Development and Developmental Disorders of the Cerebral Cortex

The cerebral cortex can be divided into a large isocortex, a much smaller allocortex (the hippocampal formation and the olfactory cortex), and a transition zone (the mesocortex) in between. Although many individual variations exist in the sulcal pattern and in the extent of the various cortical areas, the remarkable conservation of the pattern of areal divisions within the human brain suggests the existence of a highly conserved and rather rigidly regulated regional specification programme that controls their development. Histogenesis of the cerebral cortex progresses through three major phases: cell production, cell migration, and cortical differentiation and maturation. Migrating cells from the ventricular zone to the cortical plate form ontogenetic radial cell columns. An important role in neurogenesis for the outer part of the subventricular zone became evident. During the last decades, analysis of the genetic control of cortical development became possible. Mechanisms for induction and regionalization of the cerebral cortex are being unravelled and genes that are implicated in controlling regionalization, arealization, and differentiation have been discovered in the mouse brain. This neurogenetic approach has given a great impetus to the study of neuronal migration disorders (NMDs). Advances in neurogenetics and the increasing application of magnetic resonance imaging (MRI) resulted in the distinction of a growing number of NMDs, of many of which the gene involved has been discovered. In this chapter, after a brief overview of the cerebral cortex (• Sect. 10.2) and its main connections (• Sect. 10.3), the development of the isocortex (• Sect. 10.4), the hippocampus (• Sect. 10.5), and their main fibre systems, including diffusion tensor imaging data in the fetal brain (• Sect. 10.6), are discussed, followed by an overview of developmental disorders of the cerebral cortex. Malformations of cortical development (MCDs) include malformations due to abnormal cell production (• Sect. 10.7.1), abnormal migration (• Sect. 10.7.2), abnormal cortical organization (• Sect. 10.7.3), vascular disorders (• Sect. 10.7.5), and disorders of cortical connectivity (• Sect. 10.7.6). Many of these result in epilepsy (• Sect. 10.7.4) and/or intellectual disability (• Sect. 10.7.7). In • Sect. 10.7.8, some neurobehavioural disorders are briefly reviewed, followed by a brief discussion of the development of language and some congenital language disorders (• Sect. 10.8). Throughout the chapter, clinical cases are presented and illustrated with MRI and autopsy data.