Eligibility Criteria:
Control Group:
Inclusion Criteria:
(4) Ability to tolerate small, enclosed spaces without anxiety; (6) English fluency.
Exclusion Criteria:
* Pregnant or trying to become pregnant.
* history of serious head injury;
* possibility of ferrous metals within the body, e. g. aneurysm clips, retained particles; or metal that would impair the magnetic resonance (MR) signal, e.g., some dental hardware;
* Smoking usage \> 10 cigarettes per day
* Daily intake of caffeine exceeds 2 cups of coffee per day
* Unstable cardiac problems (e.g. severe or poorly treated hypertension, unstable arrhythmia, etc.) or concurrent medications for which anesthesia would be contraindicated
* Patients with a current general medical illness that is life threatening or inadequately treated will be excluded: moderate-to-severe chronic pain, evidence of fracture or malignancy, inflammatory joint disease, severe physical impairment (e.g., bilateral amputation, blindness), morbid obesity, autoimmune/inflammatory diseases, cardiopulmonary disorders (i.e., angina, congestive heart failure, COPD), chronic renal insufficiency, uncontrolled endocrine or allergic disorders (i.e., hyper-/hypothyroidism, diabetes, allergic rhinitis), malignancy.
* Taking any medication, prescription or non-prescription, with psychotropic effects.
* History of psychiatric or neurological illness; History of substance abuse or dependence Positive urine toxicology screen.
Refractory Depression Group:
* Meets all above control group screening criteria except history of psychiatric illness and prescription medication usage
* Included subjects will have a Diagnostic and Statistical Manual of Mental Disorders IV (DSM-IV) diagnosis of major depressive disorder, recurrent or chronic, moderate-to-severe, without psychotic features, with medication resistance, accepted with agreement by two different psychiatrists. For this study, treatment resistance is defined as ≥2 failed adequate antidepressant trials.
* Patients with a DSM-IV diagnosis of bipolar disorder, schizophrenia, or schizoaffective disorder will be excluded. Any history of antidepressant- or substance- induced hypomania or mania will be excluded.
* Subjects will be free of comorbid substance abuse or dependence for at least 3 months, with a negative urine toxicology screen.
* No current suicide plan or intent.
* Comorbid Axis I anxiety disorder diagnoses will be permitted if they do not require current treatment.