Decreased practice effects in preclinical Alzheimer’s disease: a multicenter, longitudinal, cohort study
Authors: Tort‐Merino Adrià , Pérez‐Millan Agnès , Martínez Neus Falgàs , Borrego‐Écija Sergi , Guillén Núria , Sarto Jordi , Esteller Diana , Bosch Bea , Castellví Magdalena , Juncà‐Parella Jordi , Val‐Guardiola Andrea , Fernandez‐Villullas Guadalupe , Antonell Anna , Sánchez‐Saudinós M Belen , Rubio‐Guerra Sara , Zhu Nuole , Martínez María García , Pozueta Ana , Estanga Ainara , Ecay Mirian , Lopez Carolina , Tainta Mikel , Altuna Miren , Rodríguez Eloy Rodríguez , Sanchez‐Juan Pascual , Martinez‐Lage Pablo , Lleo Alberto , Fortea Juan , Illán‐Gala Ignacio , Balasa Mircea , Lladó Albert , Rami Lorena , Sánchez‐Valle Raquel 
Published: January 2025

Background

Practice effects are a well‐known cognitive phenomenon that is reduced in patients with Alzheimer’s disease (AD). We aimed to investigate whether cognitively unimpaired (CU) individuals within the Alzheimer’s continuum (i.e., positive amyloid‐β biomarker) display decreased practice effects on serial neuropsychological testing.

Methods

We included 310 CU from four Spanish research centers, classified into controls (n = 250) or Aβ+ (n = 60). In the main cohort (Cohort A; n = 209), participants underwent neuropsychological assessment at baseline and annually during a 2‐year follow‐up (FU1 and FU2). A “long‐term cohort” (Cohort B; n = 101) was employed to assess practice effects over longer time periods (i.e., two follow‐up sessions at years 3 and 6 from baseline). Practice effects were defined as simple discrepancy scores (SDS) by subtracting Z‐scores at FU2 from Z‐scores at baseline for each neuropsychological variable, and linear mixed effects models (LME) were run to assess the temporal evolution of practice effects according to the two groups.

Results

There were no cross‐sectional differences between the control and Aβ+ groups in none of the neuropsychological scores at baseline (Fig. 1). The Aβ+ group displayed lower practice effects than the controls in terms of SDS in several neuropsychological outcomes (Fig. 2). In Cohort A, LME showed negative slopes by the Aβ+ group in verbal memory measures such as the free learning score (β = ‐0.37, SD = 0.12, p = 0.0034), delayed free recall (β = ‐0.43, SD = 0.15, p = 0.0047) and delayed total recall (β = ‐0.46, SD = 0.17, p = 0.0069) from the Free and Cued Selective Reminding Test; as well as in language tasks (Boston Naming Test; β = ‐0.26, SD = 0.087, p = 0.0025) and executive function measures (Trail Making Test; β = ‐0.33, SD = 0.12, p = 0.0094) (Fig. 3A). In Cohort B, similar findings were observed in visual memory measures, such as the Rey‐Osterrieth Complex Figure immediate (β = ‐0.80, SD = 0.35, p = 0.024) and delayed (β = ‐1.25, SD = 0.34, p = 0.00038) recall (Fig. 3B).

Conclusions

Individuals with normal cognition who are in the Alzheimer’s continuum show decreased practice effects over serial neuropsychological testing. Our findings suggest the reduction of practice effects, particularly in memory measures, as an indicator of subtle cognitive decline in the earliest phase of the Alzheimer’s continuum and could be particularly relevant for the design and interpretation of primary prevention trials on disease‐modifying therapies.