In mammals, the suprachiasmatic nucleus (SCN) is the site of the pacemaker that is responsible for circadian rhythms in behavior and physiology, and it is currently believed that all rhythms of SCN cells are endogenously driven and independent of extra-SCN tissues. The eye has also been shown to contain an independent circadian oscillator, but the role of the ocular clock and whether it influences the SCN are unknown. They have found that a rhythm of phosphorylation of mitogen-activated protein (MAP) kinase in an anatomically distinct subdivision of the SCN was completely abolished by bilateral enucleation in hamsters and mice, indicating that the eye is necessary for a circadian rhythm within the SCN. Tech. Link