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The Journal of Neuroscience, March 25, 2009, 29(12):3939-3947; doi:10.1523/JNEUROSCI.5856-08.2009

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Behavioral/Systems/Cognitive
The Separate Neural Control of Hand Movements and Contact Forces

Vikram S. Chib,^1,2,3 Matthew A. Krutky,^1,2 Kevin M. Lynch,³ and Ferdinando A. Mussa-Ivaldi^1,2,4

¹Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois 60611, ²Department of Biomedical Engineering and ³Laboratory for Intelligent Mechanical Systems, Department of Mechanical Engineering, Northwestern University, Evanston, Illinois 60208, and ⁴Department of Physiology, Northwestern University, Chicago, Illinois 60611

Correspondence should be addressed to Vikram S. Chib at his present address: Computation and Neural Systems, California Institute of Technology, Pasadena, CA 91125. Email: vchib{at}caltech.edu

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.

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Received Nov. 26, 2008; revised Jan. 2, 2009; accepted Feb. 3, 2009.

Correspondence should be addressed to Vikram S. Chib at his present address: Computation and Neural Systems, California Institute of Technology, Pasadena, CA 91125. Email: vchib{at}caltech.edu

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