Age-related increases in Stroop interference: delineation of general slowing based on behavioral and white matter analyses.

The Stroop interference task is a widely used paradigm to examine cognitive inhibition, which is a key component of goal-directed behavior. With increasing age, reaction times in the Stroop interference task are usually slowed. However, to date it is still under debate if age-related increases in reaction times are merely an artifact of general slowing. The current study was conducted to investigate the role of general slowing, as measured by Trail-Making-Test-A, in age-related alterations of Stroop interference. We applied Diffusion Tensor Imaging (DTI) to determine the topography of neuronal networks underlying Stroop interference under control of general slowing. On the behavioral level, linear regression analysis demonstrated that age accounted for significant variance on Stroop interference, whereas TMT-A performance did not. Controlling for TMT-A, DTI based white matter analyses demonstrated a strong association of Stroop interference with integrity measures of genu of corpus callosum, bilateral anterior corona radiata, and bilateral anterior limb of capsula interna. These pathways are associated with frontal brain regions by either connecting the bilateral dorsolateral prefrontal cortex or the anterior cingulate cortex with frontal and subcortical regions or by containing fibers which are part of cortico-thalamic circuits that cross prefrontal regions. Importantly, results expand our knowledge of the neural basis of Stroop interference and emphasize the importance of white matter integrity of frontal pathways in the modulation of Stroop interference. Combining behavioral and DTI findings our results further suggest that cognitive inhibition, as measured by Stroop task, is a qualitatively distinct cognitive process that declines with age.