Effects of Deep Brain Stimulation (DBS) Frequency on Neural Synchrony

Inclusion Criteria:

   - A diagnosis of idiopathic Parkinson's disease, with bilateral symptoms at Hoehn and
   Yahr Stage greater than or equal to II.

   - Documented improvement in motor signs on versus off dopaminergic medication, with a
   change in the Unified Parkinson's Disease Rating Scale motor (UPDRS III) score of >=
   30% off to on medication.

   - The presence of complications of medication such as wearing off signs, fluctuating
   responses and/or dyskinesias, and/or medication refractory tremor, and/or impairment
   in the quality of life on or off medication due to these factors.

   - Subjects should be on stable doses of medications, which should remain unchanged until
   the DBS system is activated. After the DBS system is optimized (during which time the
   overall medication dose may be reduced to avoid discomfort and complications such as
   dyskinesias) the medication dose should remain unchanged, if possible, for the
   duration of the study.

   - Treatment with carbidopa/levodopa, and with a dopamine agonist at the maximal
   tolerated doses as determined by a movement disorders neurologist.

   - Age > 18

Exclusion Criteria:

   - Subjects with significant cognitive impairment and/or dementia as determined by a
   standardized neuropsychological battery.

   - Subjects with clinically active depression, defined according to the Diagnostic and
   Statistical manual of Mental Disorders, Fourth Edition (DSM-IV) criteria and as scored
   on a validated depression assessment scale.

   - Subjects with very advanced Parkinson's disease, Hoehn and Yahr stage 5 on medication
   (non-ambulatory).

   - Age > 80.

   - Subjects with an implanted electronic device such as a neurostimulator, cardiac
   pacemaker/defibrillator or medication pump.

   - Subjects, who are pregnant, are capable of becoming pregnant, or who are breast
   feeding.

   - Patients with cortical atrophy out of proportion to age or focal brain lesions that
   could indicate a non-idiopathic movement disorder as determined by MRI

   - Subjects having a major comorbidity increasing the risk of surgery (prior stroke,
   severe hypertension, severe diabetes, or need for chronic anticoagulation other than
   aspirin).

   - Subjects having any prior intracranial surgery.

   - Subjects with a history of seizures.

   - Subjects, who are immunocompromised.

   - Subjects with an active infection.

   - Subjects, who require diathermy, electroconvulsive therapy (ECT), or transcranial
   magnetic stimulation (TMS) to treat a chronic condition.

   - Subjects, who have an inability to comply with study follow-up visits.

   - Subjects, who are unable to understand or sign the informed consent