Cell density ratios in a foveal patch in macaque retina

Abstract

We examine the assumptions that the fovea contains equal numbers of inner (invaginating or ON) and outer (flat or OFF) midget bipolar cells and equal numbers of inner and outer diffuse bipolar cells. Based on reconstruction from electron photomicrographs of serial thin sections through the fovea of a macaque monkey, we reject both assumptions. First, every foveal L and M cone is presynaptic to one inner and one outer midget bipolar cell; however, S cones are presynaptic to one outer but no inner midget bipolar cell. Second, we measure the density of all foveal cells in the same patch of fovea, affording accurate cell density ratios. For each foveal cone pedicle, at a density of 26,500 mm Ϫ2 , there is close to one (0.88) outer diffuse bipolar cell but only 0.40 inner diffuse bipolar cells. This asymmetry may be related to differences in resolution and sensitivity for light increments and decrements. We also find one (1.01) Müller cell, one (1.01) amacrine cell in the inner nuclear layer, and close to one (0.83) horizontal cell for each cone pedicle. In addition, for each S cone, there are two inner S-cone bipolar cells and two small bistratified ganglion cells. In total, there are 3.4 cone bipolar cells per cone but only 2.6 ganglion cells per cone. The latter ratio is enough to accommodate one midget ganglion cell for each midget bipolar cell.

The functional asymmetry of ON and OFF channels in the perception of contrast

“…A related but somewhat different idea was that the division of ON and OFF systems ensures that the overall range of contrasts encountered in natural scenes mapped roughly linearly to neural responses (Schiller 2010), regardless of the background luminance condition (Pandarinath et al 2010). In accord with this view, it was proposed that OFF neurons have gained a spatiotemporal dominance over ON neurons (Ahmad et al 2003;Kier et al 1995;Morigiwa et al 1989) to match the distribution of more negative than positive contrasts in the natural environment (Balasubramanian and Sterling 2009;Ratliff et al 2010;van Hateren et al 2002). Several recent physiological studies of the ON and OFF systems Kremkow et al 2014;Nichols et al 2013) have lent some support to this contrast-matching hypothesis.…”

“…More specifically, do darks have access to more neuronal resources than lights in the early visual pathway (Ahmad et al 2003;Jin et al 2008;Pandarinath et al 2010;Ratliff et al 2010;Xing et al 2010;Yeh et al 2009)? If so, is this difference sufficient to explain why psychophysically darks appear more salient and are detected faster than lights?…”

Microcircuitry for Two Types of Achromatic Ganglion Cell in Primate Fovea

“…This implies an ON density of ϳ2800 cells/mm 2 and a total for all parasols of 7800 cells/mm 2 . Using the cone density in our material (26,500/mm 2 ) (Ahmad et al, 2003) and assuming three ganglion cells per cone (Wässle et al, 1990), this would represent 9.8% of all ganglion cells. This is in good agreement with the upper bound of 8% for parasols predicted from immunocytochemical labeling (Grünert et al, 1993).…”

A model of local adaptation

“…These factors, along with consideration of the differences in the distribution of rods and cones across the retina, yield a picture of the spatial extent of light adaptation in different lighting conditions. In the central part of the fovea each cone is wired to an individual midget bipolar cell and one foveal midget ganglion cell for each bipolar cell [Ahmad et al 2003], whereas the spatial adaptation pool for rods in the human retina can be 10 minutes of arc in diameter [Hess et al 1990, p. 82].…”