Dream is a mental event or series of events that takes place during sleep. Throughout history, many people have thought that dreams are caused by supernatural agents trying to send a message to the dreamer. Others have believed that dreams are actual experiences, reflecting the wanderings of the soul at night. Today, scientists consider dreams to be the result of naturally occurring biological processes in the brain.
Everyone dreams, even if they seem never to remember their dreams. Many dreams are easily forgotten.
The content of dreams.
Many dream experiences resemble sensory experiences in waking life. For most people, vision is the main sense in dreams. The events of dreams, especially the most vivid ones, usually take the form of a story. In some dreams, the dreamer takes part in the story. In others, the dreamer merely “watches” the tale unfold.
In most dreams, the dreamer cannot control what is happening. There is little logical thought, and events occur that could not happen in waking life. Dreamers are usually unaware such events are unlikely or illogical. Generally, dreamers do not recognize that they are dreaming. But occasionally, they do. Such a dream is known as a lucid dream. Dreamers may be able to alter the events in a lucid dream.
Dreams can be quite emotional. Certain emotions are more likely than others. Anger, fear, and joy, for example, are more common than guilt, sadness, and shame.
Some themes are also more likely to occur. For example, being chased by an unknown pursuer is a common theme of dreams across a wide range of cultures. Events and elements experienced recently in waking life are less likely to appear in dreams than older events, unless the events are emotionally significant or intense.
The biology of dreams.
Dreaming, like all mental processes, is a product of the brain and its activity. Whether a person is awake or asleep, the brain produces electrical waves. Scientists measure these waves with an instrument called an electroencephalograph. Most of the time during sleep, the brain waves are large, slow, and fairly regular in shape. But at times, they become smaller, faster, and irregular in shape.
During periods of fast brain waves, the person’s eyes move rapidly, as though the sleeper were watching a series of events. This stage of sleep, called _REM (r_apid _e_ye _m_ovement) sleep, is when most dreams occur, especially dreams with a vivid, storylike quality. If awakened during REM sleep, the dreamer will likely recall details of the dream. Not all dreams come from REM periods, however. Many people report dreamlike states when awakened from non-REM sleep or while falling asleep.
During REM sleep, the pathways that carry nerve impulses from the brain to muscles are blocked. Therefore, the body does not move during dreams.
Most adults have three to five REM periods during the night. The sessions occur about every 90 minutes and last from about 5 to 30 minutes each. REM periods get longer as the night progresses. Dreams also become longer throughout the night.
Most of a part of the brain called the cerebral cortex is highly active during REM sleep. The cortex is stimulated by neurons (nerve cells) that carry impulses from part of the brain called the brain stem. During dreaming, activity is suppressed in the part of the cerebral cortex that receives visual information. Also, a portion of the frontal lobe (front part of the brain) is inhibited. This area is involved in higher thought and goal-directed activity. A different portion of the frontal lobe is highly active. This area is involved in emotion, especially anxiety.
Another part of the brain that is highly active during REM sleep is the amygdala. The amygdala is also important for emotion, especially fear.
Two parts of the brain seem important in producing dreams. One area is in the part of the cerebral cortex where the occipital, temporal, and parietal lobes meet. The other area is deep within the frontal lobe. If either of these areas is damaged, dreams are reduced or absent.
The meaning and function of dreams.
No one knows exactly why we dream. Many experts believe that dreams are related to our deep wishes and fears. They think that dreams ultimately are important for mental health. During the 1890’s, Sigmund Freud, the Austrian physician who originated psychoanalysis, developed one of the best-known theories of dream interpretation. Freud suggested that dreams are fulfillment of wishes, usually in disguised form. Other scientists study the evolutionary origins of dreaming. They suggest that dreams enable people to mentally rehearse behaviors that are critical for survival, such as running or fighting. Still others maintain that dreams perform no particular function. To them, dreams are merely extensions of the kind of mental activity that we experience while awake. Others see dreams as meaningless responses of the cerebral cortex to random stimulation from the brain stem.
Sleep researchers have found that REM sleep is important for establishing long-term memories. REM sleep may also help with creative problem-solving. But scientists do not yet know if dreaming during REM sleep is simply a by-product of these brain processes or an essential component of them.
