• Unified Parkinson's Disease Rating Scale (UPDRS) [ Time Frame: 6 weeks ]
  Motor function (including tremor, bradykinesia, postural instability and gait), non-motor symptoms, activities of daily living and complications of therapy will be investigated per UPDRS (parts I-IV); staging of PD and ability to perform activities of daily living will also be investigated via UPDRS parts V and VI. We already have experience using this assessment in several previous brain stimulation PD studies.
• Leg Agility [ Time Frame: 6 weeks ]
  kinematic changes will be assessed with kinematic metrics (e.g., speed (m/s)) taken with a biomechanical assessment suite throughout the study.
• Arising from a chair [ Time Frame: 6 weeks ]
  kinematic changes will be assessed with kinematic metrics (e.g., time to complete task) taken with a biomechanical assessment suite throughout the study.
• Balance [ Time Frame: 6 weeks ]
  kinematic changes will be assessed with kinematic metrics taken during a modified Romberg exam (e.g., change in center of pressure over a fixed time interval (cm)) with a biomechanical assessment suite throughout the study.
• Gait [ Time Frame: 6 weeks ]
  changes in the walking speed, gait asymmetry, stride length, walking smoothness, and gait freezing kinematic characteristics (e.g., m/s) will be assessed with a biomechanical assessment suite throughout the study
• Toe tapping [ Time Frame: 6 weeks ]
  kinematic changes will be assessed with kinematic metrics (e.g., speed (m/s)) taken with a biomechanical assessment suite throughout the study.

• Unified Parkinson's Disease Rating Scale (UPDRS) [ Time Frame: 6 weeks ]
  Motor function (including tremor, bradykinesia, postural instability and gait), non-motor symptoms, activities of daily living and complications of therapy will be investigated per UPDRS (parts I-IV); staging of PD and ability to perform activities of daily living will also be investigated via UPDRS parts V and VI. We already have experience using this assessment in several previous brain stimulation PD studies.
• Leg Agility [ Time Frame: 6 weeks ]
  kinematic changes will be assessed with kinematic metrics (e.g., speed (m/s)) taken with a biomechanical assessment suite throughout the study.
• Arising from a chair [ Time Frame: 6 weeks ]
  kinematic changes will be assessed with kinematic metrics (e.g., time to complete task) taken with a biomechanical assessment suite throughout the study.
• Balance [ Time Frame: 6 weeks ]
  kinematic changes will be assessed with kinematic metrics taken during a modified Romberg exam (e.g., change in center of pressure over a fixed time interval (cm)) with a biomechanical assessment suite throughout the study.
• Gait [ Time Frame: 6 weeks ]
  changes in the walking speed, gait asymmetry, stride length, walking smoothness, and gait freezing kinematic characteristics (e.g., m/s) will be assessed with a biomechanical assessment suite throughout the study

• Device: Active Comparator: Active tDCS and Active TUS

  Device: Transcranial Direct Current Stimulation (tDCS) Subjects will receive 20 minutes of either active or sham tDCS at intensity of 2mA. The anodal electrode will be placed over the primary motor cortex contralateral to the most painful side, and the cathodal electrode will be placed over the contralateral supraorbital area. In the sham group, the tDCS device will not be active for the full 20 minutes.

  Device: Transcranial Ultrasound (TUS) Subjects will receive 20 minutes of either active or sham TUS. During active stimulation the ultrasound will be active for the full 20 minutes- however, during sham stimulation the ultrasound will not be active for the full 20 minutes.

• Device: Sham Comparator: Sham TDCS and Sham TUS

  Device: SHAM Comparator Device: transcranial Direct Current Stimulation (tDCS) Subjects will receive 20 minutes of either active or sham tDCS at intensity of 2mA. The anodal electrode will be placed over the primary motor cortex contralateral to the most painful side, and the cathodal electrode will be placed over the contralateral supraorbital area. In the sham group, the tDCS device will not be active for the full 20 minutes.

  Device: Transcranial Ultrasound (TUS) Subjects will receive 20 minutes of either active or sham TUS. During active stimulation the ultrasound will be active for the full 20 minutes- however, during sham stimulation the ultrasound will not be active for the full 20 minutes.

• Other: Physical Therapy
  All subjects will enroll in a conventional PT balance and gait focused training program, and will receive PT 3x/week over the two weeks of stimulation for 45 minutes following the stimulation sessions when applicable.

• Experimental: Active tDCS and Active TUS
  Active tDCS and Active TUS for 20 min
  Interventions:

  • Device: Active Comparator: Active tDCS and Active TUS
  • Other: Physical Therapy
• Sham Comparator: Sham TDCS and Sham TUS
  Sham TDCS and Sham TUS for 20 min
  Interventions:

  • Device: Sham Comparator: Sham TDCS and Sham TUS
  • Other: Physical Therapy

Inclusion Criteria:

1. Diagnosis of "probable" or "possible" PD, as defined by the current clinical criteria (Gelb D, Oliver E, Gilman S. Diagnostic Criteria for Parkinson's Disease. Arch Neurol.1999;56:33-39) as confirmed by co-investigator neurologist, or confirmation via medical records or a letter from patient physician;
2. Complaints about balance impairment or postural instability due to PD (self-report);
3. Age from 40 to 90 years old;
4. Taking stable medications for PD for at least 30 days.

Exclusion Criteria:

1. Features suggestive of other causes of parkinsonism/Parkinson's-plus syndromes;
2. History of deep brain stimulation or brain ablation surgeries, malignant mass brain lesions;
3. History of schizophrenia, bipolar illness; history of alcohol/drug abuse within the past 6 months;
4. Need for rapid clinical response due to conditions such as initiation, psychosis, or suicidality;
5. Contraindications to transcranial brain stimulation or TUS, i.e. metal in the head, implanted brain medical devices, etc.;
6. Unstable medical conditions (e.g., uncontrolled diabetes, uncompensated cardiac issues, heart failure, uncompensated pulmonary disease, or chronic obstructive pulmonary disease);
7. Pregnancy.
8. Epilepsy or disorders that significantly increase likelihood of seizures including: severe traumatic brain injury, congenital birth defects leading to seizures, brain tumor, metabolic disorders associated with seizures, intracranial or subarachnoid hemorrhage, and nonlacunar strokes.
9. Recent (<= 2 months) or planned enrollment in an additional physician prescribed physical therapy program during their time in the trial.
10. Presence of another disorder that might have a significant impact on balance (as assessed by a co-investigator neurologist).
11. Bed or wheelchair-bound