A Pilot Study of tDCS for Mild to Moderate Alzhemier's Disease

Inclusion Criteria: * Subjects who have Korean version of Mini Mental Status Examination score 10 to 24 * Subjects who have SVLT and RCFT delayed recall test scores lower than 1.5SD * Subjects who have had other cognitive impairments besides memory * Subjects who have Seoul-Instrumental Activities of Daily Living score (S-IADL) of 8 or more. * Subjects who are only dementia of Alzheimer's type * Subjects who are right-handed * Subjects who are able to read and write * Both patient and legally responsible caregiver has provided informed consent * According to the latest MRI result, periventricular white matter cap or band is less than 10mm, or the deep white matter hyper-intensity is less than 25 mm Exclusion Criteria: * Subjects who have a history of stroke and seizures * Subjects who have any illnesses that may disturb the patients completing the trials, including stroke, Parkinson's disease, type 1 diabetes, uncontrollable high blood pressure, Huntington's disease, cerebral palsy, liver failure, nephritis, encephalitis, meningitis, scleroma, seizures and a transient ischemic attack. * Subjects who have a History of DSM-IV Axis I disorders * Subjects who have neurologic problems on physical examination that cause memory disturbances * Subjects who have Extremely sensitive skin * Subjects who have suffered from the cancer in 3 years * Subjects who have had a cerebrovascular neurosurgery in medical history * Subjects who have dyspnea in sitting position * Subjects who have problems with memory, language and problem-solving for 2 hours after the heart attack. * Subjects who have a history of drug or alcohol abuse (in the past 5 years) * Subjects who have a history of mental or emotional disorders (in the past 5 years) * Subjects who have been lapsed into unconsciousness for an hour because of other reasons than general anesthesia * Subjects who have a history of hospitalization due to head injury * Subjects who are unable to read even with glasses * Subjects who are unable to understand the conversation due to the hearing defect (even with the hearing aid)