Transcranial Direct Current Stimulation of the Posterior Parietal Cortex Reduces Kinematic Asymmetry Between Dominant and Nondominant Arm Movements

Mental rotation (MR) is the ability to manipulate mental representations of objects. There may be a link between MR, particularly in discriminating mirror-reversed objects, and the ability to perform symmetrical movements with the nondominant limb, as both processes involve mirror-reversed representations. However, this relationship has not been extensively studied. In this study, we investigated whether excitatory transcranial direct current stimulation (tDCS) over the right posterior parietal cortex (rPPC)-a region involved in spatial abilities related to mirror-reversed cognition-enhances MR performance and symmetry between movements of the dominant and nondominant arm. Thirty healthy participants were randomly assigned to either the tDCS or sham group. Participants performed an MR task and symmetric overarm throwing movements with the nondominant arm, before and after receiving a combination of tDCS over the rPPC and visual motion feedback. At baseline, MR performance was positively correlated with dominant/nondominant movement symmetry, as assessed by motion capture. The combination of visual motion feedback and excitatory tDCS over the rPPC improved not only MR performance but also reduced asymmetry between movements of both arms compared to the sham group. In conclusion, greater ability in mentally rotating mirror-reversed objects is associated with symmetry between dominant and nondominant limb movements. tDCS-induced improvements in spatial cognition may facilitate mirror-reversed movements via visual feedback, and excitatory tDCS over the rPPC may enhance motor skill learning on the nondominant limb.