The Quick Inventory of Depressive Symptomatology - Clinician-Rated (QIDS-C16) will be the primary clinical outcome measure and will be collected at baseline and at each treatment visit. Additionally, levels of glutamate in the prefrontal regions of the brain will be measured by MRS. Clinical response will be defined as a decrease of 50 percent or greater in QIDS-C16 score from baseline, and remission will be defined as a QIDS-C16 score of less than 6.