[Current understanding of sleep, dreaming and related memory consolidation].

Sleep is a naturally recurring state found throughout the animal kingdom and characterized by a reversible loss of consciousness. Although in humans the daily amount of sleep decreases with aging, the total amount of time spent for sleep is estimated as up to one-third of one's lifetime. In mammals, sleep shows a clear daily rhythmicity as well as nightly phases, which are strongly controlled by the circadian clock located in the hypothalamic suprachiasmatic nuclei and are also regulated by ambient light. While it is certain that sleep is critical for survival in general, the functional significance of sleep is still under investigation. Dreaming is a common psychological phenomenon occurring during human sleep, yet its content and natural function, if any, are still a matter of debate. In recent years, accumulated evidence strongly supports the notion that new information acquired during the day time is processed and transformed into long-term memory in a complicated and sophisticated way during sleeping. Such information processing is commonly referred to as memory consolidation.