David Snowdon was a cold, calculating researcher, trained to keep science and emotions separate.

Until he met Sister Carmen Burg.

“Those sisters on Good Counsel Hill turned me into a marshmallow, and Sister Carmen led the charge,” said Snowdon, who heads an international study on aging and Alzheimer’s at the University of Kentucky.

Burg, who died Friday in Mankato, was the key to Snowdon’s unique study, which looked at all aspects of the nuns’ lives — and their deaths — to unlock information on the aging brain. So far, the brains of 500 nuns have been studied and are being saved for future research.

Burg, who was a convent leader in Mankato, met Snowdon in St. Paul in 1986 to listen to his idea for doing an aging study on Notre Dame nuns in Mankato and at other convents. She was the first Notre Dame nun he’d met and her approval was vital if the project was to happen.

“She said, you can come to Mankato, but you have to assure me you’re not going to treat them as research subjects,” he said in an interview Tuesday. “You’re going to get to know them and they’re going to get to know you.

“Those were my marching orders.”

Developing a personal relationship with research subjects was not what Snowdon had been taught to do. But, he said, he believes it is a better way to conduct research, particularly one of this unique nature.

“Normally, research subjects don’t want you do have sleepovers at their house. I’ve spent hundreds of nights at Notre Dame convents,” Snowdon said. “Because of Sister Carmen, I’m greeted like family throughout Notre Dame.”

While Burg is credited with making the nun study happen, she was not one of the participants in the study because she was too young — the cutoff at the time the study started was 75.

The study began 21 years ago with 678 nuns. Today, there are only 71 of the nuns still alive, including 13 in Mankato. All are 90 or older with many in their 100s.

Snowdon said the project will live long past his career and the nuns’ lives. “The brain material will be used for decades,” Snowdon said. “We’re creating a genetic library of the sisters.”

Burg, who was also known as Sister Rose Marie Burg, was 84. She died of complications from diabetes.

Burg, who became a nun in 1943, held several positions in the Archdiocese of St. Paul and Minneapolis.

“She was very smart, sensitive, a humanitarian,” Snowdon said. “I can’t think of anybody who has had a greater impact on my career and the nun study than Sister Carmen.”