Alan gets wired up for the sleep experiment

Most sleep scientists believe dreams result from the random signals that flood our visual and audio cortices during REM sleep. But if those signals are so haphazard, why do dreams seem to make sense?

In "What's in a Dream?" Alan Alda spends a night at Harvard University's sleep lab to help find out. Once he's wired up, the researchers test his brain's associative powers by flashing two words across a monitor. Alan must determine if the words are related, but sometimes the second word isn't a word at all.

Before Alan falls asleep, he's pretty good at catching the fake words. But when he's woken up from REM sleep, his brain is quicker to make associations between the pairs of words—even if one is a nonsense word. According to Dr. Robert Stickgold, that may parallel how the brain takes the nonsense signals it receives during REM sleep and turns them into dreams.