Scientists looked at the brains of eight people older than 90 who had superior memories until their deaths. They were surprised to find widespread and dense Alzheimer’s plaques and tangles that were, in some cases, considered full-blown Alzheimer’s pathology.
“This is amazing,” said lead investigator Changiz Geula, research professor at the Cognitive Neurology and Alzheimer’s Disease Center (CNADC) at Northwestern University.
“We never expected it. It tells us there are some factors that are protecting their brains and memories against the Alzheimer’s pathology of plaques and tangles. Now, we have to find out what those are.”
The findings are the first to indicate that full-blown Alzheimer’s pathology can exist in the brains of elderly who show superior cognitive performance.
Extensive plaques and tangles in the brain result in the death of neurons and are an indicator of Alzheimer’s dementia. The fact that some elderly with the pathology still had superior memory points to mechanisms that offer protection. Discovery of what these are could likely help the development of therapies to treat or prevent Alzheimer’s disease, Geula says.
“We have to search for factors that protect these elderly against memory loss. We will look at genetic, dietary, and environmental influences that could confer protection for neurons against Alzheimer’s pathology.”
If scientists can find a protective environmental factor, it could help both the normal elderly and those with the Alzheimer’s pathology, Geula says.
A number of recent studies suggest some elderly individuals harbor extensive Alzheimer’s pathology in the brain without any evidence of the cognitive decline seen in Alzheimer’s disease.
In the CNADC study, scientists examined the brains of eight individuals older than 90 who were selected for superior performance in memory tests compared to their same-age peers who performed normally on a memory test.
Three of the eight individuals qualified pathologically as having Alzheimer’s disease, but displayed superior memory performance when they were alive. When researchers examined nerve cells in the hippocampus, the part of the brain that is responsible for memory formation, they found cells in this area were relatively intact.
They also examined the brains of five patients with Alzheimer’s dementia and full Alzheimer’s pathology. Those brains showed significant cell death in the hippocampus. A similar pattern was observed in other areas of the brain that control cognitive function.
“These findings clearly demonstrate the brains of some elderly are immune to the toxic effects of plaques and tangles,” Geula said.
To count the neurons, they examined a series of tissue sections, which were stained to make the neurons visible. Then, using a microscope, they counted the number of neurons in sections of the hippocampus and the frontal cortex. When plaques and tangles appear in the frontal cortex, it means Alzheimer’s pathology has spread throughout the brain.
Geula and his team are now beginning a large-scale study to determine the factors, including genetic factors, that help protect the brains of some elderly people against Alzheimer’s pathology.
Geula presented the results at the Society for Neuroscience 2016 Annual Conference.