![]() 45° rotation of the arena commensurately rotates the grid pattern despite prominent distal cues remaining stationary ( Fig. In contrast we found that in geometrically polarised enclosures, such as squares, greater control is exercised by the arena. In geometrically symmetrical enclosures such as circles, distal cues control the orientation of grid-patterns which follow cue rotation 1. Under certain circumstances, it can overcome internal network processes and lead to profound distortions of the grid-pattern. Here we demonstrate that environmental geometry exerts an important and permanent influence on grid-cell firing. These changes ameliorate with time and cells tend to return towards their canonical patterns, reinforcing the idea that internal processes at the individual cell or network level predominantly determine the grid-pattern 2. Grid cells may also be influenced by changes to boundaries, in particular reflecting distortions of a familiar enclosure by rescaling in the same direction 7. The spatial activity of boundary and place cells is known to be affected by environmental geometry 17– 19. In mammals the hippocampal formation is required for spatial navigation 14 and its neurons encode the animal’s position (place cells 15 and grid cells 1), head direction (head direction cells 16) and proximity to boundaries (boundary cells 17, 18). Navigation is performed on the basis of information about self-motion and external cues, including enclosure geometry, the latter dominating non-geometric information such as visual landmarks, textures and smells 11– 13. Importantly, grid cell activity is more local than previously thought and as a consequence cannot provide a universal spatial metric in all environments. Our results provide compelling evidence for the idea that environmental boundaries compete with the internal organisation of the grid cell system to drive grid firing. Furthermore, the hexagonal grid symmetry is permanently broken in highly polarised environments such as trapezoids, the pattern being more elliptical and less homogeneous. We found that grid-patterns orient to the walls of polarised enclosures such as squares but not circles. Here, we show that grid orientation, scale, symmetry and homogeneity are strongly and permanently affected by environmental geometry. Nonetheless several studies indicate that environmental boundaries influence grid-firing 7– 10 though the strength, nature and longevity of this effect is unclear. Originally the properties of grid-patterns were believed to be independent of the shape of the environment and this notion has dominated all mainstream theoretical grid cell models 3– 6. Such a profound and constant regularity prompted suggestions that grid cells represent a universal and environment-invariant metric for navigation 1, 2. Grid cells represent an animal’s location by firing in multiple fields arranged in a striking hexagonal array 1.
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