Contributions of memory and brain development to the bioregulation of naps and nap transitions in early childhood

Benefits of napping habits in healthy adults: Maintaining alerting performance and cortisol levels change within 90 min of habitual napping time

BACKGROUND

Napping is garnering increased attention as a strategy for adults to sustain alertness and alleviate stress in contemporary society. The nuances of napping habits are emerging as an independent factor influencing the extent of individual benefits. This study aimed to demonstrate the long-term benefits of napping and explore the impact of napping habits on individual alertness, as well as whether this effect was correlated with cortisol levels.

METHODS

The study involved 80 healthy adults categorized into two groups based on self-reported napping habits: habitual nappers (n = 49) and non-habitual nappers (n = 31). Karolinska Sleepiness Scale (KSS), psychomotor vigilance task (PVT), and saliva collection were performed every 30 min within 90 min in the absence of napping during the afternoon dip. The measurements were analyzed using repeated measures ANOVA and Pearson correlation analyses.

RESULTS

There was an interaction between groups and time in reaction speed and lapse number of PVT and cortisol (all p < 0.05). Post hoc analysis found that habitual nappers maintained higher objective alertness and experienced more significant increases in cortisol over time (all p < 0.05). The cortisol levels at sleepiness time were negatively associated with the slowest 10 % reaction speed of PVT in non-habitual nappers (r = -0.409, p = 0.022).

CONCLUSION

Under the premise of mitigating the impacts of acute nap deprivation on sleep homeostasis and rhythm, napping habits emerge as a potential factor influencing the ability of individuals to sustain heightened alertness.

Age differences in generalization, memory specificity, and their overnight fate in childhood

Memory enables generalization to new situations, and memory specificity that preserves individual episodes. This study investigated generalization, memory specificity, and their overnight fate in 141 4- to 8-year-olds (computerized memory game; 71 females, tested 2020-2021 in Germany). The results replicated age effects in generalization and memory specificity, and a contingency of generalization on object conceptual properties and interobject semantic proximity. Age effects were stronger in generalization than in memory specificity, and generalization was more closely linked to the explicit regularity knowledge in older than in younger children. After an overnight delay, older children retained more generalized and specific memories and showed greater gains but only in generalization. These findings reveal distinct age differences in generalization and memory specificity across childhood.

Exploring the Relationship Between Age at Nap Cessation and Social-Emotional Functioning in Children

OBJECTIVE

The objective of this study was to examine variations in age at nap cessation and identify whether there is an association with social-emotional functioning (SEF) as measured by internalizing/externalizing behavior, child temperament, and social skills in a sample of early childhood education and care-attending children.

METHODS

The sample comprised 1117 children from the Australian Effectiveness Early Educational Experiences for Children longitudinal early childhood study. We used children's age at nap cessation as retrospectively recalled by caregivers in 2011 or 2013 when children were between ages 2 and 7 years. Each child's SEF was reported by a caregiver using the Strengths and Difficulties Questionnaire, the Short Temperament Scale for Children, and the Social Skills Inventory Scale. Associations between children's age of nap cessation and SEF were tested using linear regressions.

RESULTS

The children's age at nap cessation ranged from 6 months to 6 years. For each additional year of napping, children's total , conduct , externalizing , and peer behavior problems decreased by 0.39 (95% confidence interval [CI], -0.70 to -0.09), 0.11 (95% CI, -0.21 to -0.01), 0.11 (95% CI, -0.51 to -0.06), and 0.11 (95% CI, -0.20 to -0.02) units on the Strengths and Difficulties Questionnaire scale, respectively. No further significant associations were found.

CONCLUSION

This is the first study reporting the age range of nap cessation and its associations with social-emotional functioning. Our findings demonstrate earlier cessation ages in Australian children attending Early Childhood Education and Care programs than previously reported and a small association with externalizing and peer problems.

Sleep-A brain-state serving systems memory consolidation

Although long-term memory consolidation is supported by sleep, it is unclear how it differs from that during wakefulness. Our review, focusing on recent advances in the field, identifies the repeated replay of neuronal firing patterns as a basic mechanism triggering consolidation during sleep and wakefulness. During sleep, memory replay occurs during slow-wave sleep (SWS) in hippocampal assemblies together with ripples, thalamic spindles, neocortical slow oscillations, and noradrenergic activity. Here, hippocampal replay likely favors the transformation of hippocampus-dependent episodic memory into schema-like neocortical memory. REM sleep following SWS might balance local synaptic rescaling accompanying memory transformation with a sleep-dependent homeostatic process of global synaptic renormalization. Sleep-dependent memory transformation is intensified during early development despite the immaturity of the hippocampus. Overall, beyond its greater efficacy, sleep consolidation differs from wake consolidation mainly in that it is supported, rather than impaired, by spontaneous hippocampal replay activity possibly gating memory formation in neocortex.

Temporal Associations between Actigraphy-Measured Daytime Movement Behaviors and Nap Sleep in Early Childhood

The purpose of this micro-longitudinal study was to explore daily associations between daytime movement behaviors (sedentary time and physical activity) and nap sleep in young children. In 298 children (age = 51.0 ± 9.6 months, 43.6% female), wrist-based actigraphy (mean wear time = 10 days) assessed sedentary time, total physical activity, and provided an estimate of nap sleep duration and efficiency. Multilevel logistic and linear regression models were used to examine temporal within-person relations between wake behaviors and nap sleep, and adjusted for overnight sleep duration between days of interest, age, sex, and socioeconomic status. Movement behaviors were not related to the likelihood of next-day napping, but when children were less sedentary (OR = 0.96; p < 0.001) or more active (OR = 1.01; p = 0.001) in the morning, they were more likely to nap that same day. Movement behaviors were not associated with nap sleep duration or efficiency. Conversely, on days children napped, they were less sedentary (B = -2.09, p < 0.001) and more active (B = 25.8, p < 0.001) the following day. Though napping and movement behaviors had some reciprocal relations, effect sizes in the present study were small. Further studies should examine children with more diverse sleep health and from different childcare settings.

The functions of sleep: A cognitive neuroscience perspective

This Special Feature explores the various purposes served by sleep, describing current attempts to understand how the many functions of sleep are instantiated in neural circuits and cognitive structures. Our feature reflects current experts' opinions about, and insights into, the dynamic processes of sleep. In the last few decades, technological advances have supported the updated view that sleep plays an active role in both cognition and health. However, these roles are far from understood. This collection of articles evaluates the dynamic nature of sleep, how it evolves across the lifespan, becomes a competitive arena for memory systems through the influence of the autonomic system, supports the consolidation and integration of new memories, and how lucid dreams might originate. This set of papers highlights new approaches and insights that will lay the groundwork to eventually understand the full range of functions supported by sleep.