The nature of automatic semantic retrieval in individuals with mild cognitive impairment

The number of people diagnosed with Alzheimer’s disease (AD), a progressive and terminal kind of dementia, continues to rise with an estimated 14 million Americans affected by 2050. Prior to an AD diagnosis, many individuals are diagnosed with mild cognitive impairment (MCI) and have similar, but less severe, symptoms as those with AD. A common occurrence in even the early stages of AD is word finding deficits, which significantly impact effective communication. Semantic priming studies have shown that word finding deficits in AD may partly be due to limitations in the automaticity of semantic retrieval. However, it is unknown if the automaticity of semantic retrieval underlies word finding difficulties in individuals with MCI or if the deficit in semantic retrieval occurs later in the AD continuum. The current study uses semantic priming to examine the extent to which semantic retrieval is automatic in individuals with MCI in four categories: distinctive attributes (e.g., zebra – stripe), shared attributes (e.g., pigeon – wing), category coordinates (e.g., cat – dog), and abstract words with neutral arousal levels (e.g., motive – reason). Experiments 1 and 2 establish our stimuli in a group of healthy younger and older adults, respectively. Experiment 3 directly compares semantic retrieval in healthy older adults and a group of individuals with MCI. The results demonstrate that individuals with MCI only show priming on shared attributes when evaluating the raw data. When the data were transformed to control for slowing (a commonly utilized strategy because individuals with MCI are known to have both slower response times and executive functioning deficits), individuals with MCI exhibited priming in three of the four categories (shared attributes, category coordinates and abstract words) which was identical to the healthy older adults in Experiment 2. We found priming for distinctive attributes only in the healthy younger adults. Finally, an exploratory analysis showed individuals with MCI and an additional diagnosis did not exhibit significant priming in any category while those individuals with MCI alone showed priming effects for shared attributes and category coordinates. These findings suggest individuals with MCI exhibit functional automaticity of semantic retrieval on a broad range of word types. However, the presence of additional neurological and/or psychological conditions (not including dementia) negatively impacts the automaticity of semantic retrieval.