A neural stem cell generates multipotent progeny which can differentiate into neurons, astrocytes, and oligodendrocytes. A neural progenitor cell possesses limited self-renewal capacity and differentiation potential3. Neural stem and progenitor cells are collectively referred to as NPCs. Historically, NPCs were thought to exist only in the developing brain, while the adult mammalian brain was presumed post-mitotic and devoid of regenerative capacity. However, seminal works by Reynolds and Weiss showed the presence of NPCs in the adult mammalian central nervous system (CNS). These studies used a colony forming assay which involved the dissection and plating of mouse CNS cells, including the periventricular region lining the forebrain lateral ventricles. Cells were cultured in the presence of epidermal growth factor (EGF) and after 7 d in vitro, clonally derived free floating colonies (termed neurospheres) were observed. Individual neurospheres could be dissociated, replated in EGF, and passaged indefinitely thereby revealing the stem cell property of self-renewal. The cells were also shown to differentiate into the three CNS cell-types, confirming their multipotentiality. The discovery of NPCs in the adult brain offered new hope for the possibility of regeneration in the adult brain.