Sleep (IMAGE) Johns Hopkins Medicine Caption The area of the brain known as the suprachiasmatic nucleus (SCN) is the body's master clock. It uses light to synchronize the body's rhythms with night and day. It directly controls sleep/wake cycles and indirectly controls other processes, like hunger and thirst, by controlling the body's thermostat, the preoptic area of the brain. Credit Johns Hopkins Medicine Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.