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Samuel G. Solomon, Neel T. Dhruv, Peter Lennie; Spatial organization of L- and M-cone inputs to neurons in the macaque lateral geniculate nucleus. Journal of Vision 2005;5(8):264. doi: 10.1167/5.8.264.
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© ARVO (1962-2015); The Authors (2016-present)
In chromatically opponent retinal ganglion cells and LGN neurons in macaque it has been hard to establish how the different types of cones contribute to centers and surrounds of receptive fields. To pursue this we recorded in anaesthetized macaque monkeys from parafoveal LGN neurons driven by drifting gratings that modulated only L-cones or only M-cones (cone isolating) or modulated both in concert (L+M). A receptive field that has few cones in its center should be orientation-selective when driven by gratings of preferred or higher-than-preferred spatial frequencies. If both L and M cones provide input to the center, preferred orientation should vary with grating chromaticity. If both cone types provide input to the surround, we should see band-pass rather than low-pass spatial frequency tuning for cone-isolating stimuli. Among magnocellular cells, both cone types provided input to center and surround: neurons showed band-pass tuning, and orientation specificity for cone isolating and L+M gratings could vary significantly. Parvocellular (P) cells behaved differently. Receptive field centers were usually driven by one class of cone: orientation specificity was found in most cells, and was strongest in cells with M-cone centers, but did not depend on chromaticity. In cells with M-cone dominated centers, band-pass spatial frequency tuning was rarely observed for M-cone isolating gratings, and spatial resolution for L-cone isolating gratings was low. In cells with L-cone dominated centers, band-pass spatial frequency tuning for cone isolating gratings was more common, and spatial resolution for M-cone gratings was often close to that for L-cone gratings. Nevertheless, L- and M-cone inputs remained antagonistic at high spatial frequencies. Since L-cones are more prevalent, the different characteristics of P-cells that have L- rather than M-cone centers is consistent with unspecific wiring of cone inputs to the surround. Cone inputs to the center seem substantially more specific.
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