Adaptation-related changes in the spatial and temporal summation of frog retinal ganglion cells

The spatial and temporal summation of light by the receptive field centre of frog retinal ganglion cells were studied by extracellular recording in the eyecup preparation. The purpose was to quantify how summation changes with the state of light and dark adaptation and to clarify whether changes are due to the transition between rod and cone vision. Spatial summation was found to decrease by 30-50% as the cell was light-adapted to a threshold some 4 log units above the dark-adapted one. Temporal summation for threshold responses fell as the power -0.17 of the intensity of an adapting steady background. Neither change was bound to the rod-cone transition but occurred in the ranges of both receptor types; at equal sensitivities the summation of both receptor systems was matched.