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W. Li, S.H. DeVries; Bipolar Cell Pathways for Color and Luminance Vision in a Dichromatic Mammalian Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2310.
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In dichromats, which comprise most mammals, a minority population of short wavelength (blue or UV)–sensitive cones is distributed among a much larger population of medium wavelength (green)–sensitive cones. The cone array is then sampled by roughly ten bipolar cell types, and the sampling pattern determines how retinal ganglion cells, and ultimately higher visual centers, encode color, luminance, and spatial detail. With the exception of a blue cone specific bipolar cell, little is known about how the signals in blue and green cones are processed by the remaining "diffuse" bipolar cell types.
Using anatomical methods and simultaneous whole cell recordings from presynaptic cones and postsynaptic bipolar cells, we have examined the synapses between both blue and green cones and a systemic sample of different bipolar cell types in the ground squirrel retina.
We have identified a luminance pathway consisting of two bipolar cell types in which green and blue signals are mixed. All other recorded diffuse bipolar cells carry signals from only green cones, facilitating the discrimination of color and spatial detail.
The blue cone signals are included in the bipolar cells for the achromatic luminance pathway and, perhaps more importantly, excluded from the bipolar cells processing color and high–acuity visual information. Parallel visual channels are sorted according to cone type into distinct bipolar cell pathways at the first synapse in the retina.
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