STOCKHOLM — A U.S.-British scientist who grew up in the South Bronx and a husband-and-wife research team from Norway won the Nobel Prize in medicine Monday for discovering the brain’s navigation system – the inner GPS that helps us find our way in the world. Their revelations could lead to advances in diagnosing Alzheimer’s disease.

The research by John O’Keefe, May-Britt Moser and Edvard Moser represents a “paradigm shift” in neuroscience that could help researchers understand the sometimes severe spatial memory loss associated with Alzheimer’s, the Nobel Assembly said.

“This year’s Nobel Laureates have discovered a positioning system, an ‘inner GPS’ in the brain, that makes it possible to orient ourselves in space,” the assembly said.

O’Keefe, 74, a dual U.S. and British citizen at the University College London, discovered the first component of this system in 1971 when he found that a certain type of nerve cell was always activated when a rat was at a certain place in a room. He demonstrated that these place cells were building up a map of the environment, not just registering visual input.

Decades later, in 2005, May-Britt and Edvard Moser, married neuroscientists at the Norwegian University of Science and Technology in Trondheim, identified another type of nerve cell – the grid cell – that generates a coordinate system for precise positioning and path-finding, the assembly said.

Monday’s award was the fourth time that a married couple has shared a Nobel Prize and the second time in the medicine category.

“This is crazy,” an excited May-Britt Moser, 51, said from Trondheim. “This is such a great honor for all of us and all the people who have worked with us and supported us. We are going to continue and hopefully do even more groundbreaking work in the future.”

Her 52-year-old husband didn’t immediately find out about the prize because he was flying Monday to the Max Planck Institute in Munich to demonstrate their research. Edvard Moser only discovered he had won after he landed in Munich, turned on his cellphone and saw a flood of emails, text messages and missed calls.

“It’s a great moment. I am grateful to everyone who has contributed to this, including everyone who is and has been in our lab,” he said. “And it shows that it is possible to create good science, if you do it in the right way. I think it’s a big stimulation for science both at home in Norway and throughout the world.”

The Nobel Assembly said the discoveries marked a shift in scientists’ understanding of how specialized cells work together to perform complex cognitive tasks. They have also opened new avenues for understanding cognitive functions such as memory, thinking and planning.

O’Keefe, speaking from his office at University College London, was born in Harlem and raised in the South Bronx. “If you can survive the South Bronx, you can survive anything,” he said.