It’s snowing heavily, and everyone in the backyard is in a swimsuit, at some kind of party: Mom, Dad, the high school principal, there’s even an ex-girlfriend. And is that Elvis, over by the piñata?
Dreams are so rich and have such an authentic feeling that scientists have long assumed they must have a crucial psychological purpose. To Freud, dreaming provided a playground for the unconscious mind; to Jung, it was a stage where the psyche’s archetypes acted out primal themes. Newer theories hold that dreams help the brain to consolidate emotional memories or to work though current problems, like divorce and work frustrations.
Yet what if the primary purpose of dreaming isn’t psychological at all?
In a paper published last month in the journal Nature Reviews Neuroscience, Dr. J. Allan Hobson, a psychiatrist and longtime sleep researcher at Harvard, argues that the main function of rapid-eye-movement sleep, or REM, when most dreaming occurs, is physiological. The brain is warming its circuits, anticipating the sights and sounds and emotions of waking.
“It helps explain a lot of things, like why people forget so many dreams,” Dr. Hobson said in an interview. “It’s like jogging; the body doesn’t remember every step, but it knows it has exercised. It has been tuned up. It’s the same idea here: dreams are tuning the mind for conscious awareness.”
Drawing on work of his own and others, Dr. Hobson argues that dreaming is a parallel state of consciousness that is continually running but normally suppressed during waking. The idea is a prominent example of how neuroscience is altering assumptions about everyday (or every-night) brain functions.
“Most people who have studied dreams start out with some predetermined psychological ideas and try to make dreaming fit those,” said Dr. Mark Mahowald, a neurologist who is director of the sleep disorders program at Hennepin County Medical Center, in Minneapolis. “What I like about this new paper is that he doesn’t make any assumptions about what dreaming is doing.”
The paper has already stirred controversy and discussion among Freudians, therapists and other researchers, including neuroscientists. Dr. Rodolfo Llinás, a neurologist and physiologist at New York University, called Dr. Hobson’s reasoning impressive but said it was not the only physiological interpretation of dreams.
“I argue that dreaming is not a parallel state but that it is consciousness itself, in the absence of input from the senses,” said Dr. Llinás, who makes the case in the book “I of the Vortex: From Neurons to Self” (M.I.T., 2001). Once people are awake, he argued, their brain essentially revises its dream images to match what it sees, hears and feels — the dreams are “corrected” by the senses.
These novel ideas about dreaming are based partly on basic findings about REM sleep. In evolutionary terms, REM appears to be a recent development; it is detectable in humans and other warm-blooded mammals and birds. And studies suggest that REM makes its appearance very early in life — in the third trimester for humans, well before a developing child has experience or imagery to fill out a dream.
In studies, scientists have found evidence that REM activity helps the brain build neural connections, particularly in its visual areas. The developing fetus may be “seeing” something, in terms of brain activity, long before the eyes ever open — the developing brain drawing on innate, biological models of space and time, like an internal virtual-reality machine. Full-on dreams, in the usual sense of the word, come much later. Their content, in this view, is a kind of crude test run for what the coming day may hold.
None of this is to say that dreams are devoid of meaning. Anyone who can remember a vivid dream knows that at times the strange nighttime scenes reflect real hopes and anxieties: the young teacher who finds himself naked at the lectern; the new mother in front of an empty crib, frantic in her imagined loss.
But people can read almost anything into the dreams that they remember, and they do exactly that. In a recent study of more than 1,000 people, researchers at Carnegie Mellon University and Harvard found strong biases in the interpretations of dreams. For instance, the participants tended to attach more significance to a negative dream if it was about someone they disliked, and more to a positive dream if it was about a friend.
In fact, research suggests that only about 20 percent of dreams contain people or places that the dreamer has encountered. Most images appear to be unique to a single dream.
Scientists know this because some people have the ability to watch their own dreams as observers, without waking up. This state of consciousness, called lucid dreaming, is itself something a mystery — and a staple of New Age and ancient mystics. But it is a real phenomenon, one in which Dr. Hobson finds strong support for his argument for dreams as a physiological warm-up before waking.
In dozens of studies, researchers have brought people into the laboratory and trained them to dream lucidly. They do this with a variety of techniques, including auto-suggestion as head meets pillow (“I will be aware when I dream; I will observe”) and teaching telltale signs of dreaming (the light switches don’t work; levitation is possible; it is often impossible to scream).
Lucid dreaming occurs during a mixed state of consciousness, sleep researchers say — a heavy dose of REM with a sprinkling of waking awareness. “This is just one kind of mixed state, but there are whole variety of them,” Dr. Mahowald said. Sleepwalking and night terrors, he said, represent mixtures of muscle activation and non-REM sleep. Attacks of narcolepsy reflect an infringement of REM on normal daytime alertness.
In study published in September in the journal Sleep, Ursula Voss of J. W. Goethe-University in Frankfurt led a team that analyzed brain waves during REM sleep, waking and lucid dreaming. It found that lucid dreaming had elements of REM and of waking — most notably in the frontal areas of the brain, which are quiet during normal dreaming. Dr. Hobson was a co-author on the paper.
“You are seeing this split brain in action,” he said. “This tells me that there are these two systems, and that in fact they can be running at the same time.”
Researchers have a way to go before they can confirm or fill out this working hypothesis. But the payoffs could extend beyond a deeper understanding of the sleeping brain. People who struggle with schizophrenia suffer delusions of unknown origin. Dr. Hobson suggests that these flights of imagination may be related to an abnormal activation of a dreaming consciousness. “Let the dreamer awake, and you will see psychosis,” Jung said.
For everyone else, the idea of dreams as a kind of sound check for the brain may bring some comfort, as well. That ominous dream of people gathered on the lawn for some strange party? Probably meaningless.
No reason to scream, even if it were possible.