Aboitiz Francisco, Montiel Juan, Morales Daniver, Concha Miguel
Programa de Morfología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
Brain Res Brain Res Rev. 2002 Sep;39(2-3):141-53. doi: 10.1016/s0165-0173(02)00180-7.
The isocortex is a distinctive feature of the mammalian brain, with no clear counterpart in other amniotes. There have been long controversies regarding possible homologues of this structure in reptiles and birds. The brains of the latter are characterized by the presence of a structure termed dorsal ventricular ridge (DVR), which receives ascending auditory and visual projections, and has been postulated to be homologous to parts of the mammalian isocortex (i.e., the auditory and the extrastriate visual cortices). Dissenting views, now supported by molecular evidence, claim that the DVR originates from a region termed ventral pallium, while the isocortex may arise mostly from the dorsal pallium (in mammals, the ventral pallium relates to the claustroamygdaloid complex). Although it is possible that in mammals the embryonic ventral pallium contributes cells to the developing isocortex, there is no evidence yet supporting this alternative. The possibility is raised that the expansion of the cerebral cortex in the origin of mammals was product of a generalized dorsalizing influence in pallial development, at the expense of growth in ventral pallial regions. Importantly, the evidence suggests that organization of sensory projections is significantly different between mammals and sauropsids. In reptiles and birds, some sensory pathways project to the ventral pallium and others project to the dorsal pallium, while in mammals sensory projections end mainly in the dorsal pallium. We suggest a scenario for the origin of the mammalian isocortex which relies on the development of associative circuits between the olfactory, the dorsal and the hippocampal cortices in the earliest mammals.
新皮质是哺乳动物大脑的一个显著特征，在其他羊膜动物中没有明显的对应结构。关于这种结构在爬行动物和鸟类中可能的同源物一直存在长期争议。后者的大脑以存在一种称为背侧室嵴（DVR）的结构为特征，该结构接收听觉和视觉的上行投射，并被假定与哺乳动物新皮质的部分区域（即听觉和纹外视觉皮质）同源。现在有分子证据支持的不同观点认为，DVR起源于一个称为腹侧皮质的区域，而新皮质可能主要起源于背侧皮质（在哺乳动物中，腹侧皮质与屏状核 - 杏仁复合体有关）。尽管在哺乳动物中胚胎腹侧皮质可能为发育中的新皮质提供细胞，但尚无证据支持这一观点。有人提出，哺乳动物起源时大脑皮质的扩张是皮质发育中普遍的背侧化影响的产物，代价是腹侧皮质区域的生长。重要的是，证据表明哺乳动物和蜥形纲动物的感觉投射组织有显著差异。在爬行动物和鸟类中，一些感觉通路投射到腹侧皮质，另一些投射到背侧皮质，而在哺乳动物中，感觉投射主要终止于背侧皮质。我们提出了一种关于哺乳动物新皮质起源的设想，它依赖于最早的哺乳动物中嗅觉皮质、背侧皮质和海马皮质之间联合回路的发展。
