Neurons show their true colours

How do we tell red from green? Work on the primate retina shows how neural circuitry combines signals from individual cone photoreceptor cells to provide the basic building blocks for colour vision. See Article p.673 Colour vision arises in the retina, and in primates the first stage of processing consists of overlapping lattices of cone cells and ganglion cells, each of which samples visual space uniformly. Colour perception arises from the comparison of signals from different cone types, but how these inputs are combined by the ganglion cells, which transmit the output of the retina, has been an issue of contention over the years. Using large-scale multi-electrode arrays and fine-grained visual stimulation, Field et al. have now mapped out the location and type of single-cone inputs to entire populations of ganglion cells, resulting in input–output maps at an unprecedented resolution and scale.