Use-Dependent Plasticity in Patients with Multiple Sclerosis

Background: In patients with multiple sclerosis (MS), cumulative tissue injury develops in the central nervous system. Axonal damage is known to occur early on in the disease. Cortical reorganization has been observed in MS patients during the performance of motor and cognitive tasks and may prevent functional deficits. A better understanding of cerebral plasticity could help optimize therapeutic options. Methods: In the current study, we analyzed the effects of training a simple motor task on cortical organization. Functional MRI activation patterns of patients with relapsing-remitting MS and of healthy control subjects were evaluated before and after a thirty-minute training period with a random effects analysis (SPM99). Kinematic properties of the trained movement as well as a control movement were controlled with an accelerometer; potential mirror movements were detected with an EMG attached to the passive hand. Results: Performance of the thumb movements before, during and after the training phase was comparable in both groups; mirror movements were not observed. Before the training, MS patients showed a more pronounced activation of the contralateral dorsal premotor cortex (PMd) than healthy controls. After the training, patients did not exhibit a task-specific reduction of activation in the contralateral somatosensory cortex (S1), motor cortex (M1) and parietal association cortex (BA 40). Conclusions: These findings indicate that patients recruit the contralateral PMd more than healthy subjects in order to perform a simple untrained motor task. The absence of a task-specific reduction of activation in S1, M1 and BA 40 suggests a reduced capacity among MS patients to optimize neuronal recruitment with training.