Conceptual saliency: Core and peripheral semantic knowledge in Alzheimer’s disease

Abstract

AbstractBackgroundSemantic memory impairment in Alzheimer’s disease (AD) is indicative of an actual degradation of semantic knowledge – the conceptual and factual knowledge necessary to engage with others and the physical world – rather than merely to a retrieval deficit. Historically, studies in semantic knowledge in AD have relied on predetermined sets of stimuli to probe knowledge. The analysis presented here compares the contents, sequences and organization of lists of salient concepts generated by 19 patients at the mild to moderates stages AD and by 15 age‐matched cognitively normal control individuals by means of a free‐listing task, for two semantic categories, living kinds and man‐made objects. The free elicitation by participants prevents the imposition of a priori ideas by the experimenter, which might not correspond to the native knowledge of the specific cultural group studied.MethodData collection starts with the ‘demarcation’ of a domain of knowledge X by a sample of participants who are being asked to write the names of as many items as they can conjure up, which they think belong to that domain X. Terms that appear earlier, or with higher frequency, on free‐lists indicate high consensus among respondents (i.e., the concept is an important component of the category); those items are considered as more salient in the domain under investigation.ResultEvidence of knowledge devolution is detected in the lists of participants with AD for both semantic categories. However, the core conceptual information and central aspects of the structuration of those knowledge domains are preserved to an extent. The peripheral conceptual knowledge is showing the greatest disease impact.ConclusionThe study starts the investigation of the aspects of living kinds and artefactual categorial knowledge especially resilient as neurodegeneration sets. Semantic knowledge holds the information about what one knows. Its integrity is critical in daily functioning, and interactions with others and the world at large. Because semantic memory supports various aspects of daily life, it is a prime candidate for therapeutic targets that can lead to meaningful outcomes for both patients and their care partners.