Visual paired associate learning deficits associated with elevated beta-amyloid in cognitively normal older adults

Objective: Previous studies have shown that paired associate learning (PAL), a type of episodic memory, is impaired in early Alzheimer's disease (AD). Such tasks require that a set of associations (e.g., pattern-location) be learned over several trials, and the objective is to reduce errors with each trial. Currently, the nature and magnitude of impairment and decline on PAL measures in cognitively normal (CN) older adults with elevated levels of beta-amyloid (Aβ +) is unknown. Method: This study examined PAL errors in Aβ + and Aβ - CN older adults, both within a single assessment and over time. Participants (210 Aβ - CN, 146 Aβ + CN) from the Australian Imaging, Biomarkers, and Lifestyle (AIBL) study underwent three assessments over 36-months (baseline, and 18- and 36-month follow-ups) using a computerized paired associate learning task (CPAL). Aβ status was determined by positron emission tomography (PET) neuroimaging. Results: No significant group differences in PAL were evident at baseline. Significant groupxtime interactions were observed, with the Aβ - CN group, but not the Aβ + CN group, evidencing improvement over time (Cohen's d = 0.30 [0.08, 0.51]). Despite this, no group differences were evident at 36-months. Conclusions: Results suggest that PAL dysfunction is evident over time in Aβ + CNs. This indicates a lack of benefit from repeated exposure to the task over time associated with Aβ+, which is not the case for Aβ - CNs. Further, results suggest that assessing change in Aβ+ related cognition over time, rather than at a single assessment, provides greater understanding of dysfunction in early AD.