Neural Deterioration and Compensation in Visual Short-term Memory Among Individuals with Amnestic Mild Cognitive Impairment

Abstract

Amnestic mild cognitive impairment (aMCI) is considered to carry a high risk of progression to Alzheimers Disease (AD) and it has been characterized by deficits in visual short-term memory (VSTM). However, the relationship between VSTM deficits and pathological brain damage in individuals with MCI has remained unknown. In the current study, we examined a group of 123 elder adults, including 55 with aMCI and 68 age-matched controls. Participants performed color change-detection VSTM tasks, and structural and functional magnetic resonance images were acquired during rest. Compared to the normal control (NC) group, individuals with aMCI exhibited poorer accuracy and longer reaction time in VSTM tasks, along with reduced VSTM capacity. Additionally, structural atrophy was observed in aMCI participants in several brain regions, including the left medial temporal lobe (MTL), the left thalamus, the right frontal pole (FP) and the right postcentral gyrus (postCG). Interestingly, VSTM accuracy and capacity were found to be associated with the volume of the left MTL in the NC group but not in the aMCI group, suggesting alterations in the relationship between VSTM and brain regions in aMCI. However, VSTM capacity was correlated with the volume of the right FP in both groups, suggesting potential compensatory mechanisms involving the prefrontal cortex in aMCI. Moreover, using the atrophic left MTL as a seed, functional connectivity to the right FP was significantly higher in aMCI compared to NC. Notably, this FP area showed overlap with the atrophic frontal areas in terms of structural abnormalities. Furthermore, for individuals with aMCI who had a larger left MTL, the compensatory involvement of the right FP in VSTM, as assessed by brain-behavior correlations, was diminished. In summary, the present study uncovered a mechanism involving MTL dysfunction and prefrontal compensation in aMCI when performing VSTM tasks. These findings may offer valuable insights into potential intervention targets for individuals with aMCI.