The purpose of this study is to explore whether active transcranial direct current stimulation during cognitive rehabilitation tasks can boost cognitive enhancement without severe side effects in mild cognitive impairment or mild dementia patients.

This study explores the additive effect of transcranial direct stimulation compared to sham stimulation during cognitive rehabilitation tasks in mild cognitive impairment or mild dementia patients. Potential participants are recruited by physicians' referral or self-entry. Informed consent by a clinical research coordinator and research physician is performed followed by screening. Participants who passed screening go through 10 sessions of active or sham transcranial direct current stimulation and are evaluated their cognitive function at screening, at the end, and two weeks after the intervention. For quality assurance, independent researcher regularly monitor and audit as participants are enrolled in the trial.

Inclusion Criteria:

• participants with a diagnosis of either major neurocognitive disorder or mild neurocognitive disorder, defined in Diagnostic and Statistical Manual of Mental disorder (DSM-5)
• taking the stable dose of psychotropic medication, such as cholinesterase inhibitors or NMDA(N-methyl-D-aspartate) receptor antagonist, for the past two weeks
• ambulant by oneself with or without aiding devices.

Exclusion Criteria:

• with severe psychotic symptoms requiring antipsychotic treatment
• with risks of hospitalization within 6 weeks because of severe depression and/or suicide ideation
• clinically contraindicated to electroconvulsive therapy (ECT) or transcranial direct current stimulation (tDCS)
• with the Mini-Mental State Examination (MMSE) score of less than 18 or the Clinical Dementia Rating Scale (CDR) score of more than 2,
• unable to participate for more than 2 days during the trial
• unable to write a sentence or copy a figure on MMSE at screening.