Bill Gurolnick will celebrate his 87th birthday next month.
Two years ago he joined a study looking at people whose memory function is significantly better than the average for other people their age.
These are the so-called "superagers".
"Well, I don't feel my age. What do I feel like? If I was to give a number, I probably feel like I'm about my early 70s."
Bill attributes his sharp memory to his active lifestyle and regular social engagements.
Having a good memory is not something that runs in Bill's family.
His father developed Alzheimer disease in his 50s.
A person's genetic inheritance is believed to contribute about 70% of the risk for developing Alzheimer's.
Neuroscientist Emily Rogalski leads the Super Aging study at Chicago's Northwestern University.
She believes her work can help fight or prevent Alzheimer's disease, a condition for which conventional medicine currently offers no effective treatment or cure.
"And we think if we can understand the factors contributing to superaging, it may offer new hypotheses and new ways to explore the challenges in Alzheimer's disease."
Emily's team found that superagers tend to be extroverts with strong social networks, and that their brains shrink much more slowly than those of their peers.
Research shows that the brains of superagers contain a lot more of a special kind of nerve cell that is important for attention, and that parts of their brain are packed with neurons thought to improve social processing and awareness.
Scientists are currently exploring how the brains of superagers resist and repair damage.
Heather Snyder from the Alzheimer's Association says studying the brains of superagers can help unpick the cause and provide potential treatments for Alzheimer's and other types of dementia.
"By studying superagers, we can get information about what might be contributing factors of how our brains are structured, our social interactions, how our heart health feeds into our brain health and use that information for thinking about strategies for prevention and treatment of Alzheimer's and other dementias."
Emily says that the existence of superagers might help change negative attitudes towards ageing.
"Perhaps, if we expected a bit better from ourselves, then we would understand that not all aging is 'doom and gloom' and talking about things changing for the worse."
For CRI, this is Li Yi.
1. attribute to 把…归因于；把…归咎于；
例句：Never attribute your accomplishments to luck or chance.
2. contribute to 促成；促使；是导致…的原因之一；
例句：Medication side effects and balance issues, which are exacerbated by a sedentary lifestyle, also contribute to fall risks, she said.
3. be packed with 充满…的；富含…的；
例句：Fish and chips are packed with protein.
4. change for the worse 向着更坏(或更糟的)情况(转变)；
例句：The grandparents sigh and say how things have changed for the worse.