Effective connectivity decreases in specific brain networks with postparalysis facial synkinesis: a dynamic causal modeling study

Currently, the treatments for postparalysis facial synkinesis are still inadequate. However, neuroimaging mechanistic studies are very limited and blurred. Instead of mapping activation regions, we were devoted to characterizing the organizational features of brain regions to develop new targets for therapeutic intervention. Eighteen patients with unilateral facial synkinesis and 19 healthy controls were enrolled. They were instructed to perform task functional magnetic resonance imaging (eye blinking and lip pursing) examinations and resting-state scans. Then, we characterized group differences in task-state fMRI to identify three foci, including the contralateral precentral gyrus (PreCG), supramarginal gyrus (SMG), and superior parietal gyrus (SPG). Next, we employed a novel approach (using dynamic causal modeling) to identify directed connectivity differences between groups in different modes. Significant patterns in multiple regions in terms of regionally specific actions following synkinetic movements were demonstrated, although the resting state was not significant. The couplings from the SMG to the PreCG (p = 0.03) was significant in the task of left blinking, whereas the coupling from the SMG to the SPG (p = 0.04) was significant in the task of left smiling. We speculated that facial synkinesis affects disruption among the brain networks, and specific couplings that are modulated simultaneously can compensate for motor deficits. Therefore, behavioral or brain stimulation technique treatment could be applied to alter reorganization within specific couplings in the rehabilitation of facial function.