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Today's story begins in a dimly lit underground room.

It's alive with swirling clouds of freezing air

and rows of glass jars stretch back as far as the eye can see.

Within these 700 containers is something unexpected.

Each one is home to its own, perfectly preserved human brain.

I'm Hannah Fry, a mathematician who studies patterns in human behaviour.

And from BBC Radio 4, this is uncharted. Tales of data and discovery.

It was 1991 when a young and inexperienced neuroscientist called David Snowden first got to meet the unusual nun at the centre of today's story.

Like many others around her, she dressed head to toe in a traditional black and white habit.

She was eternally optimistic, rarely idle, and at one hundred and one years old,

David was astonished to find that Sister Mary's memory was as sharp as a pin. He couldn't

have known then, while sitting in this chair, that there was something extraordinary about her,

something exceptional that set

her apart from all the other nuns. Since 1986, David and his team had been travelling up and down

the United States, visiting convents, persuading 678 nuns to come on board, making this one of the most unique

and ambitious human studies ever conducted.

You wouldn't really put a nunnery in science together, but this is gold.

That is the voice of the neuroscientist Julia Ravy.

What you have is really control population, which is what science is all about.

We want to control everything. We want to control the uncontrollable.

Each nun agreed to complete a battery of tests, which they would repeat year on year until they passed away, in the hope that it would teach us about the secrets of longevity and age.

...