Our knowledge of dreams can be explained under three main headings - pre-scientific, psychoanalytical, and contemporary dream physiology and psychology.
Dreams have long been accounted for by a wide range of myths, interpretations and speculation. In Homer's Iliad, dreams are said to have affected the outcome of the Trojan War. Hippocrates, the father of medicine, claimed that dreams indicated the way in which a sickness should be cured. The earliest-known written documents, dating back thousands of years before the birth of Christ, contain a number of dream interpretations.
Sigmund Freud, the founder of psychoanalysis, was of the opinion that interpreting a person's dreams led to an understanding of the subconscious mind and its functions. Dreams have meaning, even though that meaning may not always be clear. Freud described what he called the manifest dream sequence, in which the latent meaning of a dream can be understood by means of association when the person is asked on waking to account for details of the dream. Freud regarded dreams as the processing of what has happened during the day - a perception also held by many contemporary thinkers.
Neuro-psychological dream researchers regard dreams as being the means by which the central nervous system processes accumulated information. Researchers are now trying to more closely define the differences between:
A. Thought and experiences during the daytime, i.e. when a person is conscious and awake.
B. Activities during the night, when a person is sleeping and dreaming.
The processing of information takes place both during waking hours and sleep. If a sleeping person is aroused, he or she can almost always account for the more straightforward dream experiences. Dream experiences can be lively and highly complex, depending on how deeply the person sleeps. Most dreams, however, are exceedingly trivial. Dramatic dreams with an element of horror, or those of a more erotic nature, are rarer than might be expected. In fact, most dreams are completely forgotten. Some researchers believe that people dream in order to forget, that dreams can be an expression of the way in which information stored in our brain is sorted and cleared.