Wolf F, Geisel T
Max-Planck-Institut für Strömungsforschung, Göttingen, Germany.
Nature. 1998 Sep 3;395(6697):73-8. doi: 10.1038/25736.
Neurons in the visual cortex respond preferentially to edge-like stimuli of a particular orientation. It is a long-standing hypothesis that orientation selectivity arises during development through the activity-dependent refinement of cortical circuitry. Unambiguous evidence for such a process has, however, remained elusive. Here we argue that, if orientation preferences arise through activity-dependent refinement of initially unselective patterns of synaptic connections, this process should leave distinct signatures in the emerging spatial pattern of preferred orientations. Preferred orientations typically change smoothly and progressively across the cortex. This smooth progression is disrupted at the centres of so-called pinwheels, where neurons exhibiting the whole range of orientation preferences are located in close vicinity. Assuming that orientation selectivity develops through a set of rules that we do not specify, we demonstrate mathematically that the spatial density of pinwheels is rigidly constrained by basic symmetry principles. In particular, the spatial density of pinwheels, which emerge when orientation selectivity is first established, is larger than a model-independent minimal value. As a consequence, lower densities, if observed in adult animals, are predicted to develop through the motion and annihilation of pinwheel pairs.
视觉皮层中的神经元优先对特定方向的边缘样刺激做出反应。长期以来的一个假设是，方向选择性在发育过程中通过依赖活动的皮质回路精细化而产生。然而，这种过程的确切证据仍然难以捉摸。在这里，我们认为，如果方向偏好是通过对最初无选择性的突触连接模式进行依赖活动的精细化而产生的，那么这个过程应该会在新兴的偏好方向空间模式中留下独特的印记。偏好方向通常在整个皮层中平滑且逐渐地变化。这种平滑的变化在所谓的风车中心被打乱，在那里展示了整个方向偏好范围的神经元紧密相邻。假设方向选择性是通过一组我们未详细说明的规则发展而来，我们通过数学证明，风车的空间密度受到基本对称原理的严格限制。特别是，当方向选择性首次确立时出现的风车空间密度大于一个与模型无关的最小值。因此，如果在成年动物中观察到较低的密度，预计是通过风车对的移动和湮灭而形成的。
