Suppression of cone signal in the dark-adapted frog retina as indicated by the electroretinogram

Electroretinogram (ERG) cone acitvity is depressed in the dark-adapted frog retina. The strength of this effect is examined over a large range of flash energy, for 618 nm flashes extending up to about 4 log10 units above the "threshold" (10-25 micron V b-wave) of the cone ERG "released" in the early stage of rapid dark-adaptation (RDA). Cone signal depression is remarkably strong over this flash energy range. The cone ERG is practically absent for flashes up to about I log unit above cone RDA threshold. For stronger flashes, the suppression becomes time-dependent, that is, cone signal is very small for the first few hundred msec. after the flash, cone intrusion then becoming detectable. The results suggest that the cone suppression phenomena arises distally in the retina, probably near the receptor layer, and that cone signal intrusion a few hundred msec. after a strong flash may be due to light-adaptation of rods by the flash itself.