Short-term repeat cognitive testing and its relationship to hippocampal volumes in older adults.

BACKGROUND: Practice effects are improvements in cognitive test scores due to repeated exposure to testing materials. If practice effects provide information about Alzheimer's disease pathology, then they could be useful for clinical trials enrichment. The current study sought to add to the limited literature on short-term practice effects on cognitive tests and their relationship to neuroimaging biomarkers.
METHODS: Twenty-five, non-demented older adults (8 cognitively intact, 17 with mild cognitive impairment) received magnetic resonance imaging and two testing sessions across one week to determine practice effects on seven neuropsychological test scores. A series of correlations examined if hippocampal volume was associated with baseline, one-week, or practice effects scores on these tests. Next, a series of stepwise multiple regression models examined which of the three test scores best predicted hippocampal volumes
RESULTS: In the correlation analysis, baseline scores on 5 of the 7 tests were significantly associated with hippocampal volumes, one week scores were significantly related for 7 of the 7 tests, and practice effects scores were significantly correlated for 4 of the 7 tests. In the stepwise regression models, 5 of the 7 tests indicated that one-week scores best predicted hippocampal volumes. For the other models, baseline score and practice effects score each best predicted hippocampal volume.
CONCLUSIONS: These results add to the growing body of evidence suggesting that diminished practice effects on short-term repeat testing is related to neuroimaging biomarkers of Alzheimer's disease and may serve as a screening tool for clinical practice and to enrich samples for research trials.