尽管哺乳动物大脑皮层最常被描述为六层结构,有皮质区域(初级运动皮质)和物种(大象,鲸目动物,和河马),在细胞结构上模糊的地方,或缺席,注意层4。丘脑皮质从核心投射,或一阶,丘脑系统主要终止于层4/内层3。我们使用囊泡谷氨酸转运蛋白2的免疫定位,探索了皮质区域和没有细胞结构上不同的层4的物种中核心丘脑皮质投射的终止位点,囊泡谷氨酸转运蛋白2是核心丘脑皮质轴突末端的已知标记,在31种哺乳动物中跨越了异路人的辐射。注意到第4层的规范皮质柱轮廓和核心丘脑皮质输入的几种变化。在泼妇/小翅目动物中,第4层存在,但是除了层4和内层3之外,许多核心的丘脑皮质突起在层1中终止。在灵长类初级视觉皮层,次层压层4与特殊的核心丘脑皮质投射模式相关。在灵长类初级运动皮层,没有明显的细胞结构上不同的层4,并且整个层3的核心丘脑皮质突起终止。在非洲大象中,鲸目动物,河马,未观察到细胞结构上不同的层4,核心丘脑皮质突起主要在内层3中终止,而在外层3中密度较低。这些发现在皮层处理方面进行了背景化,感知,以及导致皮层模糊或缺失的进化轨迹4。
Although the mammalian cerebral cortex is most often described as a hexalaminar structure, there are cortical areas (primary motor cortex) and species (elephants, cetaceans, and hippopotami), where a cytoarchitecturally indistinct, or absent, layer 4 is noted. Thalamocortical projections from the core, or first order, thalamic system terminate primarily in layers 4/inner 3. We explored the termination sites of core thalamocortical projections in cortical areas and in species where there is no cytoarchitecturally distinct layer 4 using the immunolocalization of vesicular glutamate transporter 2, a known marker of core thalamocortical axon terminals, in 31 mammal species spanning the eutherian radiation. Several variations from the canonical cortical column outline of layer 4 and core thalamocortical inputs were noted. In shrews/microchiropterans, layer 4 was present, but many core thalamocortical projections terminated in layer 1 in addition to layers 4 and inner 3. In primate primary visual cortex, the sublaminated layer 4 was associated with a specialized core thalamocortical projection pattern. In primate primary motor cortex, no cytoarchitecturally distinct layer 4 was evident and the core thalamocortical projections terminated throughout layer 3. In the African elephant, cetaceans, and river hippopotamus, no cytoarchitecturally distinct layer 4 was observed and core thalamocortical projections terminated primarily in inner layer 3 and less densely in outer layer 3. These findings are contextualized in terms of cortical processing, perception, and the evolutionary trajectory leading to an indistinct or absent cortical layer 4.