Additional Study Information: In this research study, you may receive treatment for depression with an FDA approved medication called escitalopram (Lexapro) or placebo. Escitalopram is a Selective Serotonin Reuptake Inhibitor (SSRI) medication that appears to help with symptoms of depression by increasing the availability of specific chemicals in the brain. A placebo is a sugar pill. The purpose of this study is to determine how treatment response may change depending on how studies are designed. Participants in this study will also undergo Magnetic Resonance Imaging (MRI) in order to investigate the brain responses associated with depression.