As we age, our brain shrinks, but a select group of elders known as "super-agers" lose less brain volume than regular seniors, which may help them stay sharp, researchers said Tuesday.
The findings in the Journal of the American Medical Association show that super-agers, 80 and older, have a significantly thicker brain cortex than people who are aging normally.
The cortex is the largest part of the brain, a wrinkly outer mass that is divided into four lobes and is in charge of everything from thinking and speaking to processing sounds, sights, tastes and other sensory information.
"Increasing age is often accompanied by 'typical' cognitive decline or, in some cases, more severe cognitive decline called dementia," said first author Amanda Cook, a clinical neuropsychology doctoral student at Northwestern University in Chicago.
"Super-agers suggest that age-related cognitive decline is not inevitable."
For the study, reported as a research letter in JAMA, super-agers were defined as people over 80 who scored as well on memory tests as people aged 50-65.
Two dozen of these agile elders took part in the research, along with 12 average counterparts.
Like most elderly people, the super-agers lost brain mass over the course of the 18-month study, but they lost about half as much as their cognitively average counterparts.
Just 1.04 percent of brain volume was lost in super-agers compared to 2.24 percent in average seniors.
Since the study did not track the participants from birth, it is impossible to know whether super-agers simply had more brain mass from the outset.
The possibility that super-agers were "endowed with larger brains throughout life cannot be ruled out," said the letter, calling for larger studies in the future to explore the findings.
- Connections matter -
According to Gayatri Devi, a neurologist at Lenox Hill Hospital in New York, brain size is not the only important factor.
The number of connections between nerve cells in the brain is also key to how well we age, said Devi, who was not involved in the study.
"We have 80 plus billion cortical nerve cells. They can be destroyed by things like stroke, or injury," she told AFP.
"But the connections between them can make trillions of connections, and you can still amp up those."
Previous research has shown that exercising, eating well and making social contacts are all key parts of building new brain connections.
"Just because you may be born with a smaller number of nerve cells it doesn't preclude you from aging well," Devi said.
A number of studies on super-agers -- what makes them age so successfully and why -- are being conducted around the world.
Using autopsied brains, some researchers have even discovered that some super-agers had significant plaque buildup, which should have indicated they were in the throes of dementia. But somehow, they were still able to function well.
"We are all intrigued when we see an elderly person that is fully functioning and is 'as sharp as a tack,'" said Paul Wright, chair of neurology at North Shore University Hospital in Manhasset, New York.
"The most important aspect is to determine the possible genetic, social and environmental factors that contribute to the super-agers' thicker cortices," added Wright, who was not involved in the study.
"This may unlock the key to successful aging."