The FOG LIGHTS (Lessening Impairments in Gait with Hybrid Therapeutic Stimulation) Study is investigating the effectiveness of a new therapy for freezing of gait in people with Parkinsons who have an implanted deep brain stimulator. The purpose of the study is to determine whether or not CereGateTherapy can reduce freezing of gait in people with Parkinsons. CereGate therapy uses the Gevia™ DBS system that you already have, to create perceptible rhythmic sensations, or "cues", that may help to reduce your freezing of gait.