tDCS for Late-Life Depression

Inclusion Criteria: Participants must meet all of the following criteria: 1. age 60 years or older; 2. diagnosis of unipolar major depressive disorder according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), confirmed by the Mini International Neuropsychiatric Interview (MINI); 3. score of 17 or higher on the 17-item Hamilton Depression Rating Scale (HDRS-17) at screening; 4. stable antidepressant regimen for at least four weeks prior to enrollment, if applicable; 5. capacity to provide informed consent; 6. Clinical Dementia Rating scale of 0 or 0.5. Exclusion Criteria: Participants meeting any of the following criteria will be excluded: 1. contraindications to tDCS including metallic cranial implants, skin conditions at electrode sites (eczema, open wounds, burns, lesions), or history of adverse reaction to tDCS; 2. contraindications to magnetic resonance imaging (MRI) including pacemaker, cochlear implants, ferromagnetic implants, or claustrophobia; 3. history of seizures or epilepsy; 4. bipolar disorder, psychotic disorders, or severe personality disorder; 5. dementia or MoCA score below 17; 6. substance use disorder within the past six months; 7. neuromodulation treatment including electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), tDCS, or vagus nerve stimulation (VNS) within the past six months; 8. active suicidal ideation with plan or intent requiring a higher level of care; 9. concurrent use of medications that substantially lower seizure threshold; 10. pregnancy.