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Color Vision Goes Full Circuit

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By comparing a high-resolution visual input with the electrical output of the retina, E.J. Chichilnisky and his team were able to draw the first cell-by-cell circuit diagram of the retina, helping to explain how our brains perceive color.

Their measurements, published in the journal Nature, not only reveal computations in a neural circuit at the elementary resolution of individual neurons but also shed light on the neural code used by the retina to relay color information to the brain.

"Nobody has ever seen the entire inputoutput transformation performed by complete circuits in the retina at single-cell resolution," says senior author Chichilnisky, an associate professor in the Systems Neurobiology Laboratories. "We think these data will allow us to more deeply understand neuronal computations in the visual system and ultimately may help us construct better retinal implants."

Visual processing begins when photons entering the eye strike one or more of the 125 million light-sensitive nerve cells in the retina. This first layer of cells, which are known as rods and cones, converts the information into electrical signals and sends them to an intermediate layer, which in turn relays signals to the 20 or so distinct types of retinal ganglion cells, the neurons that carry visual signals to the brain.

It is known that color perception arises from the comparison of signals from different types of cones, but how these inputs are combined by ganglion cells has been less clear. The diagrams put together by Chichilnisky and his colleagues demonstrate how individual cones connect with complete populations of retinal ganglion cells, providing input-output maps of the retina at unprecedented resolution and scale that help to resolve an age-old debate.