Temperament moderates the association between sleep duration and cognitive performance in children.

The importance of sufficient sleep for cognitive performance has been increasingly recognized. Individual differences in susceptibility to effects of sleep restriction have hardly been investigated in children. We investigated whether individual differences in temperament moderate the association of sleep duration with sustained attention, inhibition, and working memory in 123 children (42% boys) aged 9 to 11 years. Sleep duration was assessed using parental diaries, and temperament traits of extraversion and negative affectivity were assessed by child self-report (Early Adolescent Temperament Questionnaire-Revised). Computerized assessment of sustained attention (short-form Psychomotor Vigilance Task, PVT), inhibition (PVT Go/No-Go adaptation), and working memory (visual Digit Span) were performed at school. Our findings demonstrate that long-sleeping introverted and negatively affective children show worse sustained attention and working memory than short-sleeping children with these temperaments.

Sleep spindle and slow wave frequency reflect motor skill performance in primary school-age children.

BACKGROUND AND AIM: The role of sleep in the enhancement of motor skills has been studied extensively in adults. We aimed to determine involvement of sleep and characteristics of spindles and slow waves in a motor skill in children. HYPOTHESIS: We hypothesized sleep-dependence of skill enhancement and an association of interindividual differences in skill and sleep characteristics. METHODS: 30 children (19 females, 10.7 ± 0.8 years of age; mean ± SD) performed finger sequence tapping tasks in a repeated-measures design spanning 4 days including 1 polysomnography (PSG) night. Initial and delayed performance were assessed over 12 h of wake; 12 h with sleep; and 24 h with wake and sleep. For the 12 h with sleep, children were assigned to one of three conditions: modulation of slow waves and spindles was attempted using acoustic perturbation, and compared to yoked and no-sound control conditions. ANALYSES: Mixed effect regression models evaluated the association of sleep, its macrostructure and spindles and slow wave parameters with initial and delayed speed and accuracy. RESULTS AND CONCLUSIONS: Children enhance their accuracy only over an interval with sleep. Unlike previously reported in adults, children enhance their speed independent of sleep, a capacity that may to be lost in adulthood. Individual differences in the dominant frequency of spindles and slow waves were predictive for performance: children performed better if they had less slow spindles, more fast spindles and faster slow waves. On the other hand, overnight enhancement of accuracy was most pronounced in children with more slow spindles and slower slow waves, i.e., the ones with an initial lower performance. Associations of spindle and slow wave characteristics with initial performance may confound interpretation of their involvement in overnight enhancement. Slower frequencies of characteristic sleep events may mark slower learning and immaturity of networks involved in motor skills.

The caudate: a key node in the neuronal network imbalance of insomnia?

Insomnia is prevalent, severe and partially heritable. Unfortunately, its neuronal correlates remain enigmatic, hampering the development of mechanistic models and rational treatments. Consistently reported impairments concern fragmented sleep, hyper-arousal and executive dysfunction. Because fronto-striatal networks could well play a role in sleep, arousal regulation and executive functioning, the present series of studies used an executive task to evaluate fronto-striatal functioning in disturbed sleep. Patients with insomnia showed reduced recruitment of the head of the left caudate nucleus during executive functioning, which was not secondary to altered performance or baseline perfusion. Individual differences in caudate recruitment were associated with hyper-arousal severity. Seed-based functional connectivity analysis suggested that attenuated input from a projecting orbitofrontal area with reduced grey matter density contributes to altered caudate recruitment in patients with insomnia. Attenuated caudate recruitment persisted after successful treatment of insomnia, warranting evaluation as a potential vulnerability trait. A similar selective reduction in caudate recruitment could be elicited in participants without sleep complaints by slow-wave sleep fragmentation, providing a model to facilitate investigation of the causes and consequences of insomnia.

Modulation of γ and spindle-range power by slow oscillations in scalp sleep EEG of children.

Deep sleep is characterized by slow waves of electrical activity in the cerebral cortex. They represent alternating down states and up states of, respectively, hyperpolarization with accompanying neuronal silence and depolarization during which neuronal firing resumes. The up states give rise to faster oscillations, notably spindles and gamma activity which appear to be of major importance to the role of sleep in brain function and cognition. Unfortunately, while spindles are easily detectable, gamma oscillations are of very small amplitude. No previous sleep study has succeeded in demonstrating modulations of gamma power along the time course of slow waves in human scalp EEG. As a consequence, progress in our understanding of the functional role of gamma modulation during sleep has been limited to animal studies and exceptional human studies, notably those of intracranial recordings in epileptic patients. Because high synaptic density, which peaks some time before puberty depending on the brain region (Huttenlocher and Dabholkar, 1997), generates oscillations of larger amplitude, we considered that the best chance to demonstrate a modulation of gamma power by slow wave phase in regular scalp sleep EEG would be in school-aged children. Sleep EEG was recorded in 30 healthy children (aged 10.7 ± 0.8 years; mean ± s.d.). Time-frequency analysis was applied to evaluate the time course of spectral power along the development of a slow wave. Moreover, we attempted to modify sleep architecture and sleep characteristics through automated acoustic stimulation coupled to the occurrence of slow waves in one subset of the children. Gamma power increased on the rising slope and positive peak of the slow wave. Gamma and spindle activity is strongly suppressed during the negative peak. There were no differences between the groups who received and did not receive acoustic stimulation in the sleep parameters and slow wave-locked time-frequency analysis. Our findings show, for the first time in scalp EEG in humans, that gamma activity is associated with the up-going slope and peak of the slow wave. We propose that studies in children provide a uniquely feasible opportunity to conduct investigations into the role of gamma during sleep.

Chronic stress undermines the compensatory sleep efficiency increase in response to sleep restriction in adolescents.

To investigate the effects of real-life stress on the sleep of adolescents, we performed a repeated-measures study on actigraphic sleep estimates and subjective measures during one regular school week, two stressful examination weeks and a week's holiday. Twenty-four adolescents aged 17.63 ± 0.10 years (mean ± standard error of the mean) wore actigraphs and completed diaries on subjective stress, fatigue, sleep quality, number of examinations and consumption of caffeine and alcohol for 4 weeks during their final year of secondary school. The resulting almost 500 assessments were analysed using mixed-effect models to estimate the effects of mere school attendance and additional examination stress on sleep estimates and subjective ratings. Total sleep time decreased from 7:38 h ± 12 min during holidays to 6:40 h ± 12 min during a regular school week. This 13% decrease elicited a partial compensation, as indicated by a 3% increase in sleep efficiency and a 6% decrease in the duration of nocturnal awakenings. During examination weeks total sleep time decreased to 6:23 h ± 8 min, but it was now accompanied by a decrease in sleep efficiency and subjective sleep quality and an increase in wake bout duration. In conclusion, school examination stress affects the sleep of adolescents. The compensatory mechanism of more consolidated sleep, as elicited by the sleep restriction associated with mere school attendance, collapsed during 2 weeks of sustained examination stress.

Sleep, cognition, and behavioral problems in school-age children: a century of research meta-analyzed.

Clear associations of sleep, cognitive performance, and behavioral problems have been demonstrated in meta-analyses of studies in adults. This meta-analysis is the first to systematically summarize all relevant studies reporting on sleep, cognition, and behavioral problems in healthy school-age children (5-12 years old) and incorporates 86 studies on 35,936 children. Sleep duration shows a significant positive relation with cognitive performance (r = .08, confidence interval [CI] [.06, .10]). Subsequent analyses on cognitive subdomains indicate specific associations of sleep duration with executive functioning (r = .07, CI [.02, .13]), with performance on tasks that address multiple cognitive domains (r = .10, CI = [.05, .16]), and with school performance (r = .09, CI [.06, .12]), but not with intelligence. Quite unlike typical findings in adults, sleep duration was not associated with sustained attention and memory. Methodological issues and brain developmental immaturities are proposed to underlie the marked differences. Shorter sleep duration is associated with more behavioral problems (r = .09, CI [.07, .11]). Subsequent analyses on subdomains of behavioral problems showed that the relation holds for both internalizing (r = .09, CI [.06, .12]) and externalizing behavioral problems (r = .08, CI [.06, .11]). Ancillary moderator analyses identified practices recommended to increase sensitivity of assessments and designs in future studies. In practical terms, the findings suggest that insufficient sleep in children is associated with deficits in higher-order and complex cognitive functions and an increase in behavioral problems. This is particularly relevant given society's tendency towards sleep curtailment.