| NORMAL
SLEEP
What is sleep?
Sleep is a
behavioral state characterized by little physical activity and
almost no awareness of the outside world. Most scientists think
that sleep does something important -- something vital for life,
although research has not yet identified specifically what sleep
does. Nevertheless, we all know when we need to sleep -- we can
feel this need. We also know when sleep has done its work -- we
feel rested and that we have slept enough. Another important feature
of normal sleep is that it can end quickly. Although a sleeper
may appear to be unconscious; unlike someone who is actually knocked-out,
anesthetized or in a coma; a sleeping person can be easily awakened
and can resume normal waking activity within a minute or two.
Sleep Stages
Sleep is an
active, highly organized sequence of events and physiological
conditions. Sleep is actually made up of two separate and distinctly
different states: 'non-rapid eye movement sleep' (NREM sleep)
and 'rapid eye movement sleep' (REM sleep) or dreaming sleep.
The NREM and REM types of sleep are as different from one another
as both are different from wakefulness.
NREM sleep
is further divided into stages 1 - 4 based on the size and speed
of the brain waves generated by the sleeper. Stages 3 and 4 of
NREM sleep have the biggest and slowest brain waves. These big,
slow waves are called delta waves and stages 3 and 4 sleep combined
are often called 'slow-wave sleep' or 'delta sleep'.
During REM sleep you can watch the sleeper's eyes move around
beneath closed eyelids. Some scientists think that the eyes move
in a pattern that relates to the visual images of the dream. We
are almost completely paralyzed in REM sleep -- only the heart,
diaphragm, eye muscles and the smooth muscles (such as the muscles
of the intestines and blood vessels) are spared from the paralysis
of REM sleep.
Deep Sleep
Doctors have
tried to determine what type of sleep is the deepest sleep. To
do this, they measure how much noise or other alerting stimulation
is required to awaken a sleeper from the various types of sleep.
It is always possible to awaken someone who is sleeping, as opposed
to, say, someone who is in a coma. However, people in stages 3
and 4 sleep require the most stimulation to awaken. Therefore,
this phase of sleep is often thought of as 'deep sleep'. Also,
large spurts of growth hormone are secreted during stages 3 and
4 NREM sleep. Consequently, these stages of sleep are thought
to restore the body from the wear and tear of waking activity.
REM or Dream
Sleep
People in
REM sleep also tend to be quite difficult to awaken, but this
finding is variable -- sometimes even the slightest noise can
awaken a person in REM sleep. Nevertheless, because it is often
difficult to awaken a person from REM sleep, many doctors think
also of REM sleep as a 'deep' phase of sleep.
There are
many theories about the function of REM sleep and dreaming --
ranging from 'safe, socially acceptable, wish fulfillment' to
'consolidation of memories' to 'providing necessary stimulation
to the entire nervous system during development'. Researchers
used to think that REM sleep was necessary for normal psychological
function, because experimental REM deprivation caused some subjects
to behave strangely. The notion that we need REM sleep for our
mental health is not accepted now, because, among other reasons,
people have uneventfully withstood long and almost complete REM
deprivation. Some experiments have shown that REM deprivation
improves depression. However, REM sleep must still do something,
because rats will die after 2 - 3 weeks if they are deprived of
REM sleep by a special experimental computer that wakes them up
each time REM sleep is achieved. Whatever REM sleep does, it is
clear that every aspect of existence, from the body's manufacture
of proteins to sexual arousal including orgasm, is influenced
by REM sleep. It is likely that the ultimate explanation of REM
sleep will be very broad -- not simply focused on one physiologic
function.
Why do we
sleep?
We sleep because
we get sleepy and we cannot work if we get too sleepy. That is
the simplest and yet the most profound answer to this question.
The scientific truth is, however, that we do not yet know why
we get sleepy. We know that all mammals as well as some birds
and reptiles sleep. Many doctors think sleep comes in order to
get rid of certain chemicals that build up in our bodies during
the day's activities. Brain research in the 1960's and 1970's
has identified several molecules involved in cell-to-cell communication
within the brain as being important for sleep. More recent work
has isolated products of the body's immune system that seem to
be sleep-inducers.
Circadian
Rhythm or Our Biological Clock
Feeling sleepy
is not the whole story of our sleep-wake cycle. Some timing mechanism
is also involved. We know that every living thing composed of
cells with a nucleus has a daily cycle of activity and inactivity
(if not actual wakefulness and sleep). The timing and control
of the wakefulness-sleep cycle depends on one or more biological
clocks in our bodies. These clocks are sensitive to light and
have evolved over the ages in close approximation to the 24-hour
light-dark cycle of our world. Thus, sleep seems to be an unavoidable
part of human behavior. In humans, sleep is physiologically programmed
to come each day, either in one long bout (about 6 - 8 hours each
night) or in two shorter bouts (a 5 - 6 hour sleep at night and
a 1 - 2 hour nap in the afternoon). The timing of sleep and wakefulness
is controlled to a great extent by our exposure to the natural
light and dark cycles of the earth. All humans tend to sleep in
the dark and move about in the light. It takes the human body
several days to change to a different light-dark schedule such
as when one flies from New York to New Dehli. In fact, the influence
of light on the timing of sleep is so powerful that doctors are
now using exposure to bright light as a treatment to reset the
sleep clock of people who have somehow disrupted their schedule.
In the extreme,
sleep does seem to be necessary for life. Experimental rats die
if they are completely deprived of sleep for longer than 1 - 4
weeks. However, do not worry. The experimental deprivation was
done by means of special computers and alarm systems -- it is
not possible for even the poorest of human sleepers to lose so
much sleep that life is threatened.
The figure
illustrates this interplay and shows over a period of 48 hours,
a two-peak pattern for each day. There is a period with markedly
increased sleep tendency in the early morning hours between 3
and 6 AM and a smaller but reliable afternoon peak between 1 and
3 PM. This is the so-called siesta effect or afternoon slump.
Both periods of increased sleep tendency can be exaggerated by
sleep promoting factors such as alcohol consumption and sleep
deprivation. Errors and reduced productivity peak at the times
of maximum sleep tendency.
How much sleep do we need?
There is no
'normal' amount of sleep. The average amount of sleep for adults
is 7 - 8 hours. But the range of nighttime sleep duration must
be expanded to between 6 - 9 hours in order to include the large
majority of people. Therefore, a few people feel fine with as
little as 5 hours of sleep, while others require more than 10
hours to feel refreshed and alert throughout the day. The amount
of sleep you need is that optimum amount which allows you to function
throughout the day without feeling drowsy when you sit quietly
and try to pay attention to something.
We cannot,
for very long, force ourselves to sleep much less or much more
than this optimum amount. Several nights of sleeping an hour less
than our usual amount will leave us sleepy and ineffective in
the day. Conversely, several nights of staying in bed and trying
to sleep an hour more than our optimum amount will leave us sleeping
poorly with more awakenings -- particularly in the early morning.
Doctors believe that the optimum amount of sleep each person needs
to remain alert during the day is biologically different from
person to person. To a great degree, our optimum sleep need is
determined by heredity. Scientists have found, for instance, that
strains of mice can be selectively bred to sleep considerably
more or considerably less than the average mouse.
Sleep and
Aging
Many people
believe we need less sleep as we get older. This is probably not
true. It seems that during infancy and in adolescence there are
increases in sleep need, perhaps brought on by developmental changes.
However, the best research available indicates that healthy elderly
people sleep about as much as they did when they were young adults.
The idea that the elderly sleep less probably comes from the fact
that elders often have medical conditions that interfere with
their sleep. This is why most elderly people are 'light sleepers'
at night, yet they frequently dose-off during the day.
This type
of light sleep and dozing pattern is what sleep researchers would
expect if a person is awakened again and again while they try
to sleep. In fact, research on repetitive sleep disruption, called
'sleep fragmentation', has shown that the rate of sleep disruptions
determines whether or not the sleep is felt to be satisfactorily
restorative, and whether or not there is proper alertness the
next day. These kinds of studies show that disruptions every minute
will greatly reduce the restorative value of sleep. However, disruptions
every five minutes will affect restoration much less -- even when
total sleep time is the same for the one-per-minute and five-per-minute
rates of disruption. Thus, scientists believe that for refreshing
sleep, it is not just the total amount of sleep that is important.
Sleep must be continuous as well.
Napping and
"Siestas"
Certain cultures
use the siesta very successfully. However, siesta cultures are
relatively consistent in napping. In most western cultures, napping
is not consistent day after day. If you want to nap, nap at the
same time each day and for the same duration, particularly if
you are prone to insomnia. Many people complain about Sunday-night
insomnia. What usually happens in these cases is that the person
napped on Sunday from, say, 2 to 5 in the afternoon and then could
not get to sleep at the usual time Sunday night. That is why keeping
a consistent schedule is the best strategy.
With respect
to occasional napping, one important advantage is that even a
30 - 60 minute nap greatly helps a person counter sleep loss.
Studies have shown that the first hour or so of sleep is most
potent in relieving the effects of missing a night's sleep.
What should
I do if I am not sleeping well?
Try and identify
the nature of your sleep problem. Is it difficulty sleeping or
excessive sleepiness? There are a number of screening tests that
can help you determine if you have normal sleep or might have
a sleep problem. Take our sleep screening test and see if you
fit in to one of the categories identified. Then you can get more
information about that problem and how to help yourself or how
and where to obtain professional help if needed.
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