A Systematic Review of Resting-State fMRI in Traumatic Brain Injury Across Injury Age, Severity, Mechanism, Chronicity, and Imaging Methods
Kevin Bickart1, Christopher Sheridan3, Daniel Frees4, Kaylee Kang2, Jesse Fischer2, Christian Parks2, Alex Kashou5
1Neurology, UCLA, 2UCLA, 3Dept. of Radiology; Wake Forest School of Medicine, 4Stanford, 5Loma Linda
Objective:
To systematically review studies comparing resting-state fMRI (rsfMRI) in healthy people to patients with traumatic brain injury (TBI) across the spectrum of injury age, severity, mechanism, and chronicity, as well as imaging methods.
Background:
rsfMRI in TBI captures functional differences due to both the injury and compensatory processes independent from structural abnormalities. Deriving a consensus across studies has been difficult due to heterogeneity in injured populations, the brain injury itself, and the imaging methodologies.
Design/Methods:
We searched PubMed, Web of Science, Google Scholar, and ScienceDirect to identify studies published prior to July 2020 that compared rsfMRI connectivity between patients with TBI and healthy people, and categorized findings into increased, decreased, or no difference in connectivity for canonical networks (i.e., default mode, executive control/frontoparietal, ventral attention/salience, dorsal attention, somatomotor, visual, and limbic/subcortical).
Results:
From 1097 studies identified, 50 fit inclusion criteria, including 179 comparisons in connectivity, 3.58 per manuscript, from 1397 patients with TBI and 1179 healthy people. TBI cohorts included mostly young to middle aged civilian men in the subacute to chronic stage after mild TBI due to motor vehicle accidents. An equal number of comparisons showed increased, decreased, and no differences in connectivity when collapsing across all networks and injury characteristics and when parsing the findings by injury age, severity, mechanism, and network. Parsing by chronicity however, demonstrated a pattern of hypoconnectivity in the acute stage and hyperconnectivity in the chronic stage after TBI. Among methodological variables, we found a pattern of decreased null findings in studies that had a greater number of rsfMRI volumes or instructed patients to have eyes open during scans.
Conclusions:
Despite taking into account injury, network, and methodological characteristics, rsfMRI findings in TBI vary so greatly that it is impossible to generate a consensus. We discuss limitations to this work and guidelines for future studies.