The deregulated cholinergic system, neurodegenerative frontal and subcortical regions, pathological features of AD and PD, gray matter atrophy, altered neurotrophin levels (Devos et al., 2010; Rovio et al., 2010; Dada et al., 2014; Beauchet et al., 2016; Hsueh et al., 2018; Blumen et al., 2019). Here, BDNF is linked to Alzheimer disease.