Manger P R, Rosa M G P
School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa.
Neuroscience. 2005;130(2):497-511. doi: 10.1016/j.neuroscience.2004.09.047.
We studied thalamic projections to the visual cortex in flying foxes, animals that share neural features believed to resemble those present in the brains of early primates. Neurones labeled by injections of fluorescent tracers in striate and extrastriate cortices were charted relative to the architectural boundaries of thalamic nuclei. Three main findings are reported: First, there are parallel lateral geniculate nucleus (LGN) projections to striate and extrastriate cortices. Second, the pulvinar complex is expansive, and contains multiple subdivisions. Third, across the visual thalamus, the location of cells labeled after visual cortex injections changes systematically, with caudal visual areas receiving their strongest projections from the most lateral thalamic nuclei, and rostral areas receiving strong projections from medial nuclei. We identified three architectural layers in the LGN, and three subdivisions of the pulvinar complex. The outer LGN layer contained the largest cells, and had strong projections to the areas V1, V2 and V3. Neurones in the intermediate LGN layer were intermediate in size, and projected to V1 and, less densely, to V2. The layer nearest to the origin of the optic radiation contained the smallest cells, and projected not only to V1, V2 and V3, but also, weakly, to the occipitotemporal area (OT, which is similar to primate middle temporal area) and the occipitoparietal area (OP, a "third tier" area located near the dorsal midline). V1, V2 and V3 received strong projections from the lateral and intermediate subdivisions of the pulvinar complex, while OP and OT received their main thalamic input from the intermediate and medial subdivisions of the pulvinar complex. These results suggest parallels with the carnivore visual system, and indicate that the restriction of the projections of the large- and intermediate-sized LGN layers to V1, observed in present-day primates, evolved from a more generalized mammalian condition.
我们研究了果蝠丘脑向视觉皮层的投射，果蝠具有一些被认为与早期灵长类动物大脑中存在的神经特征相似的神经特征。通过在纹状皮层和纹外皮层注射荧光示踪剂标记的神经元，相对于丘脑核的结构边界进行了绘图。报告了三个主要发现：第一，外侧膝状体核（LGN）向纹状皮层和纹外皮层有平行投射。第二，丘脑枕复合体范围广泛，包含多个亚区。第三，在整个视觉丘脑中，视觉皮层注射后标记细胞的位置有系统地变化，尾侧视觉区域从最外侧的丘脑核接收最强的投射，而头侧区域从内侧核接收强投射。我们确定了LGN中的三个结构层以及丘脑枕复合体的三个亚区。LGN外层包含最大的细胞，并向V1、V2和V3区有强投射。LGN中间层的神经元大小居中，投射到V1区，投射到V2区的密度较低。最靠近视辐射起始处的层包含最小的细胞，不仅投射到V1、V2和V3区，还微弱地投射到枕颞区（OT，类似于灵长类动物的中颞区）和枕顶区（OP，位于背中线附近的“第三层”区域）。V1、V2和V3区从丘脑枕复合体的外侧和中间亚区接收强投射，而OP和OT区从丘脑枕复合体的中间和内侧亚区接收主要的丘脑输入。这些结果表明与食肉动物视觉系统有相似之处，并表明在现代灵长类动物中观察到的LGN大、中尺寸层投射仅限于V1区的情况，是从更普遍的哺乳动物状态演变而来的。
