Several 90-year-olds with superior memory were found to have the hallmarks of Alzheimer’s disease yet never developed dementia in their lifetimes.
“This was a surprising finding,” said Changiz Geula, who is a research professor at Northwestern Medicine’s Cognitive Neurology and Alzheimer’s Disease Center. “What that means is this Alzheimer’s pathology didn’t seem to have caused loss of neurons.”
In other words, something protected these 90-year-olds brains from developing the disease, and scientists are now researching what that could be.
“Discovering these factors will be very significant because it can then help individuals with Alzheimer’s disease to have their neurons protected,” he said.
Plaques and tangles are the hallmarks of Alzheimer’s disease. They are accumulations of abnormal proteins in the skull, either outside of neurons (plaques) or inside neurons (tangles). They’re known to have detrimental and toxic effects on nerve cells, which can eventually lead to nerve cell death. While they’re part of the normal process of aging, in high density and wide distribution, they become defining features of Alzheimer’s disease, Guela said.
Recently, studies have found some elderly with extensive Alzheimer’s markers, or pathology, never developed cognitive decline like that seen in Alzheimer’s disease.
“If a pathologist just looked at the brain, [based] on the look they would say this person has Alzheimer’s disease, but they’re cognitively normal,” he said.
Geula and his colleagues focused their research on people who were at least 90 years old and had superior memory compared to their peers (as determined by various cognitive tests). Researchers were interested in identifying factors that allowed these individuals to be cognitively high-functioning, Geula said.
Researchers made a “surprising” discovery when analyzing the brains postmortem. While some of the elderly had typical signs of cognitive aging, others had “full-blown” Alzheimer’s pathology, he said.
When examining the hippocampus – the part of the brain responsible for memory formation – researchers discovered the nerve cells were largely intact in the elderly with superior memory despite the presence of Alzheimer’s pathology.
Researchers also examined the brains of Alzheimer’s dementia patients, and they discovered the nerve cells in the hippocampus, as well as other areas of the brain that control cognition, were significantly damaged.
This led researchers to conclude that “some factor or factors are protecting neurons against the damage of plaques and tangles, against toxicity,” Geula said. Researchers are investigating whether genetic or environmental factors played a role.
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