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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.

Although cognitive training usually improves cognitive test performance, the capability to transfer these training gains into respective or functionally related cognitive domains varies significantly. Since most studies demonstrate rather limited transfer effects in older adults, aging might be an important factor in transfer capability differences. This study investigated the transfer capability of logical reasoning training gains to a measure of Fluid Intelligence (Gf) in relation to age, general intelligence, and brain structural integrity as measured by diffusion tensor imaging. In a group of 41 highly educated healthy elderly, 71% demonstrated successful transfer immediately after a 4-week training session (i.e. short-term transfer). In a subgroup of 22% of subjects transfer maintained over a 3-month follow-up period (i.e. long-term transfer). While short-term transfer was not related to structural integrity, long-term transfer was associated with increased structural integrity in corpus and genu of the corpus callosum. Since callosal structural integrity was also related to age (in the present and foregoing studies), previously observed associations between age and transfer might be moderated by the structural integrity. Surprisingly, age was not directly associated with transfer in this study which could be explained by the multi-dependency of the structural integrity (modulating factors beside age, e.g. genetics). In this highly educated sample, general intelligence was not related to transfer suggesting that high intelligence is not sufficient for transfer in normal aging. Further studies are needed to reveal the interaction of transfer, age, and structural integrity and delineate mechanisms of age-dependent transfer capabilities. Hum Brain Mapp 35:309–318, 2014. © 2012 Wiley Periodicals, Inc.

However, longitudinal and quantitative studies clarifying the temporal relationships between these changes have been exceptionally rare. Therefore, we used longitudinal MRI to assess associations between hippocampus atrophy and changes of hippocampal FC in cognitively normal elders (CN). Methods: Forty-six CN elders (mean age: 75.26 6.9 years) received resting state functional and structural MRI scans at 1.5T field strength, as well as detailed clinical evaluations, at two time points (mean interval: 2.5 6 0.5 years). The hippocampus was manually traced on each structural MRI, and the gray matter (GM) tissue maps were generated from SPM5. Hippocampal FC was calculated as the Fisher-Z transformed Pearson correlation between the mean functional MRI time series among each individual hippocampal voxels and the time series of other voxels throughout the brain. Hippocampal FC change (DFC) map, hippocampal atrophy volume (DHV), and GM atrophy map were calculated for each individual. Multiple regression models were applied for the relationships between DFC and DHV throughout the brain, controlling for age, gender, education, inter-scan interval (Dtime), baseline hippocampus volume and GM atrophy map. AlphaSim was applied for multiple comparison correction with a p < 0.01 threshold. Results: A cluster of voxels on the thalamus and caudate nucleus showed a significant association between DFC and DHV, which indicated that CN elders with more hippocampus atrophy had greater FC increases or less FC decreases. Local gray matter atrophy did not affect this association. There was no evidence of an association between greater hippocampus atrophy and greater hippocampus FC reduction or less FC increases (see figure). Conclusions: The hippocampus and thalamus are structurally connected via the cingulum bundle as part of an extended neuronal network that is critical for successful memory function. Our results reflected this structural connection. Moreover, the relationship between the quantitative measures ofDHVandDFC showed a compensatory effect of FC changes against HVatrophy in CN elders, and implies that FC may play an important role in cognitive reserve.