Eligibility Criteria:
* INCLUSION CRITERIA:
* Male and female, 22-70 years old
* Use of effective method of birth control for women of childbearing capacity. Women who are able to get pregnant must be willing to use at least one form of effective birth control during the entire period of study participation (or until last clinical labs and rating) and have a negative pregnancy test at screening.
* DSM-5 diagnosis of major depressive disorder, confirmed by the structured clinical interview for the DSM 5 (SCID)
* Eligible for ECT, including patients receiving maintenance ECT
* Each subject must have a level of understanding sufficient to agree to all required tests and examinations and sign an informed consent document
* Subjects are willing and able to adhere to the intensive treatment schedule and all required study procedures
* On a stable dose of all psychotropic medications (no new medications, discontinuations or dose changes) for 4 weeks prior to baseline assessment and agreement not to change psychotropic medications during the experimental phase (Phase II) of the study, unless advised otherwise by the Investigator.
EXCLUSION CRITERIA:
* Pregnant or nursing women or women who plan to become pregnant during the study period.
* Current or recent (within the past 6 months) substance abuse or dependence (excluding nicotine and caffeine)
* Current serious medical illness, such as high blood pressure, diabetes, heart or lung disease that is not controlled by treatment and/or judged by the investigators to significantly affect the validity of the study or the safety of study participation.
* History of seizure except those therapeutically induced by ECT (childhood febrile seizures are acceptable and these subjects may be included in the study), history of epilepsy in self or first degree relatives, stroke, brain surgery, concussion resulted in loss of consciousness or hospitalization, cranial metal implants that are not safety-compatible with magnetic resonance imaging (MRI) and/or electroconvulsive therapy (ECT), known structural brain lesion, devices that may be affected by TMS or MRI (pacemaker, medication pump, cochlear implant, implanted brain stimulator, vagus nerve stimulator)
* Diagnosed with the following conditions (current unless otherwise stated):
* Any other current primary mood, anxiety, or psychotic disorder
* Depression secondary to a general medical condition, or substance-induced
* Psychotic disorder (lifetime), including schizoaffective disorder, or major depression with psychotic features in the current episode
* Eating disorder (current or within the past year)
* Obsessive compulsive disorder (current or within the past year)
* Post-traumatic stress disorder (current or within the past year)
* ADHD (currently being treated)
* Subjects meeting criteria of any psychiatric illness based upon DSM-5, which in the judgment of the Investigator, may hinder the subjects in completing the procedures required by the study protocol
* Actively suicidal
* Increased risk of complications from seizures, including prior diagnosis of increased intracranial pressure (such as after large infarctions or trauma), or currently taking medication at a dose that significantly alters seizure threshold, as determined by the investigators.
* Subjects with a clinically defined neurological disorder including, but not limited to:
* Any condition likely to be associated with increased intracranial pressure
* Space occupying brain lesion
* History of stroke
* Transient ischemic attack within two years
* Cerebral aneurysm
* Dementia
* Mini Mental Status Exam (MMSE) score \< 24
* Parkinson s disease
* Huntington s disease
* Multiple sclerosis
* Subjects with any of the following treatment histories:
* Failure to respond to ECT treatment (i.e., consistent with ATHF confidence level 3 or higher) in this or any previous episode
* Lifetime history of treatment with Deep Brain Stimulation or Vagus Nerve Stimulation
* Use of any investigational drug or device within 4 weeks of the screening
* Subjects with:
* intracranial metal that are not safety-compatible with MRI and/or ECT, and/or
* extracranial metal, that are not safety-compatible with MRI and/or ECT
* A history of claustrophobia that may make it difficult for the patient to complete the MRI study or may adversely impact the quality of the images or the interpretation of the findings
* Current visual, auditory, or motor impairment that compromises ability to complete evaluations
* Positive HIV test
* NIMH employees and staff and their immediate family members will be excluded from the study per NIMH policy