Inclusion Criteria:  Diagnosis of Parkinson's disease or Essential Tremor who have been recommended to undergo deep brain stimulation for management of their movement disorder Preoperative MRI without evidence of cortical or subdural adhesions or vascular abnormalities Willingness and ability to cooperate during conscious operative procedure for up to 40 minutes  Exclusion Criteria:  Patients with recent use (within one week) of anticoagulant or antiplatelet agents Neurocognitive testing indicating amnestic cognitive deficits