fMRI in Cerebrovascular Disorders

Stroke is a major cause of long-term disability worldwide. One of the key factors underpinning recovery of function is reorganization of surviving neural networks. Noninvasive techniques such as fMRI allow this reorganization to be studied in humans. However, the design of experiments involving patients with impairment requires careful consideration and is often constrained. Difficulty with some tasks can lead to a number of performance confounds, and so tasks and task parameters that avoid or minimize this should be selected. Furthermore, when studying patients with cerebrovascular disease, it is important to consider the possibility that the blood oxygen level dependent signal may be altered and affect interpretation of results. Despite these potential problems, careful experimental design can provide real insights into system-level reorganization after stroke and how it is related to functional recovery. Currently, results suggest that functionally relevant reorganization does occur in cerebral networks in human stroke patients. For example, it is apparent that initial attempts to move a paretic limb following stroke are associated with widespread activity within the distributed motor system in both cerebral hemispheres. This reliance on nonprimary motor output pathways is unlikely to support full recovery, but improved efficiency of the surviving networks is associated with behavioral gains. This reorganization can only occur in structurally and functionally intact brain regions. Understanding the dynamic process of system-level reorganization will allow greater understanding of the mechanisms of recovery and potentially improve our ability to deliver effective restorative therapy.