Background and purpose: Freezing of gait (FOG) is one of the most disabling motor symptoms in people with Parkinson's disease (PD), and closely associates with postural instability and fall. Previous studies had shown that somatosensory stimulation could induce weight shift, and this is probably helpful for gait reinitiation. Therefore, the investogators propose a two-year project to develop a wearable device, the somatosensory stimulation system (SSS), which monitors gait real-time and provide somatosensory stimulation once FOG episodes detected. And the investigators test the effects of this SSS device on FOG, fall, and walking function.

Methods: The first-year study is to build and validate this wearable SSS device. The customized device has sensor part and stimulator part; the former is an inertial sensor module to detect FOG episodes, and the latter is a microvibrator-embedded insole to facilitate weight shift and gait reinitiation. To validate the device, patients with FOG are recruited and conduct FOG-provoking tasks during their medication "OFF" or "late On" state in a laboratory setting. The investigators test if the SSS device could facilitate lateral weight shift and help gait reinitiation, as well as the reliability. The second-year study is to test if the SSS device stands a long-term, daily wearing basis, and to evaluate its effect on FOG, fall, and walking function. The investigators recruit PD patients with FOG, and randomly assign them into the experimental and control groups. Both groups wear the SSS device during the daytime for ten weeks, and the stimulator part is turned on during the first six weeks (intervention phase) only in the experimental group. The stimulator part is then kept off during the last four weeks (follow-up phase) in both groups. The effect of the SSS device is evaluated by the outcomes including FOG severity, fall and walking function, which are measured prior/after the intervention phase and after the follow-up phase.

Clinical relevance: This project tempts to combine real-time gait analysis with somatosensory-induced postural readjustment, and using this novel approach to improve FOG and fall in people with PD. The results of this projects might also provide an objective, long-term assessment tool to measure the FOG phenomenon for clinical and research fields.

Inclusion Criteria:

• Idiopathic Parkinsonian with Hoehn-Yahr score between 2 to 4
• Suffering freezing-of-gait in the recent week
• Able to walk unassisted over 30 meters in medication OFF period

Exclusion Criteria:

• Non-idiopathic Parkinsonian
• Comorbid with uncontrolled neurological, cardiovascular and orthopedic diseases that might affect balance and mobility
• Impaired cognitive function
• Abnormal plantar sensory function
• Abnormal coagulation function