Inclusion Criteria:  60 ≦ age ≦ 90 Clinical Dementia Rating Scale = 0.5 or 1 Under treatment with donepezil、rivastigmine or galantamine with good medical adherence Get a signed informed consent from the patient or his/her family  Exclusion Criteria:  Not using or poor medical adherence to donepezil、rivastigmine or galantamine Combined using memantine or other cerebral perfusion enhancing agent, such as Piracetam, Dihydroergotoxine, Nicergoline etc. New cerebrovascular disease happens during 3-year follow up Mixed type dementia Major psychiatric disease (such as depression, bipolar disorder, schizophrenia) or substance abuser (such as alcohol, illegal drug, hypnotics) Heart failure, end stage renal disease, liver cirrhosis, or other major organ failure Severe hearing impairment results in incomplete survey of neuropsychatric evaluation No informed consent or no regular follow up