The spectral sensitivity of retinal ganglion cells in the carp

Abstract

The spectral sensitivity of ganglion cells in the carp retina was studied with microelectrode techniques. Spectral sensitivity curves represent the quantal energy necessary to elicit a fixed number of spike discharges, as a function of wavelength. Ganglion cell discharges were of “on”, “off” and wavelength-dependent “on-off” types. Only “on” or “off” curves were seen under scotopic conditions. Scotopic spectral sensitivity curves had a single maximum near 520 mμ and corresponded in shape to the absorption curve of a nomogram pigment. Under photopic conditions “on” and “off” cells exhibited maxima near 480, 530 and 620 mμ with curves of modulator-like narrowness. Most units had one or two sub-peaks which could be isolated by selective bleaching. The threshold for the main peak rose by 1–5 log units following the bleach. “On-off” units had one maximum near 480 mμ and another near 590 mμ. When one component was bleached, its threshold rose, while that of the other component fell and its spectral range of response increased. “Off” units with 590 mμ maxima became “on-off” units when bleached with long wavelength light. Evidence is presented suggesting that in “on-off” units, the short wavelength component is composed of blue and green elements; the long wavelength component of red and green elements.