Single Session of tACS in a Depressive Episode

Inclusion Criteria for individuals with depressed mood: * Ages 18-65 years * Hamilton Depression Rating Scale score \>8 * Capacity to understand all relevant risks and potential benefits of the study (informed consent) * Low suicide risk which will be determined through the use of both the Structured Clinical Interview for the DSM-5 and by scoring less than 3 (0,1, or 2) in the Hamilton rating depression scale. * Negative pregnancy test for female participants Exclusion Criteria for individuals with depressed mood: * DSM-5 diagnosis of alcohol of substance abuse (other than nicotine) within the 12 months * DSM-5 diagnosis of alcohol or substance dependence (other than nicotine) within the last 12 months * DSM-5 diagnosis of personality disorder * Eating disorder (current or within the past 3 months) * Anything that, in the opinion of the investigator, would place the participant at increased risk or preclude the participant's full compliance with or completion of the study * Neurological disorders, including but not limited to history of seizures (except childhood febrile seizures and electro-convulsive therapy (ECT) induced seizures), dementia, history of stroke, Parkinson's disease, multiple sclerosis, cerebral aneurysm. * Medical or neurological illness (unstable cardiac disease, AIDS, malignancy, liver or renal impairment) or treatment for a medical disorder that could interfere with study participation * History of traumatic brain injury, reoccurring seizures or later cognitive rehabilitation or causing cognitive sequelae * History of childhood trauma (determined by the Childhood Trauma Questionnaire) * Prior brain surgery * Any brain devices/implants, including cochlear implants and aneurysm clips * Co-morbid neurological condition (i.e. seizure disorder, brain tumor) * Use of illicit drugs, confirmed by a drug test * Non English speakers * Pregnant or nursing females * Current use of benzodiazepines or anti-epileptic drugs Inclusion Criteria for healthy controls: * Ages 18-65 years * Hamilton Depression Rating Scale score ≤8 * Capacity to understand all relevant risks and potential benefits of the study (informed consent) * Negative pregnancy test for female participants Exclusion Criteria for healthy controls: * History of major neurological or psychiatric illness, including epilepsy * Medication use associated with neurological or psychiatric illnesses * Currently undergoing counseling or psychotherapy treatment for depression, anxiety, eating disorders, PTSD or other behavioral conditions * DSM-5 diagnosis of personality disorder * First degree relative (parent, sibling, child) with major neurological or psychiatric illness * Prior brain surgery * Major head injury * Any brain devices/implants (including cochlear implants and aneurysm clips) * History of childhood trauma (determined by the Childhood Trauma Questionnaire) * Use of illicit drugs, confirmed by a drug test * Braids or other hair styling that prevents direct access to the scalp (if removal not possible) * Skin allergies or very sensitive skin * Non English speakers * Pregnant or nursing females