Local control of retinomotor activity in the fish retina.

Abstract Small circular spots of light were focussed on otherwise unilluminated retinas of paralyzed fish. Cichlasoma biocellatum . The retinas were subsequently examined histologically, and a small circular region was found within which the cones and pigmented retinal epithelium were photomechanically light adapted; rods could not be resolved. The same result was obtained with the optic nerve cut. The region was circular and about the same size as the adapting spot. There existed a transition zone between light- and dark-adapted regions within which the photomechanical state was intermediate. These results exclude the hypothesis that light-induced retinomotor phenomena are systemically controlled, and favor local control. An analysis of the transition zone favors the view that photomechanical light adaptation of a given cell may be caused by light caught by that cell or its neighbors.