DEFINING SLEEP AND MEMORY Stages of Sleep

About one-third of a person’s life is spent sleeping, yet in spite of the advances in understanding the processes that generate and maintain sleep, the functional significance of sleep remains a mystery. Numerous theories regarding the role of sleep have been proposed, including homeostatic resto-ration, thermoregulation, tissue repair, and immune control. A theory that has received enormous support in the last decade concerns sleep’s role in processing and storing memories. This article reviews some of the evidence suggesting that sleep is critical for long-lasting memories. This body of evidence has grown impressively large and covers a range of studies at themolecular, cellular, physio-logic, and behavioral levels of analysis