| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
|
|
|
counterpoints in science The Stuff Such Dreams are Made OnHuman societies throughout recorded history--the Egyptians, Babylonians, Hebrews, Greeks, Romans, Christians, and modern psychoanalysts--have agreed that dreams have deep significance. Dreams are variously viewed as a means of communicating with deities or the dear departed; an instrument of prophecy; a window on the soul; or, as Freud thought, the royal road to the unconscious mind. Dream analysis is a keystone of contemporary Freudian, Jungian, and nearly every other kind of psychological treatment. When I was in medical school, I read Freud's The Interpretation of Dreams and was so taken by his ideas that I seriously considered becoming a psychiatrist. I volunteered to be analyzed in the training program at Columbia's Psychoanalytic Institute and underwent a year of psychoanalysis. Dream interpretation played an important role in increasing self-awareness and clarifying my thoughts and personal relationships. Subsequently, I treated a number of patients, both children and adults, whose dreams seemed to provide insights into their emotional problems and unconscious thinking. In 1953, the year I graduated from medical school, a discovery was made that completely revolutionized our concepts of sleep and dreams. Working in the world's first sleep laboratory at the University of Chicago, Nathaniel Kleitman and his students, Eugene Aserinsky and William Dement, first observed and studied rapid eye movement (REM) sleep. People awakened from this phase of sleep would almost always report that they had been dreaming and would have vivid recollection of the dream content. Those awakened from other phases of sleep would rarely recall any dreams. We alternate within each 24-hour period between two very different states of existence: being awake and being asleep. Like other creatures on this planet, we evolved under the tyranny of the Earth's rotation, the relentless cycle of light and dark with which all lifestyles must comply. Our circadian rhythms, the clockworks of our vital functions--waking and sleeping, the rise and fall of body temperature and blood pressure, the secretion of growth and sex hormone--all are driven by this celestial circuit. Before 1953 no one had understood that while asleep we experience yet a third state of existence, distinct from both wakefulness and non-REM sleep. REM sleep differs from non-REM sleep not only in the rapid eye movements that led to its discovery but in a distinctive pattern of brain waves, a higher metabolic rate, greater ease of arousal from sleep, erections in men and increased vaginal blood flow in women, and above all, in dreaming. We dream much more than we realize, but most dreams are quickly forgotten. People who say that they never dream are almost always proved wrong if studied in a sleep lab. In contrast with the circadian (daily) rhythm of the sleep-wake cycle, REM sleep follows an ultradian (less than daily) cycle of about 90 minutes. An individual falling asleep goes through four ever-deepening sleep levels, as shown by the brain waves. Then, after an hour and a half of deep sleep, the first REM episode starts and lasts a few minutes. The next episode comes about 90 minutes later and lasts a few minutes longer, the third episode is longer still, until morning awakening ends the series. Dreams from the last and longest session are the ones we usually remember when we wake up. These findings inspired a new era of the scientific study of sleep and dreams which continues unabated to the present time. One of the leading investigators in this new discipline is Kleitman's student, Dement, known as Dr. Sleep because of his many contributions to the field, who started the first sleep lab on the West Coast at Stanford. After medical school, I did my residency and joined the faculty at Stanford. I was fascinated by Dement's research on REM sleep and rather disappointed when he reported that the many dreams he recorded did not fit Freud's, or indeed any other theory, as to their underlying meaning. In contrast with the dreams remembered and dissected in therapeutic sessions, the vast majority of dreams elicited in sleep labs, by waking people up right after an REM episode, deal with everyday matters. According to sleep researcher Peretz Lavie, lawyers dream about courtrooms, doctors dream about operating rooms, students dream about classrooms. Dreams early in the night tend to deal with present situations, whereas dreams in the morning are more likely to go back to the dreamer's early childhood. One surprising finding is that much of the dreamer's experience takes several days to be incorporated into dreams. French neurosurgeon Michel Jouvet, who traveled a lot and recorded his dreams every day, noticed that new places he visited didn't show up in his dreams until about a week later. Lavie, who teaches and does sleep research in Haifa, followed the dreams of 70 students during the Gulf War, when Saddam Hussein's Scud missiles were falling on Israel nightly. Although everybody was shaken up by these attacks, it took several days before the traumatic events and the ubiquitous gas masks began to appear regularly in dreams.
REM sleep occurs only in warm-blooded vertebrates, that is, in birds and mammals. It is not observed in insects, fish, amphibians, or reptiles. In birds each REM episode lasts just a few seconds, while in other mammals, as in humans, REM episodes last for several minutes or longer. The one mammalian exception is the primitive egg-laying echidna, the spiny anteater, which has no REM activity. As far as I know, the platypus, the only other living monotreme, has not yet been checked out for REM sleep. Marsupials like the opossum, the next stage up in mammalian evolution, do experience REM. REM sleep apparently developed separately in birds and in marsupial mammals, rather than being inherited by both from a common reptilian ancestor. No known reptiles have REM sleep, and its absence in the echidna breaks the link with some hypothetical common forbear. While mammals have REM sleep for minutes at a time and spend about 20 percent of their sleeping hours in this state, birds have only a few seconds of REM at one go and spend about five percent of their sleep in this phase. Given that other mammals have the eye movements and brain waves of REM sleep, do they dream too? Probably so. Dogs and cats and horses are often observed making limb movements and sounds that suggest they are having nightmares involving fight or flight. The only reason that we all don't act out our dreams is that a special center in the brain switches off muscle-activating signals during REM sleep. In effect we are paralyzed during REM sleep. This may explain the common nightmare of trying to run away from danger and being rooted to the ground. The signals that activate the eye muscles come from higher in the brain and are spared this paralysis. Jouvet, in the 1960s, operated on cats and cut the connection between the brain's inhibitory center and the spinal cord, so that muscle-activating signals were no longer blocked. During REM sleep these cats would stand up, arch their backs, and engage in fights with the figments of their dreams. Occasionally, human patients will behave like these transected cats, acting out their dreams, and actually inflict damage on those nearby. Babies sleep much more than adults, and a much larger fraction of their sleep is REM sleep. This suggests that REM sleep serves some important function in growth and development, but intensive study has so far failed to reveal what that function is. A standard scientific method for determining the function of an organ or process is to remove it and see what happens. Dement showed that when normal individuals are deprived of REM sleep for several days by being awakened in the sleep lab as soon as rapid eye movements begin, they will become anxious and irritable and have trouble concentrating. As soon as the interference stops, these individuals will go right into REM sleep without the usual 90-minute delay, and make up to some extent for the deprivation. This certainly implies that REM sleep is essential, but people have been deprived of it for as long as ten days without any serious effects. The record-holder is an Israeli veteran who had been wounded by a piece of shrapnel in his brain stem, in a nerve center known to initiate REM sleep. During several nights in the sleep lab, over a period of six years, he had virtually no REM sleep. Yet he was a very successful lawyer and an expert at solving cryptic crosswords. It's pretty clear from this one example that REM sleep is not essential for organizing thought and memory, as some leading neurophysiologists have hypothesized. It also rules out the popular theory of Crick and Mitchison that REM sleep cleans out the files and dumps the garbage by erasing the overload of memories. What then is the current scientific opinion about the meaning of dreams? Over the years, I have scanned innumerable articles by sleep scientists and recently read five different books, to see whether the age-old question of dream interpretation has yielded to the sophisticated setups and nocturnal gleanings of these enthusiastic investigators. The Freudian theory, that dreams are the expression of infantile wishes and also the guardians of sleep (that is, wish-fulfilling dreams keep us from being upset and waking up), has not held up very well. For one thing, it's much easier to be aroused from dreaming sleep than from non- dreaming sleep, so that REM sleep is viewed by many sleep experts as the gate to rather than the barrier from wakefulness. Some neuroscientists claim that dreams are meaningless by-products of nocturnal brain function, a bunch of images that flash through the mind and which we try to make sense of when we wake up. Most researchers who study dreams reject this idea, because dreams seem to have a narrative coherence and logic that goes beyond being just a random collection of impressions. They are convinced that REM sleep and dreams constitute a separate reality that plays a vital part in our lives and health, though the nature of that reality is not yet understood. On present evidence, birds and mammals have been dreaming on this gyrating perch of a planet for more than 100 million years. We shouldn't be too discouraged that half a century of research has not yet succeeded in deciphering the complex sensory images that bubble up nightly from the heated vertebrate brain. In seeking the meaning of dreams, we are exploring a hidden spring of magic and mystery, a strange state of existence whose language and laws are still unknown to us, even though they are our own. Jerold M. Lowenstein is a professor of medicine at the University of California, San Francisco. |
summer 1997
|
