Ohki Kenichi, Chung Sooyoung, Kara Prakash, Hübener Mark, Bonhoeffer Tobias, Reid R Clay
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Nature. 2006 Aug 24;442(7105):925-8. doi: 10.1038/nature05019. Epub 2006 Aug 13.
In the visual cortex of higher mammals, neurons are arranged across the cortical surface in an orderly map of preferred stimulus orientations. This map contains 'orientation pinwheels', structures that are arranged like the spokes of a wheel such that orientation changes continuously around a centre. Conventional optical imaging first demonstrated these pinwheels, but the technique lacked the spatial resolution to determine the response properties and arrangement of cells near pinwheel centres. Electrophysiological recordings later demonstrated sharply selective neurons near pinwheel centres, but it remained unclear whether they were arranged randomly or in an orderly fashion. Here we use two-photon calcium imaging in vivo to determine the microstructure of pinwheel centres in cat visual cortex with single-cell resolution. We find that pinwheel centres are highly ordered: neurons selective to different orientations are clearly segregated even in the very centre. Thus, pinwheel centres truly represent singularities in the cortical map. This highly ordered arrangement at the level of single cells suggests great precision in the development of cortical circuits underlying orientation selectivity.
在高等哺乳动物的视觉皮层中，神经元在皮层表面按照偏好刺激方向的有序图谱排列。该图谱包含“方向风车”，其结构类似车轮的辐条，使得方向围绕一个中心连续变化。传统光学成像首次证实了这些风车结构，但该技术缺乏空间分辨率来确定风车中心附近细胞的反应特性和排列方式。后来的电生理记录显示在风车中心附近存在具有敏锐选择性的神经元，但它们是随机排列还是有序排列仍不清楚。在这里，我们使用体内双光子钙成像以单细胞分辨率确定猫视觉皮层中风车中心的微观结构。我们发现风车中心高度有序：即使在最中心区域，对不同方向有选择性的神经元也明显分隔开。因此，风车中心确实代表了皮层图谱中的奇点。单细胞水平上这种高度有序的排列表明，在形成方向选择性的皮层回路的发育过程中具有很高的精确性。
