4 weeks later (after 8 weeks in total), we will bring both depressed and healthy participants back for an additional visit that will include the same blood draw, testing, and MRI as the baseline visit. A physician-investigator will meet with the depressed subjects to review their clinical responses to treatment and to make further treatment suggestions, which the subjects may use in discussions of their future treatment options with their personal physicians. If a decision is made to discontinue antidepressant treatment, the subjects will be given instructions on how to withdraw from the medication, and will be given up to a 4 week supply of the drug to facilitate this withdrawal.