Stephen J. Guerin

Brain activation during working memory 1 month after mild traumatic brain injury : A functional MRI study

Objective: To assess patterns of regional brain activation in response to varying working memory loads shortly after mild traumatic brain injury (MTBI). Background: Many individuals complain of memory difficulty shortly after MTBI. Memory performance in these individuals can be normal despite these complaints. Methods: Brain activation patterns in response to a working memory task (auditory n-back) were assessed with functional MRI in 12 MTBI patients within 1 month of their injury and in 11 healthy control subjects. Results: Brain activation patterns differed between MTBI patients and control subjects in response to increasing working memory processing loads. Maximum intensity projections of statistical parametric maps in control subjects showed bifrontal and biparietal activation in response to a low processing load, with little additional increase in activation associated with the high load task. MTBI patients showed some activation during the low processing load task but significantly increased activation during the high load condition, particularly in the right parietal and right dorsolateral frontal regions. Task performance did not differ significantly between groups. Conclusion: MTBI patients differed from control subjects in activation pattern of working memory circuitry in response to different processing loads, despite similar task performance. This suggests that injury-related changes in ability to activate or to modulate working memory processing resources may underlie some of the memory complaints after MTBI.

Differential Working Memory Load Effects after Mild Traumatic Brain Injury

The objective of this study was to explore the effects of increasing working memory (WM) processing load on previously observed abnormalities in activation of WM circuitry shortly after mild traumatic brain injury (MTBI). Brain activation patterns in response to increasing WM processing load (auditory 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. Performance accuracy on these tasks was also measured. Brain activation patterns differed between MTBI patients and controls in response to increasing WM processing loads. Controls maintained their ability to increase activation in regions of WM circuitry with each increase in WM processing load. MTBI patients showed disproportionately increased activation during the moderate processing load condition, but very little increase in activation associated with the highest processing load condition. Task performance did not differ significantly between groups on any task condition. MTBI patients showed a different pattern of allocation of processing resources associated with a high processing load condition compared to healthy controls, despite similar task performance. This suggests that injury-related changes in ability to activate or modulate WM processing resources might underlie some of the memory complaints after MTBI.

Sex differences in semantic language processing: A functional MRI study

Predictions based on two models of sex differences in cerebral organization of language were compared by examining fMRI patterns of 10 females and 9 males during a semantic processing task. Both groups displayed activation of left inferior frontal gyrus (IFG), left superior temporal gyrus (STG), and cingulate. Females, but not males, showed bilateral IFG and STG activation. Further analyses revealed females had less diffuse left activation and greater right posterior temporal and insula region activation than males. Results support both an interhemispheric and an intrahemispheric model of sex differences in language, suggesting that the models may not be mutually exclusive.

Similarities and Differences in Semantic and Phonological Processing with Age Patterns of Functional MRI Activation

In this investigation, we analyzed the effect of age on fMRI activation during semantic and phonological decision tasks using wholebrain echoplanar imaging Nine righthanded healthy younger adults were compared to nine righthanded healthy older adult volunteers While undergoing fMRI scanning, subjects completed three functional MRI auditory stimulation tasks requiring semantic or phonological decisions (match/mismatch) about word pairs (category-exemplar, category-function, pseudo-word) Performance scores on these tasks did not differ between age groups The fMRI images were motion corrected, spatially normalized, and statistically analyzed for group similarities and differences using a randomeffects model For the semantic tasks, both older and younger adults showed activity within the inferior frontal gyrus (left more than right) and left superior temporal gyrus, whereas small regional age differences (younger?>?older) were found in the left inferior precentral region For the phonologic task, common areas of activation were found in the superior temporal gyrus (left more than right) Agerelated differences in the phonologic task were observed predominantly in the right angular region The results were not changed by entry of a quantitative atrophy index as a covariate These findings highlight the similarities in semantic processing across age groups and suggest that global age related atrophy is not impacting activation significantly in healthy older adults