Increases in motor cortical excitability during mirror visual feedback of a precision grasp is influenced by vision and movement of the opposite limb.

Unimanual grasp movements with mirrored visual feedback (MVF) can improve function and increase excitability of primary motor cortex (M1) ipsilateral to the moving hand. However, no study to date has examined the contribution of vision and movement of the opposite hand during an object-directed precision grasp. In this study, we tested 15 healthy individuals in three conditions: MVF (vision + motor), Movement (motor component), and Action Observation (vision component). We hypothesized that unimanual grasp movements with MVF increases the excitability and reduces intracortical inhibition of the M1 ipsilateral to the moving hand. We found increased excitability in the right primary motor cortex (M1) ipsilateral to the moving right hand for MVF movements compared to Rest (Baseline). In contrast, no change was found in right M1 with only movement of the right hand or observation of object-directed precision grasp with left hand. We also found a reduction in short-interval intracortical inhibition in MVF movements compared to baseline. These findings suggest that excitability in M1 during an object-directed precision grasp is mediated by the combination of viewing the movement performed and performing the movement from the opposite hand.