View larger version | The brain orchestrates the daily sleep-wake cycle by responding to external cues, such as sunlight, and the body’s own rhythms. Levels of chemical messengers, hormones and proteins rise and fall in key parts of the brain to generate wakefulness and sleepiness. Tracking brain activity during sleep, scientists have also revealed regions important for other putative functions of sleep, such as memory storage and information processing. Credit: Illustration by charles floyd