During the study, researchers at the Alzheimer's Disease Research Center at Washington University School of Medicine in St. Louis found that some participants who appeared to have the brain plaques long associated with Alzheimer's disease still received high scores on tests of their cognitive ability.
Participants who did well on the tests were likely to have spent more years in school.
"The good news is that greater education may allow people to harbour amyloid plaques and other brain pathology linked to Alzheimer's disease without experiencing decline of their cognitive abilities," said first author Catherine Roe, Ph.D., research instructor in neurology.
The researchers have shown that an imaging agent for positron emission tomography scans, Pittsburgh Compound B (PIB), can reveal the presence of amyloid plaques, a key brain change that many neurologists suspect either causes Alzheimer's or is closely linked to its onset.
"This technique has been used before to analyze patients with dementia and their education levels, but our study is among the first, if not the first, to include both patients with Alzheimer's-type dementia and nondemented participants," said Roe.
Besides scanning the participants' brains with PIB, the participants took several tests that assessed their cognitive abilities and status.
They also ranked their educational experience: high-school degree or less, college experience up to an undergraduate degree, and graduate schooling.
The researchers found that those whose brains showed little evidence of plaque buildup scored high on all the tests. But while most participants with high levels of brain plaque scored poorly on the tests, those who had done postgraduate work still scored well.
Despite signs that Alzheimer's might already be ravaging the brains of this subgroup, their cognitive abilities had not declined and they had not become demented.
The study is published in the November Archives of Neurology.