Signals from blue cones in “red-green” opponent-colour ganglion cells of the macaque retina

Abstract Many opponent-colour ganglion cells of the macaque retina overt input from green and red-sensitive cones but often appear to lack input from blue-sensitive cones under usual test conditions. Comparisons of field and test action spectra of the responses of a selected group of such “red-green” ganglion cells, located in the perifovea and lacking rod input, indicate the presence of blue-sensitive cone signals having a suppressive influence upon the more direct and opponent signals from green- and red-sensitive cones to a fraction of these neurones, which seems to take place at a level distal to that of the ganglion cell. No cell excitation of inhibition mediated by blue-sensitive cone signals could be observed on intense yellow-adapting lights desensitizing the other two cone types. These neurones are characterized by a sharp fall-off in their short-wavelength test sensitivity and by a secondary shoulder in their short-wavelength field sensitivity. In addition, when cell responses overtly mediated by input from green-sensitive cones are depressed by the geometry of the stimuli, the suppressive signals from blue-sensitive cones also result in a large displacement towards the short wavelengths of the test peak sensitivity of such responses. This displacement can be described with acceptable accuracy by a two-stage model based on subtractive interactions between A1-photopigments with λmax at 445, 535 and 570 nm, which is qualitatively consistent with other spectral properties of these ganglion cells.