Direct retinal input to the SCN, as well as the direct NPY input from the retinorecipient IGL, are also possible candidates as pathology and dysfunction have been reported in these structures in AD (Erskine et al., 2016; La Morgia et al., 2016), and properly timed light exposure improves circadian rhythms and mood whereas ill-timed light exposure has deleterious effects (Bedrosian and Nelson, 2017). This evidence concerns the gene NPY and Alzheimer disease.