Newly discovered rare cells could explain how humans see color

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Scientists have long wondered how the eye's three cone photoreceptor types work together to allow humans to perceive color. A A new study in Journal of Neuroscienceresearchers University of Rochester used adaptive optics to identify rare retinal ganglion cells (RGCs) that may help fill gaps in current theories of color perception.

The retina has three types of cones to detect color that are sensitive to short, medium or long wavelengths of light. Retinal ganglion cells send input from these cones to the central nervous system.

In the 1980s, David Williams, William G. Allen, a professor of medical optics, helped map the „cardinal directions” that explain color perception. However, there are differences in how the eye perceives color and the way color appears to humans. Scientists suspected that while most RGCs followed cardinal directions, they could combine with a small number of non-cardinal RGCs to create a more complex sensation.

Recently, a team of researchers from Rochester Center for Visual ScienceThe Optical InstituteAnd this Flume Eye Institute identified some of these elusive non-cardinal RGCs in the fovea that may explain how humans see red, green, blue, and yellow.

„We still don't know anything for sure other than that these cells exist,” says Sarah Patterson, a postdoctoral researcher at the Center for Visual Science who led the study. „There's a lot we need to know about how their response properties work, but they're a compelling option as the missing link in how our retinas process color.”

Using adaptive optics to overcome light distortion in the eye

The team used adaptive optics, which uses a deformable mirror to overcome light distortion and was originally developed by astronomers to reduce image blur in ground-based telescopes. In the 1990s, Williams and his colleagues began Using adaptive optics to study the human eye. They developed a camera that compensates for distortions caused by the natural aberrations of the eye, producing a clear image of individual photoreceptor cells.

„The optics of the eye's lens are imperfect and really reduce the amount of resolution you can get with an eyepiece,” Patterson says. „Adaptive optics detects and corrects these variations, giving the eye a crystal-clear appearance. It provides unprecedented access to retinal ganglion cells, which are the brain's sole source of visual information.

Improving our understanding of the retina's complex processes could eventually lead to better methods of restoring sight to the visually impaired, Patterson says.

„Humans have more than 20 ganglion cells, and our models of human vision are based on only three,” Patterson says. „There's a lot we don't know about the retina. It's one of those rare areas where engineering completely surpasses basic visual science. People have retinal prosthetics in their eyes now, but if we knew what all those cells were doing, we could actually direct retinal prosthetics ganglion cells to their true functional roles.

Note: Godat T, Kohout K, Parkins K, et al. Cone-opposed ganglion cells in the primate fovea tuned to non-cardinal color directions. J Neurosci. 2024:e1738232024. doi: 10.1523/JNEUROSCI.1738-23.2024

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