Phase synchronization of circadian oscillators induced by a light-dark cycle and extracellular noise

In mammals, the master circadian pacemaker is considered the suprachiasmatic nucleus (SCN) of the hypothalamus. Individual cellular clocks in SCN, the circadian center, are integrated into a stable and robust pacemaker with a period length of about 24 hours, which are remarkably accurate at timing biological events despite the randomness of their biochemical reactions. In this paper, we study the effect of the Light-Dark cycle and environment noise on the daily rhythms of mammals and give some numerical analysis. The results show that the environment noise makes for phase synchronization but it can not make the oscillators get phase synchronization with period of 24-h. On the contrary, the threshold of the strength of light that makes the oscillators to get the phase synchronization with period of 24-h with environment noise is larger than that in the case without environment noise.