Sterling C. Johnson

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.

Neuroanatomic substrates of semantic memory impairment in Alzheimer's disease: patterns of functional MRI activation.

Impairment in semantic processing occurs early in Alzheimers disease (AD) and differential impact on subtypes of semantic relations have been reported, yet there is little data on the neuroanatomic basis of these deficits. Patients with mild AD and healthy controls underwent 3 functional MRI auditory stimulation tasks requiring semantic or phonological decisions (match-mismatch) about word pairs (category-exemplar, category-function, pseudoword). Patients showed a significant performance deficit only on the exemplar task. On voxel-based fMRI activation analyses, controls showed a clear activation focus in the left superior temporal gyrus for the phonological task; patients showed additional foci in the left dorsolateral prefrontal and bilateral cingulate areas. On the semantic tasks, predominant activation foci were seen in the inferior and middle frontal gyrus (left greater than right) in both groups but patients showed additional activation suggesting compensatory recruitment of locally expanded foci and remote regions, for example, right frontal activation during the exemplar task. Covariance analyses indicated that exemplar task performance was strongly related to signal increase in bilateral medial prefrontal cortex. The authors conclude that fMRI can reveal similarities and differences in functional neuroanatomical processing of semantic and phonological information in mild AD compared to healthy elderly, and can help to bridge cognitive and neural investigations of the integrity of semantic networks in AD.

The Relationship between fMRI Activation and Cerebral Atrophy: Comparison of Normal Aging and Alzheimer Disease

Functional MRI has recently been used to examine activation associated with aging and dementia, yet little is known regarding the effect of cerebral atrophy on fMRI signal. The purpose of this study was to examine the relationship between measures of global and regionally specific atrophy and fMRI activation in normal aging and in Alzheimer disease (AD). Two groups of subjects were studied with echoplanar imaging and quantitative structural volumetry: healthy controls spanning a broad age and atrophy range (n = 16) and patients with mild AD (n = 8). Results from a semantic task previously found to activate left inferior frontal (LIFG) and left superior temporal (LSTG) gyri were analyzed. The correlations between clusters of activation in the LIFG and LSTG and measures of local atrophy in the LIFG and LSTG regions were evaluated. For control subjects, there was no significant correlation between activation and regional or total brain atrophy (for LIFG r = -0.03, NS; for LSTG r = 0.20, NS). In contrast, for AD patients, there was a significant positive correlation between atrophy and activation in LIFG (r = 0.70, P = 0.05) but not LSTG (r = 0.00, NS). These results suggest that activation of language regions and atrophy within those regions may be independent among healthy adults spanning a broad age and atrophy range. However, in AD, a relationship exists in the LIFG that may reflect compensatory recruitment of cortical units or disease-specific changes in the hemodynamic response.

Brain activation on fMRI and verbal memory ability: Functional neuroanatomic correlates of CVLT performance

We have recently reported (Saykin et al., 1999b) selective activation of left medial temporal lobe structures during processing of novel compared to familiar words using functional magnetic resonance imaging (fMRI). The current study describes the relationship between a widely used clinical test of verbal learning, the California Verbal Learning Test (CVLT), and the previously reported fMRI activations. Thirteen right-handed healthy adult participants were studied with whole brain echo-planar fMRI while listening to novel and recently learned (familiar) words intermixed pseudorandomly in an event-related design. These participants were also tested with the CVLT. Scores for CVLT Trial 1 (immediate encoding of novel words) and recognition discriminability (recognition of familiar vs. novel words) were correlated with fMRI signal change during processing of novel versus familiar words using a covariance model implemented in SPM96. For the novel words analysis, voxels in the right anterior hippocampus correlated significantly with Trial 1 (r = .76 at the maxima). For the recognition analysis, a significant cluster of voxels was found in the right dorsolateral prefrontal cortex (r = .88 at the maxima). Our prior results of separable left medial temporal activation to novel and familiar words, together with results of the covariance analyses reported here, suggest that in addition to the left medial temporal lobe (MTL) regions that are engaged during novel and familiar word processing, the right hippocampus and right frontal lobe are also involved, particularly in those participants with better memory ability. This positive relationship between fMRI activation and CVLT performance suggests a role for these right hemisphere regions in successful memory processing of verbal material, perhaps reflecting more efficient encoding and retrieval strategies that facilitate memory.

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

Stimulus tracking in functional magnetic resonance imaging (fMRI)

Functional hia~etic Resonance tiagery (~~ ) is a new’ medical ima=tig technology pro~ti~mg tictional, as opposed to natomicd, mapptig of the human brain. The promise of this non-invasive technique has opened new’ ch~enges for mdtimedia researchers. A the fieId of human functional neurotia=tig e~lodes and the technology of ~W advmces, computational techniques for expertient control, subject stimu~ generation, and joint stimti-activation tiaetig are Iachg. host computational work h= focused on impro~tig the analysis of the brab S=S. Tti paper describes eomputiationa~ mechanisms for the dehery md tiactig of multimedia stimti and a correlation framework for stimti and brain responses. NIediaStim, a new integrated data co~ection fraework for stimuIus tracking

Functional differentiation of medial temporal and frontal regions involved in processing novel and familiar words: an fMRI study

hat k currently under development. NlediaSfi etiends the stimti paradi=m to composite multimedia presentations. To stiulate a real-tie sitiation as reafitica~y as possible, it is tiportant to stidy the brain