Calkins D J, Sterling P
Department of Neuroscience, University of Pennsylvania, Philadelphia 19104, USA.
Nature. 1996 Jun 13;381(6583):613-5. doi: 10.1038/381613a0.
Visual information is conveyed to the brain by the retinal ganglion cells. Midget ganglion cells serve fine spatial vision by summing excitation from a receptive field 'centre', receiving input from a single cone in the central retina, with lateral inhibition from a receptive field 'surround', receiving input from many surrounding cones. Midget ganglion cells are also thought to serve colour opponent vision because the centre excitation is from a cone of one spectral type, while the surround inhibition is from cones of the other type. The two major cone types, middle(M)- and long-(L)wavelength sensitive, are equally numerous and randomly distributed in the primate central retina, so a spectrally homogeneous surround requires that the cells mediating lateral interactions (horizontal or amacrine cells) receive selective input from only one cone type. Horizontal cells cannot do this because they receive input indiscriminately from M and L cones. Here we report that the amacrine cells connected to midget ganglion cells are similarly indiscriminate. The absence of spectral specificity in the inhibitory wiring raises doubt about the involvement of midget ganglion cells in colour vision and suggest that colour opponency may instead be conveyed by a different type of ganglion cell.
视觉信息由视网膜神经节细胞传递至大脑。侏儒神经节细胞通过整合来自感受野“中心”的兴奋来实现精细的空间视觉，该“中心”接收来自中央视网膜单个视锥细胞的输入，并受到来自感受野“周边”的侧向抑制，“周边”接收来自许多周边视锥细胞的输入。侏儒神经节细胞也被认为参与色拮抗视觉，因为中心兴奋来自一种光谱类型的视锥细胞，而周边抑制来自另一种类型的视锥细胞。两种主要的视锥细胞类型，即中波（M）和长波（L）敏感型，在灵长类动物的中央视网膜中数量相等且随机分布，因此光谱均匀的周边要求介导侧向相互作用的细胞（水平细胞或无长突细胞）仅从一种视锥细胞类型接收选择性输入。水平细胞无法做到这一点，因为它们不加区分地接收来自M和L视锥细胞的输入。在这里，我们报告与侏儒神经节细胞相连的无长突细胞同样不加区分。抑制性连接中缺乏光谱特异性，这让人怀疑侏儒神经节细胞是否参与色觉，并表明色拮抗可能反而由另一种类型的神经节细胞传递。
