Subjects will be randomized to receive either escitalopram (s-CIT) or CBT for 12 weeks. Resting-state positron emission tomography (PET) and BOLD functional magnetic resonance imaging (fMRI) scans will be done before the treatment begins, and again at the end of treatment (week 12). Non-responders to s-cIT or CBT will be crossed over to receive an additional 12 weeks of treatment with the alternative intervention.