Modulation of interhemispheric activation balance in motor-related areas of stroke patients with motor recovery: Systematic review and meta-analysis of fMRI studies

Background: Functional magnetic resonance imaging (fMRI) studies suggest that stroke-induced motor deficits are associated with an interhemispheric imbalance of motor activation. This meta-analysis aims to determine the changes of interhemispheric activation balance (IHAB) in motor-related cortices along with post-stroke motor recovery. Methods: We searched PubMed for fMRI studies that investigated IHAB in stroke patients with motor recovery. Laterality indexes (LIs, (ipsilesional activation - contralesional activation)/(ipsilesional activation + contralesional activation)) before and after motor improvement were extracted as the outcome measures of IHAB. Data were synthesized by calculating standardized mean difference (SMD, Hedges' adjusted g) with 95% confidence intervals (Cl). Results: After the rejection of 459 studies, 22 trials fulfilled the inclusion criteria and were included in the systematic review and meta-analysis. The Lis of sensorimotor cortex (SMC, 22 trials, 195 subjects), premotor cortex (PMC, 12 trials, 93 subjects), supplementary motor area (SMA, 12 trials, 92 subjects), and cerebellum (CB, 4 trials, 31 subjects) were assessed. Studies sampling from stroke patients with motor improvement showed positive changes of LI in SMC (SMD, 0.71; 95% Cl, 0.41-1.01; P<0.00001) and PMC (SMD, 0.68; 95% Cl, 0.36-1.00; P<0.0001), but not in SMA (SMD, 0.07; 95% Cl, -0.62 to 0.75; P=0.85) and CB (SMD, -0.17; 95% Cl, -1.52 to 1.19, P=0.81). Studies involving stroke patients with poor motor recovery showed non-significant changes in all of the four motor-related cortices (P>0.05). Conclusions: This meta-analysis suggests that along with good motor recovery of stroke patients, the IHAB is up-regulated in SMC and PMC, but not significantly changed in SMA and CB. Because of the limited data, further studies are needed to verify the findings. (C) 2015 Elsevier Ltd. All rights reserved.