To determine whether assessment-to-assessment fluctuations in episodic memory (EM) reflect fluctuations in olfaction over time.
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.
Individuals with higher BSIT scores (b = 0.01, SE = 0.004, p = 0.009) had slower declines in EM. High AD pathology (b = -0.06, SE = 0.02, p = 0.001) 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 = 0.08, SE = 0.034, p = 0.028), with a higher EM-BSIT association at higher levels of pathology.
BSIT and EM fluctuate together over measurement occasions, particularly for individuals with AD pathology. Repeated intra-individual measurements provide information that could lead to early detection and inexpensive monitoring of accumulating AD pathology.