Age-related deficits in the mnemonic similarity task for objects and scenes

Abstract

Using the Mnemonic Similarity Task (MST), we have demonstrated an age-related impairment in lure discrimination, or the ability to recognize an item as distinct from one that was similar, but not identical to one viewed earlier. A growing body of evidence links these behavioral changes to age-related alterations in the hippocampus. In this study, we sought to evaluate a novel version of this task, utilizing scenes that might emphasize the role of the hippocampus in contextual and spatial processing. In addition, we investigated whether, by utilizing two stimulus classes (scenes and objects), we could also interrogate the roles of the PRC and PHC in aging. Thus, we evaluated differential contributions to these tasks by relating performance on objects versus scenes to volumes of the hippocampus and surrounding medial temporal lobe structures. We found that while there was an age-related impairment on lure discrimination performance for both objects and scenes, relationships to brain volumes and other measure of memory performance were stronger when using objects. In particular, lure discrimination performance for objects showed a positive relationship with the volume of the hippocampus, specifically the combined dentate gyrus (DG) and CA3 subfields, and the subiculum. We conclude that though using scenes was effective in detecting age-related lure discrimination impairments, it does not provide as strong a brain-behavior relationship as using objects.

Keywords: Aging; Dentate gyrus; Hippocampus; Lure discrimination; Pattern separation.