Delanceyplace: The Five Stages Of Sleep
Until the middle of the twentieth century, scientists thought that sleep was an unchanging condition during which time the brain was quiet. The discovery of rapid eye movements in the 1950s upended that. Researchers then realized that sleep is
made up of five distinct stages that the body cycles through over roughly ninety-minute periods. The first is so light that if you wake up from it, you might not realize that you have been sleeping. The second is marked by the appearance of sleep-specific brain waves that last only a few seconds at a time. If you reach this point in the cycle, you will know you have been sleeping when you wake up. This stage marks the last stop before your brain takes a long ride away from consciousness, writes David K Randall.
Stages three and four are considered deep sleep. In three, the brain sends out
long, rhythmic bursts called delta waves. Stage four is known as slow-wave sleep
for the speed of its accompanying brain waves. The deepest form of sleep, this
is the farthest that your brain travels from conscious thought. If you are woken
up while in stage four, you will be disoriented, unable to answer basic questions,
and want nothing more than to go back to sleep, a condition that researchers call
sleep drunkenness. The final stage is REM sleep, so named because of the rapid movements
of your eyes dancing against your eyelids. In this type of sleep, the brain is
as active as it is when it is awake. This is when most dreams occur.
Your body prepares for REM sleep by sending out hormones to effectively paralyze
itself so that your arms and legs don't act out the storyline you are creating in
your head. This attempt at self-protection doesn't always work perfectly, and when
that happens, what follows is far from pleasant. Sometimes, it is the brain that
doesn't get the message. This can lead to waking up in the middle of the night
with the frightening sensation that you can't move your limbs. In the Middle Ages,
this was thought to be a sign that a demon called an incubus was perched on the
chest. Instead, this condition is simply a flaw in the sleep cycle, a wrong-footed
step in the choreography of the brain's functions that allows a person to become
conscious when the body thinks the brain is still dreaming.
At other times, the body doesn't fully paralyze itself like it is supposed to.
This is the root of a series of problems called parasomnias, of which sleepwalking
... is by far the most mild. Patients with REM sleep disorder, for instance, sometimes
jump out of a window or tackle their nightstand while they are acting out a dream.
Some patients I spoke with who have this disorder have resorted to literally tying
themselves to the bedpost each night out of the fear that they will accidentally
commit suicide.
Author: David K. Randall
Title: Dreamland
Publisher: Norton
Date: Copyright 2012 by David K. Randall
Pages: 23-24
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