Every night, whether you remember it or not, your brain puts on a show. Dreams have fascinated people for thousands of years, and modern science still hasn't settled on a single explanation for why we have them.
When Do We Dream?
Our most vivid and story-like dreams happen mainly during REM sleep, short for rapid eye movement. A night of sleep is made up of several cycles of about 90 minutes each, and REM periods get longer as the night goes on, which is why many of the dreams we remember come from just before waking up.
Dreams can also occur in other sleep stages, but they tend to be shorter and less visual.
Why Do We Dream? The Main Theories
Researchers have several competing ideas, and they may not be mutually exclusive. One suggests dreaming helps with memory, as the brain sorts and strengthens what you learned during the day. Another says dreams help us process emotions, which would explain why stressful periods often bring intense dreams.
A third idea, the threat simulation theory, proposes that dreams let us rehearse dangerous situations in a safe setting. Others argue dreams may be partly a by-product of the brain's random activity during sleep, which it then stitches into a story.
Why Do We Forget Them?
Most dreams fade within minutes of waking. During REM sleep, the brain chemistry that supports forming new memories is different from when we're awake, so dream content often never gets stored in the first place. Dreams you remember are usually the ones you woke up during or right after.
If you want to remember more, keep a notebook next to the bed and write down whatever you recall as soon as you open your eyes. Even a few words can help, and the habit tends to improve recall over time.
Dream Facts
Everyone dreams
Even people who say they never do, mostly forget them.
Blind people dream
Those blind from birth dream using sound, touch and emotion.
Mostly in REM
Vivid, story-like dreams cluster in REM sleep.
Forgotten fast
Much of a dream is gone minutes after waking.
Whatever their purpose turns out to be, dreams are a reminder that your brain is never really off. If you wake up with a strange one, it may be your mind doing some of its most important housekeeping.