Conserved features of the primate face code

A recent paper demonstrated that the pattern of firing rates across ∼100 neurons in the anterior medial face patch is closely related to which human face (of 2,000) had been presented to a monkey [Chang L, Tsao DY (2017) Cell 169:1013-1028]. In addition, the firing rates for these neurons can be predicted for a novel human face. Although it is clear from this work that the firing rates of these face patch neurons encode faces, the properties of the face code have not yet been fully described. Based on an analysis of 98 neurons responding to 2,000 faces, I conclude that the anterior medial face patch uses a combinatorial rate code, one with an exponential distribution of neuron rates that has a mean rate conserved across faces. Thus, the face code is maximally informative (technically, maximum entropy) and is very similar to the code used by the fruit fly olfactory system.