Most dreaming occurs during REM (rapid eye movement) sleep, which we cycle through periodically during the night. Sleep studies show our brainwaves are almost as active during REM cycles as they are when we're awake. Experts believe the brainstem generates REM sleep and the forebrain generates dreams.

Why do we dream what we dream?

One widely held theory about the purpose of dreams is that they help you store important memories and things you've learned, get rid of unimportant memories, and sort through complicated thoughts and feelings. Research shows that sleep helps store memories.

Where do dreams come from and what do they mean?

The theory states that dreams don't actually mean anything. Instead they're merely electrical brain impulses that pull random thoughts and imagery from our memories. The theory suggests that humans construct dream stories after they wake up.