RecruitingDevice studyNeurophysiology of Locomotor Adaptation and Freezing of Gait in Parkinson's DiseaseLocomotor adaptation will be studied using an established split-belt treadmill paradigm, consisting of baseline (1:1 speed ratio), split-belt adaptation (2:1) and post-adaptation (1:1) walking. Split-belt walking will be performed under DBS ON and DBS OFF conditions, while off-medication.