This study proposes to utilize recent advances in magnetic resonance spectroscopy (MRS) techniques that permit reliable measurement of Glu in humans (9) to examine whether Vilazodone and citalopram exert differential effects on Glutamatergic neurotransmission in the ACC of anxious unipolar depressed patients. Functional connectivity as measured by Blood Oxygen Level Dependent (BOLD) MRI will be assessed to determine the relationship between the change in connectivity and the change in Glu levels with treatment. We also propose to examine, in an exploratory fashion, the relative effect of the two drugs on BOLD activation in the insula cortex.