Brain PET study supports the 'cognitive reserve' hypothesis

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Individuals with higher education levels appear to score better on cognitive tests despite having evidence of brain plaques associated with Alzheimer's disease, according to a study in the November issue of Archives of Neurology.

The cognitive reserve hypothesis holds that individuals with greater cognitive abilities are able to delay symptoms of Alzheimer's disease despite underlying changes in the brain, according to background information in the study.

“Adjusting for level of Alzheimer disease pathological burden determined at autopsy, greater education has been associated with better cognitive function during life," the authors wrote. "Education interacts with Alzheimer disease pathological burden such that a greater pathological burden is required to show an effect on cognition among persons with more education.”

Catherine M. Roe, PhD, and colleagues at the Washington University School of Medicine in St. Louis, studied 37 individuals with Alzheimer dementia and 161 individuals without dementia between 2003 and 2008. Participants were injected with the marker, carbon 11–labeled Pittsburgh Compound B ([11C]PiB), and then underwent a 60-minute PET scan of the brain. Recent studies have shown that [11C]PiB adheres to beta-amyloid brain plaques associated with Alzheimer's disease, allowing researchers to identify the characteristics of the disease in living patients, according to the investigators.

The researchers found that the level of [11C]PiB uptake interacted significantly with years of education in predicting cognitive test scores. Among individuals whose brains took up higher levels of [11C]PiB, indicating the presence of beta-amyloid plaques, performance on the test increased with increasing education levels. Education was not associated with cognitive scores among those with low [11C]PiB uptake, indicating no plaques.

“The results support the hypothesis that cognitive reserve influences the association between Alzheimer disease pathological burden and cognition," the authors wrote. "Based on autopsy data, there may be a ceiling effect when extensive beta-amyloid pathological burden is present as in late-stage dementia of the Alzheimer type. Presumably, as the Alzheimer disease pathological burden increases, a greater proportion of highly educated participants reach the threshold for dementia and the initial advantage provided by cognitive reserve decreases.”