Distinctive characteristics of subclasses of red-green P-cells in LGN of macaque.

We characterized the chromatic and temporal properties of a sample of 177 red-green parvocellular neurons in the LGN of Macaca nemestrina, using large-field stimuli modulated along different directions through a white point in color space. We examined differences among the properties of the four subclasses of red-green P-cells (on- and off-center, red and green center). The responses of off-center cells lag the stimulus more than do those of on-center cells. At low temporal frequencies, this causes the phase difference between responses of the two kinds of cells to be considerably less than 180 deg. For isoluminant modulations the phases of on- and off-responses were more nearly 180 deg apart. A cell's temporal characteristics did not depend on the class of cone driving its center. Red center and green center cells have characteristically different chromatic properties, expressed either as preferred elevations in color space, or as weights with which cells combine inputs from L- and M-cones. Red center cells are relatively more responsive to achromatic modulation, and attach relatively more weight to input from the cones driving the center. Off-center cells also attach relatively more weight than do on-center cells to input from the class of cone driving the center.