Grasping in the dark activates early visual cortices.

We have previously demonstrated that the primary motor and somatosensory cortices of monkeys are somatotopically activated for action-observation as are for action-generation, indicating that the recruitment of learned somatosensory-motor representations underlies the perception of others' actions. Here we examined the effects of seen and unseen actions on the early visual cortices, to determine whether stored visual representations are employed in addition to the somatosensory-motor ones. We used the quantitative (14)C-deoxyglucose method to map the activity throughout the cortex of the occipital operculum, lunate, and inferior occipital sulci of "rhesus monkeys" who reached to grasp a 3D object either in the light or in the dark or who observed the same action executed by another subject. In all cases, the extrastriate areas V3d and V3A displayed marked activation. We suggest that these activations reflect processing of visuospatial information useful for the reaching component of action, and 3D object-related information useful for the grasping part. We suggest that a memorized visual representation of the action supports action-recognition, as well as action-execution in complete darkness when the object and its environment are invisible. Accordingly, the internal representation that serves action-cognition is not purely somatosensory-motor but also includes a visual component.