S Cone Contributions to the Magnocellular Visual Pathway in Macaque Monkey

Synaptic circuits in primate fovea have been quantified for midget/parvocellular ganglion cells. Here, based on partial reconstructions from serial electron micrographs, we quantify synaptic circuits for two other types of ganglion cell: the familiar parasol/magnocellular cell and a smaller type, termed "garland." The excitatory circuits both derive from two types of OFF diffuse cone bipolar cell, DB3 and DB2, which collected unselectively from at least 6 Ϯ 1 cones, including the S type. Cone contacts to DB3 dendrites were usually located between neighboring triads, whereas half of the cone contacts to DB2 were triad associated. Ribbon outputs were as follows: DB3, 69 Ϯ 5; DB2, 48 Ϯ 4. A complete parasol cell (30 m dendritic field diameter) would collect from ϳ50 cones via ϳ120 bipolar and ϳ85 amacrine contacts; a complete garland cell (25 m dendritic field) would collect from ϳ40 cones via ϳ75 bipolar and ϳ145 amacrine contacts. The bipolar types contributed differently: the parasol cell received most contacts (60%) from DB3, whereas the garland cell received most contacts (67%) from DB2. We hypothesize that DB3 is a transient bipolar cell and that DB2 is sustained. This would be consistent with their relative inputs to the brisk-transient (parasol) ganglion cell. The garland cell, with its high proportion of DB2 inputs plus its high proportion of amacrine synapses (70%) and dense mosaic, might correspond to the local-edge cell in nonprimate retinas, which serves finer acuity at low temporal frequencies. The convergence of S cones onto both types could contribute S-cone input for cortical areas primary visual cortex and the middle temporal area.

Section: Diffuse Bipolar Types Distribute S-cone Signals To Multiple mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microcircuitry for Two Types of Achromatic Ganglion Cell in Primate Fovea

Calkins

Sterling²

2007

“…We estimated M and S contrast weights from the data using a linear-nonlinear (LNL) model (Appendix C) (Fig. 5B) (Chichilnisky, 2001;Chatterjee and Callaway, 2002;Chichilnisky and Kalmar, 2002;Zaghloul et al, 2003).…”

Section: Measuring Horizontal Cell M S Weights: Flicker Experimentsmentioning

confidence: 99%

“…In our analysis, we followed previous authors (Chatterjee and Callaway, 2002;Diller et al, 2004;Johnson et al, 2004;Horwitz et al, 2005) and derived photoreceptor weights using a contrast measure. These weights describe the relationship between the contrast of the stimuli and the response of the postreceptoral cells.…”

Section: Contrast Versus Intensity Weightsmentioning

confidence: 99%

Chromatic Properties of Horizontal and Ganglion Cell Responses Follow a Dual Gradient in Cone Opsin Expression

Yin¹,

Smith²,

Sterling³

et al. 2006

In guinea pig retina, immunostaining reveals a dual gradient of opsins: cones expressing opsin sensitive to medium wavelengths (M) predominate in the upper retina, whereas cones expressing opsin sensitive to shorter wavelengths (S) predominate in the lower retina. Whether these gradients correspond to functional gradients in postreceptoral neurons is essentially unknown. Using monochromatic flashes, we measured the relative weights with which M, S, and rod signals contribute to horizontal cell responses. For a background that produced 4.76 log 10 photoisomerizations per rod per second (Rh*/rod/s), mean weights in superior retina were 52% (M), 2% (S), and 46% (rod). Mean weights in inferior retina were 9% (M), 50% (S), and 41% (rod). In superior retina, cone opsin weights agreed quantitatively with relative pigment density estimates from immunostaining. In inferior retina, cone opsin weights agreed qualitatively with relative pigment density estimates, but quantitative comparison was impossible because individual cones coexpress both opsins to varying and unquantifiable degrees. We further characterized the functional gradients in horizontal and brisk-transient ganglion cells using flickering stimuli produced by various mixtures of blue and green primary lights. Cone weights for both cell types resembled those obtained for horizontal cells using monochromatic flashes. Because the brisk-transient ganglion cell is thought to mediate behavioral detection of luminance contrast, our results are consistent with the hypothesis that the dual gradient of cone opsins assists achromatic contrast detection against different spectral backgrounds. In our preparation, rod responses did not completely saturate, even at background light levels typical of outdoor sunlight (5.14 log 10 Rh*/rod/s).

“…The commonest organization found in cortical neurons, Ϯ [(S ϩ M) Ϫ L], was instead that of blue-OFF cells in the LGN, which might be the major source of S-cone input to the cortex. Chatterjee and Callaway (2002) suggested that S cones also contribute, in proportion to their prevalence in the retina, to the receptive fields of M-cells. We found evidence for variable S-cone input to M-cells: S-cone inputs were negligible in seven but substantial in four.…”

Section: S-cone Contributions To Receptive Fields In the Lgn And Cortexmentioning

confidence: 99%

Chromatic Gain Controls in Visual Cortical Neurons

Solomon

Lennie²

2005

103

123

Although the response of a neuron in the visual cortex generally grows nonlinearly with contrast, the spatial tuning of the cell remains stable. This is thought to reflect the activity of a contrast gain control ("normalization") that has very broad tuning on the relevant stimulus dimension. Contrast invariant tuning on a particular dimension is probably necessary for reliable representation of stimuli on that dimension. In the lateral geniculate nucleus (LGN), V1, and V2 of anesthetized macaque, we measured chromatic tuning of neurons at several contrasts to characterize the gain controls and identify cells that might be important for representing color. We estimated separately the chromatic signature of the linear receptive field and that of the gain control. In the LGN, we found normalization in magnocellular cells and cells receiving excitatory S-cone input but not in parvocellular cells or those receiving inhibitory S-cone input. We found normalization in all types of cortical neurons. Among cells that preferred achromatic modulation, or modulation along intermediate directions in color space (making them responsive to both achromatic and chromatic stimuli), normalization was driven by mechanisms tuned to a restricted range of directions in color space, close to achromatic. As a result, chromatic tuning varied with contrast. Among the relatively few cells that strongly preferred chromatic modulation, normalization was driven by mechanisms sensitive to modulation along all directions in color space, especially isoluminant. As a result, chromatic tuning changed little with contrast. To the extent that contrast invariant tuning is important in representing chromaticity, relatively few cortical neurons are involved.