Sleep is a biological imperative critical to the maintenance of mental and physical health. It is a state of lessened consciousness and decreased physical activity during which the organism slows down and repairs itself. The sleep cycle involves two distinct phases that alternate cyclically from light sleep to deep then deeper and deepest sleep throughout the sleep period. There are two main phases of sleep.
- rapid eye movement (REM) sleep, during which dreaming occurs
- non-rapid eye movement (NREM) or slow-wave sleep (SWS)
The timing and progression of the sleep cycle and the total amount of nightly sleep required for optimal health varies from infancy to adulthood, depending on developmental stage and temperament . Children, particularly infants, require the most sleep during a 24-hour period. The natural sleep-wake cycle, governed by an internal "biological clock," tends toward a 25-hour day. It is affected by the relative balance of light and darkness in the environment. As darkness approaches, the hormone melatonin is secreted by the pineal gland and signals the brain that it is time to sleep.
NREM deep sleep
Sleep begins in stage one of the sleep phase known as NREM, or non-rapid eye movement, sleep. NREM sleep has four stages: light sleep, deeper sleep, and two stages of deepest sleep. Stage one is the "drifting off" period of light sleep in the transition between wakefulness and sleep and comprises about 5 percent of the entire sleep period. Stage two sleep involves a change in brain-wave patterns and increased resistance to arousal and accounts for 45–55 percent of total sleep time. Stages three and four are the deepest levels of sleep and occur only in the first third of the sleep period. NREM stage four sleep usually takes up 12 to 15 percent of total sleep time. Sleep terrors, sleep walking, and bedwetting episodes generally occur within stage four sleep or during partial arousals from this sleep stage.
It typically takes about 90 minutes to cycle through the four deepening stages of NREM sleep before onset of the second phase of sleep known as REM or dream sleep.
REM dream sleep
Rapid eye movement (REM) sleep is qualitatively different from NREM sleep. REM sleep is characterized by extensive central nervous system (CNS) activity with an increase in brain metabolism accompanied by the vivid imagery of dreams. During REM sleep the body is nearly paralyzed, a condition called "atonic," that serves to inhibit the dreamer from physical movement during active dreaming.
"Waking and dreaming are two states of consciousness, with differences that depend on chemistry," according to J. Allan Hobson, professor of psychiatry at Harvard Medical School. Physical activity and thought are suppressed in sleep, but the brain nonetheless remains active "processing information, consolidating and revising memory, and learning newly acquired skills." The brain self-activates, radically changing its chemical climate from wakefulness to sleep states.
REM sleep is also known as "paradoxical sleep" because muscle activity is suppressed even as the CNS registers intense brain activity and spontaneous rapid eye movements can be observed. Brain-wave monitoring of REM sleep with an electroencephalograph (EEG) reveals a low-voltage, fast-frequency, non-alpha wave record. Beyond infancy, REM sleep comprises 20–25 percent of the entire sleep period. This sleep phase is concerned with memory and the consolidation of new information.
Newborn infants usually sleep for brief periods at a time around the clock, with the total of day and nighttime sleep roughly equal. A newborn's total sleep need is from 16 to 18 hours in every 24-hour period. Newborns spend approximately 50 percent of their sleep period in the REM phase. Infants are most easily awakened during this phase of sleep that is accompanied by yawning, squirming, and quiet vocalizations.
Infants move through REM and non-REM sleep stages in a 90 minute cycle, and they rise to a near-waking state every three to four hours, more often in breastfed infants. By about six months of age, babies usually will sleep through the night for 12 or more hours and will continue to nap several times throughout the day.
Researchers conducting a 2004 survey for the National Sleep Foundation discovered that children in every age group fail to meet even the low-end requirements for adequate sleep. By the third month of life, a child's sleep requirement is about 14 to 15 out of every 24 hours, a need that continues until about 11 months of age. However, research indicates that children age three months to 11 months sleep only 12.7 hours on average.
Toddlers are far more physically active than infants, and their sleeping behavior and the timing of sleep cycles reflects their maturing brains. A toddler will spend only about 30 percent of her sleep time in REM dream sleep. Toddlers on average require 12 to 14 hours of sleep and may no longer need an afternoon nap to meet this sleep requirement. But research shows that children in the one to three-year-old range may actually average only about 11.7 hours of sleep.
Children in this age group tend to be more troubled with nightmares and night terrors than younger children. They may resist going to bed at night because of fear of the dark or of some monster lurking under the bed. Parental reassurance and comfort and the addition of a night light may alleviate some of these concerns. Preschool children may also feel anxiety around the issue of toilet training and bedwetting.
School-age children require from eight to 10 hours of sleep nightly. Adequate sleep is especially important as school children's lives become busier and stress levels rise. Sleep disruptions such as nightmares tend to increase with this age group as the child has more life experiences and anxieties to process. Parents should also monitor the child's use of caffeinated beverages which can cause sleep difficulties and add to the overall loss of adequate sleep.
Adolescents require at least 10 hours of nightly sleep. This is a busy time when many teens' lifestyles include school, work, sports , and other extracurricular activities , as well as socializing with peers. This increase in activity, together with early-morning school schedules, leaves little time for adequate sleep. Various psychological disorders also may trouble the adolescent, particularly anxiety and depression. Parents should pay attention to a young teen who shows sudden changes in eating habits, loss of interest in usual activities, and other behavioral clues that may indicate onset of depression.
According to the "2004 Sleep in America Poll" published by the National Sleep Foundation, 69 percent of children younger than age 10 experience problems with sleep that may occur as often as several times a week. Sleep disruptions in children are usually a normal symptom of central nervous system development. In older children sleep disruptions may increase and intensify due to external stressors in the home or school environment. Sleep difficulties can also be a sign of physical or mental health problems. They are often present in children with attention-deficit/hyperactivity disorder (AD/HD) and in children who have experienced physical, psychological, or sexual abuse.
Childhood sleep problems and parasomnias include:
- Bedwetting: A common sleep problem characterized by involuntary urination during sleep. This is a routine occurrence in children up to five years of age. Bedwetting is also called "nocturnal enuresis."
- Nightmares: A common parasomnia characterized by dreams with frightening psychological content, a feeling of imminent physical danger, and a sensation of being trapped or suffocated. Nightmares occur during REM, or dream-time, sleep and trigger a partial or full awakening. The word "mare" in Old English means "demon."
- Insomnia: Difficulty falling asleep and remaining asleep, or early-morning awakenings. Insomnia may be short-term, due to stress or physical or psychological problems, or may be due to the lack of a healthy bedtime routine.
- Night terrors: A common childhood sleep disruption characterized by an abrupt arousal from stage 4 sleep within the first hour of the sleep period. The child may sit bolt upright in acute terror, screaming inconsolably. Night terrors are a confusional arousal resulting from immature sleep patterns with an intense activation of the flight or fight emotion. They occur in the deepest stage of slow-wave non-REM sleep. Night terrors are also called "pavor nocturnus."
- Sleep apnea: A serious and potentially life-threatening sleep disruption characterized by brief interruptions of airflow during sleep and frequent partial arousals throughout the night. Sleep apnea is less common than other sleep disturbances, occurring in about 2 percent of children.
- Sleep bruxism: A sleep disturbance characterized by grinding the teeth or clenching of the jaws during sleep. Sleep bruxism is common among children of all ages. This sleep problem usually subsides over time.
- Sleep rocking and head banging: A sleep disturbance characterized by rhythmical movements of the body during sleep. Rhythmical movements may be observed in children as young as six months. More dramatic movements, involving head banging and rocking, occur in as many as 60 percent of nine-month-old children. These sleep disturbances tend to decrease with age, appearing in only about 5 percent of children over two years of age.
- Sleep walking: A sleep disturbance characterized by a partial-arousal involving walking about for a few steps, or for much longer distances, with a glassy, trance-like appearance to the eyes. Sleepwalking occurs in the deepest stages of slow-wave, non-REM sleep within the first few hours of sleep onset. Researchers have found that as many as 15–30 percent of children experience at least one sleepwalking episode. Sleepwalking can be triggered by external stimuli, such as an abrupt noise, or by moving a sleeping child to a standing position. This sleep disturbance tends to run in families. Sleepwalking is also called "somnambulism."
All children need regular and adequate sleep to assure optimal mental and physical health. Sleeping patterns developed in infancy usually persist into adulthood. It is important that parents help the child to establish a healthy bedtime routine that will assure adequate sleep time, minimize bedtime struggles, and help to reduce the occurrence of common childhood sleep problems.
As reported by Steven Reinberg, research by Maria M. Wong of the University of Michigan, published in 2004 in the journal Alcoholism: Clinical and Experimental Research, cautions parents to pay more attention to their children's sleep habits. "Sleep problems are a risk factor for alcohol and drug problems," Wong concluded from data obtained in the first study to link alcohol and drug use with sleep disorders in early childhood. The study obtained sleep data from 257 boys ages three to five years and followed them until they were 12–14 years old. Almost half of the children in the study who experienced childhood sleep problems began using alcohol and drugs by the time they were 14 years old.
In many households, electronic distractions interfere with the establishment of a regular bedtime routine that would help a child to settle down and prepare for restful sleep. Calming-down activities, such as being read to by a parent, have been replaced with electronic stimulation resulting in less sleep time.
As reported in Manchester Online , Luci Wiggs, a research fellow at Oxford University, is co-author of a 2004 poll of more than 1,000 parents with children four to 10 years of age. She found that 67 percent of these children had a television, computer, or game machine in their bedroom. These stimulating diversions, which she calls "digital distractions," resulted in a cumulative sleep deficit for at least one fifth of the children surveyed that may "compromise children's physical health, academic achievements, and mental health."
Children who consume caffeine throughout the day, in soda or iced tea beverages, also lose the sleep required for optimal health and cognitive functioning. A survey by the National Sleep Foundation released in 2004 found that 26 percent of children ages three and older drink at least one caffeinated beverage a day and suffer a loss of about 3.5 hours of sleep each week.
Parents are on a journey of discovery with each child whose temperament, biology, and sleep habits result in a unique sleep-wake pattern. It can be frustrating when children's sleep habits do not conform to the household schedule. Helping the child develop good sleep habits in childhood takes time and parental attention, but it will have beneficial results throughout life. An understanding of the changing patterns of the typical sleep-wake cycle in children will help alleviate any unfounded concerns. Maintaining a sleep diary for each child will provide the parent with baseline information in assessing the nature and severity of childhood sleep problems. Observant parents will come to recognize unusual sleep disruptions or those that persist or intensify.
When to call the doctor
Developmental changes throughout childhood bring differences in the sleep-wake cycle and in the type and frequency of parasomnias that may interrupt sleep. Medical consultation to rule out illness, infection, or injury is prudent if the child's sleep problems prevent adequate sleep and result in an ongoing sleep deficit. As reported by News-Medical in Child Health News , children's sleep problems should be taken seriously as they may be a "'marker' for predicting later risk of early adolescent substance use." In the same article, University of Michigan psychiatry professor Kirk Brower, who has studied "the interplay of alcohol and sleep in adults," stressed that "The finding does not mean there's a cause-and-effect relationship."
Consultation with a child psychologist may be helpful if frightening dreams intensify and become more frequent as this may indicate a particular problem or life circumstance that needs to be changed or one that the child may need extra help working through.
Most childhood sleep disturbances will diminish over time as the brain matures and a regular sleep-wake cycle is established. Parental guidance is crucial to development of healthy sleep habits in children.
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Biological clock —A synonym for the body's circadian rhythm, the natural biological variations that occur over the course of a day.
Parasomnia —A type of sleep disorder characterized by abnormal changes in behavior or body functions during sleep, specific stages of sleep, or the transition from sleeping to waking.
Suprachiasmatic nuclei (SCN) —SCN is that part of the brain that functions as a person's "biological clock" to regulate many body rhythms. The SCN is located on top of the main junction of nerve fibers that connects to the eyes.