Major events in the development of the forebrain.

The development of the central nervous system can be divided into a number of phases, each of which is characterized by particular developmental disorders. In recent years, much progress has been made in elucidating the mechanisms by which the forebrain develops and in our understanding of major developmental disorders such as holoprosencephaly and neuronal migration disorders. In this general introduction to this symposium the major stages in the development of the forebrain, its regionalization and the genes involved, and some of the developmental disorders derailing cortical development with subsequent damage to the main cortical fiber connections (pyramidal tract and corpus callosum) are discussed.