The monkey ventral premotor cortex processes 3D shape from disparity

Visual processing of the three-dimensional (3D) shape of objects is important for object recognition as well as for the control of grasping. Single cell studies have revealed that many ventral premotor cortical (F5) neurons are selective for the shape of real-world objects--the so-called canonical neurons--but there is little experimental evidence for depth structure selectivity in frontal cortex. Here we used contrast-agent enhanced fMRI in the awake monkey to investigate 3D shape processing defined by binocular disparity. We targeted regions in the monkey brain more active for curved than flat, fronto-parallel 3D surfaces. In addition to AIP (Durand et al., 2007), we observed depth structure sensitivity from disparity in a small region of infero-temporal cortex, TEs, known to house higher order disparity selective neurons. Furthermore, within ventral premotor cortex, the most rostral sector of F5, area F5a, showed sensitivity for depth structure from disparity. Within this area, 2D shape sensitivity was also observed, suggesting that area F5a processes complete 3D shape and might thus reflect the activity of canonical neurons. In conclusion, our data point to a distributed functional network, including TEs, AIP and F5a, involved in the analysis of stereoscopic 3D shape information and its potential use in the visual control of grasping.