But what surprised Snowdon was that Sister Mary, who was 101, had a good memory.

The world still does not know that there is something extraordinary about her, something that sets her apart from other nuns.

Since 1986, Snowdon has been immersed in one of the most unique and ambitious projects ever undertaken, which began at the University of Minnesota and was transferred to the University of Kentucky in 1990.

He traveled with his team across the United States, visiting the convents of the nuns of the School of Notre Dame, and convincing 678 nuns to participate in the experiment.

Neuroscientist Julia Raffy told the BBC: “Normally, you wouldn't combine a monastery with science, but this is worth its weight in gold.”

“What really exists [num convento] It is population control [com condições menos variáveis]It is the goal of science. We want to control everything, we want to control the uncontrollable.”

For the now-famous “Nun Study,” each sister agreed to undergo a series of tests that she would repeat year after year until her death, in the hope that they would reveal the secrets of longevity.

When will their brains start to fail and how quickly can they deteriorate?

“The sisters were given what we call a ‘mini-mental state test,’” Ravi explains.

Once completed, each nun received a score: the higher the score, the healthier her mind was.

Most people would get a 30 out of 30 if they had completely solid cognition.

The idea was to see how this score changed over time.

After observing hundreds of women over many years, Snowdon has an impressive set of data.

But the jewel in that crown was a fascinating graph indicating age at the bottom and cognitive ability measured from 0 to 30 points on the side.

The Snowdon team has compiled all the results on one page with amazing results.

“Once you plot all of these points on the graph, you'll have rows and rows of dots and you can see a lot of clusters in the upper left corner of the graph.”

Those who performed best were hundreds of nuns in their 70s and 80s who scored between 25 and 30 points on their tests. A strong sign that their brains were working well.

Like scraps of paper on a page, a bunch of dots sat at the bottom.

They were people who couldn't remember recent events.

“They may have remembered things from the past, but their sense of time and place was poor; they could not answer simple questions that you would expect people to know.”

Some of these women were in their 80s and 90s, so cognitive decline might have been expected, but others received a score of 0.

Snowdon knew the “use it or lose it” theory, and there was evidence that brain function, once no longer worked on, became irrecoverable.

But the graph showed something else. Something unusual.

One point on this chart stood out, much higher than the others.

“Sister Mary is at the top right of the chart. And that's where I get really excited, because she's an exception to the general trend that says, 'The older you get, the lower your scores.'

She will always be on the right side of the graph because of her age: she was one of only two participants in the entire study who were over 100 years old.

But Sister Mary is in a quadrant of her own, floating alone above many other points.

Chart told Snowdon that at the age of 101 he had the brain function of someone 20 years younger.

“What was going on in your brain?”

Let's go back to those rows of glass jars in the underground freezer, because all those brains are part of Snowdon's research.

To really understand how one brain differs from another, you have to hold it in your hands.

“For some people, the idea of ​​donating a brain may be a little uncomfortable, even though it is technically just another organ,” explains neuroscientist Ravi.

This became clear when Snowdon proposed in front of a large crowd of nuns. There was a great silence until a loud and clear voice rang out.

“Sure, I'll give you my mind.”

And so, when Sister Mary died at 6:45pm on 13 June 1994, Snowdon and his team took a moment to pay their respects and mourn the loss of the woman whose mind remained largely intact until the day of her death, before beginning the work of understanding what made her so special.

“Immediately, the researchers noticed something completely different in Sister Mary’s brain.

“It weighed 870 grams, which is one of the lightest brains: only five of the 117 brains they had at the time weighed less.

“What the low brain weight tells us is that there was a lot of brain cell death and plaques and tangles were found,” Ravi explains. [indicadores de doenças neurodegenerativas]”.

Snowdon and the team were surprised to see significant brain damage, and the twisted plaques and tangles of proteinaceous tissue suggested that Sister Mary was suffering from an advanced stage of dementia.

But how can this be possible?

How can someone not show signs of cognitive decline in old age even though their brain has been physically damaged by disease?

One theory that explains this whole situation is what is called cognitive reserve.

Brains are connected to a group of protective neurons, which, if exercised through lifelong learning, can compensate for the damage caused by Alzheimer's disease.

These neurons, in a way, act as patches around harmful plaques and disease tangles.

But all of this raises another question: If some brains are physically primed to protect against signs of cognitive decline, and others are not, would it be possible to determine who will develop dementia long before symptoms appear?

Susan Tyas is now an associate professor at the University of Waterloo, but she was a graduate student when she joined the Snowdon team to work on something new and exciting, something that had been discovered in a monastery basement, in two rust-coloured olive-green cabinets.

From the outside they looked unassuming, but inside they contained a goldmine for research.

“This included things like report cards, and the number of languages ​​they spoke. But mainly some biographical essays that these young women wrote before taking their final vows to enter the convent.”

Hidden among the articles were clues about the nuns, their level of education, vocabulary and general knowledge.

Of course, there were no direct measurements to be made, but the team decided to evaluate it through what they called idea density: the number of distinct ideas per 10 words written.

Here is an example where two nuns describe their circumstances.

One of them wrote, describing her family: “In my family there are 10 children, 6 boys, and 2 girls. “Two of the boys died.”

The syntax is simple. It goes straight to the point, and it's not too expressive and compact.

Compare it to this other one, which conveys the same kind of information but in a completely different way.

“The happiest day of my life so far was my First Communion,” he begins by saying. It ends with the words: “Now I wander down Dove Street waiting just three more weeks to follow in the footsteps of my husband, bound to him by sacred vows of poverty, chastity, and obedience.”

There is a difference in the way these women and others expressed themselves in their youth. Some described their inner lives as complex and rich, while others were dull and colorless.

Now comes the amazing part.

“That first sister, who spoke a very simple language, developed Alzheimer’s disease. The second sister did not.”

When Snowdon and his team began to compare higher scores in these early writings with the development of Alzheimer's disease later in life, a pattern began to emerge.

Sisters who wrote essays with a high density of ideas and grammatical complexity seemed to avoid symptoms later in life.

His memories and language skills remained intact.

As the team examined these pages more closely, the astonishment increased.

Articles written by these sisters when they were about 20 years old can be used to predict with 85 to 90 percent accuracy which brains will develop Alzheimer's decades later.

“I want to dig up my old high school and college essays that are in my parents' basement, but I'm afraid to look at them,” Tyas admits.

It seems that the autobiography of young people can have unimaginable prophetic power, but it also represents a chicken-and-egg dilemma.

Does cognitive reserve protect some brains from the symptoms of Alzheimer's disease, or does poor writing highlight early signs that the brain is poised to deteriorate later?

“We still don't know how all these changes develop in the brain,” says Tyas.

“However, we know that higher levels of education reduce the risk of developing Alzheimer's disease.”

Therefore, according to the scientist, this unique piece that analyzes written language skills and expression characteristics can really expand the vision of knowing what happened to them more than half a century later.

“What we discovered in the nuns study is that these changes in the brain do not always lead to lifelong Alzheimer's symptoms. And to me, that's very encouraging.”

Significant progress is being made in how to detect these changes in the brain.

MRI and even blood tests pave the way for early detection.

The question of how to treat them remains unanswered, but perhaps not for long.

Many researchers believe we are just a few years away from discovering a serum that can remove these plaques and tangles from our brains as they develop.

But for now, we just have to wait.

David Snowdon retired and his 678 nuns died. But those glass jars in the cold room are still there.

Thanks to this extraordinary donation from the nuns, the study continues at the University of Texas Health Science Center in San Antonio.

*If you want to listen to the “Usually” episode of the BBC series “Uncharted”, click here.