The purpose of this study is to investigate the brain activity associated with motor and non-motor symptoms of movement disorders, including Parkinson's disease (PD) and essential tremor. These movement disorders commonly have significant non-motor features, such as depression, cognitive and memory impairment, decreased attention, speech and language disturbances, and slower processing speeds. The investigators are interested in the brain activity associated with these motor and non-motor symptoms, and propose to investigate changes in brain activity while the investigators perform recordings of the surface and deep structures of the brain, in addition to the typical recordings the investigators perform, during routine deep brain stimulation (DBS) surgery.

Movement disorders are a prominent cause of disability worldwide. In the United States, it is estimated that more than 4 million people suffer from Parkinson's disease (PD), essential tremor (ET), and dystonia, making them some of the most prevalent of neurologic disorders. Of these, PD is the most common, and is primarily characterized by tremor, rigidity, and bradykinesia. However, though primarily characterized by motor symptoms, many patients also have prominent non-motor features, including depression and cognitive impairment, with deficiencies in processing speed, memory, attention, and learning. Some of the most debilitating cognitive deficiencies include deficits in goal-directed response selection and response inhibition, language, and/or speech difficulties, all of which substantially contribute to reduced quality of life.

Unfortunately, these features of movement disorders are less well-studied and lack effective treatment options, necessitating that new treatments be investigated. Deep brain stimulation (DBS), while a highly effective treatment for the cardinal features of PD, is essentially ineffective for, and can even worsen other cognitive domains, and there are few studies currently investigating how different parameters of DBS may improve these symptoms. In addition, speech abnormalities are common with Parkinson's disease and DBS can sometimes worsen speech problems. These impairments consists primarily of hypophonia, but cognitive deficits can result in actual language disturbance. It is often difficult to know whether the speech problems are related to language processing or articulation (related to the movement disorder). In an effort to begin addressing these questions, we propose to study motor and non-motor symptoms in patients with movement disorders, and to correlate movement and cognition with underlying neural electrophysiology.

Inclusion Criteria:

• Eligible for DBS surgery based on multi-disciplinary consensus review
• Have a diagnosis of Parkinson's disease or Essential Tremor
• A minimum of 18 years of age
• Willingness to participate in the paradigms described in the protocol

Exclusion Criteria:

• Inability to provide full and informed consent
• Are not surgical candidates due to co-morbid conditions or pregnancy
• Have not undergone an adequate trial of conservative medical management
• Have a clinical presentation for which DBS surgery is not indicated
• Are not able to participate in study-related activities