HCRT and Alzheimer disease: Outside of the SCN, other neurochemical and neuropathological changes in AD that have been linked to declined circadian and sleep function are reduced expression of orexin A and adenosine A1 receptor (Liu et al., 2019), degeneration and atrophy of cholinergic neurons and cholinergic nuclei in the basal forebrain and degeneration of hypothalamic orexin neurons (Matsumoto & Tsunematsu, 2021).