Don't Cross the Border!

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Science  19 Dec 2008:
Vol. 322, Issue 5909, pp. 1753
DOI: 10.1126/science.322.5909.1753a
CREDIT: RAYMOND SKJERPENG/NOWEGIAN UNIVERSITY OF SCIENCE AND TECHNOLOGY

At least three cell types are thought to encode an animal's position in the environment: place cells, whose activity indicates a particular location in space, head direction cells, which fire only when the animal is facing a certain direction, and grid cells, whose firing fields form a regular pattern across the environment. However, computational models suggested the existence of at least one more cell type called “boundary vector cells” whose activity patterns encode an animal's distance, in a certain direction, from a salient geometrical border. Now Solstad et al. (p. 1865) provide experimental evidence for a cell type in the spatial representation circuit of the medial entorhinal cortex, termed the border cell, that fits the bill. Border cells have firing fields that line up along selected geometric boundaries of the proximal environment, irrespective of boundary length or continuity with other boundaries. Collectively, border cells may thus perhaps define the perimeter of the environment and thereby serve as a reference frame for places inside it, controlling the activity of the other position-sensing cell types in that environment.

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