Night Life

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.