Traumatic Brain Injury Occludes Training-Dependent Cortical Reorganization in the Contralesional Hemisphere

Rehabilitative training drives plasticity in the ipsilesional (injured) motor cortex that is believed to support recovery of motor function after either stroke or traumatic brain injury (TBI). In addition, adaptive plasticity in the contralesional (uninjured) motor cortex has been well-characterized in the context of stroke. While similar rehabilitation-dependent plasticity in the intact hemisphere may occur after TBI, this has yet to be thoroughly explored. In this study, we investigated the effects of TBI and forelimb training on reorganization of movement representations in the intact motor cortex. Rats were trained to proficiency on the isometric pull task and then received a controlled cortical impact (CCI) in the left motor cortex to impair function of the trained right forelimb. After TBI, animals underwent forelimb training on the pull task for 2 months. At the end of training, intracortical microstimulation was used to document the organization of the intact motor cortex (the contralesional hemisphere). TBI significantly decreased the cortical area eliciting movements of the impaired forelimb in untrained animals. In the absence of TBI, training significantly increased forelimb map area, compared with in untrained controls. However, training of the impaired forelimb after TBI was insufficient to increase forelimb map area. These findings are consistent with other studies showing impaired rehabilitation-dependent plasticity after TBI and provide a novel characterization of TBI on rehabilitation-dependent plasticity in contralesional motor circuits.