| Twenty-four hour rhythms are an essential property of many living organisms, and arise from an internal circadian clock. In mammals, this clock resides in the suprachiasmatic nucleus (SCN), a tiny structure of 20,000 neurons at the base of the brain. This nucleus generates intrinsic circadian rhythms which are transmitted to other parts of the central nervous system. As a consequence, many behavioral, biochemical and physiological events show dramatical daily fluctuations. While circadian rhythms parallel the rotation of the earth, seasonal rhythms follow the earth revolution around the sun. Both classes of rhythms have developed as an adaptation to the considerable changes in the environment, and interestingly, both are controlled by the SCN. Although it is clear that the SCN clock is comprised of many individual oscillatory neurons, it is not clear how these neurons communicate and synchronize to one another, or how they respond to environmental light input. With state-of-the-art methods we will study how interacting neuronal populations within the clock adapt to the environmental light cycle and to changes in day length. The experimental findings will be incorporated in a multi-oscillator computational model of the circadian clock. Using this combined approach we will elucidate how system level properties of the circadian system emerge from a multitude of coupled circadian oscillators. We aim to show not only that new properties emerge at multiple levels of organization, but also how they emerge from interactions between oscillating units. |
