Sensitivity of cortical movement representations to motor experience: evidence that skill learning but not strength training induces cortical reorganization

The topography of forelimb movement representations within the rat motor co rtex was examined following forelimb strength training. Adult male rats wer e allocated to either a Power Reaching, Control Reaching or Non-Reaching Co ndition. Power Reaching rats were trained to grasp and break progressively larger bundles of dried pasta strands with their preferred forelimb. Contro l Reaching animals were trained to break a single pasta strand and Non-Reac hing animals were not trained. Power Reaching animals exhibited a progressi ve increase in the maximal size of the pasta bundle that could be retrieved during a 30-day training period. Kinematic analyses showed that this impro vement was not due to a change in reaching strategy. Intracortical microele ctrode stimulation was used to derive maps of forelimb movement representat ions within the motor cortex of all animals following training. In comparis on to Non-Reaching animals, both Power Reaching and Control Reaching animal s exhibited a significant increase in the proportion of motor cortex occupi ed by distal forelimb movement representations (wrist/digit) and a decrease in the proportion of proximal representations (elbow/shoulder). These resu lts demonstrate that the development of skilled forelimb movements, but not increased forelimb strength, was associated with a reorganization of forel imb movement representations within motor cortex. (C) 2001 Elsevier Science B.V. All rights reserved.