Efficacy and Safety of Task-specific, Biomarker-driven, HD-ctACS inTRD.

Inclusion Criteria Age between 18 and 65 years, any gender. Meets DSM-5 diagnostic criteria for Major Depressive Disorder (MDD), currently in a moderate to severe episode (total HAMD score ≥ 17). Meets the definition of Treatment-Resistant Depression (TRD): failure to respond to or intolerance of at least two antidepressant medications from different mechanistic classes, administered at an adequate dose and duration (e.g., 6-8 weeks) during the current depressive episode. Agrees to maintain a stable dosage of their current antidepressant medication regimen (if taking any) throughout the study period. Able to comprehend the study procedures and voluntarily provide written informed consent. Has intracranial deep brain electrodes implanted for research purposes, with electrodes located in the target brain regions (e.g., NAc, BNST). Exclusion Criteria History of other severe psychiatric disorders such as schizophrenia or bipolar disorder. Current severe suicide risk. History of alcohol or substance abuse/dependence (within the last year). History of epilepsy or has intracranial metal implants (other than the research electrodes). Presence of any unstable and significant somatic illness. Women who are pregnant or breastfeeding. Currently participating in another clinical trial.