The Strange World of Dreams
What are dreams? What do they mean? What is their purpose? Simply put, a dream is an experience of mental activity—images, sounds, ideas, emotions, and other sensations—when one is asleep. The dream is not constrained by facts, reality, or even physics, and its details are beyond the volitional control of the dreamer. Dreams can be the most enjoyable and fascinating aspect of sleep, or they can be the most unpleasant and horrifying aspect of sleep.
When Do We Dream?
Most scientists consider true dreaming to occur in REM sleep. Studies have been done in which subjects were awoken at different stages in their nightly sleep and asked, “Were you dreaming?”
For those awoken during deep nonREM sleep, less than 20 percent reported dreaming.
For those awoken during nonREM stage 2 sleep, 40–70 percent reported dreaming, and for those awoken during REM sleep, 80–95 percent reported dreaming.
When asked about the content of dreams, those awoken during REM sleep reported bizarre, vivid dreams, whereas the dreams reported for nonREM sleep are of the unremarkable type that could be extensions of wakeful experience.
Mentation can occur in any stage of sleep, but during REM sleep, the brain truly goes out of its mind! Dreams during REM sleep are characterized by hallucinations, delusions, disorientation, emotional instability, and amnesia—all symptoms of psychosis in awake individuals but totally normal for sleep.
What Do Dreams Mean? The Contributions of Freud and Jung
All societies and cultures throughout recorded history have asked the meaning of dreams—are they messages from the gods, produced by the soul, the expression of inner desires and fears? Sigmund Freud, a Viennese neurologist who is considered the father of psychoanalysis, used dream analysis as a means of getting at the complexity of underlying causes of the individual’s psychopathology.
In 1900, Freud published his seminal book, The Interpretation of Dreams. In it, he proposed that dreams were expressions of repressed wishes and desires. Because the frank expression of those wishes and desires would be disturbing, the sleeping brain disguised them as components of bizarre and less threatening narratives. In Freud’s view, the unconscious dream mind was a storehouse of repressed desires; thus, if he could decode the dream, he could identify a patient’s problems and treat them.
Another scientist who studied the meaning of dreams was Carl Jung, a Swiss psychologist and psychiatrist who was initially influenced by Freud. Jung disagreed with Freud’s views of dreams as disguised wishes and desires, maintaining that dreams were transparent and revealing rather than obscure.
In the mid-1970s, two Harvard scientists proposed the activation- synthesis hypothesis of dreaming. The idea was that during REM sleep, the cortex is episodically and randomly activated by bursts of action potentials, and the cortex tries to make sense of the patterns of activity they generate. These researchers postulated that dreaming is simply a random physiological process of activation of brain circuits stitched together into bizarre narratives—because that is what the cortex does: tries to make sense out of information.
Why Do We Dream?
The questions, “Why do we dream?” or “What is the function of dreaming?” are easy to ask but very difficult to answer. The most honest answer is that we do not yet know the function or functions of dreaming. This ignorance should not be surprising because despite many theories we still do not fully understand the purpose of sleep, nor do we know the exact functions of REM.
There are many hypotheses about the purpose of dreaming. For example, the hypothesis that dreams erase memories was proposed in 1993 by Sir Francis Crick and Graeme Mitchison.
￼Their idea was that during the day, the brain takes in a good deal of information, and most of it is not relevant for future purposes. Thus, memory banks have to be regularly cleared out, and valuable information stored efficiently. Crick and Mitchison hypothesized that dreaming is a meaningless byproduct of this daily memory management process.
During the day, we take in lots of information and store much of it as short-term memories.
During REM sleep, the brain sorts out these short-term memories, eliminating useless information and consolidating information that might be useful in the future.
Another hypothesis, that dreams during REM sleep may decrease the emotional intensity of memories, is based largely on indirect evidence. We say it is indirect because there is good evidence that REM sleep plays a role in emotional memory processing, and dreams with emotional content occur during REM. Therefore, dreams may be the critical process for modulating the emotional valence of the memory.
The stimulation of emotional reactions by an experience has a powerful influence on the memory of that experience. When you recall an emotional experience—an accident, the death of a loved one, planes flying into the World Trade Center, your first kiss—you also experience the associated emotion. However, with time, the intensity of the emotional component of the memory decreases.