We typically spend more than two hours each night dreaming but there is much that scientists do not know about how or why we dream.
Freud, who greatly influenced the field of psychology, believed dreaming to be a ’safety valve’ for unconscious desires, but it was not until the 1950s that scientists were able to study sleep and dreaming and come to some of their own conclusions.
In 1953, Eugene Aserinsky of the University of Chicago noticed that the eyes of sleeping babies moved beneath their eyelids at certain regular intervals. This led to the discovery of REM (rapid eye movement) sleep periods, which occur at roughly sixty to ninety minute intervals throughout the night, and contain the dreams that are the most vivid and most often remembered. Since then, EEG recordings that monitor brain activity during sleep have been used to map the various stages of sleep. Scientists soon realized that the strange, illogical experiences we call dreams almost always occur during REM sleep. Whilst 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.
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.
Like deep sleep, REM sleep is associated with an increased production of proteins. One study found that REM sleep affects the learning of certain mental skills. People taught a skill and then deprived of non-REM sleep could recall what they had learned after sleeping, whilst 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.... The Element Encyclopedia