Inclusion Criteria:  Idiopathic PD Hoehn & Yahr Stage 2-3, on levodopa FOG, resistant to dopaminergic therapy Disease duration: 5-15 years Stable clinical response to medications or stimulation parameters (in case of DBS) for at least 3 months MMSE >24/30 Able to walk on a motor-driven treadmill  Exclusion Criteria:  Severe imbalance that limits ambulation (Hoehn &Yahr score above 3) Orthopedic conditions and other systemic disease affecting locomotion Cardiac conditions limiting the ability to walk uninterrupted for 1 hour Presence of other neurological disorder Inability to be fluent in English