 While rapid neurogenesis was known to occur in the early stages of life, the production and differentiation of neural stem cells was believed to cease upon maturity.This belief was overturned in the 1960s by the work of Joseph Altman.Using injections of thymidine-H3 to label the nuclei of dividing cells, Altman was able to use autoradiography to determine a neuronal birthdate for each cell in a rat's brain.