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 (A beta+) is unknown. Method: This study examined PAL errors in A beta+ and A beta - CN older adults, both within a single assessment and over time. Participants (210 A beta - CN, 146 A beta + 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). A beta 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 A beta - CN group, but not the A beta + 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 A beta + CNs. This indicates a lack of benefit from repeated exposure to the task over time associated with A beta+, which is not the case for A beta - CNs. Further, results suggest that assessing change in A beta+ related cognition over time, rather than at a single assessment, provides greater understanding of dysfunction in early AD.