Understanding How Movements Are Transferred From Task to Task in Parkinson's Disease

The purpose of this study is to understand how a specific brain area, the Posterior Parietal Cortex (PPC), plays a role in movement transfer from walking on a split-belt treadmill (SBT) to walking on the ground in people with Parkinson's disease (PwPD). Here, investigators will apply repeated transcranial magnetic stimulation (rTMS) to upregulate the PPC. Then, the differences in the gait parameters between pre- and post-interventions will be compared between the TMS-active and the TMS-sham.

The split-belt training has been shown to modulate gait in PwPD, but the skill transfer from the SBT training to the overground walking is poorly understood. In this project, the subjects will visit the lab on three occasions: day 1 is for the clinical assessment based on the questionnaires, the 10-Meter Walk Task, as well as finding TMS targets and thresholds for the tibialis anterior (TA) and first dorsal interosseous (FDI) muscles, day 2 and day 3 are for either rTMS-active or rTMS-sham intervention. The second and third visits will take place at least 48h a part to ensure that the rTMS effects are washed out between visits. During these two visits, the participants will first perform pre-overground walking tests (3 minutes): straight walking, steering, and turning, followed by pre-SBT adaptation tests (4 minutes) where they will adapt their gait to the asymmetrical belt that changes every 30 seconds. After these walking tests, the threshold measured on the first day will be validated, and the cortical excitability of the PPC will be measured by using a dual-coil: one is over the TA hotspot, and the other is over the PPC. Then, rTMS or sham intervention will be performed, followed by measuring the cortical excitability of the PPC. Immediately after that intervention, the participants will train on the SBT for 30 minutes in total (with a one-minute break every 5 minutes) with the speed of the belt changing every 30 seconds. Following the SBT training, the participants will perform post-overground and post-SBT adaptation tests. Lastly, the cortical excitability of the PPC will be measured.