Dreaming is an episodic activity of the sleeping mind during which spontaneous sensory experiences occur that are perceived at the time as if real. Although dreaming is common, occurring in all humans, the dreams themselves are unique, based on each person’s own memory bank of images, a residue of their particular life experiences. The meaning and purpose of dreaming has been a source of speculation over the course of history. It was not until 1900, when Sigmund Freud (1856-1939) published The Interpretation of Dreams, that there was a comprehensive theory that placed dreams as centrally important for the understanding of waking behavior. This theory formed the basis of the psychoanalytic treatment method, which relied on patients’ recall of and associations to their dreams.
Dream interpretation dominated the practice of psychiatry for the next fifty years. The key to their understanding rested on Freud’s model of the mind as operating on three different levels—the conscious, preconscious, and unconscious—with all three influencing waking behavior. The conscious mind is what is in awareness in the moment; the preconscious consists of mental representations that, although not in immediate awareness, can be brought to consciousness voluntarily; the unconscious material, while not accessible by an act of will, is a major source of dream scenarios. The unconscious contains the remains of early childhood experiences related to learning to control basic impulses (particularly those of sex and aggression) and to express these only in a socially appropriate fashion. These powerful instinctual drives remain active throughout life and cause anxiety if they threaten to become conscious. They are controlled during waking by defenses, the learned ways of keeping them out of consciousness. These defenses are weakened during sleep, when the danger of a breakthrough into action, which would cause internal guilt or external punishment, is reduced due to our inability to act while sleeping.
Freud believed that dreams allow the mind to hallucinate the fulfillment of these prohibited impulses safely, without the risk of consequences. Because the risk, though lowered, is not completely absent during sleep, and to ensure that the sleeper is not shocked into wakefulness, dreams express these wishes in disguised forms. Thus, dreams require some expert interpretation to decode their true meaning. Freud distinguished the dream story, called the manifest dream, from its underlying or latent meaning, which refers to the unfulfilled instinctual wishes. The latent meanings can only be expressed symbolically to allow their safe gratification. The interpretation of dreams thus became the basis for understanding patients who came for help with emotional problems of overcontrol or undercontrol of their impulse-related behavior.
A challenge to this view followed the discovery in the 1950s of the close association of rapid eye movement (REM) sleep and the experience of dreaming. By monitoring the brain waves, eye movements, and muscle tone of persons observed while sleeping in a laboratory, three to five episodes of REM sleep could be identified each night. If the sleeper were then awakened at these times and asked to report what he or she had just been experiencing, 85 percent of the time the sleeper would describe a dream. The regularity of REM sleep, occurring approximately every ninety minutes, allowed a more complete sampling of dreaming than had ever before been available. Many people have no recall of their dreams, and even those with good recall rarely remember more than one per night. The sleep laboratory technique opened the door to studies of the continuity of a theme from first dream to last, and of the relation of the dream content to some waking, emotion-arousing stimuli, such as a frightening or sexually arousing movie, or an experimentally induced change in a basic need, such as thirst by depriving sleepers of water beforehand. For the most part, these studies showed that dreams are difficult to influence and more often follow their own agenda.
The finding that REM sleep is turned on periodically, starting at the primitive brain structure called the pons, further challenged Freud’s view. Dreams could not have any inherent meaning if they spring from the nonthinking pons. The activation-synthesis hypothesis of dreaming, proposed in 1977 by J. Allan Hobson and Robert McCarley, explained the apparent (manifest) meaning of a dream as an afterthought, most likely resulting from associations to the sensory images, which are accidental, triggered by the activation of a brain pathway that flows upward from the pons to the visual association areas of the cortex. These images are then linked into a dream story under the influence of the ongoing emotional concerns of the dreamer. In this way dreams are given meaning in the same way as are waking stimuli, when what we see is colored by the present state of our needs and interests. This theory robbed dreams of any special meaning and had a generally dampening effect on dream research for the next twenty years.
The resurgence of interest in dreaming is partly due to the development of sleep disorder centers, which attract patients with dream disorders, such as the repetitive nightmares of those suffering from posttraumatic stress disorder. The resurgence of interest is also partly a result of the development of more sophisticated technology. Brain imaging methods allow a closer look into the areas of the brain activated when REM sleep is ongoing. Using this technology, differences between those areas that are more active in REM sleep than in non-REM sleep or waking confirm that during REM the brain is more intensely active in areas related to instinctual behaviors (hypothala-mus and basal forebrain), the emotional areas (limbic and paralimbic), and the visual association areas of the cortex. Activity is lessened during REM in the areas associated with the executive functions: thinking and judgment (the prefrontal cortex).
Brain imaging studies are looking into differences between REM sleep in normal persons and in those with various psychiatric diagnoses. This method has illuminated the abnormality of REM sleep of those suffering from major depression. These patients, when most symptomatic, have increased REM sleep but greatly reduced recall of any dreaming. Their imaging studies show more activity in the emotional areas (limbic and paralimbic) than do nondepressed persons, and heightened activity in the executive cortex. Perhaps these patients are flooded with negative emotion but are overcontrolled in its expression. In Freud’s terms, the dream function has failed to allow gratification of unconscious wishes. Without dreams these patients would be difficult to treat psycho-analytically and require another approach.
