings performed on 2 non-consecutive days: one after 13 h of prior wakefulness and another at the same clock time but preceded by a daytime nap. Total slow-wave energy (SWE) was computed as cumulative slow-wave activity (SWA; EEG power in 0.75–4.5 Hz range) over time. Nap and subsequent night SWE were added and compared to SWE of the night after a missed nap. During the night following a missed nap, children fell asleep faster (11.9±8.7 min versus 37.3±22.1 min; d=1.6, p=0.01), slept longer (10.1±0.7 h versus 9.6±0.6 h; d=0.7, p<0.01) and exhibited greater SWA (133.3±37.5% versus 93.0±4.7%; d=0.9, p<0.01) compared to a night after a daytime nap. SWE for combined nap and subsequent night sleep did not significantly differ from the night following nap deprivation (12141.1±3872.9 μV²*h versus 11,588±3270.8 μV²*h; d=0.6, p=0.12). However, compared to a night following a missed nap, children experienced greater time in bed (13.0±0.8 h versus 10.9±0.5 h; d=3.1, p<0.01) and total sleep time (11.2±0.8 h versus 10.1±0.7 h; d=1.4, p<0.01). Shorter sleep latency, longer sleep duration, and increased SWA in the night following a missed nap indicate that toddlers experience a physiologically meaningful homeostatic challenge after prolonged wakefulness. Whether toddlers fully recover from missing a daytime nap in the subsequent night necessitates further examination of daytime functioning.

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During nighttime sleep following a missed nap, 2-year-olds experience shorter sleep onset latency and increased sleep duration, slow wave sleep, slow wave activity, and slow-wave energy (cumulative slow wave activity), compared to a night of sleep following a daytime nap.

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Slow-wave energy is similar in 24 h sleep recordings on a day containing nap and night sleep compared to a day containing only night sleep.

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Children show large inter-individual variability in neurophysiological recovery from a missed nap, as measured by the sleep EEG.