Dream

A dream is a succession of images, dynamic scenes, ideas, and emotions. These events occur involuntarily in the mind during specific stages of sleep. Humans typically spend more than two hours dreaming every night. Each individual dream lasts approximately 5 to 20 minutes.

The study of these experiences is known as oneirology. While scientists study the neurophysiology of dreams, many mysteries remain. It is still unknown exactly where in the brain dreams originate. Researchers do not know if a single region or multiple regions are involved. The specific purpose of dreaming for the mind and body remains a mystery.

Dreams occur primarily during the rapid-eye movement (REM) stage of sleep. During REM, brain activity is high and resembles the activity of being awake. Because REM sleep is detectable in many species, scientists conjecture that animals dream. However, humans also dream during non-REM sleep. It is difficult to prove dreaming in non-humans, human fetuses, or pre-verbal infants. This is because a dream must be reduced to a verbal report to be studied. A verbal report is only a person's memory of the dream, not the experience itself.

The visual nature of dreams is often described as phantasmagoric. This means that different locations and objects continuously blend into one another. These visuals are generally reflective of a person's own memories and experiences. However, conversations in dreams can take on highly exaggerated or bizarre forms. Some dreams may even form elaborate stories with complex, new worlds. People who are blind from birth do not have visual dreams. Instead, their dream content relates to other senses like hearing, touch, smell, or taste.

Historically, the way humans frame the dream experience has shifted significantly. In ancient Mesopotamia and Egypt, dreams often dictated post-dream behaviors. These were often "visitation dreams" involving a deity or a prominent ancestor. In these dreams, the dreamer was often passive. The visual content mostly served to frame authoritative auditory messages. For example, Gudea, a Sumerian king, rebuilt a temple because a dream commanded it. After antiquity, these passive experiences gave way to visualized narratives. In these newer styles, the dreamer becomes an active character in the story.

Significant research has helped map the content of human dreams. From 1940 to 1985, Calvin S. Hall collected over 50,000 dream reports at Western Reserve University. In 1966, Hall and Robert Van de Castle published a study using a coding system. They analyzed 1,000 dream reports from college students. Their results showed that dream content is similar across different parts of the world. The study found that anxiety was the most common emotion in dreams. Negative emotions were more frequent than positive ones. Sexual dreams occurred in only about 8% to 10% of reports.

Modern neurophysiology offers theories on how the brain constructs these narratives. Some scientists suggest that dream imagery is produced by the same structures used for waking perception. There is a theory regarding a "left-brain interpreter." This concept suggests the left hemisphere creates a plausible story from random electrical signals. The cortex may attempt to synthesize a story from sparse or distorted information. This helps the brain make sense of haphazard neural input.

This process explains why dreams often feel like they have a running narrative.

Different theories exist regarding the biological function of dreaming. In 1886, a physician named Robert suggested dreams help erase unprocessed sensory impressions. He believed dreams help develop ideas that were incomplete during the day. Conversely, Sigmund Freud argued that dreams serve to preserve sleep. He believed dreams represent fulfilled wishes to prevent the dreamer from waking up. Other views look at the Darwinian perspective of biological necessity. These theories attempt to explain if dreaming provides a benefit for natural selection or simply has no negative impact on fitness.