HD-tDCS for Adolescent Bipolar Depression Targeting S1

Inclusion Criteria: * Between 12 and 18 years of age; * Participants fulfill the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnostic criteria for bipolar disorder (BD). Participants are assessed by the Structured Clinical Interview for DSM-IV for Axis I Disorders (SCID-I, patients' age ≥18 years old), or the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime version (K- SADS-PL, patients' age\< 18 years old); * A current moderate or severe depressive episode defined by HAMD≥17 and Young Mania Rating Scale (YMRS) \<12; * Participants receive a stable psychotropic medication regimen prior to randomization to the trial and are willing to remain on the stable regimen during the HD-tDCS treatment phase; * Participants and 1 or 2 parents (patients' age\< 18 years old) provide informed consent after the detailed description of the study. Exclusion Criteria: * Prior rTMS or tDCS or electroconvulsive therapy (ECT) treatment or standard psychological therapy within 6 months prior to screening; * Comorbidity of other DSM-IV axis I disorders or personality disorders; * Judged clinically to be at serious suicidal risk; * Diabetes mellitus, hypertension, vascular and infectious diseases and other major medical comorbidities; * Unstable medical conditions, e.g., severe asthma; * Neurological disorders, e.g., history of head injury with loss of consciousness for ≥ five minutes, cerebrovascular diseases, brain tumors and neurodegenerative diseases; * Mental retardation or autism spectrum disorder; * Contraindications to MRI (e.g., severe claustrophobia, pacemakers, metal implants); * Contraindications to tDCS (e.g., metal in head, history of seizure, EEG test suggesting high risk of seizure, known brain lesion); * Current drug/alcohol abuse or dependence; * Pregnant or lactating female.