In addition, although we tried to exclude individuals with cerebrovascular disease and neurodegenerative diseases by thorough medical history and structural MRI, underlying risk factors and neuropathology were not assessed in this study, such as APOE genotype and amyloid-β, which have been observed to be related to CBF changes in normal aging (Wierenga et al., 2013; Michels et al., 2016). This evidence concerns the gene APOE and cerebrovascular disorder.