Event-related functional magnetic resonance imaging changes during relational retrieval in normal aging and amnestic mild cognitive impairment

Abstract

The earliest cognitive deficits observed in amnestic mild cognitive impairment (aMCI) appear to center on memory tasks that require relational memory (RM), the ability to link or integrate unrelated pieces of information. RM impairments in aMCI likely reflect neural changes in the medial temporal lobe (MTL) and posterior parietal cortex (PPC). We tested the hypothesis that individuals with aMCI, as compared to cognitively normal (CN) controls, would recruit neural regions outside of the MTL and PPC to support relational memory. To this end, we directly compared the neural underpinnings of successful relational retrieval in aMCI and CN groups, using event-related functional magnetic resonance imaging (fMRI), holding constant the stimuli and encoding task. The fMRI data showed that the CN, compared to the aMCI, group activated left precuneus, left angular gyrus, right posterior cingulate, and right parahippocampal cortex during relational retrieval, while the aMCI group, relative to the CN group, activated superior temporal gyrus and supramarginal gyrus for this comparison. Such findings indicate an early shift in the functional neural architecture of relational retrieval in aMCI, and may prove useful in future studies aimed at capitalizing on functionally intact neural regions as targets for treatment and slowing of the disease course. (JINS, 2012, 18, 1-12).

Fig. 1

Event-related task design with alternating blocked task periods of relational retrieval (“together previously?”) and item retrieval (“both old?”). There were four study/retrieval phases. Imaging data was acquired during the retrieval phase only. IP = intact pair; RP = rearranged pair; NP = new pair; RI = rearranged items; OI = old/new items; and NI = new items.

Fig. 2

Neural activity during relational retrieval greater than item retrieval in (a) the normal control group relative to the amnestic mild cognitive impairment (aMCI) group and (b) the aMCI group relative to the normal control group.

Fig. 3

Neural activity during item retrieval greater than relational retrieval in (a) the normal control group relative to the amnestic mild cognitive impairment (aMCI) group and (b) the aMCI group relative to the normal control group.

Fig. 4

Neural activity common to both normal control and aMCI groups during (a) relational retrieval relative to item retrieval and (b) item retrieval relative to relational retrieval.