Why do we dream?
For grown-ups: the science
While you sleep, your brain keeps working, and when it links memories with pictures in your mind, that's thought to become a dream.
The sleeping brain doesn't fully shut down, and during REM sleep especially, brain activity looks a lot like it does when we're awake. Dream reports happen in non-REM sleep too, but REM sleep tends to bring vivid, story-like dreams. Scientists think dreams involve brain activity linked to memory and imagery, but whether dreaming's purpose is sorting memories, processing emotions, or preparing for danger is still an open scientific question.
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Transcript
When you're sound asleep, how can you still see a dream?
Even while a child sleeps, the brain doesn't rest all the way. It keeps working on some things while the body relaxes.
The brain gets extra busy during a special kind of sleep - the time when most dreams happen. It moves almost as much as when you are wide awake.
Sometimes the brain links up memories with pictures floating in your mind. Many scientists think that's how dreams are made.
So dreams happen because of what your brain is doing while you sleep. Nobody knows for sure exactly why we dream, though.