Developmental changes in sleep biology and potential effects on adolescent behavior and caffeine use

Adolescent development includes changes in the biological regulatory processes for the timing of sleep. Circadian rhythm changes and changes to the sleep-pressure system (sleep homeostasis) during adolescence both favor later timing of sleep. These changes, combined with prevailing social pressures, are responsible for most teens sleeping too late and too little; those who sleep least report consuming more caffeine. Although direct research findings are scarce, the likelihood of use and abuse of caffeine-laden products grows across the adolescent years due, in part, to excessive sleepines

Heritability of REM sleep neurophysiology in adolescence.

Alterations of rapid eye movement (REM) sleep have long been observed in patients with psychiatric disorders and proposed as an endophenotype-a link between behavior and genes. Recent experimental work has shown that REM sleep plays an important role in the emotional processing of memories, emotion regulation, and is altered in the presence of stress, suggesting a mechanism by which REM sleep may impact psychiatric illness. REM sleep shows a developmental progression and increases during adolescence-a period of rapid maturation of the emotional centers of the brain. This study uses a behavioral genetics approach to understand the relative contribution of genes, shared environmental and unique environmental factors to REM sleep neurophysiology in adolescents. Eighteen monozygotic (MZ; n = 36; 18 females) and 12 dizygotic (DZ; n = 24; 12 females) same-sex twin pairs (mean age = 12.46; SD = 1.36) underwent whole-night high-density sleep EEG recordings. We find a significant genetic contribution to REM sleep EEG power across frequency bands, explaining, on average, between 75 to 88% of the variance in power, dependent on the frequency band. In the lower frequency bands between delta and sigma, however, we find an additional impact of shared environmental factors over prescribed regions. We hypothesize that these regions may reflect the contribution of familial and environmental stress shared amongst the twins. The observed strong genetic contribution to REM sleep EEG power in early adolescence establish REM sleep neurophysiology as a potentially strong endophenotype, even in adolescence-a period marked by significant brain maturation

Naps not as effective as a night of sleep at dissipating sleep pressure

The two-process model of sleep posits that two processes interact to regulate sleep and wake: a homeostatic (Process S) and a circadian process (Process C). Process S compensates for sleep loss by increasing sleep duration and intensity. Process C gates the timing of sleep/wake favouring sleep during the circadian night in humans. In this study, we examined whether taking six naps throughout a 24-hr period would result in the same amount of dissipation of homeostatic pressure at the end of the day as a night of sleep, when time in bed is equivalent. Data from 46 participants (10-23 years; mean = 14.5 [± 2.9]; 25 females) were analysed. Slow-wave energy, normalized to account for individual differences in slow-wave activity, was used as a measure of sleep homeostasis. In the nap condition, slow-wave energy of six naps distributed equally during a 24-hr period was calculated. In the baseline condition, slow-wave energy was measured after 9-hr time in bed. A paired t-test was used to compare nap and baseline conditions. A linear regression was used to examine whether slow-wave energy varied as a function of age. Slow-wave energy was greater during baseline than the nap condition (p < .001). No association between age and slow-wave energy was found for baseline or nap conditions. Our findings indicate that multiple naps throughout the day are not as effective at dissipating sleep pressure as a night of sleep. This is likely due to the influence of the circadian system, which staves off sleep during certain times of the day

The relationship between sleep disturbance and self-harming behaviours in high-risk clinical adolescents

Emerging research has identified sleep disturbance as an important risk factor for predicting self-harming behaviours. However, the temporality of this relationship, particularly in clinical adolescent samples remains poorly understood. This study examines the relationship between sleep disturbance and self-harming behaviours (namely nonsuicidal self-injury and suicide attempts) in clinical adolescents engaging in risk-taking and self-harming behaviours using secondary analyses from a clinical cohort study. Cross-lagged structural equation modelling was used to determine whether baseline sleep disturbance and self-harming behaviours were predictors of each other over a one-year follow-up period in a sample of adolescents (n = 238, 89.5% female) attending and receiving treatment from an outpatient clinic specializing in risk-taking and self-harming behaviours. When controlling for age, sex and depressive symptoms, greater sleep disturbance (p = 0.001) at baseline independently predicted higher numbers of suicide attempts at follow-up. No bidirectional relationship was found when sleep disturbance was modelled with the frequency of nonsuicidal self-injury. This study adds to the growing evidence that sleep disturbance may predict suicidal behaviours. Clinicians should thus regularly assess for sleep disturbances when evaluating suicidal behaviours in high-risk adolescents. Further research and clinical trials should investigate whether sleep-based interventions may be efficacious in reducing the prevalence of suicidal behaviours

Local slow wave activity in regular sleep reveals individual risk preferences

In many everyday life situations, we have to make decisions under varying degrees of risk. Even though previous research has shown that the manipulation of sleep affects risky decision-making, it yet remains to be understood how regular, healthy sleep relates to risk preferences. Therefore, we investigated the relationship between individual, temporally stable neural sleep characteristics and individual differences in risk preferences in healthy adults. Sleep data were collected using a portable high-density EEG system at participants’ home. Results revealed a significant negative correlation between local sleep depth, as reflected in slow-wave activity (SWA) in a cluster of 5 electrodes located over the right prefrontal cortex and risk-taking behavior. This finding remained significant when controlling for total sleep time. Moreover, the association between SWA over the right prefrontal cortex and risk preferences was very similar in all sleep cycles. Our findings suggest that sleep depth in the right prefrontal cortex, an area involved in self-regulation, might serve as a dispositional indicator of lower self-regulatory abilities, which is expressed in greater risk-taking behavior

Local slow-wave activity over the right prefrontal cortex reveals individual risk preferences.

In everyday life, we have to make decisions under varying degrees of risk. Even though previous research has shown that the manipulation of sleep affects risky decision-making, it remains unknown whether individual, temporally stable neural sleep characteristics relate to individual differences in risk preferences. Here, we collected sleep data under normal conditions in fifty-four healthy adults using a portable high-density EEG at participants' home. Whole-brain corrected for multiple testing, we found that lower slow-wave activity (SWA, an indicator of sleep depth) in a cluster of electrodes over the right prefrontal cortex is associated with higher individual risk propensity. Importantly, the association between local sleep depth and risk preferences remained significant when controlling for total sleep time and for time spent in deep sleep, i.e., sleep stages N2 and N3. Moreover, the association between risk preferences and SWA over the right prefrontal cortex was very similar in all sleep cycles. Because the right prefrontal cortex plays a central role in cognitive control functions, we speculate that local sleep depth in this area, as reflected by SWA, might serve as a dispositional indicator of self-regulatory ability, which in turn reflects risk preferences

Sleep and physical activity: results from a long-term actigraphy study in adolescents.

PURPOSE Research to date suggests that physical activity is associated with improved sleep, but studies have predominantly relied on self-report measures and have not accounted for school day/free day variability. To address these gaps in the literature, the aim of the present study was to (a) quantify physical activity in adolescents using long-term daily actigraphy measurement and (b) to examine the association between actigraphically assessed steps and sleep behavior in a sample of healthy adolescents. To be able to capture intra- and inter-individual differences in the daily physical activity of adolescents, we examined within as well as between subjects effects and its association with sleep. METHODS Fifty adolescents between 10 and 14 years of age were included in the present study. In total 5989 days of actigraphy measurement (average of 119 ± 40 days per participant; range = 39-195 days) were analyzed. We use multilevel modeling to disentangle the within and between subject effects of physical activity on sleep. In this way, we examine within an individual, the association between steps during the day and subsequent sleep on a day-to-day basis. On the other hand, our between subjects' analysis allows us to ascertain whether individuals with more overall physical activity have better sleep. RESULTS Within a subject more steps on school and free days were associated with later bed times on school and free days as well as later rise times on school days only. On the other hand, comparing between subjects' effects, more steps were associated with lower sleep efficiency on free and school days. No other significant associations were found for the other sleep variables. CONCLUSION Our results obtained through objective and long-term measurement of both sleep and number of steps suggest weak or non-significant associations between these measures for most sleep variables. We emphasize the importance of the methodology and the separation of within subject from between subject features when examining the relationship between physical activity and sleep