This technology development project will be informed and guided by initial data collection of human subject data. For this purpose, the investigators will recruit n=100 people with mild to moderate depression in a double-blinded, parallel-arm, sham-controlled data collection period administered at home and using the investigator's remotely supervised (RS) tDCS protocol. Enrolled participants will complete 10 days of 30-minute tDCS (2.0, DLPFC left anodal) using the RS-tDCS protocol. During each daily session, standard HR and impedance-based HR (i-HR), obtained from the tDCS headset, will be collected to identify a possible marker of response to tDCS in depression. Participants will be randomized 2:1 to active vs. sham tDCS.

Inclusion Criteria:

• Mild to moderate depression (Beck Depression Inventory(BDI)-II 14-28)
• Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-V-TR) Depressive episode
• Wide Range Achievement Test (WRAT)-4th Reading Recognition subtest standard score >85

Exclusion Criteria:

• Primary neurologic, psychiatric (e.g., multiple sclerosis, stroke, Parkinson's disease, spinal cord injury, intracranial mass, traumatic brain injury (TBI), epilepsy, mild cognitive impairment (MCI), or dementia), or major medical disorder (e.g., history of myocardial infarction, diabetes, thyroid disease, arrhythmia, atrial fibrillation) (medical history review)
• DSM-V-TR bipolar depression, psychotic disorder, or alcohol or substance use disorder (M.I.N.I.)
• Active or high suicidality risk (Columbia-Suicide Severity Rating Scale, C-SSRS), or otherwise judged as inappropriate by the study clinicians
• History of a heart transplant, presence of permanent pacemaker implant or Left Ventricular Assist Device
• Use of certain medications that can affect heart rate variability, such as beta-blockers, calcium channel blockers, or cardiac glycosides
• Use of antidepressant, antipsychotic, anxiolytic, or stimulant medications
• Pregnant or planning pregnancy during the study period
• Seizure disorder or recent (<5 years) seizure history
• Presence of metal objects in the head/neck
• Any skin disorder or skin sensitive area near stimulation locations

The de-identified participant data from the final research dataset used in the published manuscript will be shared upon reasonable request beginning 9 months and ending 36 months following article publication or as required by a condition of awards and agreements supporting the research provided the investigator who proposes to use the data executes a data use agreement with NYU Langone Health. Requests may be directed to: Giuseppina.Pilloni@nyulangone.org. The protocol and statistical analysis plan will be made available on Clinicaltrials.gov only as required by federal regulation or as a condition of awards and agreements supporting the research.

Beginning 9 months and ending 36 months following article publication or as required by a condition of awards and agreements supporting the research.

The investigator who proposes to use the data will be granted access upon reasonable request. Requests should be directed to Giuseppina.Pilloni@nyulangone.org. To gain access, data requestors will need to sign a data access agreement.