Proc. Natl Acad. Sci. USA 106, 19150–19155 (2009)

Patients undergoing irradiation for brain tumours often display signs of cognitive dysfunction, owing in part to the loss of healthy neural stem and precursor cells. To investigate possible treatments, Charles Limoli of the University of California, Irvine, and his colleagues injected human embryonic stem cells into the brains of irradiated rats. After four months, the researchers confirmed the cells' survival in the rats' brains and found that the animals performed much better in a place-recognition task compared with irradiated rats that did not receive the transplant.