[Layer I neurons and their significance in the neocortex embryogenesis]

Abstract

The literature data and the results of authors own investigations are presented on microarchitectonics and development of molecular layer (layer I) of mammalian neocortex. It originates from the marginal zone of primordial plexiform layer, common with primitive neopallial primordium of reptiles and amphibia, which maintains its initial organization during phylo- and ontogenesis of vertebrates. During initial stages of corticogenesis all migrating neurons establish contacts with Cajal-Retzius cells which coordinate location and exact spatial stratification of neuroblasts in growing cortical plate. The detailed analysis of fundamental mechanisms controlling embryogenesis of neocortex is presented including a) histogenesis of pyramidal and non-pyramidal neurons; b) unifying theory of cytoarchitectonic differentiation of neocortex proposed by M. Marin-Padilla; c) factors of cytoarchitectonic differentiation of cortical areas and specialization of brain hemispheres in mammalian ontogenesis and evolution. The thesis, according to which morphofunctional maturation of both pyramidal and non-pyramidal neurons begins as a result of their contacts with a system of thalamocortical afferent fibers, is substantiated. They grow from the subcortical white matter, initiate layer-by-layer ascending cortical maturation and, ultimately, divide it into descrete functional territories.