As most of the corticospinal fibers cross over to the contralateral side, the right side of the body is controlled by the left primary motor cortex, while the left side of the body is controlled by the right primary motor cortex. However, because callosal connections between the two hemispheres and ipsilateral corticospinal pathways convey the same information to bilateral homologous muscles, interference can occur between the left and the right motor system when we use bilateral hand simultaneously. This interference could work as a cost-effective measure in symmetric movements and a resource-demanding measure in asymmetric movement. In this paper, I discuss how the brain represents cost-effective and resource-demanding bimanual interaction.