Abstract
The earliest stage of Alzheimer’s disease (AD) pathology begins in one of the main components of the olfactory pathway, the entorhinal cortex, making deficits in smell a potential prospective biomarker for the early detection of AD. A bivariate longitudinal coupling model was used to determine whether assessment-to-assessment variation in olfaction mirrors variation in cognition over time. The model included terms for age, sex, education, ApoE e4 allele, and autopsy diagnosed AD pathology.
Using a sub-sample of 573 individuals: the between-person variation in odour identification had a robust positive association to episodic memory (b = 0.129, SE = 0.0135, P < 001; conditional R-squared = 0.86). Higher AD pathology was related to both lower episodic memory at baseline (b = -0.236, SE = 0.0685, P < 001), and faster declines in episodic memory (b = -0.059, SE = 0.017, P < 001). Additionally, more rapid declines in olfactory identification were robustly associated with more rapid declines in episodic memory scores (b = 0.011, SE = 0.0039, P < 0.001). The within-person coupling between olfaction and episodic memory was robust and positive (b = 0.07, SE = 0.016, P < 001), indicating that odour identification and episodic memory scores fluctuated together over time.
This research indicates that at a given occasion, individuals with higher olfactory scores also have higher episodic memory scores. This coupled relationship indicates that olfactory testing can be a useful tool for assessing cognitive decline and possibly an inexpensive screener for pathological brain changes.