Association of CSF Biomarkers With Hippocampal-Dependent Memory in Preclinical Alzheimer Disease
Alexandra N. Trelle, Valerie A. Carr, Edward N. Wilson, Michelle S. Swarovski, Madison P. Hunt, Tyler N. Toueg, Tammy Tran, Divya Channappa, Nicole K. Corso, Monica K. Thieu, Manasi Jayakumar, Ayesha Nadiadwala, Wanjia Guo, Natalie Tanner, Jeffrey D. Bernstein, Celia Litovsky, Scott A. Guerin, Anna M. Khazenzon, Marc Harrison, Brian K. Rutt, Gayle K. Deutsch, Frederick T. Chin, Guido Davidzon, Jacob Hall, Sharon J. Sha, Carolyn Fredericks, Katrin I. Andreasson, Geoffrey A. Kerchner, Anthony D. Wagner, Elizabeth C. Mormino
Abstract
<h3>Objective</h3> To determine whether memory tasks with demonstrated sensitivity to hippocampal function can detect variance related to preclinical Alzheimer disease (AD) biomarkers, we examined associations between performance in 3 memory tasks and CSF β-amyloid (Aβ)<sub>42</sub>/Aβ<sub>40</sub> and phosopho-tau<sub>181</sub> (p-tau<sub>181</sub>) in cognitively unimpaired older adults (CU). <h3>Methods</h3> CU enrolled in the Stanford Aging and Memory Study (n = 153; age 68.78 ± 5.81 years; 94 female) completed a lumbar puncture and memory assessments. CSF Aβ<sub>42</sub>, Aβ<sub>40</sub>, and p-tau<sub>181</sub> were measured with the automated Lumipulse G system in a single-batch analysis. Episodic memory was assayed using a standardized delayed recall composite, paired associate (word–picture) cued recall, and a mnemonic discrimination task that involves discrimination between studied “target” objects, novel “foil” objects, and perceptually similar “lure” objects. Analyses examined cross-sectional relationships among memory performance, age, and CSF measures, controlling for sex and education. <h3>Results</h3> Age and lower Aβ<sub>42</sub>/Aβ<sub>40</sub> were independently associated with elevated p-tau<sub>181</sub>. Age, Aβ<sub>42</sub>/Aβ<sub>40</sub>, and p-tau<sub>181</sub> were each associated with (1) poorer associative memory and (2) diminished improvement in mnemonic discrimination performance across levels of decreased task difficulty (i.e., target–lure similarity). P-tau mediated the effect of Aβ<sub>42</sub>/Aβ<sub>40</sub> on memory. Relationships between CSF proteins and delayed recall were similar but nonsignificant. CSF Aβ<sub>42</sub> was not significantly associated with p-tau<sub>181</sub> or memory. <h3>Conclusions</h3> Tests designed to tax hippocampal function are sensitive to subtle individual differences in memory among CU and correlate with early AD-associated biomarker changes in CSF. These tests may offer utility for identifying CU with preclinical AD pathology.