Inclusion Criteria:  age 18 to 80; chronic stroke lesion >6 months after a cerebrovascular accident OR diagnosis of cerebral palsy OR Parkinson's Disease; presence of some degree of motor function in the ankle flexor (Soleus motor power >1); able to ambulate 10 meters without physical assistance.  Exclusion Criteria:  medically unstable condition; presence of other concurrent neurological illness; cognitive impairment (Montreal Cognitive Assessment score <23); presence of any potential TMS risk factor: damaged skin at the site of stimulation; presence of an electrically, magnetically or mechanically activated implant, an intracerebral vascular clip, or any other electrically sensitive support system; family history of medication-resistant epilepsy; past history of seizures or unexplained spells of loss of consciousness.