Verbal Behavior. New York: Appleton-Century-Crofts, 1957.
Beyond Freedom and Dignity. New York: Knopf, 1971.
Brian D. Midgley
Edward K. MorrisSLEEPING
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 peace-
ful appearance of the sleeping child, sleep is an active
process with cycles of physiological arousal alternat-
ing 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 pat-
terns 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 deep-
er 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 de-
creases during adolescence.
Because infant sleep patterns do not approxi-
mate adult patterns until well into the first year, infant
sleep states are described differently. Infants slip easi-
ly 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 in-
clude occasional startle movements or sucking. Active
sleep, although similar to adult REM sleep, is charac-
terized 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 sec-
ond 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 min-
utes after falling asleep) is not established until ado-
lescence.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 agree-
ment that sleep has restorative functions, evidence
linking sleep to various waking behaviors is largely
circumstantial. Sleep appears to play a role in behav-
ioral regulation and in emotional and cognitive func-
tioning. (Irritability, overactivity, and decreased
attention span have been associated with sleep dis-
ruptions 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 com-
pared to six-month-olds whose REM approximates
that of adults (25–30% of sleeping time). Many re-
searchers believe that the heightened activity occur-
ring during REM sleep stimulates brain growth.Measuring Sleep
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, oxy-
gen 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 strik-
ing 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, to-
taling 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, and370 SLEEPING