Cerebellar Hemispheric Contribution to the Dynamics of Visuomotor Learning during Interlimb Coordination: Insights from an rTMS Study.

This study investigated the effects of repetitive transcranial magnetic stimulation (rTMS) over the right cerebellar hemisphere on visuomotor adaptation and interlimb coordination learning. Specifically, we examined the impact of cerebellar stimulation on the acquisition of new visuomotor transformations and subsequent adaptation under interference conditions during a bimanual tracking task. A total of 42 healthy adults performed a bimanual visuomotor tracking task in which the left and right hands controlled horizontal and vertical cursor movements, respectively. The experiment consisted of two phases: (1) an Initial learning phase involving adaptation to a visuomotor transformation, and (2) an Interference adaptation phase, defined as adaptation to a new visuomotor mapping under interference from the previously learned transformation, in which only the right-hand mapping was altered. Participants received either active or sham 1Hz rTMS over the right cerebellar hemisphere before the task. Performance was assessed using tracking error and interlimb error structure measures. Tracking errors decreased over trials in both learning phases. While rTMS had no significant effect during the Initial learning phase, it significantly reduced tracking errors during the Interference adaptation phase. In the active-rTMS group, interlimb error correlation and the directional error slope also declined across trials, suggesting reduced cross-limb interference and enhanced coordination flexibility. These findings suggest that cerebellar rTMS facilitates the adaptation of altered visuomotor mappings, particularly during interference adaptation, by modulating interlimb coordination. The results support the hypothesis that bimanual coordination relies on modular internal models that dynamically interact during motor learning. This study underscores the cerebellum's essential role in optimizing interlimb adaptation, especially under interference adaptation, and highlights the potential of cerebellar neuromodulation for motor rehabilitation.