LAGUNA WOODS, Calif. — The women are playing bridge, and, at their age, the game is no hobby. It is a way of life, a daily comfort and challenge, the last communal campfire before all goes dark.
"We play for blood," says Ruth Cummins, 92, before taking a sip of Red Bull at a recent game.
"It's what keeps us going," said Georgia Scott, 99. "It's where our closest friends are."
In recent years scientists have become intensely interested in what could be called a super memory club — the fewer than one in 200 of us who, like Scott and Cummins, have lived past 90 without a trace of dementia.
It is a group that, for the first time, is large enough to provide a glimpse into the lucid brain at the furthest reach of human life, and to help researchers tease apart what is essential in preserving mental sharpness to the end.
Laguna Woods, a retirement community of 20,000 south of Los Angeles, is at the center of the world's largest decades-long study of health and mental acuity in the elderly. Begun by University of Southern California researchers in 1981 and called the 90+ Study, it has included more than 14,000 people aged 65 and older, and more than 1,000 aged 90 or older.
Such studies can take years to bear fruit, and the results of this study are starting to alter the way scientists understand the aging brain.
The evidence suggests that people who spend long stretches of their days, three hours and more, engrossed in mental activities like cards may be at reduced risk of developing dementia. Researchers are trying to tease apart cause from effect: Are they active because they are sharp, or sharp because they are active?
The researchers have also demonstrated that the percentage of people with dementia after 90 does not plateau or taper off, as some experts had suspected. It continues to increase, so that for the one in 600 people who make it to 95, nearly 40 percent of the men and 60 percent of the women qualify for a diagnosis of dementia.
At the same time, findings from this and other continuing studies of the very old have provided hints that some genes may help people remain lucid even with brains that show all the biological ravages of Alzheimer's disease. In the 90+ Study, researchers regularly run genetic tests, test residents' memory, track their activities, take blood samples, and in some cases do postmortem analyses of their brains.
So far, scientists here have found little evidence that diet or exercise affects the risk of dementia in people over 90. But some researchers argue that mental engagement — doing crossword puzzles, reading books — may delay the arrival of symptoms. And social connections, including interaction with friends, may be very important. In isolation, a healthy human mind can go blank and quickly become disoriented, psychologists have found.