Much excitement has been generated by the identification of adult brain regions harboring neural stem cells and their continual generation of new neurons throughout life. This is an important departure from traditional views of the germinal potential of the postnatal brain. However, a more profound paradigm shift may be emerging. Studies of adult neurogenesis in the subventricular zone (SVZ) have revealed unexpected properties of neuronal progenitors and new mechanisms of neuronal migration. Here we discuss some recent findings that examine the origin, migration, and function of SVZ-derived new neurons in adult brain and highlight areas that offer exiting opportunities for future research.

Along much of the lateral walls of the lateral ventricles lies the largest germinal zone of the adult mammalian brain, the SVZ (Doetsch and Alvarez-Buylla, 1996). In fully adult mammals, mew neurons born in the SVZ of adults migrate anteriorly into the olfactory bulb (OB), where they mature into local interneurons (Altman, 1969; Lois and Alvarez-Buylla, 1994; Kornack and Rakic, 2001; Pencea et al., 2001a)(Fig. 1). SVZ neural stem cells can be grown in culture with epidermal growth factor (EGF), fibroblast growth factor (FGF), or the two combined (Weiss et al., 1996; Temple and Alvarez-Buylla, 1999; Gage, 2000). As such, the SVZ represents an important reservoir of progenitors in the adult brain, perhaps harboring cell populations that could be used for neuroregenerative therapy. These findings dramatically change the way we think about the adult brain. However, a deeper paradigm shift may be emerging as these discoveries raised basic mechanistic questions not easily explained by classical views of brain development.