Autobiographical Memory Fluency Reductions in Cognitively Unimpaired Middle-Aged and Older Adults at Increased Risk for Alzheimer's Disease Dementia

Abstract

Objective: Recent research has revealed that cognitively unimpaired older adults who are at higher risk for developing Alzheimer's disease (AD) dementia often exhibit subtle cognitive alterations in their neuropsychological profiles. Emerging evidence suggests that autobiographical memory, which is memory for personal events and knowledge, may be sensitive to early AD-related cognitive alterations. In the present study, we investigated whether the rapid generation of autobiographical memory category exemplars, a retrieval process that taxes the neural network that is vulnerable to early AD, is compromised in cognitively unimpaired middle-aged and older carriers of the e4 allele of the apolipoprotein E gene (APOE4), which increases risk for AD dementia.

Methods: In addition to standard neuropsychological tests, we administered a fluency task that requires generating exemplars for two types of autobiographical memory, namely episodic memories and personal semantics, to a group of cognitively unimpaired middle-aged and older adults (n = 45) enriched with APOE4 carriers (n = 20).

Results: While no APOE4 deficits were found on standard neuropsychological tests, episodic and personal semantic exemplar generation was reduced in the APOE4 group.

Discussion: Autobiographical memory aberrations associated with a higher risk for AD are evident in fluency and affect both episodic memory and personal semantics.

Keywords: Alzheimer’s disease; Apolipoprotein E; Autobiographical memory; Cognitive aging; Episodic memory; Medial temporal lobe; Semantic memory.

Figure 1.. APOE4 carriers were not significantly reduced on general semantic fluency.

Figure 1 shows a hybrid violin/box/dot plot of exemplar generation for APOE4 carriers and non-carrier groups on the standard neuropsychological tests of category fluency, which required generating category exemplars of animals, fruits/vegetables, and the letters “F”, “A”, and “S”. APOE4 carriers were not significantly reduced on these general semantic fluency tasks. The contour of the violin plot represents the distribution of the data, and the dots are jittered. For the boxplot, the line within the box represents the medians, horizontal edges represent first and third quartiles, and whiskers represent 1.5 standard deviations above the upper quartile and below the lower quartile. Figure created using RStudio and the ggplot2 package (Wickham, 2016).

Figure 2.. APOE4 carriers were significantly reduced for both personal semantic and episodic memory fluency.

Figure 2 shows a hybrid violin/box/dot plot of exemplar generation for APOE4 carriers and non-carrier groups on the autobiographical category fluency tasks. The APOE4 carriers, as a group, generated fewer familiar name (personal semantic) and episodic memory exemplars. The contour of the violin plot represents the distribution of the data, and the dots are jittered. For the boxplot, the line within the box represents the medians, horizontal edges represent first and third quartiles, and whiskers represent 1.5 standard deviations above the upper quartile and below the lower quartile. Figure created using RStudio and the ggplot2 package (Wickham, 2016).