Researchers studying older men and women who do not have dementia or mild cognitive impairment found that those with Alzheimer's pathology, or the brain changes associated with the disease, scored lower on tests of episodic memory. The study was published in a Neurology, the scientific journal of the American Academy of Neurology.
The study evaluated 134 older men and women who didn't have cognitive impairment at the time of their death.
Participants came from the Religious Orders Study and the Memory and Aging Project. Both are longitudinal, clinical-pathologic studies of older persons without dementia who underwent annual clinical evaluations and several cognitive performance tests. After they died, their brains were autopsied.
More than a third of the participants (50) met criteria for a pathologic diagnosis of Alzheimer's disease. Criteria included lesions of brain tissue on the autopsy.
Scores on the Mini Mental State Examination, an assessment of cognitive mental status, were nearly identical for participants with and without a pathologic diagnosis of Alzheimer's disease. However, the group with a pathologic diagnosis scored lower than the other participants on tests for episodic memory, such as recalling stories and word lists.
"The results provide evidence in support of the idea that some type of neural reserve can allow a large number of older persons to tolerate a significant amount of Alzheimer's pathology without manifesting obvious dementia," says study author David A. Bennett, MD, director of the Rush Alzheimer's Disease Center.
While all of the study participants appeared cognitively intact and were highly functional, the data suggests that even slight impairment of episodic memory in older persons may signify the presence of Alzheimer's pathology.
From a public health perspective, the number of people with Alzheimer's is probably much larger than current estimates, according to Bennett.
The Rush researchers are extremely grateful for the remarkable dedication and altruism of the volunteers participating in the Rush Memory and Aging Project and the Religious Orders Study. The research was supported by grants from the National Institute on Aging, which leads the Federal effort to support and conduct basic, clinical, and social and behavioral studies on aging and on Alzheimer's disease.
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