Multi-synaptic cortical organization for stereopsis of macaque

灵长类动物的视觉系统有两个主要特征：平行（背侧和腹侧）通路和分层信号处理。人们普遍认为，立体视觉信息不仅在背侧皮质区域加工，而且在腹侧皮质区域加工。然而，这两种通路的多突触结构尚不清楚。在这些平行路径中，MT和V4被认为位于相似的层次级别。为了重新评估MT和V4之间的层次关系，我们分析了狂犬病毒注射猕猴MT和V4后V1和LGN逆行转神经元标记的模式。结果表明，MT和V4可能在背侧和腹侧通路中通过LGN和V1的4C层处理信号，处于不同的层次。此外，LGN与MT或LGN与V4之间可能存在另一条通路。来自LGN的收敛的M和P输入可能有助于这些“捷径”路径中的信号处理。

The primate visual system is characterized by two principal rules : parallel (dorsal and ventral) pathways and hierarchic signal processing. It is well accepted that the information for stereopsis is processed not only in the dorsal cortical areas but also ventral cortical areas. However, multi-synaptic architecture of these two pathways is poorly understood. Within these parallel pathways, MT and V4 are recognized as being situated at a similar hierarchical rank. To re-evaluate the hierarchic relationship between MT and V4, the patterns of retrograde transneuronal labeling in V1 and LGN were analyzed after rabies virus injections into MT and V4 of macaque monkeys. The present results suggest that MT and V4 may be posited at different hierarchic ranks in signal processing in the dorsal and ventral pathways by way of LGN and layer 4C of V1. Moreover, there may be another pathway linking LGN and MT or LGN and V4. It is likely that converging M and P inputs from LGN may contribute to signal processing in these "short-cut" pathways.