That dream was a small anomaly, but one that ripped opened my perspective: if in a dream I could know what someone looked like before I actually met him, then the dreaming mind is capable of spectacular range. That is the only precognitive dream I've ever had, but, like most of us, I've found my dreams to be deep and shallow, beautiful, nutty, mysterious, chaotic, and sometimes meaningful enough to trigger big life decisions.
From the Australian aborigines, who believe that the dreaming and waking worlds are equally real; to Freud, who felt dreams were a braid of repressed wishes; from Jung, who saw dreams as stories dipped in our collective unconscious; to Nobel prize-winning scientist Francis Crick, who has suggested dreams are just the brain's way of forgetting, a sloughing-off of each day's meaningless events; from the cognitive neuroscientists who have discovered that dreams and REM sleep are linked to our ability to learn and remember; to those who believe dreaming is the meaningless and random sputtering of nerve cells, dreams are the sphinx-like riddle we keep trying to solve.
Robert Stickgold, Ph.D., a Harvard neuroscientist, has his own fascinating description: "The mind becomes clinically insane while dreaming." Stickgold says we're so comfortable with dreaming "that we don't realize how strange it is to lie in bed hallucinating patently impossible things without ever noticing that these things might be impossible."
"You're delusional and hyper-emotional and you might even suddenly wonder, 'Is this a dream?' but nine times out of ten you'll decide it's definitely real." Even stranger, Stickgold observes, is the fact that "for every person in the world, the same brain that works one way during the day shifts into a completely different mode at night."
According to Stickgold, dreams are proof that "the mechanism for producing insanity is present in all of us." The only questions are: "How do we throw that switch every night?" and "Why do we bother to do it at all?" He and others are now beginning to sketch out some intriguing answers.
Do we dream to forget? Or to remember? The answer seems to lie in new findings about REM sleep and its unique biological function. First, however, let's shatter a myth. Dreams and rapid-eye-movement (REM) sleep are not one and the same. We dream throughout the night, sometimes while in deep sleep—the sleep marked by slow EEG waves, during which the body repairs itself, releasing growth hormone. REM sleep, in contrast, is a violently "awake" sleep; the muscles are at rest but the brain and nervous system are highly active.
The brain cycles through REM sleep about four to six times a night, each time marked by irregular breathing, increased heart rate and brain temperature, general physiological arousal, and, in men, erections. Arousal is such that ulcer sufferers secrete twenty times more stomach acid in REM than in non-REM sleep.
The first REM cycle follows ninety minutes of slow-wave deep sleep and lasts about ten minutes. REM cycles lengthen through the night and the dreams in them get more bizarre and detailed, like wacky movies. REM dreams tend to be uniformly more emotional and memorable than non-REM ones. One of the most interesting aspects of REM sleep is that, for its duration, we are paralyzed from the neck down, and our threshold for sensory input is raised, so that external stimuli rarely reach and wake us. The brain is soaked in acetylcholine, which seems to stimulate nerve cells while it strips muscles of tone and tension. At the same time, serotonin levels plummet. The changes are swift and global. It's as if during these cycles we are functioning with a different brain entirely.
Because we are literally paralyzed while we dream, we do not act out our nightly hallucinations. Otherwise, we might gesticulate, twitch, and actually stand up and play out our dreams. It's interesting that our eye muscles do not become paralyzed, and researchers have speculated that nature did not bother to develop a mechanism to paralyze our eye muscles simply because eye movement is a kind of gratuitous detail—it doesn't have much impact on the dreamer. Whatever the reason, REM has been a boon to dream researchers, since it's a clear indication that we've slipped into that particular phase of sleep.
As the biology of dreams is being pieced together, the theories of Freud have begun to seem more improbable. Dreams are likely not the eruptions of the repressed primal self, disguised in clever puzzles that only your psychoanalyst can decipher at $180 an hour. The first blow to this theory was dealt in 1977, when Harvard's J. Allan Hobson, Ph.D., proposed that dreams are a kind of narrative structure we impose on the random firing of neurons in the brainstem. The neocortex, our meaning-maker, creates stories out of this neuronal chaos—just as it does of waking life.
Those stories may indeed be clues to our inner selves. But when brains are scanned during dreaming, researchers find that the frontal lobes, which integrate information, are shut down, and the brain is driven by its emotional centers. Just last year, researchers Allen R. Braun, M.D., of the National Institutes of Health, and Thomas J. Balkin, M.D., of the Walter Reed Army Institute, scanned the brain in both slow-wave and REM sleep and found that during the latter, the visual cortex and frontal lobes were both shut down. That deals yet another blow to Freud: if dream content were being monitored, with unconscious wishes being actively repressed and disguised, the frontal lobes would have to be active.
What is the purpose of the neural chaos of dreaming? Scientists are still puzzling that out. In 1983, Nobelist Francis Crick, of the Salk Institute in La Jolla, suggested that the brain was actually "reverse learning," that REM sleep allows the neurons to spew out each day's spurious and extra stimuli, cleansing the brain. "We dream to forget," Crick wrote, to enormous outcry. In 1986, he revised the hypothesis, noting that perhaps we dream to reduce fantasy and obsession—that dreams are a way of forgetting material that might otherwise needlessly intrude on everyday life.
Then, in 1994, two researchers showed that our ability to learn seems dependent on REM sleep. Scientists Avi Karni and Dov Sagi, at Israel's Weitzman Institute, found that if someone is trained in a task and allowed a normal night's sleep, they will show improvement the next day. But if sleep is interrupted in each REM cycle, they show no improvement at all.
And the particular cycle of REM that gets interrupted is crucial. It's REM sleep in the last quarter of the night that counts. Bob Stickgold trained 57 individuals in a task and then tested them 3, 6, 9, or 12 hours later the same day, or overnight after an interval of 13, 16, or 22 hours. The task involved visual discrimination: a subject looks for diagonal lines against a background of horizontal lines.
The time interval had no influence on performance; the amount of sleep did. "If they had less than six hours of sleep, they did not improve," says Stickgold.
One might simply conclude that people need a lot of sleep in order to learn. The truth seems to be: they need certain cycles of sleep, and when awakened before their last REM cycle, the brain is unable to consolidate the memory of the task. But Stickgold and his colleagues found that more than REM cycles were at stake.
"A student of mine did another experiment and found that the amount of slow-wave sleep in the first two hours of the night is highly correlated with the amount of learning as well." How might the two sleep cycles—REM and deep slow-wave sleep—work together? There may be a two-step process of memory enhancement. "We know that levels of acetylcholine are high in REM sleep and low in slow-wave sleep. Perhaps as you cycle from one to the other, you're passing information back and forth between different parts of the brain. It's as if the brain is holding a conversation with itself and identifying exactly what it needs to know."
Stickgold thinks REM sleep may have yet another purpose: to actually alter intrusive experiences and memories from the day. "I was putting my son, who is ten, to bed after a day of skiing together. We were lying there with our eyes closed and I said, 'I feel I'm back on the ski slope.' He said, 'Really? I'm on the ski lift.'" There's a tendency to have an intrusive replay of novel experiences when you go to sleep, says Stickgold, especially ones that involve the vestibular system of the brain, which plays a role in balance. "If I fall asleep, go through one REM cycle, and wake two hours later, the feeling is gone. I can't reproduce it. Something has happened to that memory in those two hours."
Stickgold is looking at this effect in people who play the computer game Tetris, which requires rotating small blocks that float down the screen. "More than one person has told me that the day they first got hooked on the game, they went to bed, closed their eyes, and could see these blocks floating. It's gone the next day. Something in your brain in that first two hours has taken a memory that at sleep onset is incredibly intrusive and altered it so that it no longer behaves that way."
Rosalind Cartwright, Ph.D., the doyenne of dream research, has also found that sleep softens intrusive experiences, especially depressing feelings and moods. Director of the sleep disorders service and head of psychology at Chicago's Rush Presbyterian-St. Luke's Medical Center, she has evidence that dreams help regulate and stabilize mood, defusing negative feelings.
By observing sixty normal and seventy clinically depressed adults, Cartwright found that among those who had a mildly unpleasant day or experience, dreams were negative at the beginning of the night and became pleasant by the end. Among the clinically depressed, dreams were bland at the beginning and negative by night's end. "Normal individuals wake up in a better mood after a depressing day," she says. "Depressed individuals wake up feeling worse."
Cartwright adds a coda: "I'll tell you the kicker: a few of the depressed people showed the opposite pattern. Their dreams got more positive across the night. And those were the ones who got over their depression. You could predict it from a single night of dreaming."
Dreams, Cartwright believes, are our "internal therapist"; they offer an emotional information processing system. When that therapist isn't functioning—if, for example, you suffer from post-traumatic stress disorder manifested by recurrent nightmares—you may actually be able to lend it some help. Recently, researchers in Canada have found that consciously changing your dream in any direction while awake may stop the recurrence.
Tony Zadra, Ph.D., of the Dream and Nightmare Laboratory at the University of Montreal, studied six cases of recurrent nightmares—"and all got better," he says. The technique? While awake, the dreamers were taken on a guided visualization into the nightmare, and, at an emotional moment in the dream, were asked to visualize a simple task, such as looking at their hands. Then they were asked to respond differently—say, confront an aggressor or otherwise create a positive outcome.
After rehearsing the new ending while awake, the dreamers go to sleep as usual. And then an interesting thing happens: "Some people actually remember to look at their hands at the right moment, and then become aware that they are dreaming and that they can consciously carry out their dream differently. Others don't remember to look at their hands, but they dream the new dream they created while awake."
Either way, the nightmares stop. Says Zadra: "Some studies show that you can change absolutely anything in the nightmare, rehearse that change, and the nightmare will get better." It's the change that counts—it dismantles the dream and pries loose its hold on the dreamer.
It seems that dreams are many-purposed. They invite us into the truly interesting frontier of the mind. That may be why Stickgold says, "I love dreaming. And I love dreams."