Date Published: December 20, 2012
Publisher: Public Library of Science
Author(s): Dazhi Yin, Fan Song, Dongrong Xu, Bradley S. Peterson, Limin Sun, Weiwei Men, Xu Yan, Mingxia Fan, Yu-Feng Zang. http://doi.org/10.1371/journal.pone.0052727
Previous studies have noted changes in resting-state functional connectivity during motor recovery following stroke. However, these studies always uncover various patterns of motor recovery. Moreover, subgroups of stroke patients with different outcomes in hand function have rarely been studied.
We selected 24 patients who had a subcortical stroke in the left motor pathway and displayed only motor deficits. The patients were divided into two subgroups: completely paralyzed hands (CPH) (12 patients) and partially paralyzed hands (PPH) (12 patients). Twenty-four healthy controls (HC) were also recruited. We performed functional connectivity analysis in both the ipsilesional and contralesional primary motor cortex (M1) to explore the differences in the patterns between each pair of the three diagnostic groups.
Compared with the HC, the PPH group displays reduced connectivity of both the ipsilesional and contralesional M1 with bilateral prefrontal gyrus and contralesional cerebellum posterior lobe. The connectivity of both the ipsilesional and contralesional M1 with contralateral primary sensorimotor cortex was reduced in the CPH group. Additionally, the connectivity of the ipsilesional M1 with contralesional postcentral gyrus, superior parietal lobule and ipsilesional inferior parietal lobule was reduced in the CPH group compared with the PPH group. Moreover, the connectivity of these regions was positively correlated with the Fugl-Meyer Assessment scores (hand+wrist) across all stroke patients.
Patterns in cortical connectivity may serve as a potential biomarker for the neural substratum associated with outcomes in hand function after subcortical stroke.
Strokes are a prevalent cause of adult-onset disability. Although a full recovery may occur after a stroke, more than 50% of the patients are left with residual motor deficits . Particularly, deficits in hand function have a severe impact on the quality of life for stroke patients. Previous studies have consistently indicated that cerebral reorganization underlies motor recovery after stroke , , , , , , , , , . However, various patterns of cerebral reorganization that contribute to motor recovery after a stroke have been reported using task-based, functional neuroimaging. For instance, shifts of primary sensorimotor cortex (S1M1) activation toward the infarct rim have been reported in patients with cortical infarcts, ,  in regard to subcortical infarcts, both Pineiro et al  and Calautti et al  observed a posterior shift of S1M1 activation; Marshall et al  described an increase in the ratio of ipsilesional to the contralesional S1M1 activation, whereas Calautti et al  noted a decrease in activation of non-primary motor regions largely in the affected hemisphere; Ward et al  demonstrated that task-related activation decreased over sessions as a function of recovery in a number of primary and non-primary motor regions, however, Feydy et al  suggested that ipsilateral recruitment after stroke will persist if primary motor cortex (M1) is lesioned, otherwise, it will be transient. The disparity of the patterns of task-related activation might be attributed to the heterogeneity of the samples (e.g., variances in age, side of hemispheres, location and extent of lesion), degree of motor deficit at the time of imaging, differences in task paradigms, time from stroke onset, and synkinesia (mirror movement) . Therefore, many factors that are not well-controlled may confound investigators in identifying the pattern of cerebral reorganization underlying motor recovery after a stroke. Furthermore, it is difficult to investigate severe hand function disabilities by task-based functional neuroimaging.
To the best of our knowledge, this is the first study to use resting-state functional connectivity analysis to investigate subgroups of stroke patients with different outcomes in hand function. The differences in functional connectivity in both the ipsilesional and contralesional M1s were assessed between each pair of the three diagnostic groups.
Our current study suggests, for the first time, that different outcomes in hand function in subgroups of stroke patients may be attributed to specific patterns of cortical connectivity. Therefore, reorganization of cortical connectivity may not only serve as a potential biomarker of neural substratum associated with hand function after subcortical stroke, but may also provide a valuable reference for understanding post-stroke outcomes of hand function. In addition, resting-state functional connectivity reflecting functional integrity could provide an effective method for evaluating the efficiency of post-stroke rehabilitative therapies.