Why Do We Dream?

Given that we are asleep about one-third of our lives, and given that dreaming is a predominant part of sleeping, dreaming must be important. Researchers have been working on this problem for many years and an article1 in the New Scientist summarizes some recent research. Changes in electrical activity in the brain and movements of the eyes allow us to identify five stages of sleep. Sleep begins with two stages of light sleep, followed by two stages of deep sleep, followed by a stage of Rapid Eye Movement (REM) sleep. This sleep cycle lasts approximately 90 minutes and is repeated until we awaken.

One of the roles of dreaming is memory consolidation (See the Healthymemory Blog Post, “To Remember It, Sleep on It). There are a substantial number of studies reporting that sleep facilitates memory. The New Scientist article reported a study in which non-REM dreams boost people’s performance on a problem. The research participants were given an hour of training on a complex maze. Some participants were allowed to take a ninety-minute nap, while other participants were kept awake. When tested again on the maze, people who dreamed showed bigger improvements than people who did not dream. The largest improvements were in people who dreamed about the maze. This dream content could be somewhat bizarre. One of the participants who showed the largest improvement reported the following dream: “there were people at checkpoints in the maze as well as bat caves that he had visited a few years earlier.”

REM dreams contain more emotion, more aggression, and more unknown characters than non-REM dreams, whereas non-REM dreams are more likely to involve friendly encounters. A conjecture is that non-REM dreams help us practice friendly encounters, whereas REM dreams help us to rehearse threats. REM sleep strengthens negative emotional memories2 . The notion here is that if we don’t remember bad experiences, we will not learn from them. It is also thought that reliving the upsetting experience in the absence of the hormonal rush that accompanied the actual event helps to strip away the raw emotion from the memory. This is somewhat analogous to desensitization techniques employed by therapists. Although these REM dreams can be helpful for many situations, they do not work for people with Post Traumatic Stress Disorders. This is unfortunate.

So sleep and dreaming are activities that are important to both cognitive and emotional health. Shortchanging yourself of this needed activity has adverse effects on your memory health.

1Young, E. (2011). The I in Dreaming. New Scientist, 12 March, 36-39.

2Cerebral Cortex, vol 19, p.1158

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