Lateral spread of light adaptation in the rat retina.

Recordings from the rat optic tract fibers were used to assess changes in sensitivity under various conditions of adaptation. An adapting background which excites only a small fraction of the rods can yet cause a several-fold change in sensitivity. A small adapting spot much more effectively decreases the cell’s sensitivity to a superimposed test than to test spots in positions far from the adapting locus. Thus, adaptation spreads laierally but not uniformly throughout the ganglion cell center. Scattered lieht does not account for the spread, since a displaced adapting spot can be more effective than one &perimposed on the test spot. _