Before revision:  In mammals, the receptor neurons are replaced regularly, and the receptor distribution changes in response to olfactory experience.
After revision:  We propose an explanation for this striking fact: the receptor distribution is tuned to maximally represent information about the olfactory environment in a little-studied regime of efficient coding that is sensitive to the global context of correlated sensor responses. This model predicts further that in mammals, where olfactory sensory neurons are replaced regularly, and the receptor distribution changes in response to olfactory experience.