The circadian clock is an internal biological system that regulates sleep-wake cycles, as well as many physiological functions such as body temperature and hormone production. In many animals, this clock relies on a network of neurons that generates rhythms of approximately 24 hours.
Dopamine is the molecule used by the biological clock to transmit information to a region of the brain involved in sleep and awakening. This discovery stems from work done by scientists from the University of Geneva on the Drosophile fly.