Functional magnetic resonance imaging and multiple sclerosis: the evidence for neuronal plasticity.

Blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) has emerged as a powerful technique to visualize the localization of cerebral activity in both healthy and diseased brains. BOLD fMRI has been used to assess brain function in a variety of diseases, including multiple sclerosis (MS), and has shown that altered patterns of connectivity are used to recruit more widespread eloquent brain networks engaged in tasks relating to motor activity, sensory and cognitive function, and memory when compared to normal controls. This review will examine the evidence that functional reorganization is a consequence of demyelination and tissue loss in MS that may serve as an adaptive response to limit clinical disability. It remains unclear whether cerebral plasticity is a marker of permanent functional restructuring or a short-term compensatory response to injury. Long-term longitudinal studies that correlate fMRI activity with other MRI markers of disease burden and activity, as well as with clinical measures of disease activity and progression, are badly needed to determine fMRI's relevance to clinical practice and its place as a surrogate outcome measure in MS.