Temporal synchronization during bilateral foot-tapping and its relationship with gait disturbance in patients with Parkinson's disease.

Objective: Previous studies using finger-tapping tasks have shown that patients with Parkinson's disease (PD) exhibit a deficit of temporal processing linked to gait disturbance. In this study, we aimed to investigate abnormalities in lower-limb rhythmic control and their association with freezing of gait in PD using a bilateral foot-tapping task. Methods: Fifteen patients with PD and 25 healthy controls performed foot-tapping tasks synchronized with auditory tones at fixed intervals (500-2,400 ms). The tasks included unilateral and bilateral foot-tapping, with bilateral movements performed either in-phase (simultaneous) or antiphase (alternating). Data on synchronizing tapping error and inter-tap interval variability were analyzed and correlated with scores from clinical assessments, including the Unified Parkinson's Disease Rating Scale and Freezing of Gait Questionnaire. Results: Patients with PD showed greater negative synchronizing tapping error (negative asynchrony) and higher inter-tap interval variability than did controls, especially in antiphase condition. Exploratory within-PD-group analyses suggested associations between clinical severity and abnormalities in bilateral foot-tapping performance. Conclusion: These findings indicate altered temporal accuracy and stability of rhythmic lower-limb movements in PD, particularly during bilateral antiphase foot-tapping. Bilateral foot-tapping measures may help characterize lower-limb timing deficits that are relevant to gait rehabilitation in PD.