By comparing brain activation as subjects prepared to reach towards or grasp an object using their hands or a tool, Gallivan et al. identified four networks that code for distinct components of object-directed actions. Some brain regions code for planned actions that involve the hands but not tools (red), and others for actions that involve tools but not the hands (blue). A third set of regions codes for actions involving either the hands or tools, but uses different neural representations for each (pink). A final set of areas code the type of action to be performed, distinguishing between reaching towards an object as opposed to grasping it, irrespective of whether a tool or the hands alone are used (purple). The red lines represent the frontoparietal network implicated in hand actions, with the short dashes showing the subnetwork involved in reaching, and the long dashes, the subnetwork involved in grasping. The blue solid lines show the network implicated in tool use, while the green line connects areas comprising a subset of the perception network.
FIGURE CREDIT: IMAGE ADAPTED FROM FIGURE 7 IN GALLIVAN ET AL., 2013B