Within-session Learning of an Object Identification Task Predicts Elevated Brain Aβ

CSF was collected from participants near to the time of completing the baseline Computer- Administered Neuropsychological Screen for MCI (CANS). CSF levels of Aβ (threshold = 250pg/ml) were used to group participants as elevated (Aβ+) and not elevated (Aβ-) brain amyloid. A linear mixed model (LMM) with object identification response time at each (correct) trial as the dependent variable and age, sex, education, depression, and trial as independent variables, a random slope of trial for participants. Slope for each participant was extracted and used to predict brain amyloid status and mean response time on the same task 6 months later (logistic regressions).

Results: Of 96 participants, 57 were Aβ- and 39 were Aβ+. The groups did not differ statistically in sex, education, depression, or prior CANS administrations, ps > 0.33. The Aβ+ group (76.6y) was slightly older than Aβ- (73.9y), p =0.05. The LMM indicated age (β = 0.02, p < 0.001) and depression (β = 0.03, p = 0.04) significantly slowed response time, and response time was significantly faster with successive trials (β = -0.04, p < 0.001). Age (β = -0.06, p = 0.06) and participant slopes for trial (β = -75.16, p = 0.01) correctly classified 36 Aβ- (63.2%) and 28 Aβ+ (71.8%) participants. For the Aβ+ group, follow-up response times varied little by slope, whereas Aβ- participants with steeper slopes had faster times at follow-up.

Conclusion: Aβ+participants exhibited significantly steeper learning slopes than Aβ-. This may reflect slight retrieval delays early in the task and subsequent hyperactivation. Learning slopes at baseline also predicted improved performance at follow-up, in line with existing research on within-session practice effects. Implications and future directions discussed.