Mary A. Carskadon

Chapter 2 - Normal Human Sleep : An Overview

Normal human sleep comprises two states—rapid eye movement (REM) and non–REM (NREM) sleep— that alternate cyclically across a sleep episode. State characteristics are well defined: NREM sleep includes a variably synchronous cortical electroencephalogram (EEG; including sleep spindles, Kcomplexes, and slow waves) associated with low muscle tonus and minimal psychological activity; the REM sleep EEG is desynchronized, muscles are atonic, and dreaming is typical. A nightly pattern of sleep in mature humans sleeping on a regular schedule includes several reliable characteristics: Sleep begins in NREM and progresses through deeper NREM stages (stages 2, 3, and 4 using the classic definitions, or stages N2 and N3 using the updated definitions) before the first episode of REM sleep occurs approximately 80 to 100 minutes later. Thereafter, NREM sleep and REM sleep cycle with a period of approximately 90 minutes. NREM stages 3 and 4 (or stage N3) concentrate in the early NREM cycles, and REM sleep episodes lengthen across the night. Age-related changes are also predictable: Newborn humans enter REM sleep (called active sleep) before NREM (called quiet sleep) and have a shorter sleep cycle (approximately 50 minutes); coherent sleep stages emerge as the brain matures during the first year. At birth, active sleep is approximately 50% of total sleep and declines over the first 2 years to approximately 20% to 25%. NREM sleep slow waves are not present at birth but emerge in the first 2 years. Slow-wave sleep (stages 3 and 4) decreases across adolescence by 40% from preteen years and continues a slower decline into old age, particularly in men and less so in women. REM sleep as a percentage of total sleep is approximately 20% to 25% across childhood, adolescence, adulthood, and into old age except in dementia. Other factors predictably alter sleep, such as previous sleep-wake history (e.g., homeostatic load), phase of the circadian timing system, ambient temperature, drugs, and sleep disorders. A clear appreciation of the normal characteristics of sleep provides a strong background and template for understanding clinical conditions in which “normal” characteristics are altered, as well as for interpreting certain consequences of sleep disorders. In this chapter, the normal young adult sleep pattern is described as a working baseline pattern. Normative changes due to aging and other factors are described with that background in mind. Several major sleep disorders are highlighted by their differences from the normative pattern.

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.

Understanding adolescent's sleep patterns and school performance: a critical appraisal

The present paper reviews and critiques studies assessing the relation between sleep patterns, sleep quality, and school performance of adolescents attending middle school, high school, and/or college. The majority of studies relied on self-report, yet the researchers approached the question with different designs and measures. Specifically, studies looked at (1) sleep/wake patterns and usual grades, (2) school start time and phase preference in relation to sleep habits and quality and academic performance, and (3) sleep patterns and classroom performance (e.g., examination grades). The findings strongly indicate that self-reported shortened total sleep time, erratic sleep/wake schedules, late bed and rise times, and poor sleep quality are negatively associated with academic performance for adolescents from middle school through the college years. Limitations of the current published studies are also discussed in detail in this review.

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 total sleep loss on sleep tendency.

Effects of two nights of sleep loss were assessed in six young adult (18—21 yr.) volunteers (2 women, 4 men). Performance on the Wilkinson Addition Test fell significantly below baseline values during the sleep-loss procedure and recovered after one or two full nights of sleep. Performance on a Serial Alternation Task also declined during sleep loss. Mood and sleepiness, assessed by subjective self-rating scales, showed a significantly less positive mood and a greater degree of sleepiness during sleep loss, with a recovery to baseline levels after one full night of sleep. Sleep tendency, measured at 2-hr. intervals during all waking periods, was assessed using an objective measure of latency to sleep onset, the Sleep Latency Test. The scores fell to about 1 min. at 0600 on the first night of sleep loss and remained at similarly low values Throughout the sleep loss period. After one night of recovery sleep the scores remained significantly below baseline levels, which were not achieved until after the second recovery night. The multiple sleep latency test appears to be a valuable operationally defined tool for measuring daytime sleepiness.

Sleep fragmentation in the elderly: Relationship to daytime sleep tendency

Sleep in the elderly is known to be disturbed, and many elderly persons also complain of daytime sleepiness. The present study assessed sleep and waking behavior in 12 male (aged 63 to 86) and 12 female (ages 63 to 82) subjects. Sleep stages, respiration, and movement were recorded at night, and daytime sleep tendency was measured using the Multiple Sleep Latency Test during a single 24-hour period. Daytime sleepiness did not correlate with total sleep time or any sleep stage, but was significantly correlated with measures of sleep fragmentation. The latter included transient arousals, a measure of less than 15-sec awakenings, and sleep-related respiration disturbance. These findings suggest that fragmented nocturnal sleep is a significant cause of reduced daytime well-being in elderly individuals. The continuity of both sleep and wakefulness appears to be disrupted with age. Experimental strategies for achieving a rational sleep hygiene are discussed.

Developmental aspects of sleep hygiene: Findings from the 2004 National Sleep Foundation Sleep in America Poll

OBJECTIVE To examine the associations between sleep hygiene and sleep patterns in children ages newborn to 10 years. The relationships between key features of good sleep hygiene in childhood and recognizable outcomes have not been studied in large, nationally representative samples. PARTICIPANTS AND METHODS A national poll of 1473 parents/caregivers of children ages newborn to 10 years was conducted in 2004. The poll included questions on sleep hygiene (poor sleep hygiene operationally defined as not having a consistent bedtime routine, bedtime after 9:00 PM, having a parent present when falling asleep at bedtime, having a television in the bedroom, and consuming caffeinated beverages daily) and sleep patterns (sleep onset latency, frequency of night wakings, and total sleep time). RESULTS Across all ages, a late bedtime and having a parent present when the child falls asleep had the strongest negative association with reported sleep patterns. A late bedtime was associated with longer sleep onset latency and shorter total sleep time, whereas parental presence was associated with more night wakings. Those children (ages 3+) without a consistent bedtime routine also were reported to obtain less sleep. Furthermore, a television in the bedroom (ages 3+) and regular caffeine consumption (ages 5+) were associated with shorter total sleep time. CONCLUSIONS Overall, this study found that good sleep hygiene practices are associated with better sleep across several age ranges. These findings support the importance of common US based recommendations that children of all ages should fall asleep independently, go to bed before 9:00 PM, have an established bedtime routine, include reading as part of their bedtime routine, refrain from caffeine, and sleep in bedrooms without televisions.

Sleep in Adolescents: The Perfect Storm

A reduction in sleep amount from late childhood through the second decade has long been known; however, the weight of current evidence holds that sleep need does not decline across this span. This article will describe how the loss of sleep through adolescence is not driven by lower need for sleep but arises from a convergence of biologic, psychological, and socio-cultural influences.

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.

Adolescent Changes in the Homeostatic and Circadian Regulation of Sleep

Sleep deprivation among adolescents is epidemic. We argue that this sleep deprivation is due in part to pubertal changes in the homeostatic and circadian regulation of sleep. These changes promote a delayed sleep phase that is exacerbated by evening light exposure and incompatible with aspects of modern society, notably early school start times. In this review of human and animal literature, we demonstrate that delayed sleep phase during puberty is likely a common phenomenon in mammals, not specific to human adolescents, and we provide insight into the mechanisms underlying this phenomenon.