Neural representations of graspable objects: are tools special?

Recent cognitive and neuroimaging studies have examined the relationship between perception and action in the context of tools. These studies suggest that tools "potentiate" actions even when overt actions are not required in a task. Tools are unique objects because they have a visual structure that affords action and also a specific functional identity. The present studies investigated the extent to which a tool's representation for action is tied to its graspability or its functional use. Functional magnetic resonance imaging (fMRI) was used to examine the motor representations associated with different classes of graspable objects. Participants viewed and imagined grasping images of 3D tools with handles or neutral graspable shapes. During the viewing task, motor-related regions of cortex (posterior middle temporal gyrus, ventral premotor, and posterior parietal) were associated with tools compared to shapes. During the imagined grasping task, a frontal-parietal-temporal network of activation was seen with both types of objects. However, differences were found in the extent and location of premotor and parietal activation, and additional activation in the middle temporal gyrus and fusiform gyrus for tools compared to shapes. We suggest that the functional identity of graspable objects influences the extent of motor representations associated with them. These results have implications for understanding the interactions between "what" and "how" visual processing systems.