dream

dream A series of thoughts, visions, and other sensations that occupy the mind during sleep. Dreams occur during that part of sleep when there are rapid eye movements (REM sleep). People have three to five periods of REM sleep per night, which usually come at intervals of 1 to 2 hours and are quite variable in length. An episode of REM sleep might be brief and last just 5 minutes, or it might be much longer. Experiments have shown that a person can communicate with a person who is dreaming. Dreaming is not uniquely human; cats and dogs dream, judging from the physiologic features, and so, apparently, do many other animals. The content of dreams is sometimes the topic of psychoanalysis. Although this method of therapy is less common today than it once was, some physicians still look at dreams as a diagnostic clue to medical disorders. For example, children with bipolar disorder have been found to frequently have a particular type of nightmare, and especially lucid dreams are a side effect of certain medications. These clues indicate that chemicals in the brain, as well as life events and individuals’ preoccupations, influence dreams. See also REM sleep.