Journal of Neuroscience, Vol 9, 1433-1442, Copyright © 1989 by Society for Neuroscience
Nonlinear summation of M- and L-cone inputs to phasic retinal ganglion cells of the macaque
BB Lee, PR Martin and A Valberg
Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Gottingen, Federal Republic of Germany.
We have studied the responses of ganglion cells in the macaque retina to
stimuli that alternate in color. With most color combinations, the phasic
retinal ganglion cells, which sum input from M- and L-cones in both center
and surround, showed a response with twice the alternation frequency at
equal luminance. This frequency doubling was directly related to the degree
to which the M- and L-cones were stimulated out- of-phase with one another,
and thus varied with the wavelength combinations used. It was absent with
wavelength combinations that lay along tritanopic confusion lines, when at
equal luminance the M- and L- cones are not modulated. Such a
frequency-doubled response is evidence for a nonlinearity at or before M-
and L-cone summation. The effect became much smaller or was abolished when
the receptive field center alone was stimulated, indicating that its
mechanism lies in the surround or in a center-surround interaction. Also,
it was much more marked at high luminance levels, being almost absent at
retinal illuminances below 100 td. Its origin is not clear, but it seems to
derive more from the L- than the M-cone. The results imply that phasic
cells, through this nonlinearity, could respond to the red-green equal
luminance borders used in some psychophysical experiments.