This picture shows Purkinje cells (green), proliferating cells (cyan), and cell nuclei (purple) in a postnatal day 7 mouse cerebellum. The p75 neurotrophin receptor promotes cell-cycle exit by proliferating cerebellar granule cell precursors. Loss of this receptor prolongs granule cell precursor proliferation, resulting in increased glutamatergic input to Purkinje cells and deficits cerebellum dependent learning. For more information, see the article by Zanin et al. (pages 9119–9129).