The purpose of this study is to test whether the structural and functional connectivity between the dorso-lateral prefrontal cortex (DLPFC) and amygdala will decline as symptoms of co-morbid anxiety (Anxiety Factor Score) increase in patients with MDD. This decrease in connectivity will also account for decrease in treatment response. The structural connectivity will be assessed using Diffusion Tensor Imaging (DTI) and the functional connectivity will be assessed using resting state BOLD fMRI.We propose to use the fMRI and DTI to identify biological markers that are associated with treatment response in a cohort of patients with a spectrum of Anxiety Factor Scores.