<qa>  What is the risk of metal fragments in the eyes or head?Subjects who show no FOG during testing in the lab in response to a FOG provoking protocol, any diagnosed psychiatric or other neurological disorder, stroke, unbalanced and high blood pressure, pregnancy, participation in any clinical trial in the last three months, unwillingness to be randomized; implanted with deep brain stimulation, pacemakers, intracranial electrodes, implanted defibrillators or any other prosthesis; or a perceived inability to complete the study. Additional exclusion criteria related to tDCS safety will include a personal or family history of epilepsy, the use of neuro-active drugs, or risk of metal fragments in the eyes or head. 