The tremendous complexity of the adult forebrain makes it a challenging task to elucidate
how this structure forms during embryonic development. Nevertheless, we are beginning to
understand how a simple epithelial sheet of ectoderm gives rise to the labyrinthine network
of cells that constitutes the functional forebrain. Here, we discuss early events in forebrain
development—those that lead to the establishment of the anterior neural plate and the
regional subdivision of this territory into the different domains of the prospective forebrain.