Why Do We Dream?

Everyone dreams every night -- even if we don't remember our dreams.

Tom Scammell, MD, associate professor of neurology at Harvard Medical School and Beth Israel Deaconess Medical Center, says no one knows why we dream. "There is a strong movement in the research community to research how sleep improves memory and learning," Scammell says. "One speculative possibility is that dreaming allows you the opportunity to practice things you may or may not ever have to do, like running away or fighting off a predator."

Three or four times a night, you have a period of sleep that lasts approximately 90 minutes called REM -- rapid eye movement -- sleep. It is during REM sleep that your brain is more active. And according to Scammell, it's then that conditions are right for "story-like" dreams that are rich in action, complexity, and emotion.

"You are most likely to recall dreams if you wake at the end of a REM episode," says Scammell. "Americans, who are chronically sleep-deprived, probably miss out on some REM sleep. This builds up pressure for REM sleep. So when you're catching up on your sleep, you may have more REM sleep with more intense dreams."