Maunsell J H, Nealey T A, DePriest D D
Department of Physiology, University of Rochester, New York 14642.
J Neurosci. 1990 Oct;10(10):3323-34. doi: 10.1523/JNEUROSCI.10-10-03323.1990.
Many lines of evidence suggest that the visual signals relayed through the magnocellular and parvocellular subdivisions of the primate dorsal LGN remain largely segregated through several levels of cortical processing. It has been suggested that this segregation persists through to the highest stages of the visual cortex, and that the pronounced differences between the neuronal response properties in the parietal cortex and inferotemporal cortex may be attributed to differential contributions from magnocellular and parvocellular signals. We have examined this hypothesis directly by recording the responses of cortical neurons while selectively blocking responses in the magnocellular or parvocellular layers of the LGN. Responses were recorded from single units or multiunit clusters in the middle temporal visual area (MT), which is part of the pathway leading to parietal cortex and thought to receive primarily magnocellular inputs. Responses in the MT were consistently reduced when the magnocellular subdivision of the LGN was inactivated. The reduction was almost always pronounced and often complete. In contrast, parvocellular block rarely produced striking changes in MT responses and typically had very little effect. Nevertheless, unequivocal parvocellular contributions could be demonstrated for a minority of MT responses. At a few MT sites, responses were recorded while magnocellular and parvocellular blocks were made simultaneously. Responses were essentially eliminated for all these paired blocks. These results provide direct evidence for segregation of magnocellular and parvocellular contributions in the extrastriate visual cortex and support the suggestion that these signals remain largely segregated through the highest levels of cortical processing.
许多证据表明，通过灵长类动物背侧外侧膝状体的大细胞和小细胞亚区传递的视觉信号，在皮质处理的几个层次中基本保持分离。有人提出，这种分离一直持续到视觉皮层的最高阶段，并且顶叶皮层和颞下皮层神经元反应特性的显著差异可能归因于大细胞和小细胞信号的不同贡献。我们通过记录皮质神经元的反应，同时选择性地阻断外侧膝状体大细胞或小细胞层的反应，直接检验了这一假设。在颞中视觉区（MT）记录单个神经元或多神经元簇的反应，该区是通向顶叶皮层的通路的一部分，被认为主要接收大细胞输入。当外侧膝状体的大细胞亚区失活时，MT区的反应持续减弱。这种减弱几乎总是很明显，而且常常是完全的。相比之下，小细胞阻断很少能引起MT区反应的显著变化，通常影响很小。然而，少数MT区反应能明确显示小细胞的贡献。在少数MT区位点，同时进行大细胞和小细胞阻断时记录反应。对于所有这些成对阻断，反应基本消失。这些结果为纹外视觉皮层中大细胞和小细胞贡献的分离提供了直接证据，并支持了这些信号在皮质处理的最高层次中基本保持分离的观点。
