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

In this study the investigators aim to enroll patients for intra-operative testing. Specifically, the investigators will recruit patients already undergoing DBS implantation for movement disorders. In addition to standard-of-care subcortical mapping using micro-electrode recording (MER) and macro-stimulation mapping during DBS placement, cortical local field potentials (LFPs) will be simultaneously recorded from primary motor (M1) and somatosensory (S1) cortical areas by placement of a temporary strip electrode (1X6) in the subdural space. Appropriate localization of this grid over M1 and S1 will be confirmed by the so-called phase-reversal of somatosensory evoked potentials (SSEPs). Once M1 is localized, the strip electrode over M1 will be used to produce motor evoked potentials to contralateral hand muscles from direct cortical stimulation (DCMEPs). The stimulation threshold of the DCMEPs will be used as a direct measure of the excitability of the cortical spinal tract and compared with and without stimulation of the VOP/VIM nuclei. Cortical and subcortical LFPs will be obtained alongside electromyographic (EMG) data while the patient performs contralateral upper extremity movement tasks measuring velocity, grip strength, and strength modulation and while the patient perform a variety of articulation exercises. Along with the DCMEP stimulation thresholds, these parameters of motor output will be obtained both with and without VOP/VIM stimulation to assess for stimulation induced potentiation of motor output.

Inclusion criteria

• Essential tremor patients who are scheduled to undergo deep brain stimulation surgery at UPMC Presbyterian with asymmetric essential tremor symptoms will be included, with the tested limb corresponding to the least affected arm to better approximate normal function. These patients are implanted bilaterally regardless of symptom laterality, as the natural history of essential tremor indicates eventual bilateral symptoms.
• Parkinson's Disease patients who are scheduled to undergo deep brain stimulation surgery at UPMC Presbyterian with a history of Parkinson's Disease will also be recruited for intra-operative stimulation of their STN-targeted implants, to assess if VIM/VOP has high specificity for improving motor output.

Confirmation that subjects' terms of insurance coverage for their standard of care procedure will not be altered by study enrollment.

Exclusion criteria

• Patients will be excluded from the study if there is any seizure history, to avoid the increased epileptogenic risk of intraoperative stimulation.
• Patients with significant bilateral tremor that precludes completion of motor tasks.