Involvement of aSPOC in the online updating of reach-to-grasp to mechanical perturbations of hand transport.

Abstract

Humans adjust their movement to changing environments effortlessly via multisensory integration of the effector's state, motor commands, and sensory feedback. It is postulated that frontoparietal (FP) networks are involved in the control of prehension, with dorsomedial (DM) and dorsolateral (DL) regions processing the reach and the grasp, respectively. This study tested (5F, 5M participants) the differential involvement of FP nodes (ventral premotor cortex - PMv, dorsal premotor cortex - PMd, anterior intraparietal sulcus - aIPS, and anterior superior parietal-occipital cortex - aSPOC) in online adjustments of reach-to-grasp coordination to mechanical perturbations that disrupted arm transport. We used event-related transcranial magnetic stimulation (TMS) to test whether the nodes of these pathways causally contribute to the processing of proprioceptive information when reaching for a virtual visual target at two different perturbation latencies. TMS over aSPOC selectively altered correction magnitude of arm transport during late perturbations, demonstrating that aSPOC processes proprioceptive inputs related to mechanical perturbations in a movement phase-dependent manner.Significance Statement Detailed knowledge regarding specific brain regions, the timing of their involvement, and roles in the online updating of sensory input during the control of the reach-to-grasp movement is critical for understanding the deficits resulting from various diseases, such as stroke, as well as for the development of effective intervention strategies. Our results provide evidence for the involvement of aSPOC in the modulation of the response to a mechanical perturbation of arm transport during the later stage of the movement, suggesting that this area participates in estimating the effector state based on proprioceptive input. Our results can provide key information for identifying brain targets of engagement in therapeutic applications of noninvasive brain stimulation to ameliorate motor deficits stemming from parietal damage.