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Some of Dr. Snowdon's research suggests she might be right. Sister Nicolette's autobiography, written when she was 20, was full of what Dr. Snowdon calls ''idea density,'' many thoughts woven into a small number of words, a trait correlating closely with nuns who later escaped Alzheimer's.
One sentence in Sister Nicolette's essay, for example, reads, ''After I finished the eighth grade in 1921 I desired to become an aspirant at Mankato but I myself did not have the courage to ask the permission of my parents so Sister Agreda did it in my stead and they readily gave their consent.''
Compare that to the essay of another Mankato nun, who is in her late 90's and has performed steadily worse on the memory tests. The nun, who sat quietly by a window the other day, wrote in her essay, ''After I left school, I worked in the post-office.''
The Nun Study's latest published findings offer similarly provocative ideas about how positive emotional state in early life may contribute to living longer. Experts say linking positive emotions in the autobiographies to longer life echoes other studies showing that depression increases risk of cardiovascular disease and that people rated as optimists on personality tests were more likely than pessimists to be alive 30 years later.
The findings also raise questions like, What underlies the positive emotions?
''How much of this is temperament?'' Dr. Suzman said. ''How much of it is affected by life events and critical relationships with parents, friends, teachers, peers?''
Overall, Dr. Snowdon says, the nuns live significantly longer than other women. Of the 678 in the study, 295 are alive and are all 85 or older. In the Mankato convent alone, there have been seven centenarians, many free of dementia.
One is Sister Esther Boor, who at 106 speeds through the labyrinth of halls with a royal blue walker, glazes ceramic nativity scenes for the gift shop and pedals an exercise bike every day, her black veil flapping, an orange towel draped over her legs for modesty.
''Sometimes I feel like I'm 150, but I just made up my mind I'm not going to give up,'' said Sister Esther, who gives her exercise therapists yellow notes with phrases from books she reads. ''Think no evil, do no evil, hear no evil,'' she wrote recently, ''and you will never write a best-selling novel.''
Sister Esther's autobiographical essay, written 80 years ago, is similarly upbeat, speaking fondly of her family and her decision to become a nun.
Dr. Snowdon's condition that nuns donate their brains was a stumbling block for some of the sisters.
''I had a hard time with it,'' said Sister Claverine, who delayed signing up. ''I had an image of myself being buried intact.''
But Sister Rita Schwalbe, the convent's health administrator when the study began, said she had told them that as nuns they had made ''the difficult decision not to have children. This is another way of giving life.''
Many nuns now see brain donation through a liturgical lens -- or a humorous one.
Sister Nicolette said: ''After the resurrection, our bodies will be perfect. We'll be so happy we won't care what happens to our brains.''
And Sister Miriam Thissen, 89, said: ''Que será será. After you're dead, so what?''
After completing the cognitive and physical tests -- including identifying everyday objects and opening small doors with different latches -- the nuns get summaries of their results and can see if their performance has changed.
''Every time I get out of there I feel like an idiot,'' said Sister Blanche Becker, 88, who does crossword puzzles and reads Danielle Steel novels. ''Here I am of sound mind and body and I sit there and open and close little doors and look at pictures and try to remember them all. But maybe it's made me more tolerant of people with Alzheimer's. I am afraid of what's going to happen to me, yes. How stupidly am I going to act? Will I know people? How long will it take me to die?''
Dr. Snowdon, 48, has become unusually close to his subjects. He says that when he was in Catholic school as a child, the nuns were more rigid and strict than the warm, good-humored School Sisters he sees almost as grandmothers. That relationship has made him acutely aware of sensitive ethical issues, like how forthright to be with nuns who show slight signs of Alzheimer's.
''Do we really want to tell these dear women who are having memory loss that they are in the early phases of Alzheimer's, that they should start taking something?'' he asked.
Dr. Snowdon is quick to agree with other experts who say his conclusions need to be corroborated by other studies. There are limitations to the autobiographies, for instance, since the nuns knew a mother superior would see their writing and therefore may not have been totally candid.
''He's pointed us in some directions,'' said Dr. Bill Thies, vice president for medical and scientific affairs at the Alzheimer's Association, based in Chicago, ''but I think it's going to take a fair amount of work before we start making public health recommendations about behaviors that will prevent Alzheimer's.''
Still, Dr. Snowdon hopes his study will encourage people to do things to ward off the disease, like quit smoking and other stroke-causing behaviors, and read to children to stimulate language development. His current project involves analyzing old photographs of nuns for personality clues in their face muscles to see if personality correlates to Alzheimer's or longevity.
And, although he cannot prove it scientifically, he contends the nuns' spirituality and community living helps them too.
''You don't necessarily have to join a church or join a convent,'' Dr. Snowdon said. ''But that love of other people, that caring, how good they are to each other and patient, that's something all of us can do.''
Several nuns agree.
''The science is important,'' Sister Miriam said. ''But the science is dictated by providence anyway.''
Photos: Sisters Claverine and Nicolette with their sibling Sister Mary Ursula, who has Alzheimer's symptoms. (Nicole Bengiveno/The New York Times)(pg. A1); Dr. David A. Snowdon, center, and his colleagues Cecil Runyons and Ann Tudor examining a cross-sectioned brain from the Nun Study. Dr. Snowdon's study involves not only pathology on nuns who have died but also a study of autobiographical essays the nuns wrote in their 20's.; ''Sometimes I feel like I'm 150, but I just made up my mind I'm not going to give up,'' says Sister Esther Boor, right, who is a dementia-free 106. (Photographs by NICOLE BENGIVENO/The New York Times)(pg. A15)
