Additional Study Information: This is a research study to understand what causes bipolar disorder and how medications treat bipolar depression. Particularly, we are looking at the importance of inflammation in the process. If you participate, you will receive an experimental medication for your depression named ethyl eicosapentaenoic acid (ethyl EPA), an omega 3 fatty acid. You will also have genetic testing and three different brain scans (one MRI and two PET scans). The study is funded by the Columbia University Irving Institute to improve the treatment of bipolar disorder. Please contact us if you are interested in participating.