There is increasing evidence that sleep promotes off-line enhancement of a variety of explicitly learned motor tasks in young adults. However, whether sleep promotes off-line consolidation of implicitly learned motor tasks is still under question. Furthermore, the role of sleep in promoting transfer of learning remains unknown. This study examined the role of sleep in learning and transfer of learning of an implicit continuous motor task. Twenty-three neurologically intact individuals (mean age 26.4 years) were randomly assigned to either a sleep group or a no-sleep group. The sleep group practiced a continuous tracking task in the evening and underwent retention and transfer testing the following morning, while the no-sleep group practiced the tracking task in the morning and underwent retention and transfer testing in the evening. The results show that in both the sleep and no-sleep groups, performance improved off-line without further practice for both the general skill and the sequence-specific skill. The results also indicate that sleep and time promote transfer of learning of both sequence-specific and general skill learning to a spatial and temporal variation of the motor task. These findings demonstrate that sleep does not play a critical role in promoting off-line learning and transfer of learning of an implicit continuous motor task.

Functional magnetic resonance imaging (fMRI) was used to investigate the cerebral correlates of motor sequence memory consolidation. Participants were scanned while training on an implicit oculomotor sequence learning task and during a single testing session taking place 30 min, 5 hr, or 24 hr later. During training, responses observed in hippocampus and striatum were linearly related to the gain in performance observed overnight, but not over the day. Responses in both structures were significantly larger at 24 hr than at 30 min or 5 hr. Additionally, the competitive interaction observed between these structures during training became cooperative overnight. These results stress the importance of both hippocampus and striatum in procedural memory consolidation. Responses in these areas during training seem to condition the overnight memory processing that is associated with a change in their functional interactions. These results show that both structures interact during motor sequence consolidation to optimize subsequent behavior.

When toddlers hear a novel word, they quickly and independently link it with a novel object rather than known-name objects. However, they are less proficient in retaining multiple novel words. Sleep and even short naps can enhance declarative memory in adults and children and this study investigates the effect of napping on children’s memory for novel words. Forty two-and-a-half-year-old children were presented with referent selection trials for four novel nouns. Children’s retention of the words was tested immediately after referent selection, four hours later in the afternoon, and the following morning. Half of the toddlers napped prior to the afternoon retention test. Amongst the toddlers who napped, retention scores remained steady four hours after exposure and the following morning. In contrast, for the wake group, there was a steady decline in retention scores by the following morning and significantly lower retention scores compared to the nap group. Napping following exposure to novel word–object associations could help in maintaining memories and limiting decay. Nap duration was also associated with better retention scores, but there were no effects of sleep quality, habitual napping, or sleepiness. The findings have implications for the role of napping in children’s language acquisition.

In this first study of the impact of sleep on infants' problem solving of a locomotor task, 28 newly walking infants who were within a week of having given up crawling trained to navigate a shoulder-height tunnel to reach a caregiver waiting at the end. During the transitional window between crawling and walking, infants are reluctant to return to crawling, making this task uniquely challenging. Infants were randomly assigned to either nap or stay awake during a delay between training and a later test session. For the Nap group, efficiency of problem solving improved from training to test, but there was no change for the No Nap group. These findings suggest that for newly walking infants, sleep facilitates learning to solve a novel motor problem.Published by Elsevier Inc.

It is now recognized that extensive maturational changes take place in the human brain during adolescence, and that the trajectories of these changes are best studied longitudinally. We report the first longitudinal study of the adolescent decline in non-rapid eye movement (NREM) delta (1-4 Hz) and theta (4-8 Hz) EEG. Delta and theta are the homeostatic frequencies of human sleep. We recorded sleep EEG in 9- and 12-year-old cohorts twice yearly over a 5-year period. Delta power density (PD) was unchanged between age 9 and 11 years and then fell precipitously, decreasing by 66% between age 11 and 16.5 years (P <.000001). The decline in theta PD began significantly earlier than that in delta PD and also was very steep (by 60%) between age 11 and 16.5 years (P <.000001). These data suggest that age 11-16.5 years is a critically important maturational period for the brain processes that underlie homeostatic NREM EEG, a finding not suggested in previous cross-sectional data. We hypothesize that these EEG changes reflect synaptic pruning. Comparing our data with published longitudinal declines in MRI-estimated cortical thickness suggests the theta age curve parallels the earlier maturational thinning in 3-layer cortex, whereas the delta curve tracks the later changes in 5-layer cortex. This comparison also reveals that adolescent declines in NREM delta and theta are substantially larger than decreases in cortical thickness (>60% vs. <20%). The magnitude, interindividual difference, and tight link to age of these EEG changes indicate that they provide excellent noninvasive tools for investigating neurobehavioral correlates of adolescent brain maturation.

Massive changes in brain morphology and function in the first years of life reveal a postero-anterior trajectory of cortical maturation accompanied by regional modifications of NREM sleep. One of the most sensible marker of this maturation process is represented by electroencephalographic (EEG) activity within the frequency range of sleep spindles. However, direct evidence that these changes actually reflect maturational modifications of fast and slow spindles still lacks. Our study aimed at answering the following questions: 1. Do cortical changes at 11.50 Hz frequency correspond to slow spindles? 2. Do fast and slow spindles show different age trajectories and different topographical distributions? 3. Do changes in peak frequency explain age changes of slow and fast spindles?We measured the antero-posterior changes of slow and fast spindles in the first 60 min of nightly sleep of 39 infants and children (0-48 mo.).We found that (A) changes of slow spindles from birth to childhood mostly affect frontal areas (B) variations of fast and slow spindles across age groups go in opposite direction, the latter progressively increasing across ages; (C) this process is not merely reducible to changes of spindle frequency.As a main finding, our cross-sectional study shows that the first form of mature spindle (i.e., corresponding to the adult phasic event of NREM sleep) is marked by the emergence of slow spindles on anterior regions around the age of 12 months.Copyright © 2017 Elsevier B.V. All rights reserved.

The importance of sleep to overall health and well-being is becoming increasingly appreciated; however, clinicians may not have a sound understanding of the fundamentals of sleep. This review of normal pediatric sleep is meant to provide a foundation for the pediatric nurse practitioner to develop and use in clinical practice. Key concepts such as normal sleep physiology including biological rhythms and stages of sleep are discussed. Developmental changes in sleep seen in the transition from infancy to young childhood are highlighted, and strategies for instituting and maintaining normal sleep behaviors are recommended. Part 2 of this series will address common sleep problems experienced by young 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.

Sleep benefits memory consolidation. The reviewed studies indicate that this consolidating effect is not revealed under all circumstances but is linked to specific psychological conditions. Specifically, we discuss to what extent memory consolidation during sleep depends on the type of learning materials, type of learning and retrieval test, different features of sleep and the subject population. Post-learning sleep enhances consolidation of declarative, procedural and emotional memories. The enhancement is greater for weakly than strongly encoded associations and more consistent for explicitly than implicitly encoded memories. Memories associated with expected reward gain preferentially access to sleep-dependent consolidation. For declarative memories, sleep benefits are more consistently revealed with recall than recognition procedures at retrieval testing. Slow wave sleep (SWS) particularly enhances declarative memories whereas rapid eye movement (REM) sleep preferentially supports procedural and emotional memory aspects. Declarative memory profits already from rather short sleep periods (1-2 h). Procedural memory profits seem more dose-dependent on the amount of sleep following the day after learning. Children's sleep with high amounts of SWS distinctly enhances declarative memories whereas elderly and psychiatric patients with disturbed sleep show impaired sleep-associated consolidation often of declarative memories. Based on the constellation of psychological conditions identified we hypothesize that access to sleep-dependent consolidation requires memories to be encoded under control of prefrontal-hippocampal circuitry, with the same circuitry controlling subsequent consolidation during sleep.

During the first year of life, infants spend most of their time in the sleeping state. Assessment of sleep during infancy presents an opportunity to study the impact of sleep on the maturation of the central nervous system (CNS), overall functioning, and future cognitive, psychomotor, and temperament development. To assess what is currently known regarding sleep during infancy and its effects on cognitive, psychomotor, and temperament development, we assessed the relevant literature published over the last several decades. To provide a foundation for a more in-depth understanding of this literature, we preface this with an overview of brain maturation, sleep development, and various assessment tools of both sleep and development during this unique period. At present, we do not have sufficient data to conclude that a causal relationship exists between infant sleep and cognitive, psychomotor, and temperament development. Caution should be used in predicting outcomes, as the timing and subjectivity of evaluations may obviate accurate assessment. Collectively, studies assess a wide array of sleep measures, and findings from one developmental period cannot be generalized readily to other developmental periods. Future studies should follow patients longitudinally. Additionally, refinements of existing assessment tools would be useful. In view of the relatively high reported pediatric prevalence of cognitive and behavioral deficits that carry significant long-term costs to individuals and society, early screening of sleep-related issues may be a useful tool to guide targeted prevention and early intervention.

This study aimed to (1) compare sleep problems between children and adolescents with epilepsy and non-epileptic controls, and (2) examine whether there is an association between sleep problems and quality of life, Attention-Deficit Hyperactivity Disorder (ADHD) and mothers' emotional symptoms.Fifty-three patients from a cohort of epilepsy (aged 7-18 years) and 28 controls with minor medical problems (aged 7-18 years) were included. Parents completed Children's Sleep Habits Questionnaire (CSHQ) and Kinder Lebensqualitätsfragebogen: Children's Quality of Life Questionnaire-revised (KINDL-R) for patients and controls. Turgay DSM-IV Disruptive Behavior Disorders Rating Scale (T-DSM-IV-S) parent and teacher forms were used to assess ADHD symptoms for patients. Mothers of the patients completed Beck Depression Inventory and State-Trait Anxiety Inventory (STAI). Neurology clinic charts were reviewed for the epilepsy-related variables.Children with epilepsy had a higher CSHQ Total score than the control group. Those with a CSHQ score >56 (which indicates moderate to severe sleep problems) had lower scores on KINDL-R. Parent-rated T-DSM-IV-S Total and Hyperactivity-Impulsivity scores, STAI trait and Beck scores were found to be higher in those with a CSHQ score >56. Significant positive correlations were found between CSHQ Total score and T-DSM-IV-S, STAI trait and Beck scores. Binary logistic regression analysis revealed that T-DSM-IV-S Total, Inattention and Hyperactivity-Impulsivity scores were significantly associated with a higher CSHQ Total score. None of the epilepsy-related variables were found to be related with the CSHQ Total score.Among children with epilepsy, sleep problems lead to a poor quality of life. The link between sleep problems and psychiatric symptoms must be conceptualized as a bilateral relationship. ADHD appears to be the strongest predictor of sleep problems.Copyright © 2016 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.

Three-month-old infants learned to activate an overhead crib mobile by operant footkicking and received a visual reminder of the event (a "reactivation treatment") 2 weeks later, after forgetting had occurred. Subsequent manifestation of the association was a monotonic increasing function of time since the reactivation treatment, and performance of infants tested 8 hours after the remainder was related to the time spent sleeping in the interim (r = 0.75). These data demonstrate that normal retrieval is time-dependent. Moreover, individual data suggest that retrieval may be continuous rather than discontinuous.

Sleep plays an important role in stabilizing and reinforcing memory of newly acquired information. Like nocturnal sleep, a daytime nap is shown to effectively contribute to memory processing. However, studies are often focused on nocturnal sleep. This review has aimed at systematically compiling the results of studies which have examined the effects of napping on declarative memory performance in healthy adults. Such studies have focused on different aspects of memory reinforcement following a diurnal nap including the involved mechanisms in memory reconsolidation, type of declarative tasks, cross-gender differences, the role of age, duration of nap and its delayed onset. One of the reviewed studies reported that even as short as 6 min of napping exerts a positive effect on memory function. Evidence from these studies indicates hippocampal-dependent enhancement of the learned information. Diurnal naps predominantly include non-rapid eye movement sleep with slow waves yielding potential effects on declarative memory. Evidence has shown that the empowered learning and retrieval depends upon spindle density during the nap. Moreover, the role of coordinated autonomic and central events in enhancing declarative memory has also been reported. Slow waves and sleep spindles are known to fuel declarative memory function during the NREM-2 (N2) stage of sleep.Copyright © 2021 Elsevier B.V. All rights reserved.

Slow wave activity (SWA, 0.5-4.5 Hz) is a well-established marker for sleep pressure in adults. Recent studies have shown that increasing sleep pressure is reflected by an increased synchronized firing pattern of cortical neurons, which can be measured by the slope of sleep slow waves. Thus we aimed at investigating whether the slope of sleep slow waves might provide an alternative marker to study the homeostatic regulation of sleep during early human development.All-night sleep electroencephalography (EEG) was recorded longitudinally at 2, 4, 6, and 9 months after birth.Home recording.11 healthy full-term infants (5 male, 6 female).None.The slope of sleep slow waves increased with age. At all ages the slope decreased from the first to the last hour of non rapid-eye-movement (NREM) sleep, even when controlling for amplitude differences (P < 0.002). The decrease of the slope was also present in the cycle-by-cycle time course across the night (P < 0.001) at the age of 6 months when the alternating pattern of low-delta activity (0.75-1.75 Hz) is most prominent. Moreover, we found distinct topographical differences exhibiting the steepest slope over the occipital cortex.The results suggest an age-dependent increase in synchronization of cortical activity during infancy, which might be due to increasing synaptogenesis. Previous studies have shown that during early postnatal development synaptogenesis is most pronounced over the occipital cortex, which could explain why the steepest slope was found in the occipital derivation. Our results provide evidence that the homeostatic regulation of sleep develops early in human infants.

Friedrich, Manuela Humboldt Univ, Dept Psychol, D-12489 Berlin, Germany. Friedrich, Manuela; Friederici, Angela D. Max Planck Inst Human Cognit & Brain Sci, Dept Neuropsychol, D-04103 Leipzig, Germany. Wilhelm, Ines Univ Childrens Hosp, Child Dev Ctr, CH-8032 Zurich, Switzerland. Wilhelm, Ines; Born, Jan Univ Tubingen, Inst Med Psychol & Behav Neurobiol, D-72076 Tubingen, Germany. Wilhelm, Ines; Born, Jan Univ Tubingen, Ctr Integrat Neurosci, D-72076 Tubingen, Germany.

From the age of 3 months, infants learn relations between objects and co-occurring words [1]. These very first representations of object-word pairings in infant memory are considered as non-symbolic proto-words comprising specific visual-auditory associations that can already be formed in the first months of life [2-5]. Genuine words that refer to semantic long-term memory have not been evidenced prior to 9 months of age [6-9]. Sleep is known to facilitate the reorganization of memories [9-14], but its impact on the perceptual-to-semantic trend in early development is unknown. Here we explored the formation of word meanings in 6- to 8-month-old infants and its reorganization during the course of sleep. Infants were exposed to new words as labels for new object categories. In the memory test about an hour later, generalization to novel category exemplars was tested. In infants who took a short nap during the retention period, a brain response of 3-month-olds [1] was observed, indicating generalizations based on early developing perceptual-associative memory. In those infants who napped longer, a semantic priming effect [15, 16] usually found later in development [17-19] revealed the formation of genuine words. The perceptual-to-semantic shift in memory was related to the duration of sleep stage 2 and to locally increased sleep spindle activity. The finding that, after the massed presentation of several labeled category exemplars, sleep enabled even 6-month-olds to create semantic long-term memory clearly challenges the notion that immature brain structures are responsible for the typically slower lexical development.Copyright © 2017 Elsevier Ltd. All rights reserved.

This is a systematic review of the scientific literature with regard to normal sleep patterns in infants and children (0-12 years). The review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Mean and variability data for sleep duration, number of night wakings, sleep latency, longest sleep period overnight, and number of daytime naps were extracted from questionnaire or diary data from 34 eligible studies. Meta-analysis was conducted within age-bands and categories. In addition, fractional polynomial regression models were used to estimate best-fit equations for the sleep variables in relation to age. Reference values (means) and ranges (±1.96 SD) for sleep duration (hours) were: infant, 12.8 (9.7-15.9); toddler/preschool, 11.9 (9.9-13.8); and child, 9.2 (7.6-10.8). The best-fit (R(2)=0.89) equation for hours over the 0-12 year age range was 10.49-5.56×[(age/10)^0.5-0.71]. Meta-regression showed predominantly Asian countries had significantly shorter sleep (1h less over the 0-12 year range) compared to studies from Caucasian/non-Asian countries. Night waking data provided 4 age-bands up to 2 years ranging from 0 to 3.4 wakes per night for infants (0-2 months), to 0-2.5 per night (1-2 year-olds). Sleep latency data were sparse but estimated to be stable across 0-6 years. Because the main data analysis combined data from different countries and cultures, the reference values should be considered as global norms.Copyright © 2011 Elsevier Ltd. All rights reserved.

Infants engage in an extraordinary amount of learning during their waking hours even though much of their day is consumed by sleep. What role does sleep play in infant learning? Fifteen-month-olds were familiarized with an artificial language 4 hr prior to a lab visit. Learning the language involved relating initial and final words in auditory strings by remembering the exact word dependencies or by remembering an abstract relation between initial and final words. One group napped during the interval between familiarization and test. Another group did not nap. Infants who napped appeared to remember a more abstract relation, one they could apply to stimuli that were similar but not identical to those from familiarization. Infants who did not nap showed a memory effect. Naps appear to promote a qualitative change in memory, one involving greater flexibility in learning.

Age is probably the single most crucial factor determining how humans sleep. Age and level of vigilance significantly influence the electroencephalogram (EEG) and the polysomnogram (PSG). The Pediatric Task Force provide an evidence-based review of the age-related development of the polysomnographic features of sleep in neonates, infants, and children, assessing the reliability and validity of these features, and assessing alternative methods of measurement. We used this annotated supporting text to develop rules for scoring sleep and arousals in infants and children. A pediatric EEG or PSG can only be determined to be normal by assessing whether the EEG patterns are appropriate for maturational age. Sleep in infants at term can be scored as NREM and REM sleep because all the polysomnographic and EEG features of REM sleep are present and quiet sleep, if not NREM sleep, is at least "not REM sleep." The dominant posterior rhythm (DPR) of relaxed wakefulness increases in frequency with age: (1) 3.5-4.5 Hz in 75% of normal infants by 3-4 months post-term; (2) 5-6 Hz in most infants 5-6 months post-term; 3) 6 Hz in 70% of normal children by 2 months of age; and 3) 8 Hz (range 7.5-9.5 Hz) in 82% of normal children age 3 years, 9 Hz in 65% of 9-year-olds, and 10 Hz in 65% of 15-year-old controls. Sleep spindles in children occur independently at two different frequencies and two different scalp locations: 11.0-12.75 Hz over the frontal and 13.0-14.75 Hz over the centroparietal electrodes; these findings are most prominent in children younger than 13 years. Centroparietal spikes are often maximal over the vertex (Cz), less often maximal over the left central (C3) or right central (C4) EEG derivation. About 50% of sleep spindles within a particular infant's PSG are asynchronous before 6 months of age, 30% at 1 year. Based on this, we recommend that: (1) sleep spindles be scored as a polysomnographic signature of NREM stage 2 sleep (N2) at whatever age they are first seen in a PSG, typically present by 2 to 3 months post-term; (2) identify and score sleep spindles from the frontal and centroparietal EEG derivations, especially in infants and children younger than 13 years. NREM sleep in an infant or child can be scored if the dominant posterior rhythm occupies <50% of a 30-second epoch, and one or more of the following EEG patterns appear: (1) a diffuse lower voltage mixed frequency activity; (2) hypnagogic hypersynchrony; (3) rhythmic anterior theta of drowsiness; (4) diffuse high voltage occipital delta slowing; (5) runs or bursts of diffuse, frontal, frontocentral, or occipital maximal rhythmic 3-5 Hz slowing; (6) vertex sharp waves; and/or (7) post-arousal hypersynchrony. K complexes first appear 5 months post-term and are usually present by 6 months post-term, whereas clearly recognizable vertex sharp waves are most often seen 16 months post-term. Vertex sharp waves are best seen over the central (Cz, C3, C4) and K complexes over the frontal (Fz, F3, F4) electrodes. Slow wave activity (SWA) of slow wave sleep (SWS) is first seen as early as 2 to 3 months post-term and is usually present 4 to 4.5 months post-term. SWA of SWS in an infant or child often has a peak-to-peak amplitude of 100 to 400 microV. Based on consensus voting we recommended scoring N1, N2, and N3 corresponding to NREM 1, 2, and SWS whenever it was recognizable in an infant's PSG, usually by 4 to 4.5 months post-term (as early as 2-3 months post-term). Epochs of NREM sleep which contain no sleep spindles, K complexes, or SWA would be scored as N1; those which contain either K complexes or sleep spindles and <20% SWS as N2, and those in which >20% of the 30-second epoch contain 0.5 to 2 Hz >75 microV (usually 100-400 microV) activity as N3. The DPR should be scored in the EEG channel that is best observed, (typically occipital), but DPR reactive to eye opening can be seen in central electrodes. Because sleep spindles occur independently over the frontal and central regions in children, they should be scored whether they occur in the frontal or central regions. Because sleep spindles are asynchronous before age 2 years, simultaneous recording of left and right frontal and central activity may be warranted in children 1-2 years of age. Simultaneous recording of left, right, and midline central electrodes may be appropriate because of the asynchronous nature of sleep spindles before age 2 years, but reliability testing is needed. Evidence has shown that the PSG cannot reliably be used to identify neurological deficits or to predict behavior or outcome in infants because of significant diversity of results, even in normal infants. Normal sleep EEG patterns and architecture are present in the first year of life, even in infants with severe neurological compromise. Increasing evidence suggests that sleep and its disorders play critical roles in the development of healthy children and healthy adults thereafter. Reliability studies comparing head-to-head different scoring criteria, recording techniques, and derivations are needed so that future scoring recommendations can be based on evidence rather than consensus opinion. We need research comparing clinical outcomes with PSG measures to better inform clinicians and families exactly what meaning a PSG has in evaluating a child's suspected sleep disorder.

Cross-sectional studies provide evidence that in pre-schoolers poor sleep is by this age already associated with both poor psychological functioning and an increased cortisol secretion. However, long-term studies on the stability of sleep in pre-schoolers are scarce. The aim of the present study was therefore to investigate objectively assessed sleep in pre-schoolers longitudinally, and to predict sleep, psychological functioning and cortisol secretion prospectively as a function of sleep 12 months earlier.A total of 58 pre-schoolers (mean age: 5.43 years; 47% females) were re-assessed 12 months later (mean age: 6.4 years). Sleep-EEG recordings were performed, saliva cortisol was analysed, and parents and experts rated children's psychological functioning.Longitudinally, poor objective sleep at age 5.4 years was associated with poor objective sleep and psychological difficulties but not cortisol secretion 12 months later. At age 6.4 years, poor sleep was concurrently associated with greater psychological difficulties and increased cortisol secretion.In pre-schoolers, poor sleep objectively assessed at the age of 5.4 years was associated with poor sleep and psychological difficulties one year later. Data indicate that in pre-schoolers, sleep remains stable over a 12-months-period. Pre-schoolers with poor sleep appear to be at risk for developing further psychological difficulties.Copyright © 2013 Elsevier Ltd. All rights reserved.

Studies of the long-term stability of sleep in pre-schoolers are scarce. The aim of the present study was to investigate objectively assessed sleep via actigraphy in pre-schoolers longitudinally, and to predict sleep, psychological functioning and cortisol secretion prospectively as a function of sleep 12 months earlier.A total of 73 pre-schoolers (mean age: 5.45 years; 53% females) were assessed again after 12 (mean age: 6.4 years). Sleep-actigraphy recordings were performed, saliva cortisol was analysed, and parents and experts rated children's psychological functioning.Longitudinally, poor sleep at age 5.45 years was associated with poor sleep and internalizing and peer problems but not with externalizing problems and hyperactivity, and cortisol secretion 12 months later. At age 6.4 years and cross-sectionally, poor sleep was concurrently associated with greater psychological difficulties and increased cortisol secretion.In pre-schoolers, poor sleep objectively assessed at age five was associated with psychological difficulties and poor sleep as assessed via actigraph and one year later. Results indicate that in pre-schoolers sleep remains stable over a 12-mont interval. Pre-schoolers with poor sleep appear to be at risk for developing further psychological difficulties.Copyright © 2014. Published by Elsevier Ltd.

One of the key processes in language development is generalization--the selection and extension of relevant features and information to similar objects and concepts. Little is known about how sleep influences generalization, and studies on the topic are inconclusive. Our aim was to investigate how a nap affects generalization in 16-mo-olds. We hypothesized that a nap is necessary for successful generalization of word meanings.Twenty-eight 16-mo-old, typically developing toddlers were randomly assigned to nap and wake groups. We trained toddlers with two novel object-word pairs and tested their initial ability to generalize. Toddlers took part in an intermodal preferential looking task, in which they were shown different colored versions of the original objects and heard one of the trained labels. If toddlers understand the label, they are expected to increase their looking time to the target. Looking behavior was measured with an automated eye tracker. Afterward, the nap group went to sleep, while the wake group stayed awake for approximately 2 h. We then repeated the test of their performance on the generalization task.A significant interaction of group and session was found in preferential looking. The performance of the nap group increased after the nap, whereas that of the wake group did not change.Our results suggest that napping improves generalization in toddlers.© 2016 Associated Professional Sleep Societies, LLC.

Little is known about the role that night-time sleep and daytime naps play in early cognitive development. Our aim was to investigate how napping affects word learning in 16-month-olds. Thirty-four typically developing infants were assigned randomly to nap and wake groups. After teaching two novel object-word pairs to infants, we tested their initial performance with an intermodal preferential looking task in which infants are expected to increase their target looking time compared to a distracter after hearing its auditory label. A second test session followed after approximately a 2-h delay. The delay contained sleep for the nap group or no sleep for the wake group. Looking behaviour was measured with an automatic eye-tracker. Vocabulary size was assessed using the Oxford Communicative Development Inventory. A significant interaction between group and session was found in preferential looking towards the target picture. The performance of the nap group increased after the nap, whereas that of the wake group did not change. The gain in performance correlated positively with the expressive vocabulary size in the nap group. These results indicate that daytime napping helps consolidate word learning in infancy. © 2015 European Sleep Research Society.

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.

Sleep has been shown to aid a variety of learning and memory processes in adults (Stickgold, 2005). Recently, we showed that infants' learning also benefits from subsequent sleep such that infants who nap are able to abstract the general grammatical pattern of a briefly presented artificial language (Gomez, Bootzin & Nadel, 2006). In the present study, we demonstrate, for the first time, long-term effects of sleep on memory for an artificial language. Fifteen-month-old infants who had napped within 4 hours of language exposure remembered the general grammatical pattern of the language 24 hours later. In contrast, infants who had not napped shortly after being familiarized with the language showed no evidence of remembering anything about the language. Our findings support the view that infants' frequent napping plays an essential role in establishing long-term memory.

The main purpose of the present study was to calculate percentile curves for total sleep duration per 24 hours, for nighttime and for daytime sleep duration from early infancy to late adolescence to illustrate the developmental course and age-specific variability of these variables among subjects.A total of 493 subjects from the Zurich Longitudinal Studies were followed using structured sleep-related questionnaires at 1, 3, 6, 9, 12, 18, and 24 months after birth and then at annual intervals until 16 years of age. Gaussian percentiles for ages 3 months to 16 years were calculated for total sleep duration (time in bed) and nighttime and daytime sleep duration. The mean sleep duration for ages 1 to 16 years was estimated by generalized additive models based on the loess smoother; a cohort effect also had to be included. The standard deviation (SD) was estimated from the loess smoothed absolute residuals from the mean curve. For ages 3, 6, and 9 months, an alternative approach with a simple model linear in age was used. For age 1 month, empirical percentiles were calculated.Total sleep duration decreased from an average of 14.2 hours (SD: 1.9 hours) at 6 months of age to an average of 8.1 hours (SD: 0.8 hours) at 16 years of age. The variance showed the same declining trend: the interquartile range at 6 months after birth was 2.5 hours, whereas at 16 years of age, it was only 1.0 hours. Total sleep duration decreased across the studied cohorts (1974-1993) because of increasingly later bedtime but unchanged wake time across decades. Consolidation of nocturnal sleep occurred during the first 12 months after birth with a decreasing trend of daytime sleep. This resulted in a small increase of nighttime sleep duration by 1 year of age (mean 11.0 +/- 1.1 hours at 1 month to 11.7 +/- 1.0 hours at 1 year of age). The most prominent decline in napping habits occurred between 1.5 years of age (96.4% of all children) and 4 years of age (35.4%).Percentile curves provide valuable information on developmental course and age-specific variability of sleep duration for the health care professional who deals with sleep problems in pediatric practice.

OBJECTIVE. Our goal was to describe the variability of sleep duration (time in bed per 24 hours) in healthy children from 1 to 10 years of age in comparison with growth measures.

Despite the fact that midday naps are characteristic of early childhood, very little is understood about the structure and function of these sleep bouts. Given that sleep benefits memory in young adults, it is possible that naps serve a similar function for young children. However, children transition from biphasic to monophasic sleep patterns in early childhood, eliminating the nap from their daily sleep schedule. As such, naps may contain mostly light sleep stages and serve little function for learning and memory during this transitional age. Lacking scientific understanding of the function of naps in early childhood, policy makers may eliminate preschool classroom nap opportunities due to increasing curriculum demands. Here we show evidence that classroom naps support learning in preschool children by enhancing memories acquired earlier in the day compared with equivalent intervals spent awake. This nap benefit is greatest for children who nap habitually, regardless of age. Performance losses when nap-deprived are not recovered during subsequent overnight sleep. Physiological recordings of naps support a role of sleep spindles in memory performance. These results suggest that distributed sleep is critical in early learning; when short-term memory stores are limited, memory consolidation must take place frequently.

Sleep is increasingly recognized as a key process in neurodevelopment. Animal data show that sleep is essential for the maturation of fundamental brain functions, and growing epidemiological findings indicate that children with early sleep disturbance suffer from later cognitive, attentional, and psychosocial problems. Still, major gaps exist in understanding processes underlying links between sleep and neurodevelopment. One challenge is to translate findings from animal research to humans. In this review, we describe parallels and differences in sleep and development of the cortex in humans and animals and discuss emerging questions.

Sleep enhances integration across multiple stimuli, abstraction of general rules, insight into hidden solutions and false memory formation. Newly learned information is better assimilated if compatible with an existing cognitive framework or schema. This article proposes a mechanism by which the reactivation of newly learned memories during sleep could actively underpin both schema formation and the addition of new knowledge to existing schemata. Under this model, the overlapping replay of related memories selectively strengthens shared elements. Repeated reactivation of memories in different combinations progressively builds schematic representations of the relationships between stimuli. We argue that this selective strengthening forms the basis of cognitive abstraction, and explain how it facilitates insight and false memory formation.Copyright © 2011 Elsevier Ltd. All rights reserved.

This paper presents an overview of the current knowledge of the neurophysiology and cellular pharmacology of sleep mechanisms. It is written from the perspective that recent years have seen a remarkable development of knowledge about sleep mechanisms, due to the capability of current cellular neurophysiological, pharmacological and molecular techniques to provide focused, detailed, and replicable studies that have enriched and informed the knowledge of sleep phenomenology and pathology derived from electroencephalographic (EEG) analysis. This chapter has a cellular and neurophysiological/neuropharmacological focus, with an emphasis on rapid eye movement (REM) sleep mechanisms and non-REM (NREM) sleep phenomena attributable to adenosine. The survey of neuronal and neurotransmitter-related brainstem mechanisms of REM includes monoamines, acetylcholine, the reticular formation, a new emphasis on GABAergic mechanisms and a discussion of the role of orexin/hypcretin in diurnal consolidation of REM sleep. The focus of the NREM sleep discussion is on the basal forebrain and adenosine as a mediator of homeostatic control. Control is through basal forebrain extracellular adenosine accumulation during wakefulness and inhibition of wakefulness-active neurons. Over longer periods of sleep loss, there is a second mechanism of homeostatic control through transcriptional modification. Adenosine acting at the A1 receptor produces an up-regulation of A1 receptors, which increases inhibition for a given level of adenosine, effectively increasing the gain of the sleep homeostat. This second mechanism likely occurs in widespread cortical areas as well as in the basal forebrain. Finally, the results of a new series of experimental paradigms in rodents to measure the neurocognitive effects of sleep loss and sleep interruption (modeling sleep apnea) provide animal model data congruent with those in humans.

We tested amnesic patients, patients with frontal lobe lesions, and control subjects with the deferred imitation task, a nonverbal test used to demonstrate memory abilities in human infants. On day 1, subjects were given sets of objects to obtain a baseline measure of their spontaneous performance of target actions. Then different event sequences were modeled with the object sets. On day 2, the objects were given to the subjects again, first without any instructions to imitate the sequences, and then with explicit instructions to imitate the actions exactly as they had been modeled. Control subjects and frontal lobe patients reproduced the events under both uninstructed and instructed conditions. In contrast, performance by the amnesic patients did not significantly differ from that of a second control group who had the same opportunities to handle the objects but were not shown the modeled actions. These findings suggest that deferred imitation is dependent on the brain structures essential for declarative memory that are damaged in amnesia, and they support the view that infants who imitate actions after long delays have an early capacity for long-term declarative memory.

Recall of paired-associate lists (declarative memory) and mirror-tracing skills (procedural memory) was assessed after retention intervals defined over early and late nocturnal sleep. In addition, effects of sleep on recall were compared with those of early and late retention intervals filled with wakefulness. Twenty healthy men served as subjects. Saliva cortisol concentrations were determined before and after the retention intervals to determine pituitary-adrenal secretory activity. Sleep was determined somnopolygraphically. Sleep generally enhanced recall when compared with the effects of corresponding retention intervals of wakefulness. The benefit from sleep on recall depended on the phase of sleep and on the type of memory: Recall of paired-associate lists improved more during early sleep, and recall of mirror-tracing skills improved more during late sleep. The effects may reflect different influences of slow wave sleep (SWS) and rapid eye movement (REM) sleep since time in SWS was 5 times longer during the early than late sleep retention interval, and time in REM sleep was twice as long during late than early sleep (p < 0.005). Changes in cortisol concentrations, which independently of sleep and wakefulness were lower during early retention intervals than late ones, cannot account for the effects of sleep on memory. The experiments for the first time dissociate specific effects of early and late sleep on two principal types of memory, declarative and procedural, in humans.

Nonhuman research has implicated developmental processes within the hippocampus in the emergence and early development of episodic memory, but methodological challenges have hindered assessments of this possibility in humans. Here, we delivered a previously learned song and a novel song to 2-year-old toddlers during natural nocturnal sleep and, using functional magnetic resonance imaging, found that hippocampal activation was stronger for the learned song compared with the novel song. This was true regardless of whether the song was presented intact or backwards. Toddlers who remembered where and in the presence of which toy character they heard the song exhibited stronger hippocampal activation for the song. The results establish that hippocampal activation in toddlers reflects past experiences, persists despite some alteration of the stimulus, and is associated with behavior. This research sheds light on early hippocampal and memory functioning and offers an approach to interrogate the neural substrates of early memory.

The main aim of our study was to examine whether there was a relationship between psychological characteristics such as self-efficacy, self-control and chronotype as well as procrastination on the one hand and sleep problems on the other. There were 315 young adults aged between 18 and 27 years ( = 20.57). We used the General Procrastination Scale, the General Self-Efficacy Scale (GSES), Brief Self-Control Scale, the Composite Scale of Morningness (CSM) and the Pittsburgh Sleep Quality Index (PSQI). Our results indicated that low self-efficacy, low self-control and eveningness were positive predictors of procrastination. The reciprocal relationship exists between procrastination and sleep problems. Procrastination positively contributed to sleep problems, whereas sleep problems were a negative predictor of procrastination.

Sleep facilitates memory consolidation. A widely held model assumes that this is because newly encoded memories undergo covert reactivation during sleep. We cued new memories in humans during sleep by presenting an odor that had been presented as context during prior learning, and so showed that reactivation indeed causes memory consolidation during sleep. Re-exposure to the odor during slow-wave sleep (SWS) improved the retention of hippocampus-dependent declarative memories but not of hippocampus-independent procedural memories. Odor re-exposure was ineffective during rapid eye movement sleep or wakefulness or when the odor had been omitted during prior learning. Concurring with these findings, functional magnetic resonance imaging revealed significant hippocampal activation in response to odor re-exposure during SWS.

Attachment theory is one of the key theoretical constructs that underpin explorations of human bonding, taking its current form in John Bowlby’s amalgamation of ideas from psychoanalysis, developmental psychology and ethology. Such a period of interdisciplinary exchange, and Bowlby’s interest in Lorenz’ concept of imprinting in particular, have been subject to rather historical and biographical studies, leaving a fine-grained theoretical scrutiny of the exact relationship between imprinting and attachment still pending. This paper attempts to remedy such an omission by exploring the relationships between these two constructs. It critically reviews the theories of imprinting in general, of human imprinting in particular, and of attachment; analysis of the links between these processes bring to the foreground the distinction between supra-individual vs. individual aspects of bonding, the relevance of ‘proto-attachment’ phases before ‘proper’ Bowlbyan attachment is attained, and the role of communicative signals during such early phases. The paper outlines potential benefits of considering such elements in the study of early social cognition, particularly in respect of the study of the gaze and the infant-directed communicative register.

It is widely accepted that sleep better facilitates the consolidation of motor memories than does a corresponding wake interval (King et al., 2017). However, no in-depth analysis of the various motor tasks and their relative sleep gain has been conducted so far. Therefore, the present meta-analysis considered 48 studies with a total of 53 sleep (n = 829) and 53 wake (n = 825) groups. An overall comparison between all sleep and wake groups resulted in a small effect for the relative sleep gain in motor memory consolidation (g = 0.43). While no subgroup differences were identified for differing designs, a small effect for the finger tapping task (g = 0.47) and a medium effect for the mirror tracing task (g = 0.62) were found. In summary, the meta-analysis substantiates that sleep generally benefits the consolidation of motor memories. However, to further our understanding of the mechanisms underlying this effect, examining certain task dimensions and their relative sleep gain would be a promising direction for future research.Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.

Human infants devote the majority of their time to sleeping. However, very little is known about the role of sleep in early memory processing. Here we test 6- and 12-mo-old infants' declarative memory for novel actions after a 4-h [Experiment (Exp.) 1] and 24-h delay (Exp. 2). Infants in a nap condition took an extended nap (≥30 min) within 4 h after learning, whereas infants in a no-nap condition did not. A comparison with age-matched control groups revealed that after both delays, only infants who had napped after learning remembered the target actions at the test. Additionally, after the 24-h delay, memory performance of infants in the nap condition was significantly higher than that of infants in the no-nap condition. This is the first experimental evidence to our knowledge for an enhancing role of sleep in the consolidation of declarative memories in the first year of life.

Research with adults has shown that a person's internal context, or state, influences how memory functions. This factor is rarely considered in research on infant memory, in part because of the practical and ethical difficulties of manipulating these variables in infants. In this article, we argue that models of infant memory will remain limited in scope and accuracy if the internal context of participants is not considered. As a case in point, we present emerging literature on sleep-dependent memory. Our review shows that for infants, timely sleep after a learning experience helps them retain and further process new memories. Studies need to explore the role of prior sleep for encoding, and to tease apart the contributions to infant memory of different types, features, and stages of sleep. We conclude that considering internal states, such as sleep, is necessary for developing a deeper understanding of early human memory.

Toddlerhood is characterized by rapid development in several domains, such as language, socio-emotional behavior and emerging math skills all of which are important precursors of school readiness. However, little is known about how these skills develop over time and how they may be interrelated. The current study investigates young children’s development at two time points, with about 7 months in between, assessing their language, socio-emotional and math language and numeracy skills with teacher ratings. The sample includes 577 children from 18 until 36 months of age of 86 childcare classrooms. The results of the autoregressive path analyses showed moderate to strong stability of language, socio-emotional and math language and numeracy skills, although the magnitude of associations was smaller for the latter. The cross-lagged path analyses highlighted the importance of language and socio-emotional skills for development in the other domains. Differential relations were found for the autoregressive and cross-lagged paths depending on gender and age. Language skills appeared a stronger predictor of boys’ socio-emotional and math language and numeracy skill development compared to girls. Girls’ socio-emotional skills predicted growth in math. For boys, socio-emotional and math language and numeracy skills appeared to be unrelated. Language skills showed stronger relations with the development of math language and numeracy skills for younger children as compared to older children. Also, for older children math language and numeracy skills negatively predicted growth in their socio-emotional skills. The findings provide more insights in how language, math language and numeracy skills and socio-emotional skills co-develop in the early years and as such have important implications for interventions aimed to support children’s development.

Sleep is recognized as a physiological state associated with learning, with studies showing that knowledge acquisition improves with naps. Little work has examined sleep-dependent learning in people with developmental disorders, for whom sleep quality is often impaired. We examined the effect of natural, in-home naps on word learning in typical young children and children with Down syndrome (DS). Despite similar immediate memory retention, naps benefitted memory performance in typical children but hindered performance in children with DS, who retained less when tested after a nap, but were more accurate after a wake interval. These effects of napping persisted 24 h later in both groups, even after an intervening overnight period of sleep. During naps in typical children, memory retention for object-label associations correlated positively with percent of time in rapid eye movement (REM) sleep. However, in children with DS, a population with reduced REM, learning was impaired, but only after the nap. This finding shows that a nap can increase memory loss in a subpopulation, highlighting that naps are not universally beneficial. Further, in healthy preschooler's naps, processes in REM sleep may benefit learning.

The fact that information acquired before the onset of amnesia can be lost (retrograde amnesia) has fascinated psychologists, biologists, and clinicians for over 100 years. Studies of retrograde amnesia have led to the concept of memory consolidation, whereby medial temporal lobe structures direct the gradual establishment of memory representations in neocortex. Recent theoretical accounts have inspired a simple neural network model that produces behavior consistent with experimental data and makes these ideas about memory consolidation more concrete. Recent physiological and anatomical findings provide important information about how memory consolidation might actually occur.

A growing body of literature suggests that sleep plays a critical role in emotional processing. This review aims at synthesizing current evidence on the role of sleep and sleep loss in the modulation of emotional reactivity, emotional memory formation, empathic behavior, fear conditioning, threat generalization and extinction memory. Behavioral and neurophysiological evidence suggesting that rapid-eye movement (REM) sleep plays an important role in emotional processing is also discussed. Furthermore, we examine the relations between sleep and emotions by reviewing the functional neuroimaging studies that elucidated the brain mechanisms underlying these relations. It is shown that sleep supports the formation of emotional episodic memories throughout all the stages that compose memory processing. On the contrary, sleep loss deteriorates both the encoding of emotional information and the emotional memory consolidation processes. Research is also progressively providing new insights into the protective role of sleep in human emotional homeostasis and regulation, promoting adaptive next-day emotional reactivity. In this respect, evidence converges in indicating that lack of sleep significantly influences emotional reactivity. Moreover, notwithstanding some contradictory findings, the processing of emotionally salient information could mainly benefit from REM sleep. However, some crucial aspects of sleep-dependent emotional modulation remain unclear.Copyright © 2017 Elsevier Ltd. All rights reserved.

Human beings are biologically adapted for culture in ways that other primates are not, as evidenced most clearly by the fact that only human cultural traditions accumulate modifications over historical time (the ratchet effect). The key adaptation is one that enables individuals to understand other individuals as intentional agents like the self. This species-unique form of social cognition emerges in human ontogeny at around 1 year of age as infants begin to engage with other persons in various kinds of joint attentional activities involving gaze following, social referencing, and gestural communication. Young children’s joint attentional skills then engender some uniquely powerful forms of cultural learning, enabling the acquisition of language, discourse skills, tool use practices, and many other conventional activities. These novel forms of cultural learning allow human beings to pool their cognitive resources both contemporaneously and over historical time in ways that are unique in the animal kingdom.

It is believed that neural representations of recent experiences become reactivated during sleep, and that this process serves to stabilize associated memories in long-term memory. Here, we initiated this reactivation process for specific memories during slow-wave sleep. Participants studied 50 object-location associations with object-related sounds presented concurrently. For half of the associations, the related sounds were re-presented during subsequent slow-wave sleep while participants underwent functional MRI. Compared with control sounds, related sounds were associated with increased activation of right parahippocampal cortex. Postsleep memory accuracy was positively correlated with sound-related activation during sleep in various brain regions, including the thalamus, bilateral medial temporal lobe, and cerebellum. In addition, postsleep memory accuracy was also positively correlated with pre- to postsleep changes in parahippocampal-medial prefrontal connectivity during retrieval of reactivated associations. Our results suggest that the brain is differentially activated by studied and unstudied sounds during deep sleep and that the thalamus and medial temporal lobe are involved in establishing the mnemonic consequences of externally triggered reactivation of associative memories.

The early years of life are critical for motor and cognitive development. A better understanding is needed on the associations between the control and development of motor and cognitive tasks.This study aimed to examine the association between gross motor skills and cognitive development in toddlers.Cross-sectional study.This study included 335 toddlers (aged 19.80 ± 4.08 months, 53.7% boys) from 30 childcare services in Australia.Children were assessed on gross motor skills (Peabody Developmental Motor Scales 2nd Edition; PDMS-2) and cognitive development (Bayley Scales of Infant and Toddler development 3rd edition; Bayley-III).A one-way ANCOVA was conducted to assess associations between gross motor skills and cognitive development controlling for childcare center, sex, age, body mass index and socioeconomic status.The average scores were 96.41 ± 9.84 for gross motor skills (range gross motor quotient 35-165) and 11.45 ± 3.03 for cognitive development (range standard score 1-19). There was a significant positive association between gross motor skills and cognition, F = 12.245, p < 0.001. Both locomotion and object manipulation were significantly positively associated with cognition, F = 14.607, p < 0.001 and F = 9.039, p < 0.001 respectively.Levels of gross motor skills are positively associated with cognitive development in this sample of Australian toddlers. Results reinforce the need for early commencement of gross motor skill promotion as this might be important for cognitive development in the early years.Copyright © 2019 Elsevier B.V. All rights reserved.

Research in the neurosciences continues to provide evidence that sleep plays a role in the processes of learning and memory. There is less of a consensus, however, regarding the precise stages of memory development during which sleep is considered a requirement, simply favorable, or not important. This article begins with an overview of recent studies regarding sleep and learning, predominantly in the procedural memory domain, and is measured against our current understanding of the mechanisms that govern memory formation. Based on these considerations, I offer a new neurocognitive framework of procedural learning, consisting first of acquisition, followed by two specific stages of consolidation, one involving a process of stabilization, the other involving enhancement, whereby delayed learning occurs. Psychophysiological evidence indicates that initial acquisition does not rely fundamentally on sleep. This also appears to be true for the stabilization phase of consolidation, with durable representations, resistant to interference, clearly developing in a successful manner during time awake (or just time, per se). In contrast, the consolidation stage, resulting in additional/enhanced learning in the absence of further rehearsal, does appear to rely on the process of sleep, with evidence for specific sleep-stage dependencies across the procedural domain. Evaluations at a molecular, cellular, and systems level currently offer several sleep specific candidates that could play a role in sleep-dependent learning. These include the upregulation of select plasticity-associated genes, increased protein synthesis, changes in neurotransmitter concentration, and specific electrical events in neuronal networks that modulate synaptic potentiation.

Improvement in motor skill performance is known to continue for at least 24 hr following training, yet the relative contributions of time spent awake and asleep are unknown. Here we provide evidence that a night of sleep results in a 20% increase in motor speed without loss of accuracy, while an equivalent period of time during wake provides no significant benefit. Furthermore, a significant correlation exists between the improved performance overnight and the amount of stage 2 NREM sleep, particularly late in the night. This finding of sleep-dependent motor skill improvement may have important implications for the efficient learning of all skilled actions in humans.

In striking contrast to adults, in children sleep following training a motor task did not induce the expected (offline) gain in motor skill performance in previous studies. Children normally perform at distinctly lower levels than adults. Moreover, evidence in adults suggests that sleep dependent offline gains in skill essentially depend on the pre-sleep level of performance. Against this background, we asked whether improving children's performance on a motor sequence learning task by extended training to levels approaching those of adults would enable sleep-associated gains in motor skill in this age group also. Children (4-6 years) and adults (18-35 years) performed on the motor sequence learning task (button-box task) before and after ~2-hour retention intervals including either sleep (midday nap) or wakefulness. Whereas one group of children and adults, respectively, received the standard amount of 10 blocks of training before retention intervals of sleep or wakefulness, a further group of children received an extended training on 30 blocks (distributed across 3 days). A further group of adults received a restricted training on only two blocks before the retention intervals. Children after standard training reached lowest performance levels, whereas in adults performance after standard training was highest. Children with extended training and adults after reduced training reached intermediate performance levels. Only at these intermediate performance levels did sleep induce significant gains in motor sequence skill, whereas performance did not benefit from sleep in the low-performing children or in the high-performing adults. Spindle counts in the post-training nap were correlated with performance gains at retrieval only in the adults benefitting from sleep. We conclude that, across age groups, sleep induces the most robust gain in motor skill at an intermediate pre-sleep performance level. In low-performing children sleep-dependent improvements in skill may be revealed only after enhancing the pre-sleep performance level by extended training.© 2012 Blackwell Publishing Ltd.

Reading the same storybooks repeatedly helps preschool children learn words. In addition, sleeping shortly after learning also facilitates memory consolidation and aids learning in older children and adults. The current study explored how sleep promotes word learning in preschool children using a shared storybook reading task. Children were either read the same story repeatedly or different stories and either napped after the stories or remained awake. Children's word retention were tested 2.5 h later, 24 h later, and 7 days later. Results demonstrate strong, persistent effects for both repeated readings and sleep consolidation on young children's word learning. A key finding is that children who read different stories before napping learned words as well as children who had the advantage of hearing the same story. In contrast, children who read different stories and remained awake never caught up to their peers on later word learning tests. Implications for educational practices are discussed.

How sleep helps learning and memory remains unknown. We report in mouse motor cortex that sleep after motor learning promotes the formation of postsynaptic dendritic spines on a subset of branches of individual layer V pyramidal neurons. New spines are formed on different sets of dendritic branches in response to different learning tasks and are protected from being eliminated when multiple tasks are learned. Neurons activated during learning of a motor task are reactivated during subsequent non-rapid eye movement sleep, and disrupting this neuronal reactivation prevents branch-specific spine formation. These findings indicate that sleep has a key role in promoting learning-dependent synapse formation and maintenance on selected dendritic branches, which contribute to memory storage. Copyright © 2014, American Association for the Advancement of Science.