Stages of Sleep:
Dreaming, and Stages of Sleep
Shakespeare wrote Hamlet today, his famous line "To sleep,
perchance to dream" might sound a little different: "To
sleep, certainly to dream--but I only remember the dreams I have
during REM sleep stages."
nearly as poetic, but then again, much more intriguing. In Shakespeare's
time, most people thought of sleep as an unchanging, dormant period
of little interest. Hardly anything was known about sleep or dreaming.
In fact, it wasn't until the discovery of REM sleep at the relatively
late date of 1953 that scientists knew much about sleep at all!
infants 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. At first they assumed that REM sleep occurred only
in babies, but later investigations proved it occurs not only in
all humans, but in all mammals-even in birds.
typically have about three to five periods of REM sleep per night.
The first rapid eye movement period usually begins about 70 to 90
minutes after we fall asleep. These periods occur at intervals of
one to two hours and vary in length from five minutes to more than
an hour. Periods of REM sleep seem to be shorter at the beginning
of the night and longer toward morning.
20 percent of sleep is REM sleep. If you sleep seven or eight hours
a night, only around an hour and half of that time is spent in REM
sleep. However, the relative amount of REM sleep varies considerably
with age: babies spend more than 80 percent of total sleep time
in REM mode, while people over 70 spend less than 10 percent.
those of us who think of sleep as a peaceful, largely static activity,
we should think again: REM sleep is characterized by rapid, low-voltage
brain waves and irregular breathing and heart rate. And the eye
movements themselves, called saccades, are indeed rapid: The saccade
is the fastest movement of an external part of the human body. The
peak angular speed of the eye during a saccade reaches up to 1,000
degrees per second. However, our muscles do largely "turn off"
during REM sleep, effectively paralyzing the body, except for involuntary
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sleep is divided into four stages of increasing depth, leading to
REM sleep. In stage one, people often believe they are fully awake,
although they are beginning to lose conscious awareness of the external
environment. This stage can be thought of as a gateway between waking
four is the deepest stage of sleep. In contrast to REM sleep, during
stage four the brain waves are slow and high voltage; breathing
and heart rate are slow and regular; and blood pressure is low.
It is very difficult to wake people who are in this state, and,
if they do wake up, they are extremely groggy. This is the stage
in which night terrors and sleepwalking occur.
no "perchance" about it: Everyone dreams, whether they
remember their dreams or not. But most dreams-and almost all the
dreams we can recall upon waking-occur during REM sleep.
that is the reason our bodies' muscles turn off during REM periods:
If they didn't, we would physically respond to the vivid dreams
we have during REM sleep. Studies of people with malfunctioning
REM systems show that those folks thrash around in their sleep,
often punching their bedmates or hurting themselves as they act
out their dreams.
Questions, Theories, and Fun Facts
know sleep is vital to our bodies and that REM sleep, in particular,
seems to be intrinsically important, as it is so physiologically
different from the other phases of sleep. If dreams turn out to
have some important function for humans (we still don't know whether
animals dream), then perhaps we need REM sleep solely in order to
theory is that the amount of REM sleep per night in a species is
closely correlated with the developmental stage of newborns. The
platypus for example, whose newborns are completely helpless and
undeveloped, has eight hours of REM sleep per night; animals that
can hunt, eat, keep warm, and defend themselves soon after birth
(for example, dolphins or horses) need almost no REM sleep.
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