Umemori spent several years scanning neurons in culture for these pioneering molecules that set in motion the linking of neural networks. In the end he fingered a molecule called FGF22, along with several of its close relatives, as key to setting in motion the construction of synapses. Umemori confirmed FGF22's role by showing that mice in which FGF22 was inactivated failed to grow synapses; conversely, when added to neurons in culture, the molecule stimulates synapse formation.

Sanes and Umemori determined that FGF22 works to build synapses in the brain's cerebellum, a critical center for motor control; it's unclear whether it also serves as a signal to foster synapse growth between neurons in other areas. Two other members of the FGF family, FGF7 and FGF10, are very similar in structure, and may play similar roles in other areas of the nervous system.