Transmission of blue (S) cone signals through the primate lateral geniculate nucleus

This study concerns the transmission of short‐wavelength‐sensitive (S) cone signals through the primate dorsal lateral geniculate nucleus. The principal cell classes, magnocellular (MC) and parvocellular (PC), are traditionally segregated into on‐ and off‐subtypes on the basis of the sign of their response to luminance variation. Cells dominated by input from S‐cones (‘blue‐on and blue‐off’) are less frequently encountered and their properties are less well understood. Here we characterize the spatial and chromatic properties of a large sample of blue‐on and blue‐off neurons and contrast them with those of PC and MC neurons. The results confirm that blue‐on and blue‐off cells have larger receptive fields than PC and MC neurons at equivalent eccentricities. Relative to blue‐on cells, blue‐off cells are less sensitive to S‐cone contrast, have larger receptive fields, and show more low‐pass spatial frequency tuning. Thus, blue‐on and blue‐off neurons lack the functional symmetry characteristic of on‐ and off‐subtypes in the MC and PC pathways. The majority of MC and PC cells received no detectible input from S‐cones. Where present, input from S‐cones tended to provide weak inhibition to PC cells. All cell types showed evidence of a suppressive extra‐classical receptive field driven largely or exclusively by ML‐cones. These data indicate that S‐cone signals are isolated to supply the classical receptive field mechanisms of blue‐on and blue‐off cells in the LGN, and that the low spatial precision of S‐cone vision has origins in both classical and extraclassical receptive field properties of subcortical pathways.