In addition, the investigators are using MRI imaging, which uses magnetic signals to make pictures of the brain's structure and also of its functioning. The purpose of MRI imaging in this study is to see whether chronic depression is associated with differences in brain structure or functioning, and whether such differences change after medication or placebo treatment. To test this MRI scans are done at the start of the study and after 12 weeks of medication or placebo treatment. Getting MRI imaging will be an option for participants in this study but is not required.