When ageing hampers memory, some people's brains compensate to stay sharp. Now scientists want to know how those brains make do, in the hopes of developing treatments to help everyone else keep up.
This is not Alzheimer's disease but the wear-and-tear of so-called normal ageing.
New research is making it clear that memory and other brain functions decline even in otherwise healthy people as they age, as anyone who habitually loses car keys probably suspected.
The question is how a person girds the brain against time's ravages, a question becoming critical as the population greys.
If you are 65 years old today, odds are you will live to 83.
But improving health care means people in their 50s today may live a minimum of another 40 years.
More investment needed
"I don't think we've recognised, as scientists or a society, (that) this is the front-and-centre public health issue we face as a nation," Dr Denise Park, director of the University of Illinois' Centre for Healthy Minds, told fellow brain specialists assembled by the US government last week.
"We need to understand how to defer normal cognitive aging, the way we've invested in fighting heart disease and cancer."
There are intriguing clues, gleaned from discoveries that some older people's brains literally work around ageing's damage, forging new pathways when old ones disintegrate.
"It's not just fanciful or pie-in-the-sky" to try harnessing that ability, said Dr Richard Hodes, director of the National Institute on Aging, which organised last week's meeting to seek advice on the most promising research.
Exercise body and mind
High on the list: Simple physical exercise. It seems to do the brain as much good as the body.
Other options are not as well-studied but range from brain-training games to medications that may keep brain networks better connected.
In fact, an old blood-pressure pill named guanfacine improves memory in old rats and monkeys by doing just that, but it has not yet been tested in older people with memory problems.
What is normal ageing, and what signals impending Alzheimer's?
That is a big question for elders worried about periodic memory lapses.
Science cannot yet tell for sure, but there seem to be distinct differences.
Consider: A healthy brain is a bushy one. Branch-like tentacles extend from the ends of brain cells, enabling them to communicate with each other. The more you learn, the more those connections form.
Alzheimer's kills neurons, so the cells disappear along with connections their neighbours need.
With normal ageing, the cells do not die but their bushes can shrivel to skinny twigs, explained Dr Carol Barnes of the University of Arizona.
Cells that are less connected have a harder time sending messages. A person might know someone's name, but be unable to recall it.
Options to fight back
Moreover, Alzheimer's seems to target first a different spot in the hippocampus, the brain's memory centre, from where ageing does.
There are two capacities for fighting back:
What's the advice for now?
Physical exercise is the best-proven prescription so far, the scientists agreed.
Memory improved when 72-year-olds started a walking programme three days a week, and sophisticated scans showed their brains' activity patterns started resembling those of younger people.
Then there's the "use-it-or-lose-it" theory, that people with higher education, more challenging occupations and enriched social lives build more cognitive reserve than couch potatoes.
It's never too late to start building up that reserve, said Columbia University neuroscientist Yaakov Stern, but: "The question is how. What is the recipe?"
Everything from doing crossword puzzles to various computer-based brain-training programs has been touted, but nothing is yet proven to work.
Johns Hopkins University has a major government-funded study under way called the "Experience Corps," where older adults volunteer to tutor school students 15 hours a week, to see if such long-term stimulation maintains the elders' brains.
What about medication?
Companies have been reluctant to test side effect-prone drugs in an otherwise healthy ageing brain, but scientists
cited animal studies that suggest low-dose oestrogen and drugs that might mimic or ramp up brain signalling are promising possibilities.
And recall that old blood pressure drug guanfacine? It is now being studied as a potential treatment for children with attention-deficit disorder - and it works in the same brain region, the prefrontal cortex, where elderly brains forge new networks.
"If it works in a six-year-old, we hope it will work in the elderly," said Yale University neurobiologist Amy Arnsten. – (Sapa)
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