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Nature Neuroscience 11, 628–630 (1 June 2008) | doi:10.1038/nn0608-628

How the clock sees the light

Russell N Van Gelder

It is ironic that the master pacemaker of the mammalian circadian clock, the suprachiasmatic nucleui (SCN), is located in a particularly dark place in the body (buried deep in the brain, at the base of the third ventricle), yet their function is to maintain synchrony with an external lighting cycle. To do this (as must occur for us to overcome jet lag, for example), the clock must somehow sense the external lighting cycle.