Dreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, philosophical intrigue and religious interest throughout recorded history. The scientific study of dreams is called oneirology. Science has proven to an extent that all mammals dream. The scientific approach to dreams has been conducted through the discovery of REM sleep.
Dreams mainly occur in the rapid-eye movement (REM) stage of sleep—when brain activity is high and resembles that of being awake. REM sleep is revealed by continuous movements of the eyes during sleep. At times, dreams may occur during other stages of sleep. However, these dreams tend to be much less vivid or memorable. Dreams can last for a few seconds, or as long as twenty minutes. A person is more likely to remember the dream if he or she is awakened during the REM phase.
Dreams are a connection to the human subconscious. They can range from normal and ordinary to the overly surreal and bizarre. Dreams can at times make a creative thought occur to the person or give a sense of inspiration. Dream imagery is often absurd and unrealistic, and the events in dreams are generally outside the control of the dreamer, with the exception of lucid dreaming. Dreamers are usually not self-aware in their dreams; thus the dreams seem as reality. Dreams can have varying natures, such as frightening, exciting, magical, melancholic, adventurous, or sexual.
The opinions about the meaning of dreams has varied and shifted through time and culture. Dream interpretations date back to 5000-4000 BC, where they were documented on clay tablets. The earliest recorded dreams were acquired from materials dating back approximately 5000 years, in Mesopotamia. In some of the earliest societies, the dream world was regarded as an extension of reality. In the Greek and Roman periods, dreams were seen through a religious lens. The people believed that they were direct messages from the gods or from the dead. The people of that time relied on their dreams for solutions on what to do, or what course of action to take. They also believed dreams forewarned and predicted the future. Throughout history, people have sought meaning in dreams or divination through dreams. Dreams have also been described physiologically as a response to neural processes during sleep; psychologically as reflections of the subconscious; and spiritually as messages from the Soul, from a god or from the deceased, or as predictions of the future. Some cultures practice dream incubation with the intention of cultivating dreams that are prophetic or contain messages from the divine. Some of these interpretations remain today embedded in the minds of individuals. The randomness or hidden meaning of dreams remains disputable.
The most prolific dream theories and interpretations were developed by Sigmund Freud, the Austrian neurologist who developed the discipline of psychoanalysis. Freud explained dreams were manifestations of our deepest desires and anxieties. During sleep, dreams would manifest childhood repressed memories and obsessions. In The Interpretation of Dreams, Freud developed a psychological technique to interpret dreams and devised a series of guidelines to understand the symbols and motifs that appear in our dreams.