Inclusion Criteria:  Idiopathic PD diagnosed by a movement disorders neurologist Presence of gait functional impairment despite optimal medical management Able to walk independently without an aid for a minimum of two minutes without rest Absence of secondary causes of gait problems Able to understand study requirements - able to provide consent Above 50 years of age  Exclusion Criteria:  The presence of another significant neurological/psychiatric disorder or significant disease Spinal anatomical abnormalities precluding SCS surgery History of stroke or structural lesions on CT that could interfere with image analysis. History of chronic pain and severe degenerative spine disease with or without chronic pain History of drug addiction or dependency Previous DBS surgery for PD Pregnancy or breast-feeding.