The generation of human embryonic stem cells (ES cells) and induced pluripotent stem cells (iPS cells) and their in vitro differentiation into potentially any desired cell type holds great promise, and may revolutionize the study of human disease (Hanna et al., 2010; Okita and Yamanaka, 2011; Blanpain et al., 2012). Given the lack of alternative sources, a major effort has been directed towards the development of differentiation protocols that convert pluripotent stem cells into neurons to allow examination of healthy human neurons and of neurons derived from patients with a variety of neurological diseases. In this approach, fibroblasts from patients with poorly understood diseases – such as schizophrenia or Alzheimer’s disease – are converted into iPS cells that are then differentiated into neurons to study the pathogenesis of these diseases (reviewed in Han et al., 2011; Ming et al., 2011; Brennand et al., 2012; Marchetto and Gage 2012). Moreover, elegant studies have described differentiation protocols that produce distinct types of neurons in vitro, although the number and properties of different types of human neurons in situ are largely unknown and
