Textual Inference Comprehension in Mild Cognitive Impairment: The Influence of Semantic Processing and Verbal Episodic Memory

Language complaints, especially in complex tasks, may occur in mild cognitive impairment (MCI). Various language measures are being studied as cognitive predictors of MCI conversion to Alzheimer's type dementia. The ability to understand textual inferences is considered a high demanding task that recruits multiple cognitive functions and therefore could be sensitive to detect decline in early stages of MCI. Thus, we aimed to compare the performance of subjects with MCI to healthy elderly and to subjects with Alzheimer's disease (AD) in a textual inference comprehension task and to determine the best predictors of performance in this ability considering two semantic and one verbal episodic memory tasks. We studied 118 individuals divided into four groups: 1) 23 individuals with amnestic mild cognitive impairment (aMCI), 2) 42 individuals with non-amnestic mild cognitive impairment (naMCI), 3) 19 individuals with Alzheimer´s disease, and 4) 34 cognitively healthy individuals for control group (CG). A reduced version of The Implicit Management Test was used to assess different types of inferential reasoning in text reading. MCI and AD patients performed poorer than healthy elderly and there were no differences between MCI subgroups (amnestic and non-amnestic) or MCI and AD. The best predictors for inference-making were verbal memory in the aMCI and semantic tasks in the naMCI group. The results confirmed that the failure to understand textual inferences can be a linguistic marker to detect MCI and showed that different cognitive skills like semantic knowledge and verbal episodic memory are necessary for inference-making.