Shearing-induced asymmetry in entorhinal grid cells

摘要

Grid cells are neurons with periodic spatial receptive fields (grids) that tile two-dimensional space in a hexagonal pattern. To provide useful information about location, grids must be stably anchored to an external reference frame. The mechanisms underlying this anchoring process have remained elusive. Here we show in differently sized familiar square enclosures that the axes of the grids are offset from the walls by an angle that minimizes symmetry with the borders of the environment. This rotational offset is invariably accompanied by an elliptic distortion of the grid pattern. Reversing the ellipticity analytically by a shearing transformation removes the angular offset. This, together with the near-absence of rotation in novel environments, suggests that the rotation emerges through non-coaxial strain as a function of experience. The systematic relationship between rotation and distortion of the grid pattern points to shear forces arising from anchoring to specific geometric reference points as key elements of the mechanism for alignment of grid patterns to the external world.%内嗅皮层的神经网格细胞在一个熟悉环境的表面上以空间网格模式发射信号，来为大脑提供关于动物周围环境情况的一幅内部地图。我们对环境边界在这一模式形成中所起作用并不是很了解。早期研究表明，网格细胞的信号发射模式的对称性、取向和尺度等特性是独立于环境形状的。但现在，本期Nature上发表的两篇单独的论文（一篇来自Edvard Moser及同事，另一篇来自John O'Keefe及同事）表明，网格取向、尺度、对称性和均一性会受到环境几何的强烈影响，其中与环境边界排列一致的网格细胞有几度的偏离，以使与边界的对称性最小化。这些发现为环境的几何特征怎样造成网格细胞的六边形信号发射模式的局部转动和变形提出了一个机制。