Given the evidence that rhythmic auditory stimulation (RAS) can modulate beta oscillation and improve gait parameters, the purpose of this study is to examine behavioral and neurophysiological rhythmic entrainment mechanisms.~Participants who complete the consent and enrollment process will remain for an additional up to 1 hour following the participants' routine clinic visit at the Jons Hopkins Outpatient Clinic.~The protocol will consist of two parts (DBS ON and DBS OFF). The order of stimulation states will be randomly assigned to the participants.~During DBS ON, participants will receive the participants' previously optimized stimulation after a 10-minute washout period. The researchers will measure participants' gait parameters (cadence, velocity, and stride length) with a 2-minute walk (a set distance of 10 meters during the 2-minute walk) and gait patterns using relevant items from the MDS-UPDRS-III rating scale during stimulation ON (Pre-RAS).~The participants will then walk to the metronome beats for a total of four minutes (2 minutes for the same beat as baseline cadence and 2 minutes for 10% faster than baseline cadence) (RAS), and the gait parameters will be recorded. The order of the tempo will be randomized across the participants.~Finally, after this 4-minute walk, the same assessment as for Pre-RAS will be conducted (Post-RAS).~Electrophysiological activity (local field potentials, LFPs) will be collected across all stages (pre, during, and post-RAS) of evaluation.~In DBS OFF, there will be a separate 10-minute washout period if it is taking place after DBS ON so that the participant's brain circuits can adjust to not being stimulated. Except for the DBS stimulation state, DBS OFF will follow the same protocol as DBS ON above.
Participants will be asked to walk along with the metronome beats (RAS) during the participants' stimulation state (ON or OFF) for four minutes for each state.~The researcher will collect the gait parameters (cadence, velocity, and stride length) of patients before, during, and after RAS in both DBS ON and OFF states.~Using MDS-UPDRS, participants' gait patterns will be collected before and after RAS while both DBS is ON and OFF. Electrophysiological activity (local field potentials, LFPs) will be collected across all stages (pre, during, and post-RAS) of evaluation.