The Nobel Assembly, which awarded the prize of 8 million Swedish crowns ($1.1 million) at Sweden's Karolinska Institute on Monday, said the discovery solved a problem that had occupied philosophers and scientists for centuries:
               
"How does the brain create a map of the space surrounding us and how can we navigate our way through a complex environment?"
               
Ole Kiehn, a Nobel committee member and professor in Karolinska's neuroscience department, said the three scientists had found "an inner GPS that makes it possible to know where we are and find our way".
               
O'Keefe, now director at the centre in neural circuits and behaviour at University College London (UCL), discovered the first element of the positioning system in 1971 when he found that a type of nerve cell in a brain region called the hippocampus was always activated when a rat was in a certain place in a room.
               
Seeing that other nerve cells were activated when the rat was in other positions, O'Keefe concluded that these "place cells" formed a map of the room.
               
Uta Frith, a UCL professor of cognitive development said O'Keefe had shown "it is possible to literally map the mind".
               
"He has done much more than discovering neuronal mechanisms in the brain: he has discovered cognitive mechanisms that explain how human beings and other animals navigate," she said.

"This beautiful work is heralding a new age of exploration of brain and mind."
 
In 1996, Edvard Moser and May-Britt Moser, who are married and now based in scientific institutes in the Norwegian town of Trondheim, worked with O'Keefe to learn how to record the activity of cells in the hippocampus.
               
Nearly a decade later, the Moser team discovered cells, in the entorhinal cortex region in brains of rats, which function as a navigation system. These so-called "grid cells", they discovered, are constantly working to create a map of the outside world and are responsible for animals' knowing where they are, where they have been, and where they are going.
               
Bill Harris, head of physiology, development and neuroscience at Britain's University of Cambridge, said the scientists' work "has not only revolutionised our understanding of this amazing puzzle (the brain), but has also opened the door into problems of place memory and how we learn and remember routes of navigation, and what sleep and dreams may be doing for memory and performance."

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