Portal de Periódicos da CAPES

Grid cell symmetry is shaped by environmental geometry

2015; Nature Portfolio; Volume: 518; Issue: 7538 Linguagem: Inglês

10.1038/nature14153

1476-4687

Julija Krupic, Marius Bauža, Stephen Burton, Caswell Barry, John O’Keefe,

Photoreceptor and optogenetics research

Neuronal grid cells fire in a spatial grid pattern laid out across the surface of a familiar environment, however the role of environmental boundaries in the construction of this pattern is not well understood; this study shows that the grid pattern orients to the walls of polarized environments such as squares but not circles and that the hexagonal grid symmetry is permanently broken in highly polarized environments such as trapezoids. The neuronal grid cells of the entorhinal cortex fire in a spatial grid pattern laid out across the surface of a familiar environment to provide the brain with an internal map of an animal's surroundings. The role of environmental boundaries in the construction of this pattern is not well understood. Early studies had suggested that properties such as symmetry, orientation and scale of grid cells' firing patterns were independent of an environment's shape. But now two separate papers in this issue of Nature — one from Edvard Moser and colleagues and the other from John O'Keefe and colleagues — demonstrate that grid orientation, scale, symmetry and homogeneity can be strongly affected by environmental geometry, with grid cells aligned with the borders of the environment at an offset of a few degrees such that it minimizes symmetry with boundaries. These findings suggest a mechanism by which the geometry of an environment causes local rotation and deformation of the hexagonal firing patterns of grid cells. Grid cells represent an animal’s location by firing in multiple fields arranged in a striking hexagonal array1. Such an impressive and constant regularity prompted suggestions that grid cells represent a universal and environmental-invariant metric for navigation1,2. Originally the properties of grid patterns were believed to be independent of the shape of the environment and this notion has dominated almost all theoretical grid cell models3,4,5,6. However, several studies indicate that environmental boundaries influence grid firing7,8,9,10, though the strength, nature and longevity of this effect is unclear. Here we show that grid orientation, scale, symmetry and homogeneity are strongly and permanently affected by environmental geometry. We found that grid patterns orient to the walls of polarized enclosures such as squares, but not circles. Furthermore, the hexagonal grid symmetry is permanently broken in highly polarized environments such as trapezoids, the pattern being more elliptical and less homogeneous. Our results provide compelling evidence for the idea that environmental boundaries compete with the internal organization of the grid cell system to drive grid firing. Notably, grid cell activity is more local than previously thought and as a consequence cannot provide a universal spatial metric in all environments.