Qualitative Comparison of Semantic Memory Impairment in Patients with Amnestic Mild Cognitive Impairment Based on beta-Amyloid Status

Abstract

Background and Purpose Semantic memory remains more stable than episodic memory across the lifespan, which makes it potentially useful as a marker for distinguishing pathological aging from normal senescence. To obtain a better understanding of the transitional stage evolving into Alzheimer's dementia (AD), we focused on the amnestic mild cognitive impairment (aMCI) stage stratified based on beta-amyloid (A beta) pathology. Methods We analyzed the raw data from Korean version of the Boston Naming Test (K-BNT) and the Controlled Oral Word Association Test (COWAT). For K-BNT, the frequencies of six error types and accuracy rates were evaluated. For a qualitative assessment of the COWAT, we computed the number of switching, number of clusters, and mean cluster size. Results The data from 217 participants were analyzed (53 normal controls, 66 with A beta-aMCI, 56 with A beta+ aMCI, and 42 disease controls). There were fewer semantically related errors and more semantically unrelated errors on the K-BNT in A beta+ aMCI than in A beta- aMCI, without a gross difference in the z score. We also found that A beta+ aMCI showed a more prominent deficit in the number of clusters in the semantic fluency task [especially for animal names (living items)] than A beta- aMCI. Conclusions In spite of similar clinical manifestations, A beta+ aMCI was more similar to AD than A beta- aMCI in terms of semantic memory disruption. Semantic memory may serve as an early indicator of brain A beta pathology. Therefore, semantic memory dysfunction deserves more consideration in clinical practice. Longitudinal research with the follow-up data is needed.