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. 2007 Jun 14;115(9):1357–1362. doi: 10.1289/ehp.10200

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The suprachiasmatic nuclei (SCN) and other circadian oscillators drive a broad range of circadian rhythms. These rhythms, in turn, can feedback on the oscillators. In addition to this feedback regulation, the oscillators are entrained by photic and nonphotic environmental time cues.