Transcranial Ultrasound Stimulation (TUS) is an emerging non-invasive brain stimulation(NIBS) technique that can be used on both superficial and deep brain targets with a high spatial resolution as small as a few cubic millimeters. Functional Electrical stimulation is a peripheral stimulation technique researched and clinically used to restore motor function following conditions like stroke and Spinal cord injury. To date, there are no studies that have looked at the neuro modulatory effects of combining TUS and FES on motor symptoms in patients with Parkinson's disease. The current study aims to understand the neuromodulatory effects of combining tbFUS to bilateral primary motor cortex (M1) in Parkinsons's disease patients immediately followed by bilateral upper extremity FES of the hand muscles for improving motor symptoms.

There are 3 study visits and for all of them patients will remain in ON dopaminergic medication condition. Each visit will be a minimum of 7 days apart.

Each visit will contain 1 of 3 combinations:

Combination #1: Real TUS +Sham FES; Combination #2: Sham TUS+ Real FES; Combination #3: Real TUS +Real FES

Definition of:

Real TUS: The Real TUS paradigm will consist of 120s train of 20ms ultrasound bursts, repeated every 200ms (Pulse Repetition Frequency (PRF)=5Hz). The Power of Real tbFUS will be set at 20W.

Sham TUS: The Sham TUS paradigm will also consist of 120s train of 20ms ultrasound bursts, repeated every 200ms (Pulse Repetition Frequency (PRF)=5Hz), however the ultrasound head will be flipped so that the active side faces away from the head.

Real FES: Motor point stimulation (MPS) of the right and left hand and forearm (Muscles stimulated may include: Opponens Pollicis Brevis (OPB), Flexor Pollicis Brevis, Abductor Pollicis Brevis (APB), 1st Lumbrical, Flexor digitorum superficialis and the First Dorsal Interosseous (FDI)) muscles will be triggered in congruence with the voluntary effort of the Participant during execution of bilateral functional tasks involving the use of two and three finger pinch grip (e.g.: picking up and moving marbles, ball bearings etc.).

Sham FES: Motor point stimulation (MPS) of both right and left Biceps and Finger flexor muscles will be triggered in congruence with the voluntary effort of the participant during execution of bilateral functional tasks involving the use of two and three finger pinch grip (e.g.: picking up and moving marbles, ball bearings etc.).

Inclusion Criteria:

• 18-90 years of age
• Confirmed diagnosis of Parkinson's disease
• Stable dopaminergic medication dose for a minimum of 4 weeks (applicable for PD patients only)

Exclusion Criteria:

History of stroke or seizure

• Comorbid dementia
• Scored below 22 on the Montreal Cognitive Assessment (MoCA)
• Has intracranial implant(s) or device(s)
• Has an implanted cardiac pacemaker or implantable cardioverter-defibrillator (ICD)
• Has a previous surgical intervention to treat the movement disorder such as lesioning or a Deep Brain Stimulation system in place.
• Presence of metal implanted in body that is contraindicated in TMS/MRI/peripheral electrical stimulation
• Pregnancy
• Major depression/psychiatric disorder that in the opinion of the Investigator will affect patient's understanding of study procedures and willingness to abide by all procedures during the course of the study
• Is on antipsychotics, anti-depressants, marijuana, or other recreational drugs that affect the nervous system
• Major musculoskeletal or neuromuscular disease or disorder of the hands, wrists and limbs
• Severe Dyskinesia
• Genetic mutations
• Major systemic illness or infection

The subject will be blind to stimulation condition (sham/active TUS). The assessor for the finger accelerometry will be blind to stimulation condition (sham/active TUS). The UPDRS examination will be video-recorded and blindly assessed by a research team member.