Non-REM sleep accounts
for about 75 to 80% of your total sleep each night, or about
six hours of non-REM sleep if you sleep eight hours in total.
You spend the remaining two hours–roughly 20% of the
night–in REM sleep.
It seems that with training,
people can gradually reduce their normal amount of sleep
by an hour or two without feeling too tired.
The main difference
between being awake and being asleep is that in the latter
state, consciousness does not intervene. When you’re
asleep, it’s somewhat as if your brain were closing
itself off and becoming a sort of “temporary autonomous
zone”. But in reality, your brain is never completely
cut off from the rest of the world: even during the deepest
stages of sleep, a strong enough stimulus from your environment
will be perceived by your brain and may cause you to wake
up.
On every normal day of our lives, each of us engages in two very
distinct kinds of behaviours:
sleeping and being awake. On the surface, these two behaviours
are so different from each other that even extraterrestrials who
came to observe life on Earth would notice the difference right
away. The entry in their ship’s log might read: “Earthlings
spend about two-thirds of each day upright and moving around and
the other third lying down and still.”
But what these extraterrestrials would
not notice right away, and what even Earth’s own scientists did not begin to discover
until the mid-20th century, is that sleep is far from a simple
matter of placing our mental and physical activities on hold. Sleep
is a genuine “second state", just as varied and complex
as the state of wakefulness, and characterized by major changes
in physiological characteristics such as body temperature, hormone
secretions, heart rate, and respiration rate. Also, far from being
uniform, sleep rotates through various stages that
occur in a characteristic order in the course of the night.
The stages of sleep that occur after
you first fall asleep consist of what is called non-REM
sleep, or slow-wave
sleep. The slow waves in question are the ones seen on the electroencephalogram
(EEG) trace (follow the Tool Module link to the left) of someone
who is in these stages of sleep; this trace consists of very slow,
high-amplitude oscillations.
These stages of non-REM sleep are followed by a stage of another
kind of sleep, in which, paradoxically, the EEG trace looks much
more like that observed in people who are awake: the waves are
faster, and their amplitude is smaller. Hence this kind of sleep
is often known as paradoxical sleep, the name
that it was given in 1959 by Michel Jouvet, a French neurobiologist
who conducted the first animal experiments concerning it. But this
form of sleep is also characterized by numerous rapid eye movements
(REMs) that take place underneath the closed eyelids, and hence
is usually referred to as REM sleep. Probably
the most fascinating characteristic of REM sleep is that it is
the stage of sleep in which we experience our most detailed and
strangest dreams.
Thus scientists go beyond
the observations of our hypothetical extraterrestrials and
distinguish not just two but three fundamental behavioural
states: wakefulness, non-REM sleep, and REM sleep. Each of
these states is generated by a specific pattern of brain
activity and accompanied by specific
changes in the activity of the body as a whole.
The
average adult human sleeps 7 to 8 hours per night. But about
10% of the adult population needs much more sleep at night –9
or even 10 hours–to feel wide awake during the day.
At the other end of the spectrum, some 5% of the population
can get along fine with only 5 or 6 hours of sleep. Thus
there is no particular amount of sleep that is ideal in itself.
The only real criterion for whether you’re getting
enough sleep is whether you feel in good shape during the
day.
The variations in the amount of sleep that people need
are determined both by their genetic make-up and by their
lifestyle, especially during adolescence. The same goes
for people’s tendency to go to bed early and wake
up early, or to go to bed late and wake up late. Thus it
would be just as silly to say that everyone should sleep
8 hours, from midnight to 8:00 AM, as it would be to say
that everyone should wear the same style of shoe, in a
size 8.
But regardless of whether people sleep 6 hours or 10 hours
per night, they all get about the same amount of deep non-REM
sleep: 100 minutes. People who sleep more total hours each
night devote some of the extra time to REM sleep, but more
of it to light non-REM sleep. Thus people who sleep less
might be said to have a higher concentration of deep non-REM
sleep than people who sleep more.
In today’s performance-obsessed society, people often
cite Napoleon, Louis XIV, and Churchill as examples of high
achievers who supposedly slept only a few hours each night.
But curiously, people fail to mention all the other high
achievers who, like Einstein, needed 10 and sometimes even
12 hours of sleep per night!
For most people, the
length of their sleep cycles remains relatively constant,
night after night, throughout their lives. Some people
have 90-minute cycles, while others have cycles of 100,
or 110, or 120 minutes, and so on.
People
who need lots of sleep and people who need less sleep all
get just about the same number of hours of deep non-REM
sleep each night. Thus it is REM sleep and especially
Stage 1 and Stage 2 non-REM sleep that vary the most
from one person to another and that are curtailed
in people who sleep fewer hours per night.
To better visualize these general patterns, researchers use a
type of graph called a hypnogram. A hypnogram
is nothing more than a minute-by-minute graphic record of a night’s
sleep, as captured by an EEG. The hypnogram thus shows not only
the sequence in which the various stages of sleep occur, but
also the times at which each stage starts and ends.
Another striking feature of the hypnogram is the recurrent cycles in
which the various stages of sleep follow one another, somewhat
like a series of waves: 1-2-3-4-3-2-1-REM-1-2-3-4-3-2-1-REM,
etc. Thus each descent into deep non-REM sleep is followed by
a climb back up directly into a period of REM (or paradoxical)
sleep.
The “train”
of a night of sleep comprises many “cars” that
are linked to one another in a specific order to form 4 or
5 major cycles.
Each cycle lasts about 1.5 to 2 hours,
and a person thus goes through 4 or 5 of these cycles in one
night’s sleep. Such
cycles are described as “ultradian rhythms”, in contrast
to the longer circadian rhythms, which have a period of about
24 hours.
The hypnogram also shows that deep
non-REM sleep (Stages 3
and 4) is deepest in the earlier part of the night. This explains
the great physically restorative powers associated with the first
few hours of sleep. Toward the end of the night, the pattern
reverses, and REM sleep, the kind of sleep generally associated
with dreaming, becomes
predominant.
We all dream every
night, even if we don’t remember our dreams. Memories
of dreams are very unstable and disappear within a few
minutes after we wake up. But it’s relatively easy
to remember your morning dreams, either by writing them
down as soon as you wake up, or by repeating
their content to yourself so that they leave
a trace in your long-term
memory.
The worries that we
experience during the day are often incorporated into our
dreams. U.S. psychologist Rosalind Cartwright studied a
large number of individuals who were going through divorces,
and she found that when these people were awakened from
REM sleep, most of the dreams that they reported dealt
with their marital concerns.
In experiments that
he conducted in the 1960s using cats, French neurobiologist
Michel Jouvet succeeded in destroying the
part of the brain that is responsible for the generalized
absence of muscle tonus during REM
sleep. This operation did not affect REM
sleep in any other way; it continued normally, except that
the cats’ muscles could now contract. What happened
then? With the inhibition on their muscle movements removed,
when the cats entered REM sleep, they would raise their
heads, get up, and arch their backs, clean themselves,
or stalk imaginary prey! In short, they engaged in the
usual behaviours that characterize their species when awake.
At the time, Jouvet had concluded that the cats were “living
their dreams”, and he thus associated REM sleep
with dreaming. But more recent findings have
raised questions about this interpretation.
DREAMS
Since
ancient times, dreams have often been regarded as divine
messages. With the work of Freud in the
early 20th century, dreams came to be seen as the “royal
road to the unconscious”. In the Freudian view, we construct
the plots for our dreams both from impressions that we have
gathered in the course of the day and from older memories that
have been transformed or disguised to escape the control of
our conscious minds.
It was not until some 50 years later, with the discovery of REM
(paradoxical) sleep in 1953, that dreams were first associated
with an observable physical state of the brain.
Henri Rousseau (1844-1910), The Dream,
1910;
Oil on canvas, 6’8½”
x 9’9½";
The Museum of Modern Art, New York.
The decisive
experiment that established this connection was conducted
by Nathaniel Kleitman and Eugene Aserinsky, the two U.S.
physiologists who had discovered REM sleep. Their experimental
protocol was quite simple: when the human subjects who
were sleeping in their laboratory displayed the rapid
eye movements typical of REM (paradoxical) sleep, the
researchers woke them up and asked them whether they had
just been dreaming. Some 75 to 95% of the subjects answered
that they had indeed been dreaming, and were able to recount
vivid dreams whose content was often fantastic, filled
with all kinds of details and emotions.
This discovery received huge attention, because it was the first
time that anyone had made an association between quantifiable
states of REM sleep and what people experience subjectively as
dreams.
But the mystery of dreams was still far from solved, because
there were still some 5 to 10% of subjects who, though awakened
from stages of non-REM
sleep rather than REM sleep, nevertheless said that they
had been dreaming. This percentage was even higher–as high
as 70%–when instead of asking the subjects “Have
you been dreaming?”, the researchers simply asked them “What
was passing through your mind?”
The states that the subjects reported in these cases were like
sensory impressions similar to the dreams of REM sleep, but of
shorter duration and with a more concrete, logical structure.
Thus REM sleep is not necessary for dreaming. A
certain kind of dream (one involving surprising juxtapositions)
does seem to be closely associated with REM sleep, but dreaming
and REM sleep are in no way synonymous. This distinction between dreaming, which
is a subjective state, and REM sleep, which
is a state of the brain, is fundamental. In other words,
dreaming is a phenomenon that can be described only qualitatively,
by the dreamer himself or herself, in an account that often involves
some distortions, whereas REM sleep can be subjected to precise
physiological measurements, in particular by means of its
EEG trace.
It turns out that
counting sheep isn’t really that much of a help in
falling asleep–it’s more of a distraction.
Source: www.ahajokes.com
There are plenty of
stories about people who went several days without any
sleep. In 1959, a disc jockey in New York stayed awake
for a week as a fundraising stunt for a charity. The researchers
who monitored him closely during this experiment found
that he soon began to have hallucinations, and then became
so paranoid that he refused to answer their questions.
Dr William C. Dement, an important sleep researcher, used
himself as the subject of a sleeplessness experiment. After
48 hours without sleep, he confirmed that he was experiencing
feelings of paranoia and suspiciousness toward his roommates.
Very soon, he also experienced problems with his vision,
as well as being unusually distracted and clumsy.
But the longest documented voluntary period of sleeplessness
involved a 17-year-old male from California who went 264
hours (11 days!) without sleeping. He did so on a bet, and
he did not use any stimulants to accomplish this feat. When
he was done, he slept like a rock for 15 hours, and after
a few more nights of sound sleep, he was as good as new.
Driving when you haven’t
had enough sleep is definitely a bad idea. In the United
States, an estimated 56 000 highway accidents per
year, involving some 1 500 fatalities, are believed
to be caused by drivers who have fallen asleep at the wheel.
If you’re feeling sleepy while you’re driving,
turning on the radio and opening your window will rarely
suffice to keep sleep at bay. The best thing to do is
stop your car on the side of the road and take a 15 to
20-minute nap. Drinking a cup of coffee may
also help for a few hours, but coffee needs about 30
minutes to take effect. Thus one good way to refresh
yourself a bit for the road is to drink a cup of coffee,
then take that nap while you wait for the coffee to kick
in.
Sleep restriction
therapy is a behavioural approach to treating
insomnia. For example, suppose you’re sleeping
only 6 hours per night because it’s taking you
2 hours to fall asleep. In this form of therapy, you
would let yourself stay in bed for a total of only 6¼ hours.
So if you always got up at 7:00 AM, you wouldn’t
let yourself go to sleep until 12:45 AM. This restriction
would help you to short-circuit the idea of performance
associated with sleep, while aggravating your sleep deprivation
very slightly. After a few nights of such treatment,
people who have been experiencing insomnia often fall
asleep in less than 15 minutes. They then gradually lengthen
the amount of time that they stay in bed, by 15 minutes
each week, until eventually they are getting a reasonable
night’s sleep.
SLEEP
DISORDERS
People
are too quick to label others as lazy if they accord a
lot of importance to their sleep. When we’re short of time, our hours of sleep are
often one of the first things we let go. But if there’s
one thing for which we should show more respect, it’s
our need for a good night’s sleep.
To understand the importance of sleep,
simply consider what happens to people who don’t sleep
enough (or, as the medical profession might put it, people
who show signs of sleep
deprivation syndrome). Obviously, these people feel
sleepy during the daytime. They may also tend to “sleep
in” on the weekend to pay back their “sleep debt”.
If they don’t manage to pay back this debt, they will
suffer several harmful consequences. First, they’ll be
less alert, and their ability to think and concentrate will be
diminished. Next, their reflexes will slow, and they will experience memory
disorders, muscle fatigue, and mood swings, and even display
aggressive behaviour and have difficulty in situating themselves
in time or space. They may also experience hallucinations similar
to those that most people experience when falling asleep, midway
between reality and dreaming. Such hallucinations are harmless
when you’re in bed, but can be fatal if you’re at
work or at the wheel (see sidebar). In fact, it is believed that
lack of sleep may be the hidden cause behind most of the “human
error” that causes accidents.
In the longer term, several studies have found, there is a relationship
between insufficient quantity and quality of sleep and a number
of chronic health problems, including obesity, diabetes, and
high blood pressure. In these three cases, the lack of sleep
disturbs regulatory mechanisms that are normally at work during
the night.
Lack of sleep may be voluntary or involuntary.
You may cut back on your hours of sleep voluntarily when
you work too far into the night, or when you stay up late to
pursue more entertaining nocturnal activities. But lack of sleep
can also be involuntary, when you try to sleep
but can’t manage to do so–in other words, when you
experience insomnia.
Insomnia often
sets in insidiously. Suppose, for example, that at first you
lose a few nights because you’re
worrying about having lost your job, or about your daughter’s
marital problems. After a few nights, when you go to bed, you
might also start worrying about whether you’ll be able
to fall asleep. These worries might be bad enough that they will
in fact make it harder for you to sleep. Having had yet another
bad night’s sleep, you’d go to bed even more worried
the next night, and the vicious cycle of insomnia would be well
under way.
More than half of all people with insomnia
can obtain some relief, if not a complete cure, by simply applying
the following recommendations for healthy living, which involve
changes both in attitudes and in habits. This “sleep re-education” approach
can be summarized as follows.
Attitudes
- If you can’t sleep, don’t blame yourself .
Putting pressure on yourself only makes it that much harder
to sleep.
- If you sleep less than 8 hours, don’t assume that
means you’re not getting enough sleep. It’s counterproductive
to expect to fall asleep when your head hits the pillow and
then sleep 8 hours straight every night.
- Don’t let yourself get
too upset about the situation.
- If you get a bad night’s sleep, try to plan a
pleasant activity when you start your day. That way,
you won’t get bogged down brooding about your sleep
habits, and you’ll prove to yourself that you can
have a good day even if you haven’t slept well.
Habits
- Wait for the right time to go to bed; do so only when
you feel very tired. If you don’t fall asleep after
15 or 20 minutes, get up and get out of your bedroom.
- Use your bed only for sleep or sex. Take the TV, reading
materials, and the telephone out of your bedroom. The
idea is to create strong mental associations between
this room and sleeping.
- Make your biological clock more regular by trying to
get up at the same time every morning (even on weekends)
regardless of how many hours of sleep you got the night
before.
- If you suffer from insomnia, don’t take any naps
during the daytime. Also, don’t engage in any intense
exercise, take a hot bath, or eat a heavy meal just before
going to bed, because all of these activities raise your
body temperature, which makes it harder to fall asleep.
Do, however, take a lukewarm bath or shower, because
that relaxes your muscles, which can help you to sleep.
- Avoid tea, coffee,
cola drinks, tobacco, alcohol,
and other stimulants before going to bed.
- Eat an evening meal, neither too light nor too heavy,
and not too close to bedtime. Dairy products and some
herbal teas may also help you to sleep.
- Regular, moderate physical exercise, not too close
to bedtime, also helps you to sleep. It can be something
as simple as an evening walk through your neighbourhood.
- Instead of worrying about whether you’ll be able
to fall asleep, try to develop some relaxing new habits
associated with bedtime–reading or writing a bit,
for example–because they too can help you to sleep.
- Doing relaxation exercises can help relieve tension that
may be keeping you from falling asleep. Breathing calmly
and deeply, or listening to soothing music, will help you
to relax. Anything that calms you down and alleviates stress
and anxiety is
conducive to sleep.
Compared with sedatives,
this sleep re-education approach does a more effective job of
modifying sleep habits permanently. When people’s insomnia
persists, taking sedatives for a few days can help them get back
into the habit of sleeping. But sedatives are only a temporary
solution, and a very imperfect one, because they can quickly
create a dependency, so that within a few weeks, they become
an integral part of the problem.
Most sedatives work by binding to GABA
receptors in the brain. In so doing, they inhibit the wakefulness
network, but they also disturb other circuits, such as those
for mood and memory. Also, sedatives often have side effects,
such as tremors, or sleepiness during the daytime. Thus the
real solution is to re-learn how to sleep.
A 20-minute nap would
do most people good, because it would make them more alert
and improve their ability to concentrate. The psychological
benefits in terms of their mood would also be appreciable.
But be careful: if you nap for too long (say, an hour),
you will go into too
deep a sleep, so you’ll feel sluggish
for a while after you wake up.
Naps are recommended for people who have accumulated a sleep
deficit, for people who are sleepy, and for people who suffer
from certain sleep disorders, such as narcolepsy.
But naps are not recommended for people with insomnia, because
they can wind up “borrowing” from their next
night’s sleep.
Research has shown that in extreme cases, such as when people
have to drive alone and cannot get several hours of sleep
in a row, taking 10-to-20-minute naps at regular intervals
over the course of the day can partly meet their need for
sleep and enable them to perform at minimally acceptable
levels for a few days. But their performance under these
conditions will always be far poorer than if they were completely
rested.
“Micronaps” lasting
no more than 5 seconds have been observed in truckers who
drive long hauls (several hundred kilometres). Even though
these drivers have slept perfectly well the night before,
these “absences”, which correspondent to the cyclical
variations in alertness, occur about
once every 90 minutes.
