immediate progenitors would need to be introduced to achieve structurally-accurate repair. In particular, it became clear that repair of the injured or diseased brain required the upfront determination of which cellular phenotypes, at which stages of their development, were most appropriate for treating which conditions. Fortunately, many diseases of the brain involve either single cell types or their immediate derivatives. Such conditions lend themselves to cell replacement, whether by the transplantation of single neuronal and glial phenotypes or their progenitors, or by the recruitment of new neurons or glia from endogenous stem and progenitor cells.
