Why We Dream
The hour or two we spend dreaming each night has long been a mystery. There are several theories, though, as to why we dream: we dream to examine what is going on in our lives and the experiences of the day; we dream because of chemical changes that occur in the brain during sleep; we dream as a means to vent our problems and bad experiences. Another theory holds that we dream as a means to interpret what others think of us. Still others say that dreams help to fix memories in the brain. Dreams probably serve a number of purposes.
One of the most important purposes of dreams seems to regulate mood. As you dream through the night, any distressing emotions you may have accumulated during the day (anger, anxiety), are neutralized by old memories. The process defuses the distressing emotions, and you awaken refreshed and released from their burden. However, when this venting process is interrupted, such as when we are deprived of the last three hours of sleep, the period during which most dreams occur, we are likely to awaken irritable. In clinically depressed people, the mood-regulating function is disrupted and dreams get more and more negative toward morning. Such people generally wake up in very foul moods.
On the average, we experience five separate dreams each night. These occur during the rapid eye movement (REM) stage of the sleep cycle, which normally occurs after 90 minutes of deep sleep and every 90 minutes thereafter.
In ancient times, people gave great significance to the dreams they could remember when they awoke. Today, we know that people who have pleasant dreams are likely to start their days with a smile while bad dreams and nightmares can cause distress and disrupt needed sleep.
You probably won't remember a dream unless you wake up right after it has occurred. That’s why the last dream of the night is the one that is most often recalled. People who say they dream a lot are usually light sleepers who awaken often.
Science Looks at Dreaming
Positron Emission Tomography (PET) scanning has allowed scientists to discover what happens in the brain of the dreamer. A tiny amount of radioactive glucose is injected into the blood and "lights up" to show what parts of the brain are active. During dreams, the visual cortex of the brain, which is the part that creates pictures in the mind, is wide awake, as is the limbic system, which generates emotions. However, the prefrontal cortex, which is the "thinking brain" that plans, makes rational connections and draws conclusions, is dormant. As that is the case, it is not surprising that dreams are almost always composed of images that are charged with emotion but lack logic.
Studies of people who recalled several dreams occurring in one night have found that dreams operate in time sequences. The first dream would involve recent images, like someone seen the day before. The second one would pertain to events from the recent past: weeks or months earlier. The third dream might be about thoughts or experiences from years ago while the final dreams of the night often come from long ago: childhood or infancy. Such dreams generally share an emotional theme, variations on a feeling: happiness, insecurity, fear, etc., that dominated a person’s thoughts when they went to sleep and throughout the night, dreams repeat the same emotional experience, as that experience occurred earlier and earlier in life.
People throughout the world obviously share the same emotions, thus certain dreams are found in virtually all cultures. One common dream is the experience of falling. One explanation for that universal dream is that we all started in life crawling on all fours and fell a great deal until we mastered walking on two feet. Feelings of uncertainty and instability in adult life may reactivate that very early memory of falling and produce itself in a dream. Another universal theme is dreaming about being back in school, unprepared for an important exam or challenge. It's a nearly universal early experience that returns when we feel inadequate and fear failure.