Sleep is known to play an important role in the health and well-being of children. But sleeping, although restful, involves more than resting. Despite the peaceful appearance of the sleeping child, sleep is an active process with cycles of physiological arousal alternating between intense activity and profound tranquility.
Stages, States, and Cycles
Two sleep states have been identified: rapid eye movement (REM) sleep, and non-REM (NREM) sleep. REM sleep is a state of heightened arousal characterized by uneven breathing, heart rate, and blood pressure; intense electrical brain activity; loss of muscle tone; and darting eye movements. NREM sleep is marked by reduced brain activity; regular patterns of heart rate, breathing, and blood pressure; and general body quiescence.
For older children and adults, NREM sleep can be further differentiated into four progressively deeper levels, with stages three and four (also called delta or slow-wave sleep) representing the deepest levels. This slow-wave activity emerges at about three to six months, peaks during early childhood, and then decreases during adolescence.
Because infant sleep patterns do not approximate adult patterns until well into the first year, infant sleep states are described differently. Infants slip easily back and forth among several states of arousal that include three awake states (crying, waking activity, and quiet alertness), a transitional state (drowsiness), and two sleeping states (active and quiet sleep). Quiet sleep resembles NREM sleep in adults, but might include occasional startle movements or sucking. Active sleep, although similar to adult REM sleep, is characterized by much movement of the limbs, as well as twitching, smiling, and rapid eye movements beneath closed or partially closed lids. Brain wave patterns are highly similar to awake patterns.
Sleeping patterns are cyclical and are controlled by two biological "clocks." The first, which originates in the suprachiasmatic nucleus of the hypothalamus, controls daily cycles. Cycles develop before birth and can be detected in utero at about twenty weeks; as the clock matures, however, there is a gradual change from multiple cycles to a single daily pattern. The second clock, originating in the pons section of the brain stem, regulates the alternation between REM and NREM sleep. Here, too, maturational changes can be seen. Newborns typically fall first into REM sleep, whereas older children may not experience REM for three hours and the adult pattern (about ninety minutes after falling asleep) is not established until adolescence.
Functions of Sleep
Despite the fact that sleep is a dominant activity during the early years, surprisingly little is known about why humans sleep. Aside from general agreement that sleep has restorative functions, evidence linking sleep to various waking behaviors is largely circumstantial. Sleep appears to play a role in behavioral regulation and in emotional and cognitive functioning. (Irritability, overactivity, and decreased attention span have been associated with sleep disruptions in children.) Sleep may also facilitate the consolidation of memories and, in older children and adults, REM sleep is associated with dreaming.
Whether or not infants dream is not known; REM sleep, however, may be important to infants in other ways. Newborns spend approximately 50 percent of sleep time in REM, an impressive amount when compared to six-month-olds whose REM approximates that of adults (25-30% of sleeping time). Many researchers believe that the heightened activity occurring during REM sleep stimulates brain growth.
Researchers use a variety of techniques to study sleep. These include parental reports, sleep diaries, direct observations, and videotaping, as well as more complicated techniques that involve recordings of heart rate, brain waves, eye and muscle activity, oxygen saturation, and airflow. Actigraphy (recording of movements via a small device worn on the arm or leg) is also used to record sleep patterns.
Developmental Trends in Sleep
Patterns of sleep and wakefulness undergo striking changes from infancy through adolescence, but within any given age group, there is great variability. Newborns do not sleep for long stretches. Instead, they experience about seven sleep periods daily, totaling about sixteen hours. Somewhere around three months, many infants begin to sleep for at least five continuous hours during the night. Like children and adults, infants awaken briefly a few times during the night but 70 percent of one-year-olds are able to soothe themselves back to sleep. Self-comforting techniques such as thumb sucking, face stroking, and body rocking are frequent. By one year, sleep time averages twelve hours distributed into a long sleep period at night and two daytime naps.
Across early childhood, daytime naps gradually disappear, resulting in decreased daily sleep. By age four, children sleep about eleven hours per day and many have given up napping. Not only do pre-schoolers sleep less than infants, they also fall asleep differently. Young children are often reluctant to go to sleep, and bedtime rituals may take on a predictable pattern with children who have been tucked in perhaps requesting a drink of water or another good-night kiss. Children over the age of three are also more likely than younger children to depend on a favorite blanket or teddy bear to help them fall asleep.
By six to ten years of age, children are generally "good sleepers," sleeping soundly for about ten hours at night and staying alert during the day. But as they approach puberty, sleep patterns undergo further change. Studies in the United States, Europe, and elsewhere reveal an increasing tendency among adolescents to sleep less, to go to bed later, to develop different patterns of sleep on weekends and weeknights, and to report increased daytime sleepiness. But contrary to popular belief, adolescents do not necessarily need less sleep. Although optimal sleep time for adolescents is about nine hours per night, most adolescents average less than eight hours. This is unfortunate because inadequate sleep is associated with poor school performance, mood and behavioral problems, and increased risk for automobile accidents.
A study of school-age children in Israel showed that sleep habits identified in adolescents may be drifting down to younger ages. In addition, girls in the study slept more and moved less in sleep than boys, a finding that has also been observed in newborns. Overall, however, researchers have found relatively few gender differences in sleeping patterns.
It is not clear how much sleep is optimal for children because most studies have been based on small samples. Until developmental norms are established for large representative samples of children and adolescents, parents may need to monitor their child's behavior. A child who has difficulty waking in the morning, or is consistently sleepy, irritable, and inattentive during the day, may not be getting enough sleep.
Two general categories of sleep disorders are recognized. Dyssomnias are problems with the initiation or maintenance of sleep, or with sleep that is inefficient. These include common sleep timing problems such as frequent night wakings and difficulty falling asleep at night or difficulty waking in the morning. Dyssomnias also include relatively rare problems such as obstructive sleep apnea (associated with enlarged tonsils and adenoids) and narcolepsy (sudden daytime sleep attacks).
Parasomnias occur during sleep but are not associated with insomnia or excessive sleepiness. Common parasomnias in children include head banging or rocking (exhibited by about 58% of children) and nightmares (most commonly of being attacked, falling, or dying). Nightmares are not the same as the rarer sleep terrors, a disorder in which a child, although asleep, appears to be awake and terrified. In sleep terrors, the child is screaming and incoherent with a glassy-eyed stare, profuse sweating, and rapid heart rate and respirations. The child is difficult to rouse and calm, and in the morning retains no memory of the episode. Both nightmares and sleep terrors occur during the transition from NREM sleep to REM sleep. They generally resolve with age. Other parasomnias are teeth grinding (bruxism), sleepwalking, and sleep talking. Bed-wetting (enuresis) is also considered a parasomnia if it continues after the age of five in the absence of physical or psychiatric pathology.
Children's dreams have often been described as bizarre and fantastical in nature. Early theories of children's emotional development (e.g., psychoanalytic theory, which maintained that dreams are wish fulfillments) contributed to this view. But how dreams are studied may also play a role. Dreams reported after they occur may have been recalled because they were bizarre. David Foulkes showed in laboratory studies that if children were awakened during REM sleep and asked to describe their dreams, a different picture emerged. Although some dreams contained bizarre elements, children generally dreamed about familiar people, settings, and actions. In addition, dreams changed with age. It was not until about age eight or nine that dream reports began to include narratives that featured activity by dream characters with the self as a participant. Foulkes concluded that dreaming in children is linked to general intellectual development with dream construction dependent on abstract, representational thought.
In general, empirical research on children's dreams has been sparse. While knowledge of many aspects of sleeping in childhood has grown since the 1950s, relatively little is known about the intriguing topic of children's dreams.
Anders, Thomas F., and Lisa A. Eiben. "Pediatric Sleep Disorders:A Review of the Past Ten Years." Journal of the American Academy of Child and Adolescent Psychiatry 36, no. 1 (1997):9-20.
Carskadon, Mary A. "Patterns of Sleep and Sleepiness in Adolescents." Pediatrician 17 (1990):5-12.
Carskadon, Mary A., ed. Encyclopedia of Sleep and Dreaming. New York: Macmillan, 1993.
Foulkes, David. Children's Dreams: Longitudinal Studies. New York:Wiley, 1982.
Kahn, André, Bernard Dan, José Groswasser, Patricia Franco, and Martine Sottiaux. "Normal Sleep Architecture in Infants and Children." Journal of Clinical Neurophysiology 13, no. 3 (1996):184-197.
Mindell, Jodi A., Judith A. Owens, and Mary A. Carskadon. "Developmental Features of Sleep." Child and Adolescent Psychiatric Clinics of North America 8 (1999):695-725.
Sadeh, Avi, Amiram Raviv, and Reut Gruber. "Sleep Patterns and Sleep Disruptions in School-Age Children." Developmental Psychology 36 (2000):291-301.
Wolfson, Amy R., and Mary A. Carskadon. "Sleep Schedules and Daytime Functioning in Adolescents." Child Development 69 (1998):875-887.