Functional connectivity in the retina at the resolution of photoreceptors

To understand a neural circuit requires knowledge of its connectivity. Here we report measurements of functional connectivity between the input and ouput layers of the macaque retina at single-cell resolution and the implications of these for colour vision. Multi-electrode technology was used to record simultaneously from complete populations of the retinal ganglion cell types (midget, parasol and small bistratified) that transmit high-resolution visual signals to the brain. Fine-grained visual stimulation was used to identify the location, type and strength of the functional input of each cone photoreceptor to each ganglion cell. The populations of ON and OFF midget and parasol cells each sampled the complete population of long- and middle-wavelength-sensitive cones. However, only OFF midget cells frequently received strong input from short-wavelength-sensitive cones. ON and OFF midget cells showed a small non-random tendency to selectively sample from either long- or middle-wavelength-sensitive cones to a degree not explained by clumping in the cone mosaic. These measurements reveal computations in a neural circuit at the elementary resolution of individual neurons. 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. Colour perception arises from the comparison of signals from different cone types, but how these inputs are combined by ganglion cells, which transmit the output of the retina, has been an issue of contention. Using large-scale multi-electrode arrays and fine-grained visual stimulation, these authors map out the locations and types of single-cone inputs to entire populations of ganglion cells, resulting in input–output maps at an unprecedented resolution and scale.