Subjects will be recruited from the population of patients who are already implanted with DBS for treatment of PD.
At the patient's follow up visit they will be asked to come to the clinic in the "off medication" state. Off medication is defined as at least 8 hours since the last medication dosing. Data will be collected during three phases: "OFF" state, transitioning state, and "ON" state. Subjects will be asked to assume different functional states (lying, sitting or walking) for 1 minute each. During these functional states, multiple measures of impedance will be collected.
* "OFF" state data collection: The subject will be examined to assess his motor examination score using the UPDRS-III. Measurements of impedance will be collected multiple times in the lying down and sitting up states.
* Transition state data collection: The subject will be asked to take their dopamine medication. The medication will take approximately 1 hour to take full effect. Measurements of impedance will be collected every 10 minutes during this transition from the "OFF" state to the "ON" state. Patients will be asked to report at what point they felt the "ON: state (they can report the state as "OFF", "unsure", "transition" or "ON").
* "ON" state data collection: The "ON" state examination will start after 1 hour from medication administration. Subjects will be examined using the UPDRS-III. Measurements of impedance will be collected in the lying down, sitting and walking states.
Summary of the study protocol:
"OFF" state Transition state "ON' state UPDRS-III x x Impedance Lying down x x Sitting up x x x Walking x UPDRS I and II x Hoehn and Yahr x x
