Prenatal Development of the Human Fetal Telencephalon

Human corticogenesis is perhaps the most complex process in the realm of biology, and also displays some unique (species-specific) features. There are major and clinically relevant differences in cortical development between rodents and humans, and they are reflected in the structure and function of the brain at every hierarchical level, from genes and cells to large neuronal assemblies and functional systems. For example, in comparison to rodents, the human cortex displays dramatically expanded fetal subplate zone, more complex and hugely expanded subventricular zone, significantly different process of initial cortical formation, more complex and diverse radial glial cells, Cajal–Retzius cells, and the subpial granular layer, as well as other unique transient fetal structures and/or features. These phylogenetic novelties contribute to the introduction of species-specific cell types (especially cortical interneurons), new cytoarchitectonic areas, and new patterns of connectivity and transmitter/receptor composition. Therefore, human-specific features of human brain are highly relevant for understanding the etiology of developmental brain disorders and for advancing their diagnostics and treatment. Fortunately, new noninvasive methods from neurohistology, neuroimaging, and genomics are making the human brain accessible for direct and detailed study as never before, and the number of these new and powerful methods for analyzing human brain development is rapidly increasing.