Criscimagna-Hemminger SE, Donchin
O, Gazzaniga MS, Shadmehr R (2003) Learned dynamics
of reaching movements generalize from dominant to non-dominant arm. Journal
of Neurophysiology 89:168-176.
Abstract Accurate performance of reaching movements depends on adaptable neural circuitry that learns to predict and compensate for dynamics of the limb. In earlier behavioral experiments we quantified how training with novel forces at one arm position was generalized to another position of the same arm. The generalization patterns suggested that neural elements that learned to predict the forces coded a limb's position and velocity in an intrinsic, muscle-like coordinate system. Here we asked whether these elements are also responsive to movements of the other arm by quantifying inter-arm generalization. We considered two possible coordinate systems: an intrinsic (joint) representation should cause generalization with mirror symmetry reflecting the symmetry of the joints; an extrinsic representation should cause generalization preserving the task's structure in extrinsic coordinates. Both extrinsic and intrinsic coordinate systems of generalization were compared to a naive control group. We tested transfer in right-handed subjects both from the dominant to the non-dominant arm (D-ND) and vice versa (ND-D). This led to a 2x3 experimental design matrix: direction of transfer (D-ND / ND-D) by coordinate system (extrinsic, intrinsic, control). We found significant generalization only from dominant to non-dominant arm and only in extrinsic coordinates. To assess the dependence of generalization on callosal inter-hemispheric communication, we tested commissurotomy patient JW. JW showed generalization from dominant to non-dominant arm in extrinsic coordinates. The results suggest that when the dominant right arm is first used in learning dynamics of reaching movements, the information is represented in the left hemisphere with neural elements that are tuned to reaching movements of both the right arm and the left arm. However, learning with the non-dominant left arm relies on neural elements in the non-dominant hemisphere that are only tuned with respect to movements of the non-dominant arm.