Functional MRI evidence of cognitive change in traumatic brain injury
Mani, Tanja Maria
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Relatively little research has focused on documenting functional recovery following brain injury using real-time neuroimaging techniques. The main objective of this study was to examine the effects of moderate to severe brain injury on brain functioning over time, using tasks with known anatomical regions of brain activation. Eleven (moderately to severely brain-injured) participants completed three (motor, visual, and cognitive) tasks while undergoing functional MRI (fMRI) at two time points, approximately 6 and 12 months post-injury. Changes in functional activation within ROIs and in dispersion of activation were evaluated across time points from a smaller subset of the sample whose data were available for comparison across both time points. Participants demonstrated significantly reduced activation intensity within the ROI over time for the motor task, but not for the visual (RPS) or cognitive (Stroop) tasks. A trend toward reduced cortical dispersion over time was evident for the RPS task, though this finding was not statistically significant. Whereas most participants demonstrated greater activation within (versus outside of) the ROI for the motor and visual tasks, the reverse was true for the Stroop task, which may indicate that recruitment of outside regions was necessary for successful task completion, at both time points. Finally, the results suggest that individuals who have sustained an injury of similar severity are nevertheless likely to demonstrate variability in terms of regional substrate damage, cognitive functioning, and functional activation patterns. Despite such variability, however, the results also suggest that such individuals are apt to demonstrate plasticity and signs of functional recovery during the first year post-injury. Ultimately, it is anticipated that further research in this area may be helpful in enhancing prognostication about cognitive and functional outcomes, and in determining the likely trajectory of recovery following a traumatic brain injury. Efforts to evaluate group-based changes in cognitive functioning and cortical activation patterns would benefit from the use of a more narrowly defined participant group, in terms of injury characteristics.