A body of research has demonstrated age-related slowing on tasks that emphasize cognitive control, such as task switching. However, little is known about the neural mechanisms that contribute to this age-related slowing. To address this issue, the present study used both fMRI and DTI in combination with a standard task switching paradigm. Results from the fMRI experiment demonstrated task switching cost (switching vs. nonswitching) activations in a network of frontoparietal and striatal regions in the young group. The older group recruited a similar network of regions, but showed decreased spatial extent of activation and recruited several regions not activated in the young group. White matter (WM) ROIs bordering the cortical network showing task switching activation were then selected to explore potential relationships between task switching reaction time (RT) cost and fractional anisotropy (FA) in the same groups of participants. Results demonstrated a negative correlation between switch cost RT and FA in left frontoparietal WM in both young and older groups. In addition, age-related FA decline in the same frontoparietal WM region was found to mediate age-related increases in RT switch costs. These findings identify decreased integrity of frontoparietal WM as one mechanism contributing to age-related increases in RT switch costs.
Copyright 2008 Elsevier Inc. All rights reserved.