Cone Mechanisms in the Electroretinogram of the Cynomolgus Monkey

¹ Department of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, Mass. 02114

Three cone mechanisms have been separated with intense chromatic adapting fields in the electroretinogram (ERG) recorded at the cornea of the cynomolgus monkey. Responses were obtained to large test stimuli (45°) superimposed on a larger adapting field (68°). Peak spectral sensitivities were near 450, 530, and 580 nm. Linear summation of these three cone mechanisms, first shown by Wald's (1964) analysis of human psychophysical data, has been confirmed by the same analysis applied to the ERG spectral sensitivity data obtained from the cynomolgus monkey. The ratios derived for the three cone mechanisms in the dark-adapted cone ERG are blue:green:red = 1:6.5:5.4, and emphasize the relatively small contribution of the blue cone mechanism to the total cone ERG. Differences in the ERG spectral sensitivity of the dark-adapted eye obtained in response to 25 and 50 Hz. flickering stimuli could be explained by a linear summation of the blue cone mechanism to the red and green cone mechanisms at the lower frequency. Stimuli known to produce antagonistic responses at the level of the lateral geniculate nucleus in the monkey were shown to summate in the ERG recorded at the cornea. These data are consistent with the idea that the three cone mechanisms act independently in generating the dark-adapted cone ERG b-wave recorded at the cornea in response to a large test stimulus.

Note:
Dr. Mehaffey's present address is Vassar College, Poughkeepsie, N. Y. 12603.

Key Words: chromatic adaptation • cones • retina • monkey • electroretinogram • psychophysics • photoreceptors • color vision