Graph-theoretical Analysis of EEG Functional Connectivity during Balance Perturbation in Traumatic Brain Injury

Abstract Traumatic Brain Injury (TBI) often results in balance impairment, increasing the risk for falls and further injuries. In this study, we investigated the postural instability in a group of 12 TBI patients vs 9 healthy controls (HC) by studying their brain’s response to an external perturbation of the computerized dynamic posturography platform. A 64-channel EEG was used to noninvasively record the brain’s anticipatory response while the participant was performing the dynamic posturography task. We used the global graph-theoretic network measures (global efficiency and modularity) derived from source-space EEG connectivity in different frequency bands as quantitative measures of the functional integration and segregation of the brain network during the task. The center of pressure (COP) displacement and the Berg Balance Scale (BBS) were used as balance outcomes. Furthermore, we used the Diffusion Tensor Imaging (DTI) data from all the participants to explore the association between the measures of the structural integrity of the white matter (Fractional Anisotropy, Mean Diffusivity, and Mode of Anisotropy) and the balance outcomes. Our findings revealed significant changes in functional segregation between the TBI group and controls during the task and also group-level differences in DTI measures. Also, we observed significant differences between theta-band modularity and global efficiency during rest vs. task within both the groups (TBI and HC). In terms of the neural correlates, we observed a distinct role played by different frequency bands; increase in theta-band modularity during the task was shown to be highly correlated with the poorer COP displacement and BBS in the TBI group; alpha-band and beta-band graph-theoretic measures were correlated with the measures of structural integrity. In terms of the regions of interest pertaining to the postural control, we noticed a significant cortical activity during the task in the paracentral lobule, post-central gyrus, cingulate gyrus, superior parietal gyrus, and other regions often reported to be involved in postural stability. Our study, although limited by small sample size, provides insights into the neural correlates of the balance deficits due to brain injury. Our future studies will focus on the larger sample size and also the effect of stabilometry platform training on the functional brain network modulation in TBI.