Patients with Parkinson's disease have internal rhythm dysfunction, which may affect the rhythmic movements such as walking. Poor regularity of the rhythmic movement may lead to freezing of gait. This study will apply rhythmic auditory cues on the stepping-in-place training and the investigators will examine if the behavior and neuroelectrophysiology would change after auditory cueing training. The investigators hypothesize the variation of rhythmic movements such as walking and stepping-in-place will be reduced, and the cortical excitability would be modulated after training.

Parkinson's disease is a common neurodegenerative disease and movement disorder. Due to the degeneration of basal ganglia, patients with Parkinson's disease also demonstrate internal rhythm dysfunction, thus will lead to difficulty in rhythmic movements such as ambulation. For improving the rhythmic movement problem, auditory cues are often used in clinical setting and shows benefits in ambulation and freezing problems. Previous studies often use finger tapping test and ambulation to assess the rhythmic movement problem. No study uses stepping in place movements as a test to examine rhythmic problem. Little study investigates the effects of auditory cues on brain cortical excitability. In this cross-over study, participants will receive 2 times of training include stepping-in-place exercise with and without auditory cues in random orders. Auditory cues are given via the metronome. There is one-week wash-out period between two trainings. Movement tests such as walking and stepping-in-place and transcranial magnetic stimulation (TMS) are carried out before and after each training.

The investigators hypothesize the variation of rhythmic movements such as walking and stepping-in-place will be reduced more, and the cortical excitability would be modulated after the training with auditory cues, comparing with the other training without auditory cues.

[Patients with Parkinson's disease]

Inclusion Criteria:

• Diagnosed with idiopathic Parkinson's disease
• No hearing impairment
• Able to walk independently for at least 10m
• Able to follow command (MMSE >=24)

[Healthy subjects]

• No hearing impairment
• Able to walk independently for at least 10m
• Able to follow command (MMSE >=24)

Exclusion Criteria:

• With other neurological diseases or psychological diseases
• Dementia
• Family history of epilepsy
• History of head trauma, surgery, or metal implants
• Having pacemaker or other electrical stimulators
• History of syncopes or frequent migraines