Functional Connectivity in Relation to Motor Performance and Recovery After Stroke

Abstract

Plasticity after stroke has traditionally been studied by observing changes only in the spatial distribution and laterality of focal brain activation during affected limb movement. However, neural reorganization is multifaceted and our understanding may be enhanced by examining dynamics of activity within large-scale networks involved in sensorimotor control of the limbs. Here, we review functional connectivity as a promising means of assessing the consequences of a stroke lesion on the transfer of activity within large-scale neural networks. We first provide a brief overview of techniques used to assess functional connectivity in subjects with stroke. Next, we review task-related and resting-state functional connectivity studies that demonstrate a lesion-induced disruption of neural networks, the relationship of the extent of this disruption with motor performance, and the potential for network reorganization in the presence of a stroke lesion. We conclude with suggestions for future research and theories that may enhance the interpretation of changing functional connectivity. Overall findings suggest that a network level assessment provides a useful framework to examine brain reorganization and to potentially better predict behavioral outcomes following stroke.

Multiscale topological properties of functional brain networks during motor imagery after stroke

“…One of the most common issues after unilateral stroke is how it alters the function of the ipsilesional hemisphere (Grefkes and Fink, 2011;Westlake and Nagarajan, 2011). Compared with the unaffected hemisphere, in which the contralateral MI effects significantly greater intrahemispheric connectivity with respect to the ipsilateral condition, the affected hemisphere experiences a similar, but weaker, difference between intrahemispheric connectivity that was 15 elicited by the contralateral and ipsilateral MI.…”

“…Starting from a network configuration in which all 185 links were arranged randomly in 1 hemisphere (N S =26 nodes), the model reassigned an increasing number of links between the hemispheres randomly until it reached a configuration that had only interhemispheric links. The choice of such model characteristics was suggested by recent evidence of the effects of stroke on interhemispheric connectivity (Grefkes and Fink, 2011;Westlake and Nagarajan, 2011).…”

“…The advantages and disadvantages of task-related connectivity with respect to resting-state connectivity in stroke were discussed recently (Westlake and Nagarajan, 2011). Essentially, task-based paradigms elicit brain activity that do not reflect the underlying anatomic structure exclusively, but they can generate many confounding effects that are difficult to isolate (Damoiseaux et al, 2006).…”

“…Although the extent to which the application of such approaches impact the study of stroke-related disturbances in cortical connectivity is unknown, they have been reviewed comprehensively, based on recent meta-analyses (Grefkes and Fink, 2011;Westlake and Nagarajan, 2011). These reviews have highlighted that stroke lesions can effect i) critical deviation from optimal "small-world" network topologies that support processing of segregated and integrated information (Bassett and Bullmore, 2006), ii) altered interhemispheric connectivity, iii) and abnormal region centrality in the ipsilesional and contralesional hemispheres, possibly due to compensatory mechanisms.…”

Cell Tracking Technologies for Acute Ischemic Brain Injury

“…The resolution required for this is not inconceivable: while it has yet to integrate stem cell imaging, functional MRI offers the opportunity to observe changes in brain connectivity (structural and functional modifications) in astonishing detail after stroke. 109,110 In addition, the use of microoptical probes with in vivo multiphoton microscopy has now enabled the technique to be used to observe the processes of individual cells. 111 Monitoring stem cell migration with high resolution will be immensely useful in refining cell therapies.…”