In this study, the investigators will monitor extracellular neurotransmitter levels using a probe that is able to perform realtime electrochemical detection during DBS neurosurgery. The overall question this study is designed to answer is: Are there neurotransmitters released during deep brain stimulation? We propose to enroll 45 patients (15 patients each at the three targets for DBS) with Essential Tremor, Parkinson's Disease, and Dystonia who are undergoing DBS neurosurgery. This will be an acute study. Patients with medically identifiable symptoms of the above diseases who have been approved by Mayo DBS committee for implantation of DBS will be selected for this study. These patients will then be consented preoperatively to undergo extracellular electrophysiology which is typical in these cases to determine the target site for implantation of the DBS electrodes. Following this electrophysiologic procedure, the patient will have electrochemical electrode implanted to (1) determine whether there is adenosine release at the site of stimulation during ventral intermediate nucleus (VIM) thalamic DBS, (2) determine whether there is dopamine and adenosine release within the caudate nucleus or putamen during subthalamic nucleus DBS, and (3) determine whether there is dopamine and adenosine release at the site of stimulation during Globus Pallidus DBS.