While the precise etiology of depression in dementia is yet unknown, the most likely explanations are as follows: (1) vascular disease; (2) alterations in glucocorticoid steroids and hippocampal atrophy; (3) increased deposition of β-amyloid plaques; (4) inflammatory changes; and (5) deficits of nerve growth factors or neurotrophins [64]. Here, BDNF is linked to major depressive disorder.