Differential contributions to the interception of occluded ballistic trajectories by the temporoparietal junction, area hMT/V5+ and the intraparietal cortex

The ability to catch objects when transiently occluded from view suggests their motion can be extrapolated. Intraparietal cortex (IPS) plays a major role in this process along with other brain structures, depending on the task. For example, interception of objects under Earth's gravity effects may depend on time-to-contact predictions derived from integration of visual signals processed by hMT/V5+ with a-priori knowledge of gravity residing in the temporoparietal junction (TPJ). To investigate this issue further, we disrupted TPJ, hMT/V5+ and IPS activities with Transcranial Magnetic Stimulation (TMS) while subjects intercepted computer-simulated projectile trajectories perturbed randomly with either hypo- or hypergravity effects. In Experiment 1, trajectories were occluded either 750 or 1250 ms before landing. Three subject groups underwent triple-pulse TMS (tpTMS, 3 pulses at 10 Hz) on one target area (TPJ | hMT/V5+ | IPS) and on the vertex (control site), timed at either trajectory perturbation or occlusion. In Experiment 2, trajectories were entirely visible and participants received tpTMS on TPJ and hMT/V5+ with same timing as Experiment 1. tpTMS of TPJ, hMT/V5+ and IPS affected differently the interceptive timing. TPJ stimulation affected preferentially responses to 1g motion, hMT/V5+ all response types, IPS stimulation induced opposite effects on 0g and 2g responses, being ineffective on 1g responses. Only IPS stimulation was effective when applied after target disappearance, implying this area might elaborate memory representations of occluded target motion. Results are compatible with the idea that IPS, TPJ and hMT/V5+ contribute to distinct aspects of visual motion extrapolation, perhaps through parallel processing.