WILTON, Conn. - When Sister Kathleen Treanor's soul ascends to heaven, her brain will go to a less ethereal realm: a medical lab in Kentucky.
Two decades ago, Sister Treanor and 677 other members of the School Sisters of Notre Dame granted a young researcher's request to test them each year in order to track the progression of Alzheimer's disease and other age-related brain disorders.
The 61 surviving nuns recently completed their last round of intellectual and physical tests for the Nun Study, one of the world's most comprehensive neurological research projects.
One final sacrifice remains: When they die, their brains will be taken for further study, joining a collection of hundreds of other brains donated by the the nuns who died before them.
Sister Treanor, a 93-year-old former school principal who is one of the last of the volunteers at a Wilton convent, looks at her participation as service, not sacrifice.
"I've tried to do good while I'm alive, and I liked the idea that I could do something good after death," she said.
With the modesty of their calling, the nuns attribute the study's success to researcher Dr. David Snowdon, downplaying their own countless hours of interviews and testing over the decades.
"I never minded having my brain checked out. It kept me out of trouble," said 96-year-old Sister Antoine Daniel.
Researchers say Snowdon's work already has produced interesting results, including a finding that people who challenge themselves intellectually can apparently delay or prevent the onset of Alzheimer's symptoms.
Snowdon's work also suggests that in people predisposed to Alzheimer's, a stroke or head trauma can speed the disease's progression -- an argument for wearing seat belts, helmets and other protective gear.
He also has researched the levels of folic acid in the blood of deceased nuns with and without dementia; why nuns with positive attitudes and creative verbal skills tend to live longer than their glass-half-empty peers; and other questions.
"We'll continue to learn from the sisters for many, many years to come," Snowdon said.
Snowdon was a nervous young epidemiology professor at the University of Minnesota when he approached the first group of nuns in 1986 at the School Sisters of Notre Dame order in Mankato, Minn.
Although Pope Pius XII had declared in 1956 that donating organs was acceptable in the Roman Catholic faith, asking nuns to leave their brains to science for post-mortem testing was a delicate task. That was especially true for Snowdon, who had attended Catholic school and still viewed nuns with a mix of reverence and intimidation.
Yet getting them to donate their brains was critical because the only indisputable diagnosis of Alzheimer's comes from examining a patient's brain after death.
"At that time, it was hard enough just to get families of Alzheimer's patients to agree to donate the brain of a loved one with the disease," he said. "What we found is that because the sisters had been teachers, they looked at this as a way to keep teaching even after they die."
Snowdon expanded his study over the years, recruiting more nuns at other School Sister convents nationwide and joining the University of Kentucky to devote himself fully to the project. By 1992, he was giving annual memory and cognitive tests to 678 nuns ranging in age from 75 to 102.
One reason the nuns are such a valuable research tool is that as members of the same religious order, they all had decades of similar medical treatment, diets, reproductive histories and preventive care. Almost nine out of 10 had been teachers.
In the general population, finding such a uniform pool of test subjects is difficult.
About half the nuns in the study developed Alzheimer's disease or other forms of dementia before they died, about similar to the general population.
"It's such a cool study. People who study aging love to have these longitudinal perspectives because we think the early life experiences probably do have an impact on exceptional longevity," said Dr. Thomas Perls, a Boston University professor and Alzheimer's specialist who directs the New England Centenarian Study, which focuses on people 100 and older.
Of the seven remaining Nun Study participants based at the Wilton convent, several still recall their first memories as toddlers, can recite lengthy poems they learned in elementary school or tell vivid stories of classes they taught at schools around the U.S.
The Connecticut sisters say that while God gets their souls when they die, they are comfortable -- comforted, even -- knowing Snowdon has dibs on their brains.
"I think of the overall picture of what good could come out of it," said Sister Alberta Sheridan, 92. As for the possibility of developing Alzheimer's, she is sanguine: "If it happens, it happens. It's part of God's plan."
