Stimulating Specific Brain Areas (VOP/VIM) With Electricity to Improve Movement and Muscle Control

This study tests whether stimulating specific areas of the brain (called VOP/VIM) with small electrical impulses during deep brain stimulation (DBS) surgery can improve movement and muscle control in patients with essential tremor or Parkinson's disease. The stimulation occurs while the patient is already having their planned DBS surgery, so no extra procedure is needed. **You may be eligible if...** - You have essential tremor or Parkinson's disease - You are already scheduled for deep brain stimulation (DBS) surgery at UPMC Presbyterian Hospital - Your insurance coverage for the standard surgery will not be affected by study participation **You may NOT be eligible if...** - You have a history of seizures - You have severe tremor in both arms that prevents you from completing simple movement tasks Talk to your doctor to see if this trial is right for you.