Patients qualified to participate in this study using a surgical tool called ExAblate 4000 system. ExAblate uses ultrasound to destroy brain cell clusters that may be causing some of your motor symptoms of Parkinson’s disease. This study is being offered to patients suffering from a type of Parkinson’s disease (PD) in which the major symptoms are motor symptoms that are no longer controlled effectively by medication. The ExAblate 4000 system will be used to destroy (ablate) a small cluster of cells that are likely associated with PD motor symptoms. The technique is called Magnetic Resonance-guided Focused Ultrasound. The ExAblate uses ultrasound to heat and destroy a small spot on one side of the brain (unilaterally). Ultrasound passes through the skin and skull without cutting or drilling through the skull. If patients decide to be in this study and meet all the study requirements they will be randomized to receive either an active ExAblate procedure or a sham control procedure, which will be like the active procedure, except that no area in the brain will be ablated. The chances of being assigned to an ExAblate procedure is three times more likely than the chance of being randomized to a sham treatment. After follow-up for three months, if randomized to a sham procedure, patients may be eligible to receive an actual ExAblate procedure. We will measure how well the procedure works using the following evaluations and questionnaires: • Neurological and general physical examination by your study physician • Eye examinations • Magnetic Resonance Imaging (MRI) exams • Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) while you are both on and off your Parkinson’s disease medications • Unified Dyskinesia Rating Scale to see how well your medications are working • Gait testing to see how well you are able to walk • Neuropsychological evaluations • Global Impression of Change completed by both the physician and the patient • Patient Treatment Satisfaction Questionnaire • Medication log and patient diary We will measure safety by recording and analyzing any complications observed from the day of treatment through up to 5 years following treatment. Participation in this study will last from approximately 1 to 5 years. The ExAblate treatment may take up to four hours. Following the treatment, you will need to complete follow-up study visits at 1 week, 1 month, 3 months, 6 months, 12 months, 2 years, 3 years, 4 years, and 5 years. Each study visit will likely be 3-4 hours in length. If randomized to the sham procedure, patients will have a “treatment visit” and attend all follow-up visits through Month 3. At that point, patients may be eligible to receive ExAblate treatment. The schedule of study visits from 1 week through 12 months, and then once a year for up to 5 years. A total of 116 subjects will participate in this study at up to 15 different centers. We expect to enroll 7 patients at Penn Neurosurgery.