The limits of functional reorganization in multiple sclerosis

Investigating the brain at rest using functional MRI is a popular new method to investigate brain function in physiologic and pathologic conditions. Avoiding traditional task-based restrictions, it enables the researcher to investigate the entire brain with minimal burden and has therefore flourished recently, leading to the discovery of several consistent networks1 that are active in the healthy brain performing no task (i.e., at rest). One of these is the so-called default-mode network (DMN), which encompasses the medial prefrontal, anterior cingulate, posterior cingulate/precuneus, and lateral parietal cortices. The DMN was initially identified since it is frequently deactivated when performing active cognitive tasks, leading to the hypothesis that this network is involved in cognitive postprocessing at rest; supporting this idea is the finding that it is completely quiet in coma.2 Most current resting state studies focus on this network and have yielded a plethora of studies in a wide spectrum of neurologic diseases, like Alzheimer disease (AD), whereas multiple sclerosis (MS) has been notably absent until now. Resting state studies alone cannot answer all questions regarding task-based functions. Combining resting state with task-based paradigms therefore allows for an optimal assessment of function in several disease states. Normal deactivation of regions of the DMN during tasks is, for example, present3 in early mild cognitive impairment (MCI) stages, combined with …