Planning and Updating in Frontoparietal Networks for Grasping

Abstract The control of movement, in spite of its seemingly effortless execution, belies a complex, multi-level collective of neuromuscular interactions tuned and coordinated through sensory experience. Efficient and flexible behavior in everyday contexts requires neural mechanisms that support rapid updating whenever objects around us, or even our own movements, are disrupted during ongoing motion. As a movement unfolds, the need for predictive or responsive control to correct for contextual perturbations changes. For example, the early stages of an action typically exhibit fast responses to perturbations, suggesting the existence of feed-forward processes that use internal models to predict the sensory consequences. On the other hand, later phases appear to employ continuous sensory feedback to adjust movements. While much is known about updating for postural and arm movements, very little is understood about the neural mechanisms of updating of dexterous movements of the hand as we interact with objects. While the reach-to-grasp cortical anatomy is well described, the causal functional roles of the regions still remain elusive. In particular, it is now becoming clear that the dominant framework which describes reach-to-grasp control as being under the control of independent frontoparietal channels is untenable because it does not explain recent empirical neurophysiological findings. Therefore, the current project aims to leverage non-invasive stimulation to induce transient cortical perturbations, paired with visual perturbations to the task goal and mechanical perturbations of the internal state of the limb, to causally evaluate the contributions of four critical brain regions in components of the reach-to-grasp action. The information derived from this work will provide a more solid background for our understanding of the functional organization of the frontoparietal reach-to-grasp network and, by extension, of hand-arm control coordination. This project will advance our empirical understanding of how dexterous updating of the upper limb, in particular reach-to-grasp actions, are orchestrated by the brain. The knowledge will be immediately applicable and translatable for rehabilitation of upper limb recovery in stroke and other similar disorders, by using error augmentation through visual and haptic platforms to facilitate skill reacquisition and identifying cortical targets for non-invasive neuromodulatory stimulation. These findings will be relevant to the mission of the NIH, with broad interest to clinicians and basic scientists, and will have direct