Christine Acebo

Regulation of Adolescent Sleep: Implications for Behavior

Abstract: Adolescent development is accompanied by profound changes in the timing and amounts of sleep and wakefulness. Many aspects of these changes result from altered psychosocial and life‐style circumstances that accompany adolescence. The maturation of biological processes regulating sleep/wake systems, however, may be strongly related to the sleep timing and amount during adolescence—either as “compelling” or “permissive” factors. The two‐process model of sleep regulation posits a fundamental sleep‐wake homeostatic process (process S) working in concert with the circadian biological timing system (process C) as the primary intrinsic regulatory factors. How do these systems change during adolescence? We present data from adolescent participants examining EEG markers of sleep homeostasis to evaluate whether process S shows maturational changes permissive of altered sleep patterns across puberty. Our data indicate that certain aspects of the homeostatic system are unchanged from late childhood to young adulthood, while other features change in a manner that is permissive of later bedtimes in older adolescents. We also show alterations of the circadian timing system indicating a possible circadian substrate for later adolescent sleep timing. The circadian parameters we have assessed include phase, period, melatonin secretory pattern, light sensitivity, and phase relationships, all of which show evidence of changes during pubertal development with potential to alter sleep patterns substantially. However the changes are mediated—whether through process S, process C, or by a combination—many adolescents have too little sleep at the wrong circadian phase. This pattern is associated with increased risks for excessive sleepiness, difficulty with mood regulation, impaired academic performance, learning difficulties, school tardiness and absenteeism, and accidents and injuries.

A self-administered rating scale for pubertal development☆

The purpose of this study was to assess the reliability and validity of a new self-rating scale to measure childrens pubertal status without pictorial representations or interviews. The scale is an adaptation of an interview-based puberty-rating scale by Petersen, and included scores for each of five items rating physical development, an overall maturation measure, and a categorical maturation score designed to be similar to Tanner staging categories. Each measure was obtained from independent ratings by students and parents, and a 3-point categorical scale was also obtained from teachers. Subjects included 698 5th- and 6th-grade students (323 boys and 375 girls) from 61 schools and their parents and teachers. Fifth-grade students rated themselves and were rated by parents as less mature than 6th graders; 6th-grade girls were consistently rated more mature than boys of the same age. Significant correlations were found between parents and students for all of the measures for 6th-graders and 5th-grade girls and several measures for 5th-grade boys. This new scale is a useful tool for assessing pubertal status in settings that require noninvasive measures.

Effects of acute sleep restriction on behavior, sustained attention, and response inhibition in children

This study examined the effects of acute sleep restriction on the daytime behavior and performance of healthy children and adolescents. 82 participants (8 to 15 years of age) completed 5 nights of baseline sleep and were randomly assigned to Optimized (10 hr.) or Restricted (4 hr.) sleep for an overnight lab visit. Behavior, performance, and sleepiness were assessed the following day. Sleep restriction was associated with shorter daytime sleep latency, increased subjective sleepiness, and increased sleepy and inattentive behaviors but was not associated with increased hyperactive-impulsive behavior or impaired performance on tests of response inhibition and sustained attention. Results are discussed in terms of current theories regarding effects of inadequate or disturbed sleep among children and adolescents.

Sleep tendency during extended wakefulness: insights into adolescent sleep regulation and behavior.

Sleep tendency (latency to sleep onset) was examined during extended waking in prepubertal and mature adolescents to determine whether sleep pressure is lower near bedtime in the latter group. Participants were nine prepubertal (pubertal stage Tanner 1, mean age 11.1 years, SD ± 1.3 years, five males) and 11 pubertally mature adolescents (Tanner 5, 13.9 ± 1.2 years, three males). They spent 10 nights at home on an identical fixed 10‐h sleep schedule followed by a 36‐h constant routine with sleep latency tests at 2‐h intervals using standard polysomnography. Saliva was collected to assess dim‐light melatonin onset (DLMO) phase. DLMO was earlier in the Tanner 1 (mean clock time = 20:33 hours, SD = 49 min) than Tanner 5 group (21:29 hours ± 42 min). Sleep latency compared at a ‘critical period’ spanning 12.5 (20:30 hours clock time) to 18.5 h (02:30 hours) after waking did not differ at 20:30 hours, but was shorter for the Tanner 1 group at 22:30 hours (Tanner 1 = 9.2 ± 6.3 min; Tanner 5 = 15.7 ± 5.8 min), 00:30 hours (Tanner 1 = 3.6 ± 1.7 min; Tanner 5 = 9.0 ± 6.4 min), and 02:30 hours (Tanner 1 = 2.0 ± 1.7 min; Tanner 5 = 4.3 ± 3.2 min; trend). These differences were apparent controlling for circadian phase by partial correlation. Sleep tendency after 14.5, 16.5, and 18.5 h awake was lower in mature versus prepubertal adolescents, supporting our hypothesis that a developmental change of intrinsic sleep–wake regulation may provide physiologically mediated ‘permission’ for later bedtimes in older adolescents.

Intrinsic circadian period of adolescent humans measured in conditions of forced desynchrony.

Circadian timing was assessed with forced desynchrony (FD) in 10 healthy adolescents (five boys, five girls; mean age 13.7 years). Following 10 days of entrainment to a fixed light-dark (LD) schedule at home, participants were studied under dim light (<20 lux) in the laboratory. A 28-h schedule (FD) was imposed for 12 x 28-h cycles. Saliva was collected at 30- or 60-min intervals throughout; core temperature was measured in constant routines (CR) before and after FD. Intrinsic circadian period was estimated by linear regression using temperature minimum from CRs and dim-light salivary melatonin onsets and offsets from FD. Average intrinsic circadian period for core temperature (n = 7) was 24.30+/-0.20, for melatonin onset was 24.33+/-0.21, and for melatonin offset was 24.35+/-0.21. Intrinsic circadian period in every adolescent was greater than 24 h.

Parental report of sleep problems in children with attentional and learning disorders

&NA; This study examined whether parents of children diagnosed with neurodevelopmental disorders (n = 79) report greater sleep‐related problems in their offspring than do parents of normal community‐based children (n = 86) on a research questionnaire developed to assess sleep and breathing problems, sleepiness, and behavioral problems. Clinical subgroups included: attention deficit/hyperactivity disorder (ADHD) (n = 43), learning disabilities (LD) (n = 11), and combined ADHD/LD (n = 25). Analyses revealed that parents of children with neurodevelopmental disorders report greater problems along all three dimensions than parents of normal control children. Sleep‐related difficulties were reported at the same frequency across all three clinical subgroups. No significant difference between clinical and control groups was noted, however, in the reported length of sleep on weeknights. These preliminary findings suggest that sleep‐related problems need to be routinely reviewed as part of the clinical evaluation of neurodevelopmental problems, because they may contribute to and/or exacerbate the behavioral manifestation of these disorders.

Child emotional insecurity and academic achievement : The role of sleep disruptions

The authors examined childrens sleep as an intervening variable in the connection between emotional insecurity in the family and academic achievement. The role of ethnicity (African American and European American) and socioeconomic status (SES) in moderating the examined relations was assessed. One hundred sixty-six children (8- and 9-year-olds) reported their emotional insecurity, and the quantity and quality of childrens sleep were examined through actigraphy and self-report. Decreased amount and quality of sleep were intervening variables in the relations between insecurity in the marital relationship and childrens achievement. The effects of disrupted sleep on achievement were more pronounced for both African American children and children of lower SES. Results highlight the importance of the contemporaneous examinations of family and sleep functioning in the prediction of child outcomes.

A Longitudinal Assessment of Sleep Timing, Circadian Phase, and Phase Angle of Entrainment across Human Adolescence

The aim of this descriptive analysis was to examine sleep timing, circadian phase, and phase angle of entrainment across adolescence in a longitudinal study design. Ninety-four adolescents participated; 38 (21 boys) were 9–10 years (“younger cohort”) and 56 (30 boys) were 15–16 years (“older cohort”) at the baseline assessment. Participants completed a baseline and then follow-up assessments approximately every six months for 2.5 years. At each assessment, participants wore a wrist actigraph for at least one week at home to measure self-selected sleep timing before salivary dim light melatonin onset (DLMO) phase – a marker of the circadian timing system – was measured in the laboratory. Weekday and weekend sleep onset and offset and weekend-weekday differences were derived from actigraphy. Phase angles were the time durations from DLMO to weekday sleep onset and offset times. Each cohort showed later sleep onset (weekend and weekday), later weekend sleep offset, and later DLMO with age. Weekday sleep offset shifted earlier with age in the younger cohort and later in the older cohort after age 17. Weekend-weekday sleep offset differences increased with age in the younger cohort and decreased in the older cohort after age 17. DLMO to sleep offset phase angle narrowed with age in the younger cohort and became broader in the older cohort. The older cohort had a wider sleep onset phase angle compared to the younger cohort; however, an age-related phase angle increase was seen in the younger cohort only. Individual differences were seen in these developmental trajectories. This descriptive study indicated that circadian phase and self-selected sleep delayed across adolescence, though school-day sleep offset advanced until no longer in high school, whereupon offset was later. Phase angle changes are described as an interaction of developmental changes in sleep regulation interacting with psychosocial factors (e.g., bedtime autonomy).

Evening Alcohol Suppresses Salivary Melatonin in Young Adults

The study objective was to determine the acute effects of a moderate evening dose of alcohol on salivary melatonin levels in humans with stable prior sleep‐wake histories and in a controlled environment. Twenty‐nine adults (nine males) ages 21 to 25 (M=22.6, SD=1.2) yrs adhered to a 10‐day at‐home stabilized sleep schedule followed by three in‐lab adaptation, placebo, and alcohol (order counterbalanced) study nights. Alcohol (vodka: 0.54 g/kg for men and 0.49 g/kg for women) or placebo beverage was consumed over 30 min, ending 1 h before stabilized bedtime. At 140 and 190 min after alcohol administration, melatonin level was reduced by 15% and 19%, respectively, in comparison to placebo. The findings indicate that a moderate dose of alcohol in the evening suppressed melatonin in young adults.

Adolescent Sleep Patterns: Influence of Irregular Sleep Patterns on Waking Behavior

Two consistent findings in the literature on adolescent sleep patterns are that time spent sleeping on school nights decreases from childhood through adolescence, and that differences between weekend and school-night sleep schedules are large for many teenagers (Billiard, Alperovitch, Perot, & James, 1987; Strauch & Meier, 1988; Carskadon, 1990; Szymczak, Jasinska, Pawlak, & Swierzykowska, 1993). In general, school-night sleep is restricted because of early school start times, whereas on weekends, bedtimes and rise times are later and total sleep time is longer. In a recent large survey of over 3,000 high school students, Wolfson and Carskadon (1998) found such irregular bedtimes related to self-reported academic difficulty in school, daytime sleepiness, depressed mood, and sleep-wake behavior problems. Lower amounts of self-reported total sleep time were also related to more difficulties with daytime functioning. We suspect that these difficulties in daytime function may result in part from disturbances in both the homeostatic and circadian timing systems regulating sleep-wake behavior. Evidence from other studies in children and adolescents supports the importance of total sleep time and sleep schedule regularity as predictors of daytime functioning. Several other survey studies have linked total sleep time with grades, daytime fatigue and struggles to stay awake, and difficulties concentrating in class (Allen, 1992; Epstein, Chillag, & Lavie, 1995).