They're the minority the majority is dying to get into. Superagers: older folks aged 80 and beyond whose razor-sharp powers of mental fitness defy their advanced years.

Just what is it that separates these enviable elderly – who are estimated to make up less than 5 percent of the population – from the rest of us probably destined to succumb to the mental decline of old age?

While the majority of scientific research into mental issues facing the elderly community focusses on the biological mechanisms that bring about cognitive decline – such as Alzheimer's disease and dementia more broadly – a smaller subset of researchers are honing in on the uplifting outliers who defy the trends.

"It's not so long ago that we thought the only trajectory there was to get old and senile," cognitive neurologist Emily Rogalski from Northwestern University told media on Sunday at the annual meeting of the American Association for the Advancement of Science in Austin, Texas.

"We need to push the envelope and see what is possible in older age and how did [people] get there."

Through a body of research done to date, Rogalski defines superagers as individuals 80 or older whose episodic memory is on par with that of cognitively average individuals in their 50s and 60s – and sometimes even younger.

In terms of lifestyle, Rogalski says that what separates superagers from their contemporaries could be enjoying more satisfying, high-quality relationships than their cognitively average peers.

"The findings suggest that superagers have unique personality profiles," Rogalski said, noting that they stood out for their optimism, resilience, and perseverance – as well as active and engaged lifestyles, marked by pursuits like travel, reading, and ­positive social relationships.

Superagers are more likely to be extroverts and less likely to be neurotic than others, and it looks like their active lifestyles aren't necessarily healthy in other ways. In at least one study, 71 percent of superagers smoked, while 83 percent drank alcohol regularly.

But not all of superagers' secrets are visible on the surface. In a 2013 study, Rogalski and her team found superagers had unusually high numbers of brain cells called von Economo neurons (aka spindle neurons).

"It's thought that these von Economo neurons play a critical role in the rapid transmission of behaviourally relevant information related to social interactions," fellow Northwestern team member Changiz Geula said in 2015, "which is how they may relate to better memory capacity."

The researchers acknowledge there's still a lot to discover about what purpose these von Economo neurons serve in terms of superageing, but the evidence revealed so far suggests their abundance in superagers isn't an accident.

"We find that in the superagers we look under the microscope and find they have more von Economo neurons than average 80-year-olds, and more VE neurons even than 20-year-olds," Rogalski said in Austin on Sunday.

"We can't explain how they ended up with more von Economo neurons or why that is important. But these are a special type of neuron that have only been found in a couple of regions of the brain."

Even more amazingly, post-mortem examinations of superagers have revealed that some died with deposits of tau protein clumps in their brains – a symptom associated with Alzheimer's disease – and yet before their death, they didn't show evidence of the cognitive decline the disease is known for.

We don't have all the answers yet, but whatever superagers' true success formula is – it may work out for them even in the presence of Alzheimer's itself.

"Excellent memory capacity is bio­logically possible in late life," Rogalski said, "and can be maintained for years even when there is significant neuropathologic burden."

The findings were presented over the weekend at the annual meeting of the American Association for the Advancement of Science in Austin, Texas.