Why Do We Dream?
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
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 (see
figure 2 ). 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
What Happens When You Sleep? ). 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.
What Happens When You Sleep?
The Different Stages of Sleep
Source: National Institute of Neurological Disorders and