Human rostral dorsal premotor cortex mediates graspability judgment of external objects by evaluating hand motor capability.

Humans can judge whether an object is graspable or not by merely glancing at it. This judgment is possible because of the brain's pragmatic function that links action with perception, i.e., the spatial property of the object is immediately associated with the motor capability of hands. In this study, we investigated the neural correlates of this cognitive-motor process by conducting an event-related functional magnetic resonance imaging experiment. Healthy right-handed participants were made to judge whether they could grasp visually presented objects with their right hand without generating any actual movements [motor evaluation (ME) task]. Objects of various sizes were presented to the participants in front of their hands; they judged the graspability of the object as soon as possible. For the control, the participants simply compared the size of the presented object and the static size of their fists [size comparison (SC) task]. Thus, only in the former task, the participants had to evaluate their motor capability by briefly simulating their range of hand motion. Rostral parts of the dorsal premotor cortices (prePMd) were activated bilaterally only during the ME task, and the activities were positively correlated with the duration of the evaluation. The prePMd participates in the judgment of graspability for external objects by evaluating hand motor capability. This function may assure a basic premise for the selection of an appropriate motor option when our hands interact with a variety of external objects. Copyright 2009 Elsevier B.V. All rights reserved.