Motor System Plasticity and Compensation in Multiple Sclerosis

Multiple sclerosis (MS) affects the central nervous system (CNS) by inflammatory lesions, direct axonal injury, and by a rather diffuse and widespread neurodegeneration. For a long time, research has mainly focused on these destructive aspects of MS, while the compensatory effects of cellular repair and neural plasticity have received little consideration. However, as current effective immunomodulatory therapies may limit rather than preclude demyelination and axonal damage, additional therapeutic strategies promoting compensation of CNS damage might be of great use for preventing persistent impairment in MS. As a precondition for the development of such strategies, which may encompass pharmacological and behavioural interventions, but also non-invasive stimulation techniques, it seems fundamental to get deeper insights into the mechanisms of plasticity and adaptation at the systemic level. This review will provide a brief overview of what is known about plasticity of the motor system in patients with MS at present, with the main focus relying on evidence from functional imaging, neurophysiology, and motor learning. Overall, rapid-onset motor plasticity seems to be preserved even in advanced stages of the disease. Reorganisation processes, which can be shown early in the course of MS, are functionally relevant for motor compensation. In advanced MS, however, the brain ́s adaptive reserve might be exhausted due to exceeding CNS injury. Future studies should address the question of how the later stages of central motor plasticity can be promoted best to preserve the patient ́s autonomy for as long as possible.