162 ChapTER 5 Body Rhythms and Mental States
leave a room.” Sleep appears to provide a time-
out period, so that the body can eliminate waste
products from muscles, repair cells, conserve or
replenish energy stores, strengthen the immune
system, and recover abilities lost during the day.
When we do not get enough sleep, our bodies
operate abnormally. Although most people can
still get along reasonably well after a day or two of
sleeplessness, sleep deprivation that lasts for four
days or longer becomes uncomfortable and soon
becomes unbearable. This is why forced sleepless-
ness is a weapon of torture.The Mental Consequences of Sleepless-
ness. Sleep is also necessary for normal mental
functioning. Chronic sleep deprivation increases
levels of the stress hormone cortisol, which may
damage or impair brain cells that are necessary
for learning and memory (Leproult, Copinschi
et al., 1997). Also, new brain cells may either fail
to develop or may mature abnormally (Guzman-
Marin et al., 2005). Perhaps in part because of
such damage, after the loss of even a single night’s
sleep, mental flexibility, attention, and creativ-
ity all suffer. After several days of staying awake,
people may even begin to have hallucinations and
delusions (Dement, 1978).
Of course, sleep deprivation rarely reaches
that point, but people do frequently suffer from
milder sleep problems. According to the National
Sleep Foundation, about 10 percent of adults are
plagued by difficulty in falling or staying asleep.
The causes of their insomnia include worry and
anxiety, psychological problems, physical prob-
lems such as arthritis, and irregular or overly
demanding work and study schedules. In addition,
many drugs interfere with the normal progression
of sleep stages—not just the ones containing caf-
feine, but also alcohol and some tranquilizers. The
result can be grogginess and lethargy the next day.they will spend a longer time than usual in the REM
phase, and it will be hard to rouse them. Electrical
brain activity associated with REM may burst
through into non-REM sleep and even into wake-
fulness, as if the person is making up for something
he or she had been deprived of. Some researchers
have proposed that this “something” is connected
with dreaming, but that idea has problems. For one
thing, in rare cases, brain-damaged patients have
lost the capacity to dream, yet they continue to show
the normal sleep stages, including REM (Bischof &
Bassetti, 2004). Moreover, although nearly all mam-
mals experience REM sleep, it seems unlikely that
rats or moles have the cognitive abilities required to
construct what we think of as dreams.
Explore the Concept Virtual Brain: Sleep and
Dreaming at MyPsychLabWhy We Sleep LO 5.6
A leading sleep scientist, Jerome Siegel (2009),
observes that sleep falls along a continuum of
states. At one extreme is hibernation, which
occurs, for example, in bears, bats, and many
rodents. At the other extreme is sleeplessness for
significant lengths of time; birds don’t sleep while
they are migrating, walruses may stop sleeping for
days at a time, and whale mothers and their calves
remain awake for several weeks after birth. The
reason for this variation in sleep patterns, Siegel
argues, has to do with which strategy is benefi-
cial for the species. Lions sleep long and deeply,
whereas their favorite prey, giraffes, have one of
the lowest recorded sleep durations—giraffes had
better not sleep deeply if they are going to survive!
In human beings and other species, sleep
increases efficiency, in part by decreasing muscle
tone and brain and body metabolism during peri-
ods of inactivity. This process, says Siegel (2009),
is “analogous to turning out the lights when youWhatever your age, sometimes the urge to sleep is irresistible, especially because in fast-paced modern societies,
many people of all ages get less sleep than they need. Late hours or inadequate sleep won’t do anything for your
grade-point average. Daytime drowsiness can interfere with reaction time, concentration, and the ability to learn.