Wässle H, Grünert U, Röhrenbeck J, Boycott B B
Max-Planck-Institut für Hirnforschung, Neuroanatomie, Deutschordenstr. Frankfurt, F.R.G.
Vision Res. 1990;30(11):1897-911. doi: 10.1016/0042-6989(90)90166-i.
The question of whether the large area occupied by the primate fovea in the visual cortex (V1) is the result of a selective amplification of the central visual field, or whether it merely reflects the ganglion cell density of the retina, has been a subject of debate for many years. Measurements of the ganglion cell densities are made difficult by lateral displacements of cells around the fovea and the occurrence of amacrine cells in the ganglion cell layer. We have now identified and counted these amacrine cells by GABA immunocytochemistry and by retrograde degeneration of ganglion cells. By reconstructing the fovea from vertical and horizontal serial sections, we were able to measure the densities of cones, cone pedicles and ganglion cells within the same retina. We found 3-4 ganglion cells for every foveal cone. This ratio decreased to one ganglion cell per cone at an eccentricity of 15-20 deg (3-4 mm) and in peripheral retina there are more cones than ganglion cells. The ganglion cell density changes by a factor of 1000-4000 between peripheral and central retina. A comparable gradient has been reported for the representation of the peripheral and central visual field in V1. We suggest that ganglion cell density can fully account for the cortical magnification factor and there is no need to postulate a selective amplification of the foveal representation.
灵长类动物中央凹在视觉皮层（V1）中占据的大面积区域，究竟是中央视野选择性放大的结果，还是仅仅反映了视网膜神经节细胞的密度，多年来一直是一个争论的话题。由于中央凹周围细胞的侧向移位以及神经节细胞层中无长突细胞的存在，使得神经节细胞密度的测量变得困难。我们现在通过GABA免疫细胞化学和神经节细胞的逆行变性来识别和计数这些无长突细胞。通过从垂直和水平连续切片重建中央凹，我们能够测量同一视网膜内视锥细胞、视锥细胞蒂和神经节细胞的密度。我们发现每个中央凹视锥细胞对应3 - 4个神经节细胞。在离心率为15 - 20度（3 - 4毫米）时，这个比例降至每个视锥细胞一个神经节细胞，并且在周边视网膜中视锥细胞比神经节细胞更多。神经节细胞密度在周边视网膜和中央视网膜之间变化了1000 - 4000倍。据报道，V1中周边视野和中央视野的表征也有类似的梯度变化。我们认为神经节细胞密度可以充分解释皮层放大因子，无需假定中央凹表征存在选择性放大。
