Convergent motifs of early olfactory processing are recapitulated by layer-wise efficient coding

The architecture of early olfactory processing is a striking example of convergent evolution. Typically, a panel of broadly tuned receptors is selectively expressed in sensory neurons (each neuron expressing only one receptor), and each glomerulus receives projections from just one neuron type. Taken together, these three motifs--broad receptors, selective expression, and glomerular convergence--constitute "canonical olfaction," since a number of model organisms including mice and flies exhibit these features. The emergence of this distinctive architecture across evolutionary lineages suggests that it may be optimized for information processing, an idea known as efficient coding. In this work, we show that by maximizing mutual information one layer at a time, efficient coding recovers several features of canonical olfactory processing under realistic biophysical assumptions. We also explore the settings in which noncanonical olfaction may be advantageous. Along the way, we make several predictions relating olfactory circuits to features of receptor families and the olfactory environment.