Schematic showing how odour-induced neuronal activity in the nose of a mouse increases the lifespans of frequently activated neurons. Imagine that the mouse can smell orange cheese or blue cheese, so olfactory receptors for orange cheese and blue cheese are scattered across the turbinates in its nose (left). If the mouse is only ever exposed to orange cheese (middle), only those neurons that express the receptor for orange cheese are active, which increases their lifespan and, over time, leads to an increase in the number of receptors for orange cheese (right). However, a small number of receptors for blue cheese remain, and if the mouse was exposed to blue cheese, the number of these receptors would increase. Santoro and Dulac show that a protein called H2be has a central role in this process.