1. No one knows for sure why you dream.
"That's the one part of sleep medicine we know the least about," says Charles Bae, a sleep medicine specialist at the Cleveland Clinic. "I think dreams help people process the multiple kinds of sensory input that come in through the day." Some people report experiencing eureka moments during dreams.
In her book about Lyndon Johnson, biographer Doris Kearns Goodwin wrote that LBJ dreamed he had a stroke and became paralyzed — and then a few months later chose not to run for president in 1968. "He had made a decision in his dream," says Myron Glucksman, author of Dreaming: An Opportunity for Change, and psychiatrist in New York City and Redding, Connecticut. "Dreams are like an internal diary. They're a nightly commentary on your life."
2. You dream throughout the night, not just during REM sleep.
Forget what you heard in college about dreams only occurring during REM sleep. You can remember stories from throughout the night, though not all are created equal. REM-sleep dreams, which are more common in the second half of the night, tend to seem more vivid and unrealistic. "If you dream you jumped out of a plane, and you saw rockets around you, that's almost certainly a REM sleep dream," says Jerry Siegel, professor of psychiatry and director of the Center for Sleep Research at UCLA. Dreams during the first three (of the four) stages of sleep may seem more mundane.
3. You remember a dream if you awake during it.
"The primary determinant of whether you'll remember a dream is being awakened during the dream," says Mark Mahowald, professor of neurology at the University of Minnesota Medical School and visiting professor of psychiatry and behavioral medicine at Stanford University. "If you don't wake up during the dream, the memory is gone. We're on a self-erasing tape while we're asleep."
4. Spicy foods may make you remember more dreams and nightmares.
"The meal makes it more likely you're going to wake up during sleep," says Mahowald. "The heavy meal has nothing to do with dream generation. It has to do with dream recall." In order to recall a dream, you have to be awake, at least for a few minutes. "Our brain isn't able to convert from short-term to long-term memory while we're asleep," says psychologist Lisa Medalie, a behavioral sleep specialist at the University of Chicago.
5. You may be able to change bad dreams.
Many therapists believe it's possible to "re-write" nightmares. People who suffer from post-traumatic stress disorder, for instance, can train themselves to recognize when they're in a dream. They tell themselves, "This is only a dream," says sleep researcher Ursula Voss, a psychology professor at the University of Frankfurt. Some of her patients came up with an idea that works: They make a bracelet that they wear to sleep. "If the bracelet is not in the dream, they know it's a dream," she says. They look out for "something that's bizarre" and then try to shift the direction of the dream.
Shelby Harris, director of behavioral sleep medicine at Montefiore Medical Center in New York City, uses "imagery rehearsal therapy" with her patients. She encourages them to clearly envision a new scenario when dreams take a bad turn. One patient kept dreaming she was surrounded by sharks and was starting to drown. "She just changed the sharks to dolphins," says Harris. "We wrote out a whole new storyline."
6. The brain is still hard at work while you're sleeping and dreaming.
"REM sleep is not a time of rest for the brain," says Mahowald. "The brain is being stimulated at an incredibly high level throughout dream sleep. The stimulation is what generates the dream imagery. And then the function of the brain is to make sense of what it's presented with. When we're awake, we're presented with the real world. When we're asleep, what the brain is presented with is dream imagery. The brain tries to make sense of all these random and presumably meaningless images and thoughts and sounds. The brain constructs the dream out of all this imagery. When we're awake, the brain perceives the real world as it is."
7. It's hard to separate the function of sleep from the function of dreams.
"The function of sleep is to downscale things so that the brain is ready and able to learn the next morning," says Mahowald. "I think that dreaming is something the brain has to generate in the process of re-equilibrating." If you start with 100 points of synapses at the beginning of the day and have 125 by the end of it, you need to rearrange it down to 100 — or you'd have 150 the next day, he says. "At some point it would not be sustainable. You'd have too many synapses to fill your scale."
8. Dreams may help people process and consolidate memories.
In one study, Harvard researchers asked subjects to navigate through a 3D maze and then either nap for 90 minutes or stay awake but quiet. Nappers who said they dreamed about the experience got much better at navigating the maze. "The brain seems to be encoding in pictures, visually," says Voss.
9. Dreams do not foretell the future.
"Everyone wants dreams to be prophetic," says Mahowald. "You forget about the 500 dreams you had about phone calls that didn't come true the next day. All of these dream-related prophecies are just pure statistical phenomenon." People want to find meaning in these night stories. "They want them to be supernatural," he says.
10. No one agrees about the meaning of dreams.
Freud called dreams "the guardians of sleep." And he believed their purpose was the censor basic impulses, such as aggression and sex, says Glucksman. Some people insist Freud was right, and others think dreams hold no meaning. "Treat it as a present, and do whatever you want with it," says Voss.