Parkinson's Disease: Enhancing Physical Therapy With Brain Stimulation for Treating Postural Instability.

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