Unlike the peripheral nervous system (PNS), the central nervous system, including the brain, contains many interneurons. In the neocortex (making up about 80% of the human brain), approximately 20-30% of neurons are interneurons.[1] Investigations into the molecular diversity of neurons is impeded by the inability to isolate cell populations born at different times for gene expression analysis. An effective means of identifying coetaneous interneurons is neuronal birthdating.[2] This can be achieved using nucleoside analogs such as EdU.[3][5]