While there are many effective options for treating a major depressive episode, there are no clinical markers that predict the likelihood of remission with an initial trial of either an antidepressant medication or psychotherapy. The goal of this study is to test how brain function changes in depress patients treated with cognitive behavioral therapy (CBT) compared to patients treated with escitalopram ((s-CIT) - Lexapro®), an FDA approved antidepressant. The study aims to determine if bran scan findings might help physicians to select the most effective antidepressant treatment for an individual patient.