I. Introduction
Alzheimer's disease (AD) is the most common form of dementia that often affect individuals over 65 years old, which strongly impacts human's thinking, memory and behavior [1]–[3]. This disease always progresses along a temporal continuum, initially from a normal control (NC) stage, subsequently to mild cognitive impairment (MCI) and eventually deteriorating to AD. According to a recent report from Alzheimer's Association [4], the total estimated prevalence of AD is expected to be 60 million worldwide over the next 50 years, thus gaining growing attention in clinical research.