Purpose: Functional MR imaging (fMRI) has been used to investigate neural correlates of cognitive domains in normal aging and dementing disorders. Mild cognitive impairment (MCI) has been implicated as an early stage of Alzheimer's Disease (AD). AD is a progressive neurodegenerative disorder, currently afflicting 1.8 million individuals in the U.S. AD is detected in 4%-36% of MCI patients annually. Delineation of neural correlates of memory impairment has the potential to distinguish normal-aging associated changes from MCI and AD. The aim of this study was to evaluate the brain activation evoked by a memory task in patients with MCI.
Methods and Materials: Nine patients with MCI (5 men, 4 women, age range: 55-80 years) and eight age-matched controls (1 man, 7 women, age range 50-71 years) underwent fMRI on a 1.5T scanner. Functional images of the brain were acquired while subjects were performing a visual working memory task. Regions of brain activation were identified in each subject. Task performance was evaluated based on true&false positive and negative responses. Brain activation was quantified based on total number of activated voxels in each region. Activation and task performance were compared between the groups using analysis of variance test.
Results: Task performance parameters were not significantly different between MCI and control groups. MCI patients showed greater activation in the right superior frontal gyrus, right middle frontal gyrus, and left posterior parietal region than controls (p<0.05). Comparison of MCI patients and controls did not reach statistical significance in left middle frontal gyrus, left anterior cingulate, and right fusiform gyrus (p=0.06).
Conclusion: FMRI documented the differences in brain activation between patients with cognitive impairment and controls who had similar task performance. MCI patients showed greater activation in several regions of the brain as well as recruitment of additional areas. These findings may be an indication of compensation for dysfunctional neural circuitry in cognitive impairment. The potential of detecting altered brain activation for early identification of cognitive impairment merits further investigation.
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