Activation of endogenous neurogenesis has therapeutic potential for neurodegenerative conditions. Walker et al. found that neurospheres of latent precursor cells derived from adult mouse hippocampus increased in number by 50% following exposure to the peptide hormone prolactin (PRL). Conversely, PRL-null mice had fewer hippocampal-derived neurospheres and showed learning and memory deficits, suggesting a link between the influence of PRL on cell proliferation and behaviour.