Receptive field asymmetries produce color-dependent direction selectivity in primate lateral geniculate nucleus.

Blue-on receptive fields recorded in primate retina and lateral geniculate nucleus are customarily described as showing overlapping blue-on and yellow-off receptive field components. However, the retinal pathways feeding the blue-on and yellow-off subfields arise from spatially discrete receptor populations, and recent studies have given contradictory accounts of receptive field structure of blue-on cells. Here we analyzed responses of blue-on cells to drifting gratings, in single-cell extracellular recordings from the dorsal lateral geniculate nucleus in marmosets. We show that most blue-on cells exhibit selectivity for the drift direction of achromatic gratings. The standard concentric difference-of-Gaussians (DOG) model thus cannot account for responses of these cells. We apply a simple, anatomically plausible, extension of the DOG model. The model incorporates temporally offset elliptical two-dimensional Gaussian subfields. The model can predict color-contingent direction and spatial tuning. Because direction tuning in blue-on cells depends on stimulus chromaticity, spatial frequency, and temporal frequency, this property is of little value as a general mechanism for image movement detection. It is possible that anatomical wiring for color selectivity has constrained the capacity of blue-on cells to contribute to spatial and motion vision.