White matter pathways associated with working memory in normal aging

INTRODUCTION Previous studies by our group have found that white matter integrity as determined by Diffusion Tensor Imaging (DTI) is associated with working memory decline. It has been proposed that subtle white matter integrity loss may lead to the disruption of working memory in particular because it relies on the dynamic and reiterative activity of cortico-cortical pathways. METHODS DTI and working memory measurement were acquired for 99 adults from our GENIE study of healthy middle aged and elderly individuals. Voxel-based statistics were used to identify clusters of voxels in mean diffusivity images specifically associated with variations in working memory performance. Tractography then identified the cortico-cortical white matter pathways passing through these clusters, between the temporal, parietal and frontal cortices. RESULTS Significant clusters were identified which were associated with working memory in the white matter of the temporal and frontal lobes, the cingulate gyrus, and in the thalamus. The tracts that passed through these clusters included the superior parietal lobule pathway, the medial temporo-frontal pathway, the uncinate fasciculus, the fronto-parietal fasciculus, and the cingulum. CONCLUSIONS Significant clusters were identified in the white matter that were associated with working memory performance. Tractography performed through these clusters identified white matter fiber tracts which pass between grey matter regions known to be activated by working memory tasks and also mirror working memory pathways suggested by previous functional connectivity imaging.