Hypothalamic integration of central and peripheral clocks

During sleep, our biological clock prepares us for the forthcoming period o f activity by controlling the release of hormones and the activity of the a utonomic nervous system. Here, we review the history of the study of circad ian rhythms and highlight recent observations indicating that the same mech anisms that govern our central clock might be at work in the cells of perip heral organs. Peripheral clocks are proposed to synchronize the activity of the organ, enhancing the functional message of the central clock. We specu late that peripheral visceral information is then fed back to the same brai n areas that are directly controlled by the central clock. Both clock mecha nisms are proposed to have a complementary function in the organization of behaviour and hormone secretion.