Repetitive Transcranial Magnetic Stimulation (rTMS) in the Treatment of Panic Disorder With Comorbid Major Depression

This study will evaluate the efficacy of 1-Hz rTMS applied to the right Dorsolateral Prefrontal Cortex (DLPFC) in patients with Panic Disorder (PD) and comorbid Major Depressive Disorder (MDD) who have not fully responded to conventional therapies. The investigators hypothesize that: 1. compared to sham (placebo), active rTMS will improve symptoms of PD and MDD as assessed with the Panic Disorder Severity Scale (PDSS), Hamilton Depression Rating Scale (HDRS), and Clinical Global Impression (CGI); 2. active (but not sham) rTMS will normalize levels of motor cortex excitability relative to pre-treatment baseline.