Executive control function, brain activation and white matter hyperintensities in older adults

Context: Older adults responding to executive control function (ECF) tasks show greater brain activation on functional MRI (fMRI). It is not clear whether greater fMRI activation indicates a strategy to compensate for underlying brain structural abnormalities while maintaining higher performance. Objective: To identify the patterns of fMRI activation in relationship with ECF performance and with brain structural abnormalities. Design: Cross-sectional analysis. Main variables of interest: fMRI activation, accuracy while performing an ECF task (Digit Symbol Substitution Test), and volume of white matter hyperintensities and of total brain atrophy. Setting: Cohort of community-dwelling older adults. Participants: Data were obtained on 25 older adults (20 women, 81 years mean age). Outcome measure: Accuracy (number of correct response/total number of responses) while performing the Digit Symbol Substitution Test. Results: Greater accuracy was significantly associated with greater peak fMRI activation, from ECF regions, including left middle frontal gyrUs and right posterior parietal cortex. Greater WMH was associated with lower activation within accuracy-related regions. The interaction of accuracy by white matter hyperintensity volume was significant within the left posterior parietal region. Specifically, the correlation of white matter hyperintensity volume with fMRI activation varied as a function of accuracy and it was positive for greater accuracy. Associations with brain atrophy were not significant. Conclusions: Recruitment of additional areas and overall greater brain activation in older adults is associated with higher performance. Posterior parietal activation may be particularly important to maintain higher accuracy in the presence of underlying brain connectivity structural abnormalities. (C) 2009 Elsevier Inc. All rights reserved.