Figure 1: Two main mechanisms may induce behavioral and psychological symptoms of dementia (BPSD) in Alzheimer’s disease (AD). One mechanism might induce rapid cognitive decline and BPSD mainly related to behavioral symptoms, while the other might induce BPSD mainly related to psychiatric symptoms and slow cognitive decline. Thus, not all patients with AD show BPSD at the mild stage as well as at the severe stage (upper panel), while a substantial group of patients only have BPSD at the severe stage (lower panel).