In ancient societies, dreams guided political, social and everyday decisions. Early books, including the Bible, are filled with references to divine visions during sleep. On the other hand, Greek philosophers attributed dream content to natural sources, which were precursors of modern theories of dream formation and significance.
In the 19th century, Sigmund Freud promoted one popular theory that dreams gave us access to our unconscious repressed conflicts. He called them "the royal road to a knowledge on the part of the unconscious plays in mental life." However, another early psychoanalyst, Alfred Adler, believed that dreams reflect current lifestyle and offer solutions to contemporary problems.
Interest in modern dream research was revived at the same time as the discovery of rapid eye movement (REM) sleep and its association with an increased frequency in dreaming by Eugene Aserinsky and Nathaniel Kleitman in 1953. "When we look at the importance of dream research we get back to the question 'Does sleep itself have a function?' We know today, if you sleep you have an improved waking experience. We also know that sleep allows dreaming to occur," according to Jim Pagel, MD, director of the Sleep Disorders Center of Southern Colorado and a participating NSF Community Sleep Awareness Partner®. "If dreaming has an actual function, it really supports why we spend a third of our lives sleeping."
While scientists still do not know much about why or how we dream, some have suggested that we typically spend more than two hours dreaming each night. Many people experience their most vivid dreams during REM sleep; less vivid dreams occur at other times of the night. Comparative research has shown that while most mammals and birds show signs of REM sleep, reptiles and other cold-blooded animals scientists still don't know—and probably never will—if animals dream during REM sleep, as humans do. "How can you prove that another person has dreams?" says Jerome Siegel, PhD, a professor of Psychiatry at the UCLA Center for Sleep Research. "You ask them."