Kinematic and Neural Dynamics of Postural Instability in Parkinson's Disease

Inclusion Criteria: Aims 1 and 2 Inclusion criteria: * All Veterans with a clinical diagnosis of Parkinson's disease as made by their treating neurologist in Hoehn and Yahr stage 2-3 with the ability to give informed consent will be considered for possible participation in this study. * Veterans cannot be past stage 3 as our measures depend on physical independence and fall risk prediction is less useful after stage 3. * Capacity to consent will be assessed with the University of California, San Diego Brief Assessment of Capacity to Consent (UBACC). * A score of less than 14.5 will be used as the cut-off to decide whether a Veteran is capable of consenting as the false positive rate is zero below this score with marginal increases in sensitivity above this score (89% sensitivity, 100% specificity). Aim 3 Inclusion criteria: * In addition to the inclusion criteria for Aims 1 and 2, Veterans with an implanted STN DBS lead with a Percept device in place. Exclusion Criteria: Aims 1 and 2 Exclusion criteria: * Veterans with dementia of sufficient severity to impair their ability to make healthcare related decisions for themselves will be excluded. * Veterans with other forms of parkinsonism (PSP, CBGD, etc.) will be excluded. * Veterans past H\&Y Stage 3 will be excluded. * Veterans with symptomatic orthostatic hypotension (defined as sustained drop in systolic blood pressure by 20 mmHg or diastolic blood pressure by 10 mmHg within 3 minutes of standing after being supine for five minutes) will also be excluded as this is an entity the investigators are not characterizing and could confound/bias the dataset. Aim 3: Exclusion criteria: * In addition to the exclusion criteria for Aims 1 and 2, Veterans with DBS leads implanted in other locations will be excluded.