| What is REM
sleep and why do we Dream?
We typically spend more than 2 hours each night dreaming.
Scientists do not know much about how or why we dream.
Sigmund Freud, who greatly influenced the field of psychology,
believed dreaming was a "safety valve" for
unconscious desires.
Only after 1953, when researchers first described REM
in sleeping infants, did scientists begin to carefully
study sleep and dreaming. They soon realized that the
strange, illogical experiences we call dreams almost
always occur during REM sleep. While most mammals and
birds show signs of REM sleep, reptiles and other cold-blooded
animals do not.
REM sleep begins with signals from an area at the
base of the brain called the pons . These signals travel
to a brain region called the thalamus, which relays
them to the cerebral cortex - the outer layer of the
brain that is responsible for learning, thinking, and
organizing information. The pons also sends signals
that shut off neurons in the spinal cord, causing temporary
paralysis of the limb muscles.
If something interferes with this paralysis, people
will begin to physically "act out" their dreams
- a rare, dangerous problem called REM sleep behavior
disorder. A person dreaming about a ball game, for example,
may run headlong into furniture or blindly strike someone
sleeping nearby while trying to catch a ball in the
dream.
REM sleep stimulates the brain regions used in learning.
This may be important for normal brain development during
infancy, which would explain why infants spend much
more time in REM sleep than adults (see Sleep: A Dynamic
Activity). Like deep sleep, REM sleep is associated
with increased production of proteins. One study found
that REM sleep affects learning of certain mental skills.
People taught a skill and then deprived of non-REM sleep
could recall what they had learned after sleeping, while
people deprived of REM sleep could not.
Some scientists believe dreams are the cortex's attempt
to find meaning in the random signals that it receives
during REM sleep. The cortex is the part of the brain
that interprets and organizes information from the environment
during consciousness. It may be that, given random signals
from the pons during REM sleep, the cortex tries to
interpret these signals as well, creating a "story"
out of fragmented brain activity.
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