This is a functional MRI study that will examine the effects of noninvasive transcranial electrical stimulation (tES) on brain function in individuals with Major Depression.

The purpose of this research study is to understand how a kind of brain stimulation, called transcranial electrical stimulation (tES), affects brain function in people with major depression.

tES delivers low electrical current to the head using electrodes applied to the skin, and is described as a "neuromodulation" or "neurostimulation" technique. This study uses a specific kind of tES called "transcranial direct current stimulation", or tDCS, where a constant (unchanging) electrical current is passed between two electrodes on the head.

Neuromodulation methods like tES have shown promise in changing brain function, as well as treating some brain disorders like major depression. Yet, how tES brain function remains unclear. To better understand how tES works, the investigators will use MRI (a type of brain scan) to measure brain function during tES in people with major depression.

Inclusion Criteria:

• ages between 18 and 55
• diagnosis of Major Depressive Disorder made by a physician, psychiatrist, or psychologist at least one year prior
• mild-to-moderate symptoms of depression (Hamilton Depression Rating Scale 17-item, HDRS-17, score 8-23)
• stable standard or no pharmacological antidepressant regimen (SSRI, SNRI, MAOI, or trycyclic/TCA) with no change in treatment 6 weeks prior to study start

Exclusion Criteria:

• suicidal thoughts, ideation, or behavior within the past month (HDRS-17 item 3 score greater than 1)
• greater than moderate symptoms of depression within the past month (HDRS-17 score >23)
• change in antidepressant medication within 6 weeks of study start
• diagnosis of any medical condition potentially affecting brain function, including neuropsychiatric or mental disorders, other mood disorders (bipolar disorder, anxiety, PTSD), psychotic states or disorders, developmental disorders, neurological disorders, including mild cognitive impairment, significant head injury, significant history of alcohol/substance abuse or dependence
• MRI contraindications: metal or other implants that are not MR-safe, claustrophobia, pregnancy or suspected pregnancy
• tES contraindications: skin conditions or injuries on the scalp, hair extensions, wigs, braids, etc. that cannot be removed prior to the study, metal implants or pacemakers
• other major medical conditions (e.g., cancer, stroke)
• current medication use potentially affecting brain function, including decongestants, antihistamines, benzodiazepines or other anticonvulsants, anti-psychotics, or antidepressants
• prisoners will not participate in this study