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Cognitive decline is typically considered a hallmark of aging -- but research suggests that not everyone is susceptible.

A study from Northwestern University looked at a group of 80-year-olds who appeared to have memory skills on par with 50-year-olds, as the researchers aimed to understand the differences in their brains.

These people were classified as "SuperAgers," defined as those 80 and older who have memories of those 30 years their junior, according to a university press release. People in this category score at least 9 out of 15 on a delayed word recall test.

The "SuperAger" term was coined by Dr. M. Marsel Mesulam, founder of the Mesulam Center for Cognitive Neurology and Alzheimer's Disease at Northwestern, in the late 1990s.

In studying nearly 300 SuperAgers for the past 25 years, the Northwestern researchers identified some common traits, including being "highly social and outgoing" and having strong interpersonal relationships.

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"It's really what we've found in their brains that's been so earth-shattering for us," noted co-author Dr. Sandra Weintraub, professor of psychiatry, behavioral sciences and neurology at Northwestern University Feinberg School of Medicine, in the release.

The research team examined 77 of the SuperAgers' donated brains after they died. They found that some of the brains showed no buildup of amyloid and tau proteins (plaques and tangles), the toxic substances that are a hallmark of Alzheimer's disease. Other brains did have the proteins, but they didn't appear to have affected cognitive health.

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"What we realized is there are two mechanisms that lead someone to become a SuperAger," Weintraub said in the release. "One is resistance: they don't make the plaques and tangles. Two is resilience: they make them, but they don't do anything to their brains."

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Unlike most aging brains, SuperAgers did not experience significant thinning of the cortex, which is the brain's outer layer. They also had a thicker anterior cingulate cortex, the region of the brain involved in decision-making, emotion and motivation.

They were also found to have a greater number of "von economo neurons," specialized cells associated with social behavior, and larger entorhinal neurons, which are crucial for memory.

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The study outcome was published as a perspective article in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.

"Our findings show that exceptional memory in old age is not only possible, but is linked to a distinct neurobiological profile," said Weintraub. "This opens the door to new interventions aimed at preserving brain health well into the later decades of life."

Armed with this information about the commonalities among SuperAgers, the researchers hope to develop new ways to boost cognitive resilience and prevent or delay Alzheimer's and other dementias, they noted.

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Dr. Marc Siegel, Fox News senior medical analyst, was not involved in the study but commented on the findings to Fox News Digital.

"The buildup of senile plaques -- beta amyloid and tau -- did not impact neuronal function in those who continued to do very well in terms of thinking, memory and decision-making," he noted.

"Those with positive outcomes shared continued socialization, interaction and a high level of intellectual engagement."

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Siegel concluded, "So the answer is a combination of genetic predisposition as well as continuing to keep exercising the brain like a muscle -- both socially and intellectually."

The study was funded by Northwestern Alzheimer's Disease Research Center (ADRC) and the National Institute on Aging (part of the National Institutes of Health).

Scientists uncover how some 80-year-olds have the memory of 50-year-olds