Interception of visible and occluded ballistic trajectories: differential contributions by areas MT/V5, V6, V6A and the vestibular premotor cortex evaluated by TMS.

INTRODUCTION: Several cortical regions have been implicated in the control of interceptive actions, such as area MT/V5, posterior parietal areas, a vestibular area in the temporo-parietal junction (TPJ) involved in an internal representation of gravity, and premotor areas. Here, we assessed the potential contributions of visual areas V6 and V6A and of another premotor region in the inferior frontal gyrus associated to the vestibular network (IFG), which could potentially contribute based on their connectivity and known functional properties, and compared them with those of MT/V5. METHODS: We applied triple-pulse transcranial magnetic stimulation (tpTMS) during interception of ballistic trajectories, either congruent with natural gravity (1g) or perturbed with constant-velocity profiles (0g). Trajectories were either fully visible or occluded prior to landing. tpTMS was applied on each cortical site right after the trajectory perturbations or occlusions. RESULTS: tpTMS of MT/V5 produced robust changes in the interceptive performance with both visible and occluded trajectories, by modulating central processing delays with continuously available visual information, while contributing to visual extrapolation with occluded motion. V6 stimulation produced significant effects only with visible trajectories by modulating the central processing delays downstream of MT/V5. IFG showed distinct contributions to the spatial and temporal aspects of the interceptive action with respect to the integration of predictive signals based on visual information and on internalized gravity information. V6A stimulation was seemingly ineffective. CONCLUSION: Altogether, the functional dissociations emerging among these cortical areas support a complex, parallel distributed organization of the cortical network involved in the interception of projectile motion.