Relationship between interhemispheric inhibition and bimanual coordination in musicians

Musical expertise provides an opportunity to explore science through art. A musician’s brain is shaped by long-term skill acquisition, and the neuroplastic changes are expressed by the complex coordinated movements between the two hands. This dissertation aimed to investigate how the communication between the two cerebral hemispheres through interhemispheric inhibition (IHI) contributes to bimanual coordination in skilled musicians, and to understand the instrument-dependent effect on this brain-behavior relationship. ❧ We first systematically determined the optimal methodology (ideal muscle contraction level and quantification method) to measure ipsilateral silent period (iSP), which is an indicator of IHI. The iSP measure was then applied to the following investigations to compare IHI in musicians and non-musicians. Musicians demonstrated significantly better bimanual coordination compared to non-musicians. Increased IHI from the left to the right hemisphere was found to significantly correlate with increased key pressing consistency, but with reduced speed during a bimanual task in skilled musicians. This IHI-bimanual coordination relationship was only evident in musicians, but not in non-musicians. We then designed both symmetric and asymmetric bimanual coordination tasks to address whether the IHI-bimanual coordination relationship in a musician was dependent on instrument type. Moreover, we investigated whether auditory sound impacts motor performance in musicians. Keyboard and string players were recruited as representatives of symmetric hand use and asymmetric hand use, respectively. Overall, there were no differences in performance of either symmetric or asymmetric tasks between keyboard and string players. There were no differences in motor performance with or without auditory feedback in either group. A similar IHI-bimanual coordination relationship was found in both keyboard and string players. Specifically, increased left to right as well as decreased right to left IHI were associated with increased speed as well as increased accuracy (i.e. better bimanual coordination) in both groups. ❧ The findings of this dissertation provided strong evidence of experience-dependent neuroplasticity associated with the brain-behavior relationship following intensive musical training. Future studies would investigate the beneficial effects of instrument playing in individuals with impaired bimanual coordination. Moreover, modulation of IHI using non-invasive brain stimulation with an individualized and instrument-specific approach may be a promising intervention for Musician’s dystonia in order to regain bimanual coordination.