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Michael B Manookin, James A Kuchenbecker, Maureen Neitz, Jay Neitz; In search of the color-coding ganglion cell. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3578. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
In 1966 De Valois et al. proposed that primate color vision is based on spectrally opponent neurons early in the visual pathway, the responses of which they had characterized with diffuse spectral lights. However, problems were soon realized when Wiesel and Hubel examined spatial aspects of the receptive fields of the same cells. Red-green spectrally opponent responses were also spatially segregated in a center-surround fashion. Such cells responded poorly to diffuse white light covering both center and surround of the receptive field, but if white light covers the center and only part of the surround then the cell is perfectly capable of mediating black and white sensations. Moreover, it became clear that red-green opponent, “type I” midget ganglion cells sample the retinal image at sufficiently high frequency to be responsible for high acuity spatial vision. In the face of these problems, the possibility has been repeatedly raised of a yet undiscovered ganglion cell type, responsible for color perception being present in the retina. Here we return to this idea and go in search of the color coding ganglion cell.
Spike responses and whole-cell currents were measured from ganglion cells in an in vitro preparation of the macaque retina. L, M and S cone isolating gratings were used to measure spatio-chromatic properties. A custom LED DLP light source provided S-cone isolating stimuli with higher contrast than possible with standard video displays. An imperial method was used to fine tune S-cone isolation at each retinal location recorded from. Lucifer yellow or neurobiotin was added to the pipette solution to recover the morphology of cells after recording.
In our case, the color coding cells are proposed to be a subset of midget ganglion cells that receive S cone input via a GABA feedforward mechanism, which is enhanced in primates for color vision. While the majority of midget ganglion cells tested gave no response to S-cone isolating stimuli, we found evidence for a minority population of midget ganglion cells in which S-cone input is added to the red-green spectrally opponent response.
Midget ganglion cells with S-cone input added to red-green opponent responses may explain aspects of human color vision physiology that have remained mysterious including why the unique hues lie along axes rotated in color space compared to the cardinal directions and how chromatic and achromatic percepts are separated.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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