We investigated the functional role of the corpus callosum (CC) in nonspecific motor transfer between the dominant and the nondominant hand in a serial reaction time task based on finger opposition movements, by combining motor behavioral with Magnetic Resonance Diffusion Tensor Imaging (DTI) data in patients with Multiple Sclerosis (PwMS), who commonly show disease-related CC damage.

We asked 19 right-handed low-disability PwMS to respond as fast and accurately as possible to the presentation of random sequences of squares displayed on the fingertip of the index, middle, ring and little finger of a pictured palm hand, by tapping the appropriate finger with the thumb. The session included 4 blocks with the right (R1right-R4right) and 2 with the left (R1left-R2left) hand. Movements were recorded by a sensor engineered glove, and mean Response Time (RT) was calculated for each block. Nonspecific transfer was calculated as the difference in RT between R2right and R2left (Delta_transfer). Five CC subregions were selected on the midsagittal plane, in which Fractional Anisotropy (FA) was calculated as index of structural damage. A linear correlation between Delta_transfer and FA was found only in the part of CC that includes fibers connecting primary motor areas (r=0.71, p=0.01) suggesting that transcallosal interactions between primary motor areas contribute to motor performance in the transfer hand optimizing the timing of visuomotor processing.