NEW FOUND WONDERS OF SLEEP
A U.S. study, published in the journal Nature, has found that sleep
apparently restores memories that were lost during a hectic day.
It's not just a matter of sleep recharging the body physically, reports The
Associated Press. Researchers say sleep can rescue memories in a biological
process of storing and consolidating them deep in the brain's complex circuitry.
"We all have the experience of going to sleep with a question and waking up with
the solution," says Daniel Margoliash, a professor of neurobiology at the
University of Chicago.
"Working parents, extracurricular activities, round-the-clock TV and easy
internet access have pushed children's bedtime later and later," writes Ana
Veciana-Suarez in The Miami Herald.
"Of the many rules I grew up with, of all those 'Don'ts' that formed the
boundaries of my childhood, a firm bedtime remains one of my favourites,
a steadfast example of commonsense parenting. I stick to it as much for myself
as for my kids. . . . Maybe it's time to make choices. Maybe that 8 p.m. tae
kwon do class is not as important as a good night's sleep."
Globe and Mail:
The following two posting from the websites Encarta and Wikipedian gives the
currently available information on SLEEP AND DREAMING in the western science....
SLEEP: WHAT, WHY & HOW
Article Outline: Introduction; Kinds of Sleep; Mechanisms of Sleep;
Patterns of Sleep; Functions of Sleep; Sleep Disorders
Sleep, natural state of rest characterized by reduced body movement and
decreased awareness of surroundings. Sleep is distinguished from other sleeplike
states, for instance, hibernation or coma, because it is easily interrupted by
external stimulation, such as a loud noise. While the
exact purpose of sleep remains a mystery, sleep researchers have made
enormous strides in understanding how sleep occurs in humans and other animals,
and the nature of sleep disorders.
All mammals and birds sleep, but scientists are unsure if reptiles, fish,
insects, and other life forms sleep. Total sleep amounts differ greatly across
species. In general, large mammals tend to sleep less than small mammals. The
giraffe and elephant, for instance, sleep only 2 to 4 hours a day, while bats,
opossums, and armadillos sleep 18 hours a day or more.
While sleeping, most animals close their eyes and adopt particular positions
referred to as sleep postures. Humans typically lie down to sleep, for example,
while giraffes kneel and bend their long necks around to rest their heads in the
crook of their hind knee. Some animals, such as dolphins, can sleep while they
Scientists measure sleep by placing metal electrodes on the scalp to record the
electrical activity of the brain. This procedure, called electroencephalography
(EEG), enables sleep researchers to evaluate levels of brain activity at
different times during sleep. Researchers use similar electrodes to record a
sleeping person’s body muscle activity and rate of eye movement.
II Kinds of Sleep
In the 1950s American physiologists Eugene Aserinsky and Nathaniel Kleitman
reported that periods of eye movement and twitching occur during sleep. They
named these periods rapid eye movement (REM) sleep. Aserinsky and Kleitman found
that when subjects were awakened during REM sleep, they reported vivid dreams.
Scientists believe that REM sleep is closely related to wakefulness because
brain wave activity during REM sleep is marked by short, rapid wave patterns
similar to brain wave activity of the waking state.
Sleep characterized by little or no eye movement is called nonrapid eye movement
(NREM) sleep. During NREM sleep, breathing and heart rates slow down, and body
temperature and blood pressure often decrease. When awakened from periods of
NREM sleep, subjects are much less likely to report vivid, action-packed dreams.
Brain wave activity during NREM sleep is dominated by large, slow waves that
contrast markedly to the short, rapid wave patterns characteristic of REM sleep
and the waking state.
Sleep studies based on EEGs have shown that during a normal night, humans cycle
between REM sleep and NREM sleep in very regular patterns. In adults aged 20 to
60, REM sleep occurs about every 90 minutes. In this 90-minute cycle, humans
fall into progressively deeper stages of NREM sleep, then cycle back through the
stages until they enter REM sleep, and then the cycle begins again. In a normal
night, the number of REM periods varies from four to six, depending on the
length of the episodes and the total time asleep. REM episodes in the beginning
of the night usually last about ten minutes and, during the night, grow
progressively longer, lasting up to 30 minutes in the early hours of the
morning. Most adults spend about 20 percent of their total sleep time in REM
III Mechanisms of Sleep
Sleep research shows that certain regions of the brain play critical roles in
sleep. The brainstem, the portion of the brain just above the spinal cord, is
critical in REM sleep control, while the forebrain is particularly important in
NREM sleep control.
REM sleep is generated by a region in the brainstem, called the pons, and
adjacent portions of the midbrain. Researchers have found that chemical
stimulation of the pons will induce very long periods of REM sleep, while damage
or injury to this brain region can greatly reduce or even prevent REM sleep.
Animal studies have found that some neurons within the pons and midbrain are
active only in REM sleep while other neurons in this region are entirely
inactive only during REM sleep. Together, these neurons control muscle tone and
other aspects of REM sleep. In REM sleep, most muscles in the body are turned
off. This lack of muscle tone, called atonia, is particularly complete in the
muscles of the back, neck, arms, and legs. Less affected are the muscles that
move the eyes and the muscles responsible for breathing.
The combined effect of the sleep-active and sleep-inactive neurons explains why
sleepers do not physically act out the vivid dreams they have during REM sleep
and instead only twitch or make small movements. Humans with malfunctioning REM
sleep-active and REM sleep-inactive systems thrash around in their sleep, often
punching their bedmates or hurting themselves as they act out their dreams.
The neurons most critical to NREM sleep control are in the basal forebrain, the
region of the brain lying in front of the hypothalamus. Researchers have found
that people who have suffered damage or injury to the neurons in the basal
forebrain have difficulty falling and staying asleep. Animal studies have shown
that this area contains neurons that become most active before and during sleep.
Many of these neurons are activated by heat, which explains how a warm bath or a
hot day at the beach causes sleepiness.
IV Patterns of Sleep
A mounts of sleep vary significantly with age and even between individuals.
Newborns sleep the most—a newborn baby sleeps between 17 and 18 hours a day,
spending nearly half of that time in REM sleep. Both REM and NREM sleep decrease
with age, and by age five, children sleep between 10 and 12 hours a day,
spending about 20 percent of that time in REM sleep.
The average young adult seems to need about 8 hours of sleep per night to
function optimally during waking hours. Some people, however, sleep just 6 or 7
hours a night, while others need more than 9 hours to feel rested. The elderly
spend less time in deep NREM sleep, and their sleep is more easily interrupted.
REM sleep amounts also vary across animal species, depending on the size of the
animal and its level of development at birth. The size of an animal seems to
affect the type of sleep it experiences—small animals tend to spend more time in
REM sleep. Animals that are born in relatively helpless states, such as opossums
and humans, generally have more REM sleep as newborns than animals that can
hunt, eat, keep warm, and defend themselves soon after birth, for instance
guinea pigs or horses. Even as animals age into adulthood, those born relatively
immature continue to spend more time in REM sleep than animals that are mature
One of the myths about sleep is that smarter animals spend longer periods in REM
sleep. REM sleep amounts in humans or primates—believed to be the most
intelligent members of the animal kingdom—are not remarkably high or low.
Rather, they seem to fit the general rule of level of maturity at birth. REM
sleep amounts in whales and dolphins—animals also recognized for their high
intelligence—are among the lowest seen in any mammal. These animals, both born
relatively mature, also seem to fit the general rule relating REM sleep amounts
to level of maturity at birth.
V Functions of Sleep
Although no one knows for sure why we sleep, there are a number of theories.
Sleep may have evolved to protect animals from their predators by reducing their
activity during the times when they are most vulnerable.
Research has shown that REM and NREM sleep may serve specific biological
functions. Sleep deprivation studies reveal that humans and other animals
respond to sleep loss in the same way. When study subjects are deprived of REM
sleep, they tend to spend longer periods in REM sleep during their next sleeping
period to make up for the loss. REM sleep after deprivation is more intense,
with more eye movements per minute than in normal REM sleep. Similarly, subjects
deprived of NREM sleep usually spend more time in NREM sleep afterward. EEGs
measuring brain activity show that this rebound NREM sleep also differs from
normal NREM sleep. This research suggests that the body needs adequate levels of
both REM and NREM sleep. This conclusion has led many sleep researchers to
believe that the two kinds of sleep serve different biological purposes,
although the exact functions remain unclear.
The relationship between maturity at birth and REM sleep suggests that REM sleep
plays a role in the development of the brain. REM sleep may have a related
function later in life as well. However, that function remains a mystery.
VI Sleep Disorders
People who suffer from the most common sleep disorder, insomnia, have difficulty
falling or staying asleep. Sleepiness caused by insomnia reduces concentration
and slows reaction time during waking hours, leading to reduced productivity and
accidents. One in three adults experiences some degree of insomnia at one time
or another, especially during periods of stress. Longer-lasting cases of
insomnia, called chronic insomnia, are less common and may be caused by a number
of factors in addition to stress, including imbalances in body chemistry or
other medical conditions.
Taken under the guidance of a qualified physician, sleeping pills are an
effective treatment for temporary insomnia and may help some chronic insomnia
patients. In some cases of insomnia, psychological treatments and physical
exercise programs help patients identify or manage stress, enabling them to
sleep better. Recent work has suggested that melatonin, a hormone naturally
released into the bloodstream during the hours of darkness, may play a role in
synchronizing sleep to a 24-hour cycle. Results from studies of the effects of
melatonin on human sleep have been inconsistent. However, some evidence suggests
that supplements of this hormone combat insomnia in older people who are
Narcolepsy is a sleep disorder that affects both NREM sleep and REM sleep
mechanisms. Narcoleptics are persistently sleepy and experience periodic losses
of muscle tone called cataplexy. During cataplectic attacks, the narcoleptic’s
muscles weaken, and if the attack is severe, the narcoleptic falls to the
ground. Cataplectic attacks are triggered by sudden strong emotional reactions,
such as laughter. A related symptom, called sleep paralysis, can occur when the
narcoleptic is lying down, prior to falling asleep or just after awakening. At
these times the person may lose muscle tone, resulting in an apparent paralysis,
while remaining fully awake. Sleep paralysis can be terrifying if the
narcoleptic does not realize that it is not life threatening. Animal studies
have shown that the loss of muscle tone experienced by narcoleptics in waking
results from an activation of the REM sleep-active and an inactivation of the
REM sleep-inactive systems that normally function to reduce muscle tone in REM
sleep. Narcoleptics are treated with stimulants to block sleepiness and with REM
sleep suppressants to block cataplexy.
Children often experience one of several sleep disorders. Nocturnal enuresis,
commonly known as bedwetting, typically occurs during NREM sleep. Sleep talking
and sleepwalking also usually occur during NREM sleep (see Somnambulism). Night
terrors, typically marked by a scream and a terrified, confused awakening,
affect many children. These disorders do not indicate any serious neurological
or behavioral problem. Children suffering from them usually outgrow them by
puberty, although sleep talking and sleepwalking may persist into adulthood.
In another common disorder, sleep apnea, relaxation of the muscles of the tongue
and the soft palate at the base of the throat, allows the breathing passage to
collapse in individuals with a narrow airway. Although chest movements may
continue, no air flows into the lungs and oxygen levels in the blood decrease.
When blood oxygen levels fall too low, the person briefly wakes to take a
breath. This gasping breath can produce a loud, characteristic snort. The cycle
of sleeping, airway collapsing, waking, and sleeping repeats, often hundreds of
times in a night. Individuals with sleep apnea do not remember these brief
awakenings and believe they slept through the night. However, the interrupted
sleep leaves the individual exhausted in the morning and sleepy throughout the
day. If left untreated, sleep apnea may also cause cardiovascular problems and
greatly shorten life span. Effective treatments are available at medical centers
specializing in sleep disorders. One treatment, called
continuous-positive-airway-pressure (CPAP), uses a mask to deliver a stream of
air through the nose, preventing airway collapse, restoring normal sleep.
Sometimes surgical treatments that enlarge the airway can be effective.
Jerome M. Siegel, B.S., Ph.D.
Professor, Department of Psychiatry, University of California, Los Angeles;
Chief of Neurobiology Research, Sepulveda Veterans Affairs Medical Center, Los
Angeles. Associate Editor, Sleep.
How to cite this article:
"Sleep," Microsoft® Encarta® Online Encyclopedia 2003
http://encarta.msn.com © 1997-2003 Microsoft Corporation. All Rights Reserved.
© 1993-2003 Microsoft Corporation. All Rights Reserved.
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Sleep is the process in which
humans and other
animals periodically rest, with decreased responsiveness to the
surrounding world. Sleep occurs cyclically, roughly every 24 hours even
though the average human inner
body clock usually runs a 24.5-25.5 hour cycle. This cycle gets reset
daily (to match 24 hours) with various stimuli such as
sunlight. One of the correlates of this cycle is the level of
melatonin, which is high at times when we tend to sleep. Some people
sleep twice every 24 hours (afternoon nap, siesta).
Animals vary widely in their amounts of sleep, from 2 hours a day for
giraffes to 20 hours for
dolphins "sleep" with alternate hemispheres of their
brains asleep and the other awake. Seals need to do this so they can
breathe above water while sleeping. Many animals
hibernate in a deep sleep during winter to save warmth and energy. A
similar kind of sleep is
estivation, which is hibernating to escape the heat of summer.
Though there is still much debate about the
evolutionary origins and purposes of sleep, it is widely
theorised that one major function that occurs during sleep is
consolidation and optimization of memories. Another function of sleep is
the conservation of energy during inactivity. Other theorised functions
- promotion of physiological processes which rejuvenate the body and the
mind: some studies suggest sleep restores
neurons and increases production of brain
proteins and certain
- unlearning during sleep prevents the brain from becoming overloaded
with knowledge; and
- avoidance of danger: prehistoric mankind adapted the pattern of
caves at night, because it protected humans from species
physiologically suited to function well in the dark, such as
Sleep proceeds in cycles of
REM phases. Each phase has a distinct physiological function.
Dreaming, for example, appears to occur during REM sleep.
Some medications (for example,
sleeping pills) can suppress selective stages of sleep. This can result
in obtaining sleep (loss of consciousness) without fulfilling its
physiological function (memory remolding).
A majority of sleep disorders which originate within the body (for
ASPS) result from errors in synchronization of sleep with the body
clock. Only a fraction of sleep problems are organic and cannot be resolved
chronotherapy. One of the simplest solutions towards getting good sleep
free-running sleep. In simple terms, free-running sleep requires
throwing away your alarm clock. Free-running sleep can resolve the majority
of synchronization-dependent sleep disorders, but usually cannot be employed
due to the resulting loss of synchronization of sleep with the outside world
(including day-night cycle).
Sleep disorder is often observed in patients with a number of
psychiatric problems (e.g.
Sleep can also refer to the state of hypnosis.