Brain mechanisms explaining postural imbalance in traumatic brain injury: a systematic review

Abstract

ABSTRACTPersisting imbalance and falls in community-dwelling traumatic brain injury (TBI) survivors – typically related to vestibular dysfunction - are linked to reduced long-term survival and re-employment rates. However, a detailed understanding of the impact of TBI upon the brain mechanisms mediating imbalance is lacking. To understand the state of the art concerning the brain mechanisms mediating imbalance in TBI, we performed a systematic review of the literature.PubMed, Web of Science, and Scopus were searched and peer-reviewed research articles in humans, with any severity of TBI (mild, moderate, severe, or concussion), that linked a postural balance assessment (objective or subjective) with brain imaging (via CT, MRI, MRS, SPECT, EEG, MEG, NIRS, and evoked potentials) were included. Out of 1940 articles, 60 were retrieved and screened, and 25 were included in the systematic review. 17 of those were MRI-based studies (e.g., DTI, fMRI), 4 EEG studies, 3 fNIRS studies, and 1 study used both MRI and EEG.The most consistent MRI finding was the link between imbalance and cerebellum, however, the regions within the cerebellum were not consistent. Functional changes in EEG studies were non-specific as all frequency bands were reportedly linked with balance. The findings from fNIRS studies were concentrated in frontal regions as these studies only used ROI analysis. Notably, only one study reported performing clinical vestibular assessment to exclude peripheral vestibular dysfunction.In conclusion, the lack of consistent findings could reflect that imbalance in TBI is due to a brain network dysfunction in contrast to focal cortical damage. Notably, the inconsistency in the reported findings may be attributed to heterogeneity of methodology e.g., data analytical techniques, small sample sizes, and choice of control groups. Future studies should include a detailed clinical phenotyping of vestibular function in TBI patients, ideally in an acute prospective manner, to exclude peripheral disorders. Choosing the appropriate control groups (i.e., well characterized patient subgroups as controls) would ensure that the findings are specific to imbalance rather than being non-specifically linked to TBI. Moreover, a whole-brain imaging analysis (vs ROI) is recommended to reduce selection bias and is also important since TBI affects the brain in a widespread manner.