Dreaming Rem Sleep - Sleep Mechanics: Sleep Disorders
Content provided by the Faculty of the Harvard Medical School
Dreaming (REM) sleep
Dreaming occurs during REM sleep, which has been described as an "active brain in a paralyzed body." Your brain races, thinking and dreaming, as your eyes dart back and forth rapidly behind closed lids. Your body temperature rises. Unless you have circulatory or other physical problems, the penis or clitoris becomes erect. Your blood pressure increases, and your heart rate and breathing speed up to daytime levels. The sympathetic nervous system, which creates the fight-or-flight response, is twice as active as when you're awake. Despite all this activity, your body hardly moves, except for intermittent twitches; muscles not needed for breathing or eye movement are quiet.
Just as deep sleep restores your body, scientists believe that REM or dreaming sleep restores your mind, perhaps in part by helping clear out irrelevant information. Studies show, for example, that REM sleep facilitates learning and memory. People tested to measure how well they had learned a new task improved their scores after a night's sleep. If roused from REM sleep, however, the improvements were lost. On the other hand, if they were awakened an equal number of times from slow-wave sleep, the improvements in the scores were unaffected. These findings may help explain why students who stay up all night cramming for an examination generally retain less information than classmates who get some sleep.
About three to five times a night, or about every 90 minutes, a sleeper enters REM sleep. The first such episode usually lasts only for a few minutes, but REM time increases progressively over the course of the night. The final period of REM sleep may last a half-hour. Altogether, REM sleep makes up about 25% of total sleep in young adults. If someone who has been deprived of REM sleep is left undisturbed for a night, he or she enters this stage earlier and spends a higher proportion of sleep time in it — a phenomenon called REM rebound.
Why do we dream?You've probably wondered whether your dreams serve any purpose. What does it mean when you arrive at your senior prom in overalls, or when you're chased through the streets of Paris by a giant turtle? Those who have studied dreaming fall into two general camps: Yes, dreams are significant, and no, they're not. Followers of the first camp can trace many of their ideas to Sigmund Freud, who in 1900 proposed that dreams are meaningful representations of the unconscious mind in which we reveal our hidden conflicts, desires, and fears, albeit in disguised form. Post-Freudian theorists and psychoanalytic thinkers subsequently elaborated on and refined his ideas, focusing on how dreams help the organization of thought and the consolidation and reinforcement of long-term memory. Other researchers, taking a physiological approach, are skeptical. Pointing to studies from the 1970s showing that dreams occur upon activation of neurotransmitter chemicals in a portion of the brain, they argue that dreams are merely aimless and chaotic images — essentially little more than the mind's attempt to make meaning out of the random chemical signals sent up from the brain stem. They also point out that we only remember a minute percentage of our dreams; if they were significant, surely we'd remember them better. More recent research on the function of dreams combines the psychological and neurochemical approaches. One scientist, for example, observed that patients who sustained injuries and lesions in the brain's frontal lobe (not the brain stem) no longer dreamed. This suggests that parts of the brain other than the brain stem — specifically in those areas in the front of the brain that are connected to urges, impulses, and appetites — may be involved in dream production, and it has prompted a reexamination of the Freudian notion that dreams may represent a window to the subconscious. Further research should offer important insights on why we dream and what role, if any, our dreams can play in maintaining mental health. |
| Last updated: | January 23, 2007 |
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Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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