O'Keefe, the Mosers and the Brain's GPS

Place cells that fire in one spot, grid cells that tile space in triangles: how John O'Keefe and May-Britt and Edvard Moser discovered the brain's positioning system and shared the 2014 Nobel Prize.

How do you know where you are? In 1971 John O'Keefe, an American-British neuroscientist at University College London, recorded from single neurons in the hippocampus of rats exploring an enclosure. Some cells fired only when the rat was in one particular spot — and different cells preferred different spots. He called them place cells.

A cognitive map

In 1978 O'Keefe and Lynn Nadel argued, in The Hippocampus as a Cognitive Map, that the hippocampus builds an internal map of the environment — reviving an idea the psychologist Edward Tolman had proposed in the 1940s from rats' maze behaviour. Place cells re-map when the animal enters a new environment, building a fresh map for each.

Grid cells

The Norwegian couple May-Britt Moser and Edvard Moser, who had trained with O'Keefe, looked for where the hippocampus gets its spatial information. In 2005, in the entorhinal cortex, they found neurons that fire at many locations — and those locations form a strikingly regular triangular grid tiling the whole floor. These grid cells behave like a coordinate system, with grids of different sizes stacked at different depths.

Along with head-direction cells (discovered by James Ranck in the 1980s and studied by Jeffrey Taube), which fire when the head points a certain way, and border cells that fire near walls, they form a positioning system that works even in the dark.

Why it matters

O'Keefe and the Mosers shared the 2014 Nobel Prize. The entorhinal cortex is one of the first regions damaged in Alzheimer's disease, which may explain why getting lost is an early symptom. And similar grid-like codes have been found for abstract "spaces" of concepts, suggesting the brain may reuse its map-making machinery for thinking.