Differential working memory load effects after mild traumatic brain injury

The objective of this study was to explore the effects of increasing workin g memory (WM) processing load on previously observed abnormalities in activ ation of WM circuitry shortly after mild traumatic brain injury (AMI). Brai n activation patterns in response to increasing WM processing load (auditor y n-back: 0-, 1-, 2-, and 3-back conditions) were assessed with fMRI in 18 MTBI patients within 1 month of their injury and in 12 healthy controls. Pe rformance accuracy on these tasks was also measured. Brain activation patte rns differed between MTBI patients and controls in response to increasing W M processing loads. Controls maintained their ability to increase activatio n in regions of WM circuitry with each increase in WM processing load. MTBI patients showed disproportionately increased activation during the moderat e processing load condition, but very little increase in activation associa ted with the highest processing load condition. Task performance did not di ffer significantly between groups on any task condition. MTBI patients show ed a different pattern of allocation of processing resources associated wit h a high processing load condition compared to healthy controls, despite si milar task performance. This suggests that injury-related changes in abilit y to activate or modulate WM processing resources might underlie some of th e memory complaints after MTBI. (C) 2001 Academic Press.