Postural instability is one of the motor features of Parkinson's disease (PD). Most patients will develop balance dysfunction, and they may get worse with disease progression. According to previous studies, people with PD had abnormal changes in corticomotor excitability, especially disinhibition in the primary motor cortex (M1). Some evidence had shown that the cortical function in the M1 is crucial for the pathophysiology of the underlying motor symptoms in PD. Furthermore, neurostimulation over the M1 could modulate the corticomotor excitability in individuals with PD, and then improve their motor and also balance performance. However, whether the impaired corticomotor inhibition relates to balance dysfunction in people with PD is still unknown. In this study, the purpose is to investigate the possible relationship between corticomotor inhibition and balance performance in individuals with PD. However, the postural position during TMS measurement may affect the corticomotor excitability. To further establish the above-mentioned relationship, the secondary purpose is to explore and confirm whether the postural position will influence the correlation.

Inclusion Criteria:

• the Hoehn and Yahr stage between 1 and 3
• age 40 to 80 years
• a stable treatment of anti-PD medications

Exclusion Criteria:

• any contraindications of TMS
• any injury histories or disorders affecting balance
• any neurosurgery experience
• neurologic conditions other than PD
• the Mini-mental State Examination (MMSE) score < 24

people with Parkinson's disease