Cognitive effects of multi-night adolescent sleep restriction: current data and future possibilities

Neurocognitive Effects of Sleep Disruption in Children and Adolescents

A main childhood task is learning. In this task, the role of sleep is increasingly demonstrated. Although most literature examining this role focuses on preadolescence and middle adolescence, some studies apply napping designs in preschoolers. Studies overall conclude that without proper sleep a child's cognitive abilities suffer, but questions on how and to what extent linger. Observational studies show the hazards of potential confounders such as an individual's resilience to poor sleep as well as developmental risk factors (eg, disorders, stressors). A better understanding of cognitive sleep neuroscience may have a big impact on pediatric sleep research and clinical applications.

Assessing 'readiness' by tracking fluctuations in daily sleep duration and their effects on daily mood, motivation, and sleepiness

STUDY OBJECTIVES

Consumer sleep trackers issue daily guidance on 'readiness' without clear empirical basis. We investigated how self-rated mood, motivation, and sleepiness (MMS) levels are affected by daily fluctuations in sleep duration, timing, and efficiency and overall sleep regularity. We also determined how temporally specific these associations are.

METHODS

119 healthy university students (64 female, mean age = 22.54 ± 1.74 years) wore a wearable sleep tracker and undertook twice-daily smartphone-delivered ecological momentary assessment of mood, motivation, and sleepiness at post-wake and pre-bedtime timings for 2-6 weeks. Naps and their duration were reported daily. Nocturnal sleep on 2471 nights were examined using multilevel models to uncover within-subject and between-subject associations between sleep duration, timing, efficiency, and nap duration on following day MMS ratings. Time-lagged analyses examined the temporal specificity of these associations. Linear regression models investigated associations between MMS ratings and sleep variability, controlling for sleep duration.

RESULTS

Nocturnal sleep durations were short (6.03 ± 0.71 h), and bedtimes were late (1:42AM ± 1:05). Within-subjects, nocturnal sleep longer than a person's average was associated with better mood, higher motivation, and lower sleepiness after waking. Effects of such longer sleep duration lingered for mood and sleepiness till the pre-bedtime window (all Ps < .005) but did not extend to the next day. Between-subjects, higher intraindividual sleep variability, but not sleep duration, was associated with poorer mood and lower motivation after waking. Longer average sleep duration was associated with less sleepiness after waking and lower motivation pre-bedtime (all Ps < .05). Longer naps reduced post-nap sleepiness and improved mood. Controlling for nocturnal sleep duration, longer naps also associated with lower post-waking sleepiness on the following day.

CONCLUSIONS

Positive connections between nocturnal sleep and nap duration with MMS are temporally circumscribed, lending credence to the construction of sleep-based, daily 'readiness' scores. Higher sleep duration variability lowers an individual's post waking mood and motivation.

CLINICAL TRIAL ID

ClinicalTrials.gov NCT04880629.

Country differences in nocturnal sleep variability: Observations from a large-scale, long-term sleep wearable study

STUDY OBJECTIVES

Country or regional differences in sleep duration are well-known, but few large-scale studies have specifically evaluated sleep variability, either across the work week, or in terms of differences in weekday and weekend sleep.

METHODS

Sleep measures, obtained over 50 million night's sleep from ∼220,000 wearable device users in 35 countries, were analysed. Each person contributed an average of ∼242 nights of data. Multiple regression was used to assess the impact country of residence had on sleep duration, timing, efficiency, weekday sleep variability, weekend sleep extension and social jetlag.

RESULTS

Nocturnal sleep was shorter and had a later onset in Asia than other regions. Despite this, sleep efficiency was lower and weekday sleep variability was higher. Weekend sleep extension was longer in Europe and the USA than in Asia, and was only partially related to weekday sleep duration. There were also cross-country differences in social jetlag although the regional differences were less distinct than for weekend sleep extension.

CONCLUSIONS

In addition to regional differences in sleep duration, cross-country differences in sleep variability and weekend sleep extension suggest that using the latter as an indicator of sleep debt may need to be reconsidered. In countries exhibiting both short sleep and high weekday sleep variability, a culturally different means of coping with inadequate sleep is likely. Country or region differences in culture, particularly those related to work, merit closer examination as factors influencing the variability in normative sleep patterns around the world.

Effects of partial sleep deprivation on prefrontal cognitive functions in adolescents

Purpose

The effect of sleep deprivation on cognitive functions associated with the frontal lobe, such as attention, executive functions, and working memory, is not well known. This study aimed to investigate the effect of partial sleep deprivation in adolescents on the cognitive tasks of the frontal lobe, including visuospatial working memory, processing speed, sustained attention, executive functions, and short-term visual memory.

Methods

Participants were recruited from voluntary students of Çukurova University. Eighteen adolescents underwent four consecutive nights of monitored sleep restriction (6-6.5 h/night) and four nights of sleep extension (10-10.5 h/night) in a counterbalanced order and separated by a washout period. Following each sleep period, the cognitive performance was assessed, at a fixed morning time, using a computerized neuropsychological test battery based on frontal lobe functions tasks, which was a timed test providing both accuracy and reaction time outcome measures.

Results

Only the spatial working memory performance of cognitive tasks was found to be statistically lower in the restricted-sleep condition than in the extended-sleep condition (p < 0.05). No significant difference was found in the performance of cognitive tasks evaluating simple attention, constant attention, executive functions, and cognitive flexibility.

Conclusions

The findings of this study indicated that partial sleep restriction negatively affects specifically working memory and strategic thinking skills among cognitive functions based on the frontal lobe. Especially the visuospatial working memory and strategic thinking skills of adolescents might be susceptible to chronic partial sleep deprivation.

A sleep schedule incorporating naps benefits the transformation of hierarchical knowledge

Study Objectives

The learning brain establishes schemas (knowledge structures) that benefit subsequent learning. We investigated how sleep and having a schema might benefit initial learning followed by rearranged and expanded memoranda. We concurrently examined the contributions of sleep spindles and slow-wave sleep to learning outcomes.

Methods

Fifty-three adolescents were randomly assigned to an 8 h Nap schedule (6.5 h nocturnal sleep with a 90-minute daytime nap) or an 8 h No-Nap, nocturnal-only sleep schedule. The study spanned 14 nights, simulating successive school weeks. We utilized a transitive inference task involving hierarchically ordered faces. Initial learning to set up the schema was followed by rearrangement of the hierarchy (accommodation) and hierarchy expansion (assimilation). The expanded sequence was restudied. Recall of hierarchical knowledge was tested after initial learning and at multiple points for all subsequent phases. As a control, both groups underwent a No-schema condition where the hierarchy was introduced and modified without opportunity to set up a schema. Electroencephalography accompanied the multiple sleep opportunities.

Results

There were main effects of Nap schedule and Schema condition evidenced by superior recall of initial learning, reordered and expanded memoranda. Improved recall was consistently associated with higher fast spindle density but not slow-wave measures. This was true for both nocturnal sleep and daytime naps.

Conclusion

A sleep schedule incorporating regular nap opportunities compared to one that only had nocturnal sleep benefited building of robust and flexible schemas, facilitating recall of the subsequently rearranged and expanded structured knowledge. These benefits appear to be strongly associated with fast spindles.

Clinical Trial registration

NCT04044885 (https://clinicaltrials.gov/ct2/show/NCT04044885).

Greater adolescent tiredness is related to more emotional arousal during a hyperventilation task: An area under the curve approach

INTRODUCTION

Approximately 36% of adolescents report sleep problems (Crowley et al., 2018). Understanding the relation between sleep and emotional experience is crucial in understanding the high incidence of mental health concerns during adolescence. The current study sought to expand understanding in the area by testing the hypothesis that baseline tiredness ratings would predict greater emotional arousal and negative valence across the course of emotional response elicited by a voluntary hyperventilation procedure.

METHODS

A community sample of 110 youth (10-18 years; 47.8% girls) provided baseline tiredness ratings and ratings of emotional valence and arousal, 2 min before, immediately after, and 3 min after a hyperventilation task. The area under the curve (AUC) was calculated using the repeated measures of valence and arousal, and correlations between the response curves and baseline tiredness were examined.

RESULTS AND CONCLUSIONS

Findings indicated baseline tiredness was positively associated with AUC arousal (r = 0.23), but not valence. This suggests daytime tiredness is associated with the degree of emotional arousal elicited by a psychobiological stressor. By extension, adolescents may experience more arousing emotional reactions when tired, and thus the common sleep deprivation observed during this developmental period may increase risk for mental health problems associated with elevated emotional reactivity.

Splitting sleep between the night and a daytime nap reduces homeostatic sleep pressure and enhances long-term memory

Daytime naps have been linked with enhanced memory encoding and consolidation. It remains unclear how a daily napping schedule impacts learning throughout the day, and whether these effects are the same for well-rested and sleep restricted individuals. We compared memory in 112 adolescents who underwent two simulated school weeks containing 8 or 6.5 h sleep opportunities each day. Sleep episodes were nocturnal or split between nocturnal sleep and a 90-min afternoon nap, creating four experimental groups: 8 h-continuous, 8 h-split, 6.5 h-continuous and 6.5 h-split. Declarative memory was assessed with picture encoding and an educationally realistic factual knowledge task. Splitting sleep significantly enhanced afternoon picture encoding and factual knowledge under both 6.5 h and 8 h durations. Splitting sleep also significantly reduced slow-wave energy during nocturnal sleep, suggesting lower homeostatic sleep pressure during the day. There was no negative impact of the split sleep schedule on morning performance, despite a reduction in nocturnal sleep. These findings suggest that naps could be incorporated into a daily sleep schedule that provides sufficient sleep and benefits learning.

Neurocognitive Effects of Sleep Disruption in Children and Adolescents

A main childhood task is learning. In this task, the role of sleep is increasingly demonstrated. Although most literature examining this role focuses on preadolescence and middle adolescence, some studies apply napping designs in preschoolers. Studies overall conclude that without proper sleep a child's cognitive abilities suffer, but questions on how and to what extent linger. Observational studies show the hazards of potential confounders such as an individual's resilience to poor sleep as well as developmental risk factors (eg, disorders, stressors). A better understanding of cognitive sleep neuroscience may have a big impact on pediatric sleep research and clinical applications.