Deep brain stimulation (DBS) of an area of the brain called the subthalamic nucleus (STN) is an effective treatment in Parkinson's disease (PD). However, stimulating the STN can lead to unwanted side effects that involve muscle movements (dyskinesias) and behavior and mood problems. DBS of a different brain structure, called the rostral zona incerta (rZI), has been demonstrated to be as effective as stimulating the STN, without any unwanted side effects in several studies. However, there is great variability in reported efficacy and adverse effects of rZI stimulation likely due to challenges in locating this area in the brain. The goals of this study are 1) to develop an improved method for targeting the rZI 2) determine efficacy of rZI with STN stimulation compared with STN stimulation alone, 3) evaluate any stimulation adverse effects of combined stimulation of the rZI and STN.