The motor cortex shows adaptive functional changes to brain injury from multiple sclerosis

Although multiple sclerosis (MS) is an inflammatory demyelinating disease, there can be substantial axonal injury and loss. We therefore hypothesized that adaptive cortical changes may contribute to limiting functional impair ment, particularly in the early stages of the disease. To test our hypothes is, we used functional magnetic resonance imaging (MRI) to characterize the localization and volumes of activation in the motor cortex during simple f lexion-extension finger movements. There were differences in the patterns o f cortical activation with movement between the 12 MS patients and the 12 n ormal controls. All patients showed greater relative supplementary motor ar ea activation than did the normal controls. The relative hemispheric latera lization of sensorimotor cortex (SMC) activation decreased in direct propor tion to the total cerebral T2-weighted MRI hyperintense lesion load. This a ppeared to be due primarily to increases in ipsilateral SMC activation with increasing lesion load in white matter of the hemisphere contralateral to the limb moved. The center of activation in the contralateral SMC was shift ed a mean of 8.8 mm posterior in patients relative to controls, providing a dditional evidence for cortical adaptive responses to injury. The magnitude of this posterior shift in the SMC activation increased with greater T2 le sion loads. These observations demonstrate that cortical recruitment for si mple finger movements can change both quantitatively and qualitatively in t he SMCs of MS patients, suggesting that cortical reorganization or "unmaski ng" of latent pathways can contribute to functional recovery. These adaptiv e changes are another factor potentially limiting the strength of the relat ionship between MRI measures of pathology and clinical measures of disabili ty.