Multisensory integration and motor adaptation in the human posterior parietal cortex

Actions are fundamental not only for survival but also for shaping our interactions with the external world. Successfully engaging with objects in our surroundings requires extracting relevant visual features, translating them into motor possibilities, and executing movements while integrating visual, tactile, and motor information. The posterior parietal cortex (PPC) plays a crucial role in this process, supporting multisensory integration and motor control. In this thesis we try to explores two main key aspects of PPC functionality: (1) the organization of the human ventral intraparietal area (hVIP) and its potential subdivisions, and (2) the role of the intraparietal sulcus (IPS) in reach-to-grasp movements. Neuroimaging research on sensorimotor interactions has traditionally been constrained by static environments with limited or absent real-time visual feedback of limb movements. To overcome these limitations, we developed MOTUM (Motion Online Tracking Under MRI), a hardware and software framework that integrates virtual reality (VR) and motion capture for real-time movement tracking during fMRI. This system allows participants to interact with a dynamic VR environment while maintaining accurate movement representation, enhancing the ecological validity of reach- to-grasp paradigms. In the first study, we investigated whether hVIP consists of functionally distinct subregions. Using functional MRI (fMRI) and neuroimaging analyses, we identified distinct activation patterns within the IPS, suggesting a subdivision into specialized areas for processing visual motion and tactile inputs. Furthermore, we examined the relationship between hVIP1 which is primarily involved in egomotion, located in the posterior IPS, and the lateral intraparietal area (LIP), which is primarily involved in eye movement control. Our findings indicate that while hVIP1 and LIP share certain functional properties. The second study, we examined the PPC’s role in reach-to-grasp movements, specially on IPS activation patterns. We implemented MOTUM to cature the movement in the real time. Our results show that IPS contributtion to planning and executing grasping movements, reinforcing the PPC’s critical role in visuomotor transformations. By integrating findings from both studies, this thesis provides new insights into the functional organization of hVIP and its broader role in multisensory integration. Additionally, MOTUM offers a novel approach for studying naturalistic sensorimotor interactions in the brain, with significant implications for cognitive neuroscience, neurorehabilitation, and the development of assistive technologies for motor control. Future research should further explore the impact of real-time movement tracking on neural representations in the PPC.