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 (CI).

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% CI, 0.41-1.01; P<0.00001) and PMC (SMD, 0.68; 95% CI, 0.36-1.00; P<0.0001), but not in SMA (SMD, 0.07; 95% CI, -0.62 to 0.75; P=0.85) and CB (SMD, -0.17; 95% CI, -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.