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Rats have innate mapping ablities — scientists discovered in 2005 that the rodents maintain a grid-like map of their location by means of a network of brain neurons dubbed 'grid cells'. These cells have also been found in mice, but whether a similar mechanism operates in humans has been unclear. Neil Burgess, a neuroscientist at the Institute of Cognitive Neuroscience of University College London, and his colleagues have now found evidence that the human brain also contains grid cells that act like a spatial map (see page 657). Burgess tells Nature more.

How do grid cells behave?

Grid cells fire according to an animal's location in its environment: different cells fire in different locations. If the geographical locations at which a grid cell fires were plotted on the ground, they would form the vertices of a regular triangular array, or grid. The grid patterns of all the cells have the same orientation. Some grid cells fire more than usual when the animal is moving in a particular direction, and these 'preferred' directions line up with the axes of the grids. In this way, the regular spatial firing patterns of grid cells provide information to the animal about the distances and directions in which it has travelled.

How did you look into the possibility that humans have grid cells?

We can't implant electrodes in people's brains to record the activity of individual neurons as grid cells were studied in rats, but we can measure the combined activity of thousands of neurons at once using functional magnetic resonance imaging. We figured that when a person explored the environment of a virtual-reality video game we would see changes in the firing patterns of all their grid cells as the person 'ran' in different directions. We believed that there would be different patterns of firing when a person was running along one of the axes of the grid compared with when they were running between axes. So we theorized that the imaging signal would be high whenever people ran in the directions of the axes and low when they ran between them. And that is what we found.

Was there much variation between people?

The part of the brain we looked at, the entorhinal cortex, is associated with being able to find your way around, and if it is damaged this ability may be compromised. We noticed that across the 42 individuals whose brains we scanned, those who had the most consistent MRI readings across voxels in the entorhinal cortex were the ones who remembered locations best. It may be that the better organized your grid is, the more easily you can find your way around.