Association of CSF Biomarkers With Hippocampal-Dependent Memory in Preclinical Alzheimer Disease

ObjectiveTo 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)42/Aβ40 and phosopho-tau181 (p-tau181) in cognitively unimpaired older adults (CU).MethodsCU 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 Aβ42, Aβ40, and p-tau181 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.ResultsAge and lower Aβ42/Aβ40 were independently associated with elevated p-tau181. Age, Aβ42/Aβ40, and p-tau181 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 Aβ42/Aβ40 on memory. Relationships between CSF proteins and delayed recall were similar but nonsignificant. CSF Aβ42 was not significantly associated with p-tau181 or memory.ConclusionsTests 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.