Subcortical white matter pathology as a mediating factor for age-related decreased performance in dichotic listening.

Cortical 'disconnection', involving disruption of white matter tracts in the brain, has been hypothesized as a mechanism of age-related cognitive decline. Diffuse hyperintensities in the white matter (so called white matter hyperintensities, WMH) on T2-weighted MRI scans are regarded to represent ischemic damage of the subcortical fiber system and are found to be increased with advanced age. In the present study, we examined whether WMH might be a mediating factor for age-effects in dichotic listening. For that purpose, we examined the association between age, deep or subcortical white matter hyperintensities (DWMH), periventricular hyperintensities (PVH) and dichotic listening performance in healthy older adults with ages ranging from 50 to 81 years. We found decreased dichotic listening performance with increasing age, specifically for the left ear (LE) but not the right ear (RE) in a standard unbiased-attention condition, and for the unattended ears but not the attended ears in conditions in which attention was controlled. Interestingly, hierarchical regression analyses revealed that the age-effect is partially mediated by DWMH specifically in the hemisphere contralateral to the attended ear. Moreover, we found indications that RE performance is specifically affected by DWMH in the right and left frontal and temporal areas, and that LE performance is mostly affected by DWMH selectively in the left hemisphere, including the left temporal area. The present study underlines the idea that disconnectivity is involved in age-related cognitive decline.