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The Journal of Neuroscience, June 1, 2005, 25(22):5425-5429; doi:10.1523/JNEUROSCI.0429-05.2005

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Behavioral/Systems/Cognitive
Common Encoding of Novel Dynamic Loads Applied to the Hand and Arm

Paul R. Davidson,¹ Daniel M. Wolpert ,³ Stephen H. Scott,² and J. Randall Flanagan¹

Departments of ¹Psychology and ²Anatomy and Cell Biology, Canadian Institutes of Health Research Group in Sensory-Motor Systems, Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada K7L 3 N6, and ³Sobell Department of Motor Neuroscience, Institute of Neurology, University College London, London WC1N 3BG, United Kingdom

In manual action, the relationship between a given motor command and the ensuing movement depends on the dynamics of both the arm and hand-held objects. Skilled performance relies on the brain learning both these dynamics, and previous studies have examined how people adapt to novel loads applied to either the hand or the arm. In this study, we ask whether these different kinds of load are represented independently as a result of changes in cutaneous feedback and hand-arm coordination. We used a robotic apparatus that could either apply forces to an object held in the subject's hand or directly to the segments of the arm. We tested whether subjects could retain learning of a force field applied to the hand after subsequently experiencing the opposing field applied to the arm (or vice versa), or whether retrograde interference would be observed. In separate experiments, we used force fields and torque fields that were linearly related to either hand or joint velocities, respectively. Our finding of complete interference between opposing fields suggests that loads applied to the arm and hand are not represented independently by the sensorimotor system. This interference occurred despite markedly different cutaneous inputs that were directly related to the movement task. This result suggests that the brain represents dynamics independently of these sensory inputs. In addition, we found that the rate at which subjects adapted to a given force field, specified either in hand or joint coordinates, was independent of whether the forces were applied to the hand or arm segments.

Key words: adaptation; motor learning; motor control; arm movement; sensorimotor integration; limb dynamics

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Received Feb 1, 2005; revised April 4, 2005; accepted April 26, 2005.

This article has been cited by other articles:

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				G. E. Ansems, T. J. Allen, and U. Proske Position sense at the human forearm in the horizontal plane during loading and vibration of elbow muscles J. Physiol., October 15, 2006; 576(2): 445 - 455. [Abstract] [Full Text] [PDF]

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