Antidepressant Effect of Deep Brain Stimulation in Parkinson's Disease Patients

The purpose of this study is: 1. To determine, in the context of a prospective clinical trial, whether stimulation parameters in PD patients treated with DBS, are associated with antidepressant effects. 2. To determine whether these antidepressant effects are related to or independent of changes in the motor features of PD. 3. To establish a computerized database that includes stimulation parameters and clinical parameters in PD patients treated with DBS. 4. To develop a computer-assisted decision making protocol for programming of DBS parameters in both depressed and non-depressed PD patients.