Handbook of Psychology

The Basics of Sleep 319

decrease in the amount of stages 3 and 4 sleep and an increase
in the number of awakenings. These changes become more
noticeable when individuals reach their forties. In late life,
nocturnal sleep is diminished, but daytime naps often main-
tain the total sleep time at about 7 hours. Nonetheless, sleep
quality is diminished with aging, as there is a marked reduc-
tion of deep sleep and an increase of time spent in stage 1.
Older adults experience more frequent and prolonged awak-
enings, which may explain the increased incidence of sleep
complaints in this population (Webb & Campbell, 1980).

Medical Conditions and Drugs

Sleep is vulnerable to medical illnesses. A variety of en-
docrine, cardiovascular, and pulmonary diseases can disrupt
sleep-wake functions. Neurological disorders such as
epilepsy, dementias, or brain injury may also induce signi“-
cant changes in sleep patterns. Sleep disturbances very fre-
quently accompany any type of medical condition producing
pain (i.e., arthritis, cancer, and chronic pain syndrome).
Indeed, pain conditions have been associated with frequent
intrusions of wakefulness into NREM sleep, a condition
called alpha-delta sleep (Moldofsky, 1989).
Numerous prescribed and over-the-counter drugs can alter
sleep patterns. Some medications prescribed for medical con-
ditions may cause insomnia (bronchodilators, steroids) and
others may produce sleepiness (antihistamines). Most psy-
chotropic medications have a marked impact on sleep.
Sedative-hypnotics induce sleep, but they also alter the un-
derlying sleep stages. Benzodiazepines increase time in
stages 1 and 2 and decrease time in stages 3 and 4 sleep.
Some antidepressant medications (e.g., amitryptiline) have
sedating properties, while others (e.g., ”uoxetine) have a
more energizing effect and produce insomnia, and still others
(e.g., tricyclics) selectively suppress REM sleep. The time of
administration of these pharmacological agents is often criti-
cal in determining how they will affect sleep.

Psychosocial Stressors

Sleep is very sensitive to stress and emotional distress. Major
life events (e.g., divorce, death of a loved one) and more
minor but daily stressors (e.g., interpersonal dif“culties, pres-
sure at work) can affect sleep patterns by heightening arousal
before falling asleep and during nocturnal awakenings. Al-
though sleep usually returns to normal once the acute stress-
ful situation has resolved, sleep disturbances may become
chronic due to a variety of perpetuating factors (Morin,
1993). There is also a clear association between sleep distur-
bances and psychopathology (discussed later).

Lifestyle and Environmental Factors

Many lifestyle factors have noticeable repercussions on sleep

patterns including diet, exercise, sleep schedules, and envi-

ronmental conditions. For example, the ingestion of heavy

meals late in the evening can disrupt sleep. Social drugs such

as caffeine, nicotine, and alcohol can alter sleep when in-

gested too close to bedtime. Physical exercise can either

promote or interfere with sleep, depending on its timing, in-

tensity, and regularity, as well as on the physical “tness of an

individual. Daytime naps, particularly late in the day, will

delay sleep onset the following night. Long naps may pro-

duce deep sleep, which will be proportionally reduced during

the next sleep episode. Environmental factors such as noise,

temperature, light, and sleeping conditions (e.g., mattress

quality) can also impact on sleep. Noise from traf“c or from

a snoring bed partner can lead to more disrupted sleep.

The Role of Sleep and the Consequences of

Sleep Deprivation

Animals totally deprived of sleep during a prolonged period

eventually die, suggesting that sleep serves a critical function

in humans and animals (Rechtschaffen, Gilliland, Bergmann,

& Winter, 1983). However, research has not yet provided a

satisfying answer to the question: Why do we sleep? Several

hypotheses have been put forward. Adaptive theories suggest

that sleep has evolved as a protective mechanism to keep the

organism out of danger during periods of inactivity. Propo-

nents of a recuperative theory postulate that sleep serves a

•maintenanceŽ role through which the integrity of organic

tissues and of psychic functions is restored. Still, other theo-

ries have suggested a role of sleep in processes such as en-

ergy conservation, the regulation of body temperature, and of

immune functions. No single theory can account for the di-

versity and complexity of the processes that occur during

sleep (Horne, 1988). Evidence from sleep deprivation studies

suggests that NREM sleep, particularly Stages 3 and 4 sleep,

is involved in restoration of physical energy, while REM

sleep, aside from its presumed role in the resolution of emo-

tional con”icts, has an important function in the consolida-

tion of newly acquired memories.

Several studies have examined the effects of total or par-

tial sleep deprivation on physiological (e.g., sleepiness),

psychological (e.g., mood, personality), and cognitive func-

tioning (e.g., memory, reaction time, vigilance). While stud-

ies performed on rodents have shown that death occurs within

three weeks of total sleep deprivation, if the animals are •res-

cuedin extremis,Žmany recover and appear normal, suggest-

ing that no permanent damage is induced by prolonged sleep