The PI (Post-Doc Craig Workman) left the university.

Parkinson's disease (PD) affects approximately 1 million people in the US, with annual health care costs approaching $11 billion. PD results from a loss of dopamine-producing cells in the brain. This decrease in dopamine is associated with shaking, stiffness, slowness, balance/walking problems, thinking, and fatigue which severely impair activities of daily living. Current medical and surgical treatments for PD are either only mildly effective, expensive, or associated with a variety of side-effects. Therefore, the development of practical and effective therapies would have significant benefits.

Transcranial direct current stimulation (tDCS) can influence how the brain works. A review of studies concluded that, overall, tDCS improves walking and balance in people with PD (PwPD). However, these studies had mixed results. For example, most have stimulated the frontal brain areas and all have used intensities of 2 mA (milliamperes; a measure of electrical current strength) or less. However, given the vital role of the cerebellum in walking and balance, and in PD impairments, the cerebellum may represent a more effective brain target. A recent review of studies also recommended performing investigations of higher intensity tDCS (greater than 2 mA), to potentially increase stimulation efficacy. No study has investigated the effects of multiple sessions of cerebellar tDCS on gait and balance in PwPD and none have used tDCS intensities greater than 2 mA. Therefore, there is a critical need to determine if repeated sessions of cerebellar tDCS might improve walking and balance in the short- and long-term.

Inclusion Criteria:

To be eligible to participate in this study, people with PD must meet the following criteria:

1. Adult (50-90 yrs) with a positive diagnosis of Parkinson's disease from a movement disorder specialist
2. On an unchanged regimen of dopaminergic medication for at least the last 3 months
3. Able to independently walk for 6 min
4. Without other severe chronic psychiatric or medical conditions
5. Not taking any psychoactive medications

To be eligible to participate in this study, the NH subjects must meet the following criteria:

1. Adult (50-90 yrs)
2. Able to independently walk for 6 min
3. Without any severe chronic psychiatric or medical conditions
4. Not taking any psychoactive medications

Exclusion Criteria:

An individual from either group who meets any of the following criteria will be excluded from participation in this study:

1. Pregnant
2. Known holes or fissures in the skull
3. Metallic objects or implanted devices in the skull/head (e.g., metal plate, deep brain stimulator)
4. Current or previous injuries or surgeries that cause unusual gait
5. A score less than 24 or 17 on the Montreal Cognitive Assessment (MoCA) or telephone-MoCA, respectively

Additional exclusion for PwPD:

1. Experience freezing of gait
2. A diagnosis of dementia or other neurodegenerative diseases

Additional exclusion for NH subjects:

1. A diagnosis of dementia or any neurodegenerative diseases

Subjects will be blind to the different stimulation intensities (sham, 4 mA) and the test administrators will also be blind to the subject's assigned stimulation condition.