Practice effects and longitudinal cognitive change in clinically normal older adults differ by Alzheimer imaging biomarker status

Objective: The objective of this study was to examine practice effects and longitudinal cognitive change in 190 clinically normal elderly classified according to a two-feature biomarker model for Alzheimer’s disease. Methods: All participants completed neuropsychological testing, MRI, FDG-PET, and PiB-PET at their baseline evaluation. We divided participants into four groups based on neuroimaging measures of amyloid (A+ or A−) and neurodegeneration (N+ or N−) and reexamined cognition at 15- and 30-month intervals. Results: The A−N− group showed significant improvements in the memory and global scores. The A+N− group also showed significant improvements in the memory and global scores as well as attention. The A−N+ group showed a significant decline in attention at 30 months. The A+N+ group showed significant improvements in memory and the global score at 15 months followed by a significant decline in the global score at 30 months. Conclusion: Amyloidosis in the absence of neurodegeneration did not have an adverse impact on practice effects or the 30-month cognitive trajectories. In contrast, participants with neurodegeneration (either A−N+ or A+N+) had worse performance at the 30-month follow-up. Our results show that neurodegeneration has a more deleterious effect on cognition than amyloidosis in clinically normal individuals.