Variability and Coupling of Olfactory Identification and Episodic Memory in Older Adults

Abstract

Objectives: To determine whether assessment-to-assessment fluctuations in episodic memory (EM) reflect fluctuations in olfaction over time. Methods: Within-person coupled variation in EM and the Brief Smell Identification Test (BSIT) was examined in 565 participants aged 58-106 with autopsy data from the Rush Memory and Aging Project. A growth model for up to 15 years of EM data, with BSIT as time-varying covariate, was estimated accounting for main effects of sex, education, ϵ4 allele, and Alzheimer's disease (AD) pathology, BSIT and time-varying BSIT, as well as the interaction between AD pathology and time-varying BSIT. Results: Individuals with higher BSIT scores (b =. 01, standard error [SE] =. 004, p =. 009) had slower declines in EM. High AD pathology (b = -.06, SE =. 02, p =. 001) was associated with more rapid declines in EM. The association between time-specific fluctuations in EM and BSIT differed by level of AD pathology (b =. 08, SE =. 034, p =. 028), with a higher EM-BSIT association at higher levels of pathology. Discussion: BSIT and EM fluctuate together over measurement occasions, particularly for individuals with AD pathology. Repeated intraindividual measurements provide information that could lead to early detection and inexpensive monitoring of accumulating AD pathology.