Effect of Levodopa on Postural Motor Learning in Parkinson Disease

The primary goal of this project is to gain a better understanding of whether and how levodopa (a common anti-Parkinson disease medication) alters postural motor learning in people with Parkinson disease. A secondary goal is to assess whether motor cortical excitability, measured via Transcranial magnetic stimulation, is related to postural motor learning. Participants with Parkinson disease will complete between 50 and 100 postural perturbations (via support surface translations), ON and OFF their dopamine replacement therapy (i.e. levodopa). Adaptation of responses to these perturbations will be tracked. Participants will also undergo transcranial magnetic stimulation to capture cortical excitability of the brain (in particular the motor cortex). Cortical excitability will be correlated to adaptation of stepping (i.e. postural motor learning) ON and OFF levodopa. Investigators will also capture postural motor learning and cortical excitability in age-matched healthy adults. Investigators hypothesize that dopamine will have a negative effect on postural motor learning, and the cortical excitability will be correlated to postural motor learning.