BACKGROUND - Imaging studies have shown disparities in resting metabolism and in functional activation between cognitively normal individuals at high and low risk for AD. A recent study has shown increased parietal activation in high-risk subjects during a paired associates recall task, which the authors postulated might overlap activation typically observed in verbal fluency.
OBJECTIVE - To determine whether parietal activation is altered in a letter fluency task in cognitively normal individuals at high risk for AD.
METHODS - fMRI was used to compare cortical activation between two groups of cognitively normal women differing in their risk for developing AD. A letter fluency task was used, which activates left frontal and parietal regions. The risk groups differed in family history of AD and APOE allele status but were matched in age, education, and measures of cognitive performance. Average age of the study participants was 53 years.
RESULTS - The regional patterns of brain activation were similar between groups and similar to patterns observed by other investigators. However, the high-risk group showed significantly increased activation in the left parietal region despite identical letter fluency performance between risk groups.
CONCLUSIONS - Cognitively normal individuals at high risk for AD show increased brain activation in the left parietal region with letter fluency, a region adjacent to that observed by others using a recall task. This convergence of results indicates disruption of functional circuits involving the left parietal lobe in asymptomatic individuals at increased risk for AD.