In the 1950's, it was discovered that RAPID EYE MOVEMENTS (REMS) were associated with dreaming, thus providing a possibility for studying the biological functions of DREAMS experimentally. This experimental work appears to support FREUD'S contention that dreams are an essential part of psychological functioning. When people are awakened during REM SLEEP and thus deprived of their dreams, they seem to experience signs of psychological disturbance. Where Freud asserted that the dream functions to keep the dreamer asleep by transforming his unacceptable wishes into a more comfortable form, some experimenters would argue that the reverse is more nearly true, that the function of sleep is actually to allow one to dream. Some people can function well on relatively little sleep but all human beings (and even higher animals) appear to have a biological need to dream when they are asleep.