Semantic Network Function Captured by Word Frequency in Nondemented APOE ε4 Carriers

Objective: Accurate identification of the earliest cognitive changes associated with Alzheimer's disease (AD) is critically needed. Item-level information within tests of category fluency, such as lexical frequency, harbors valuable information about the integrity of semantic networks affected early in AD. To determine the potential of lexical frequency as a cognitive marker of AD risk, we investigated whether lexical frequency of animal fluency output differentiated APOE epsilon 4 carriers from noncarriers in a cross-sectional design among older African-American adults without dementia. Method: We analyzed animal fluency performance using mean number of items and mean lexical frequency among 230 cognitively normal African Americans with and without the APOE epsilon 4 allele. Results: Lexical frequency was higher in APOE epsilon 4 carriers than noncarriers when analyzed as a mean score and within time bins. In contrast, we found no group difference in the number of items produced. Lexical frequency was particularly sensitive to epsilon 4 status after the first 10 s of the 60-s animal fluency task. Conclusion: Our results suggest that psycholinguistic features may hold value as a cognitive biomarker for identifying people at high risk of AD. Decline in cognition occurs years before the symptoms are distinct enough to establish a clinical diagnosis of Alzheimer's disease (AD) based on traditional neuropsychological test scores. We showed that an alternative, psycholinguistic score of the category fluency task could predict AD genetic risk (having the APOE epsilon 4 allele) in older adults whose overall cognition and function are within normal limits. These results suggest that psycholinguistic features may hold value as a cognitive biomarker for identifying people at high risk of AD.