The Separate Neural Control of Hand Movements and Contact Forces

Abstract

To manipulate an object, we must simultaneously control the contact forces exerted on the object and the movements of our hand. Two alternative views for manipulation have been proposed: one in which motions and contact forces are represented and controlled by separate neural processes, and one in which motions and forces are controlled jointly, by a single process. To evaluate these alternatives, we designed three tasks in which subjects maintained a specified contact force while their hand was moved by a robotic manipulandum. The prescribed contact force and hand motions were selected in each task to induce the subject to attain one of three goals: (1) exerting a regulated contact force, (2) tracking the motion of the manipulandum, and (3) attaining both force and motion goals concurrently. By comparing subjects' performances in these three tasks, we found that behavior was captured by the summed actions of two independent control systems: one applying the desired force, and the other guiding the hand along the predicted path of the manipulandum. Furthermore, the application of transcranial magnetic stimulation impulses to the posterior parietal cortex selectively disrupted the control of motion but did not affect the regulation of static contact force. Together, these findings are consistent with the view that manipulation of objects is performed by independent brain control of hand motions and interaction forces.

A key region in the human parietal cortex for processing proprioceptive hand feedback during reaching movements

“…The combined results of this and other studies (Chib et al, 2009;Della-Maggiore et al, 2004;Vesia et al, 2010) identify this region as a key area for processing proprioceptive information for motor control. Furthermore, this region can be clearly distinguished from an area around the anterior IPS, which is crucial for online sensorimotor processing in the presence of visual feedback about the hand position.…”

“…Studies demonstrating the necessity of the anterior IPS in grasping (Rice et al, 2006Tunik et al, 2005Tunik et al, , 2007 consistently report only changes in the temporal dynamics during the movement, but no spatial effects due to TMS. The studies of Chib et al (2009) and Reichenbach et al (2011) report spatial effects in the order of the effects reported here. The effects of Della-Maggiore et al (2004) seem to accumulate up to 30%.…”

“…This finding complements the studies based on which we included mIPS posterior into the current study. Della-Maggiore et al (2004) have shown that TMS applied over this area also interferes with the learning of novel dynamics induced by a force field, and Chib et al (2009) have demonstrated that this area is important for tracking the movement of a manipulandum in the absence of visual feedback. In both studies, processing of proprioceptive information was the key for successful task execution as in our proprioception-only condition.…”

“…Additionally, TMS over the sites aIPS, SMG superior , and SMG middle yielded significant disturbance of the correction to visual perturbations in that study. mIPS posterior was included because two TMS studies successfully used this stimulation site to interfere with the processing of proprioceptive hand/arm information during a motor task (Chib et al, 2009;Della-Maggiore et al, 2004). Finally, aIPS posterior and SMG inferior were included to complement the grid.…”

“…The tested sites constitute a compromise between feasibility of the study with respect to the testing time and covering the portions of the PPC that might be involved in online processing of sensory information about the reaching hand/ arm. We did not include more medial-posterior areas as they have mainly been associated with processing information about the target of reach (Bernier and Grafton, 2010;Diedrichsen et al, 2005;Gallivan et al, 2009;Vesia et al, 2010 (Reichenbach et al, 2011) previous TMS studies investigating online control or proprioceptive processing during reaching (Chib et al, 2009;Della-Maggiore et al, 2004;Reichenbach et al, 2011) (Table 1). With these sites, we covered a broad region of the left PPC for which sensorimotor processing related to our questions had been localized previously.…”