Spatial summation and visual adaptation in the inner part of the frog retina.

The spatial summation of the proximal negative response (PNR) of frog retina was analyzed during different states of adaptation induced by repetitive light stimulation with either 15 sec or 1 min interstimulus interval. The spatial summation area of the PNR was found to be wider during relatively more dark adapted conditions compared to relatively more light adapted ones. This finding indicates that lateral mechanisms in the inner network of the retina seem to be activated by adapting stimuli. Secondly, the results suggest that the activity of the amacrines, as reflected by the PNR, may initiate the series of neuronal events which underlie the oscillatory potentials (OPs) of the electroretinogram (ERG).