Several neuropsychological dimensions are correlated with functional outcome (e.g., ability to return to family and community roles) following traumatic brain injury (TBI). Commonly investigated neuropsychological dimensions include verbal memory, visuo-spatial construction, set-shifting, generativity, and processing speed. Unfortunately, small sample sizes across relevant studies have contributed to inconsistent results. Furthermore, no studies have concurrently measured all of the candidate neuropsychological predictors, most of which are known to be inter-correlated. Thus, the unique predictive effects associated with the candidate predictors in TBI recovery have never been investigated. Consequently, this study used both meta-analysis and multiple regression to statistically evaluate neuropsychological candidate predictors across two outcome variables (1) the Glasgow Outcome Scale-Extended (GOS-E) and (2) the Disability Rating Scale (DRS). Seven studies met inclusion criteria. Based on the meta-analyses, the following neuropsychological dimensions were found to be correlated with the GOS-E: immediate verbal memory (r = .43, 95% CI [.27, .58]), delayed verbal memory (r = .43, 95% CI [.21, .61]), visuo-spatial construction (r = .29, 95% CI [.15, .53]), set-shifting (r = -.31, 95% CI [-.45, -.15], and generativity (r = .44, 95% CI [.32, .54]). By contrast, only one neuropsychological dimension was found to be significantly related to the DRS (generativity: r = -.21, 95% CI [-.39, -.01]). Multiple regression on the GOS-E relevant meta-analytically derived correlation matrix determined that all neuropsychological dimensions were significant predictors of the GOS-E (multiple R = .31) with the exception of immediate verbal memory or learning. However, due to analytic characteristics, these findings must be interpreted with caution. Results were consistent with the need to consider multiple neuropsychological abilities in recovery and rehabilitation following TBI.

Background: Mild traumatic brain injury (mTBI) results from an external force to the head or body causing neurophysiological changes within the brain. The number and severity of symptoms can vary, with some individuals experiencing rapid recovery, and others having persistent symptoms for months to years, impacting their quality of life. Current rehabilitation is limited in its ability to treat persistent symptoms and novel approaches are being sought to improve outcomes following mTBI. Neuromodulation is one technique used to encourage adaptive neuroplasticity within the brain.Objective: To systematically review the literature on the efficacy of neuromodulation in the mTBI population.Method: A systematic review was conducted using Medline, Embase, PsycINFO, PsycARTICLES and EBM Review. Preferred Reporting Items for Systematic Reviews and the Synthesis Without Meta-analysis reporting guidelines were used and a narrative review of the selected studies was completed. Fourteen articles fulfilled the inclusion criteria which were published in English, investigating an adult sample and using a pre- and post-intervention design. Studies were excluded if they included non-mild TBI severities, pediatric or older adult populations.Results: Thirteen of fourteen studies reported positive reductions in mTBI symptomatology following neuromodulation. Specifically, improvements were reported in post-concussion symptom ratings, headaches, dizziness, depression, anxiety, sleep disturbance, general disability, cognition, return to work and quality of life. Normalization of working memory activation patterns, vestibular field potentials, hemodynamics of the dorsolateral prefrontal cortex and excessive delta wave activity were also seen. The studies reviewed had several methodological limitations including small, heterogenous samples and varied intervention protocols, limiting generalisability. Further research is required to understand the context in which neuromodulation may be beneficial.Conclusions: While these positive effects are observed, limitations included unequal representation of neuromodulation modalities in the literature, and lack of literature describing the efficacy of neuromodulation on the development or duration of persistent mTBI symptoms. Better clarity regarding neuromodulation efficacy could have a significant impact on mTBI patients, researchers, clinicians, and policy makers, facilitating a more productive post-mTBI population. Despite the limitations, the literature indicates that neuromodulation warrants further investigation. PROSPERO registration number: CRD42020161279.

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