CLOCK and Parkinson disease: Endo et al. studied the effect of chronic dopamine exposure on the function of the SCN and the expression of the circadian clock genes PER3, and Nr1d1 and -2 (nuclear receptor subfamily 1 group D member 1 and 2) at the single-neuron level in cultured mouse SCN and the clinical outcome of bright-light therapy against sleep problems in PD patients receiving DT.