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Midget pathways of the primate retina underlie resolution and red green color opponency.


Kolb H.


In: Kolb H, Fernandez E, Nelson R, editors.


Webvision: The Organization of the Retina and Visual System [Internet]. Salt Lake City (UT): University of Utah Health Sciences Center; 1995-.
2007 May 24 [updated 2012 Apr 04].


The specialized cone pathways of the central fovea of human and monkey retinas have the least convergence and the greatest resolution capabilities of the visual system. This is accomplished by making the connections as “private” as possible and narrowing them to a one to one relationship in the so-called midget pathways. Figure 1 shows an older drawing from Polyak’s book (1) that shows the very narrowest field bipolars and ganglion cells of the fovea. The midget pathways consist of midget bipolar cells and midget ganglion cells, the latter of which project to individual parvocellular layer cells of the lateral geniculate nucleus in the brain. Because of the need for the high acuity midget pathways also to be organized into ON- and OFF-center channels like the diffuse cone pathways for maximization of contrast, it means that every cone of the fovea will have dual midget pathways. The two midget bipolars will be an ON-center type and an OFF-center type and will connect with ON-center and OFF-center midget ganglion cells respectively. Because midget bipolar/ganglion cell circuits are devoted to a single cone, and the individual cones are of different spectral type maximally excited by short (S-cone/blue), medium (M-cone/green) or long (L-cone/red) wavelengths, they must carry sensitivity information about one wavelength. Thus the midget system concerned with the M- and L-cones in particular are considered also to carry L- or M-signals to the brain where further processing takes place to allow us the red and green discriminations of color vision.

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