Figure 1.

The brain's white matter is conceptualized as yarn in this diagram. The descending strands represent corticospinal control of each hand by its respective contralateral motor cortex. The callosal strands represent the capacity for interhemispheric interactions. In an asynchronous bimanual task such as shoe tying, interhemispheric inhibition is relied upon to prevent interference between control processes for the two hands. At the same time, interhemispheric facilitation may be relied upon to integrate actions of the two hands, allowing them to achieve a single unified goal.