Locomotor adaptation will be studied using an established split-belt treadmill paradigm, consisting of baseline (1:1 speed ratio), split-belt adaptation (2:1) and post-adaptation (1:1) walking. Split-belt walking will be performed under DBS ON and DBS OFF conditions, while off-medication.

We will test the hypotheses that DBS can facilitate split-belt walking adaptation with DBS ON compared with DBS OFF.

Inclusion Criteria:

• consensus diagnosis of idiopathic PD by fellowship trained movement disorders neurologists at the Normal Fixel Institute of Neurological Diseases;
• chronically stable DBS, defined as having had DBS for at least 6 months in duration with optimized DBS settings;
• Age between 18 - 80 years old per the FDA data sheet for PD DBS;
• no dementia according to the clinical diagnostic criteria for PD dementia;
• ambulatory without the use of walking aids, or another person's assistance.

Exclusion Criteria:

• other previous neurological surgery;
• suspicion of other neurologic diagnoses such as atypical parkinsonism, or Alzheimer's disease.