Online HD-tDCS Over the Left DLPFC During a Working Memory Task for Treating Negative Symptoms of Schizophrenia

Inclusion Criteria: * Subjects aged 20-65 years and diagnosed with the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition ( DSM-5 ) schizophrenia or schizoaffective disorder * Duration of illness≧1 year * With a clinical presentation of predominant negative symptoms (according to the clinical judgment of 2 experienced psychiatrists) and the Positive and Negative Syndrome Scale (PANSS) score \> 70 * Receiving stable antipsychotic drug regimen \>8 weeks. Exclusion Criteria: * Subjects with current psychiatric comorbidity or active substance use disorder with the exception of caffeine and/or tobacco * Having contraindications for tDCS, e.g., implanted brain medical devices or metal in the head * Pregnancy at enrollment * Having a history of seizures, intracranial neoplasms or surgery, severe head injuries, or cerebrovascular diseases