Intraoperative Evoked Potential Recording for Localization of Deep-Brain Stimulation Electrodes

Deep brain stimulation (DBS) has been approved for treatment of dystonia by the FDA under a humanitarian device exemption (HDE) status. DBS has been shown to be very effective in the treatment of a variety of diseases such as Parkinson's disease and essential tremor. It has been widely used for the treatment of primary and secondary dystonia as well. Surgery involves the placement of the DBS electrode in one or two of the deep nuclei constituting the basal ganglia. A subcutaneous thoracic or abdominal implantable pulse generator is placed and connected to the intracranial electrode. Pulsatile stimulation of the deep brain nuclei has been shown to result in significant improvement in many patients, including restoration of the ability to walk or make voluntary arm movements. A major difficulty with DBS is the accurate placement of the electrode. Adult patients are usually awakened during surgery and micro electrode recordings are used to determine the optimal electrode effectiveness and monitor for side effects. This requires the patient to be awake and cooperate, while on the operating table. When DBS is performed in children, such testing is often not possible because the children are scared or not cooperative when awakened during surgery, the procedure is most often done for Dystonia, which does not respond immediately, and dystonia may cause involuntary movements that could be dangerous in the operating room while the child's brain is exposed. As part of the routine clinical evaluation of target location in the operating room or Neuromodulation Unit, stimulation is performed using the deep brain or depth electrodes, typically at frequencies between 60hz and 185hz. For this research study, stimulation will occur at much lower frequencies, between 9hz and 20hz in order to be able to measure how electrical activity from the deep electrodes spreads to other electrodes or the scalp. As part of the research, peripheral nerves will also be stimulated at the wrist and knee at frequencies of 20hz to 150hz in order to measure the transmission of peripheral nerve stimulation to these areas of the brain. The investigators hope these additional studies will allow discovery for mechanisms that lead to movement disorders including dystonia, and that knowledge of these mechanisms will allow the investigators to develop new, safer, and more effective treatments in the future.