Mammalian Cerebral Cortex: Embryonic Development and Cytoarchitecture

Abstract

The prenatal developmental of the mammalian cerebral cortex, including that of humans, is characterized by two sequential and interrelated periods: an early embryonic and a late fetal one. The embryonic period is characterized by the establishment of a primordial cortical organization, which is common to all mammals and shares features with the primitive (primordial) cortex of amphibians and reptiles (Marín-Padilla 1971, 1978, 1983, 1992, 1998). Its establishment represents a prerequisite for the subsequent formation, development, and organization of the pyramidal cell plate (PCP), (cortical plate (CP) in current nomenclature), which represents a mammalian innovation. The original description of the dual origin and composition of the mammalian neocortex has been corroborated and, today, is universally accepted. The mammalian fetal period is characterized by the sequential, ascending, and stratified organization of the PCP, which represents the most distinguishing feature of the mammalian cerebral cortex. The term pyramidal cell plate (PCP), used in the present monograph, replaces the current unspecific term of cortical plate (CP) for various reasons. The early PCP is composed solely of pyramidal neurons and represents the mammalian neocortex’s most distinguishing feature (Chapters 3 and 4). Other neuronal elements are incorporated into the PCP later in prenatal development (Chapter 6). The progressive ascending and stratified anatomical and functional maturations of the PCP from lower (older) to upper (younger) pyramidal neurons are concomitant with the ascending and also stratified incorporation and maturation of its associated fibrillar, synaptic, excitatory-inhibitory, microvascular, and neuroglial systems (Chapters 4, 6–8).