Augmented neural activity during executive control processing following diffuse axonal injury.
BACKGROUND
Deficits in working memory are commonly observed after traumatic brain injury (TBI), with executive control processes preferentially impacted relative to storage and rehearsal. Previous activation functional neuroimaging investigations of working memory in patients with TBI have reported altered functional recruitment, but methodologic issues including sample heterogeneity (e.g., variability in injury mechanism, severity, neuropathology or chronicity), underspecified definitions of "working memory," and behavioral differences between TBI and control groups have hindered interpretation of these changes.


METHODS
Executive control processing in working memory was explicitly engaged during fMRI in a sample of carefully selected chronic-stage, moderate-to-severe TBI patients with diffuse axonal injury (DAI) but without focal lesions.


RESULTS
Despite equivalent task performance, we observed a pattern of greater recruitment of interhemispheric and intrahemispheric regions of prefrontal cortex (PFC) and posterior cortices in our DAI sample. Enhanced activations were recorded in the left dorsolateral PFC (middle frontal gyrus), right ventrolateral PFC (inferior frontal gyrus), bilateral posterior parietal cortices, and left temporo-occipital junction. Region-of-interest analyses confirmed that these effects were robust across individual patients and could not be attributed to load factors or slowed speed of processing.


CONCLUSIONS
Augmented functional recruitment in the context of normal behavioral performance may be a neural marker of capacity or efficiency limits that can affect functional outcome after traumatic brain injury with diffuse injury.
Turner
Gary R
GR
Rotman Research Institute, Baycrest Center for Geriatric Care, 3560 Bathurst St., Toronto, ON, M6A 2E1, Canada.
Levine
Brian
B
D000328:Adult; D001930:Brain Injuries / Q000503:physiopathology / Q000523:psychology; D020833:Diffuse Axonal Injury / Q000503:physiopathology* / Q000523:psychology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008568:Memory / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D009483:Neuropsychological Tests; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology
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