Light adaptation within the receptive field centre of rat retinal ganglion cells.

Open Access
Publisher Website
Google Scholar
Abstract
Responses from axons of single retinal ganglion cells in the rat''s optic tract were used to measure the pooling of adaptive signals within the cell''s receptive field. Computer-aided analyses of response measurements were used to evaluate sensitivity at a number of field locations. A small adapting spot caused a localized decrease in sensitivity within the receptive field centre of ON- and OFF-center ganglion cells. The functions describing response vs. test luminance were similar in shape for all test and adaptation configurations. Using a fixed criterion response, sensitivity determinations were made just as well in any receptive field location and under any of the experimental conditions. A concentric surround, antagonistic to the receptive field center, was readily apparent only under conditions of light adaptation. The local effects of small adapting spots, conducted with selective surround adaptation, revealed that non-uniform spread of adaptation within the receptive field center was not linked to surround intrusion. The possibility that the photopic mechanism intruded to contaminate the results was rejected. When a suprathreshold spot was alternated between 2 equally sensitive positions, the ganglion cell gave an approximately balanced response. An upset of this balance was produced by placing a small adapting spot at either position, again demonstrating the non-uniform spread of adaptation within the receptive field center. Significant pooling of adaptation effects apparently occurs prior to the combination of influences contributing to the center response of a ganglion cell.