We investigated how entorhinal grid cells encode volumetric space. On a horizontal surface, grid cells usually produce multiple, spatially focal, approximately circular firing fields that are evenly sized and spaced to form a regular, close-packed, hexagonal array. This spatial regularity has been suggested to underlie navigational computations. In three dimensions, theoretically the equivalent firing pattern would be a regular, hexagonal close packing of evenly sized spherical fields. In the present study, we report that, in rats foraging in a cubic lattice, grid cells maintained normal temporal firing characteristics and produced spatially stable firing fields. However, although most grid fields were ellipsoid, they were sparser, larger, more variably sized and irregularly arranged, even when only fields abutting the lower surface (equivalent to the floor) were considered. Thus, grid self-organization is shaped by the environment’s structure and/or movement affordances, and grids may not need to be regular to support spatial computations.

我们研究了内嗅网格细胞如何编码体积空间。在水平表面上，网格单元通常会产生多个空间聚焦的近似圆形的发射场，这些发射场的大小和间距均匀，形成规则的、密排的六角形阵列。这种空间规律性被认为是导航计算的基础。在三个维度上，理论上等效的发射模式将是规则的、六角形的、大小均匀的球形区域的紧密堆积。在本研究中，我们报告说，在立方晶格中觅食的大鼠中，网格细胞保持正常的时间放电特性并产生空间稳定的放电场。然而，尽管大多数网格场是椭圆形的，但它们更稀疏、更大、大小更可变且排列不规则，即使仅考虑与下表面（相当于地板）相邻的区域。因此，网格自组织由环境的结构和/或运动可供性决定，并且网格可能不需要规则来支持空间计算。