PerspectiveCircadian Rhythms

Temperatures to Communicate By

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Science  15 Oct 2010:
Vol. 330, Issue 6002, pp. 329-330
DOI: 10.1126/science.1197747

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Summary

If a large orchestra were suddenly without a conductor, the individual players could continue to play music, but the overall harmony of the symphony likely would be lost. This relationship is analogous to the circadian timing system in mammals, which governs the wake-sleep cycle and synchronizes biological processes and behaviors to roughly 24-hour time periods. In the mammalian brain, a “master clock” located in the suprachiasmatic nucleus (SCN) of the hypothalamus keeps in sync the many independent clocks located in tissues and organs throughout the body (1). The coherence of these peripheral clocks is achieved presumably through a two-tiered system in which the master clock follows the daily light-dark cycles, informed by ocular pathways that detect light. Somehow this temporal information is converted to nonphotic cues that permeate the rest of the body, coordinating the oscillation of peripheral clocks (2). On page 379 of this issue, Buhr et al. show fascinating differences in the properties of the mouse SCN and peripheral clocks that provide a simple yet elegant model for how peripheral clocks “see” the light initially perceived by the SCN (3).