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

1. 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 cells' receptive field. Computer-aided analyses of response measurements were used to evaluate sensitivity at a number of field locations. 2. A small adapting spot caused a localized decrease in sensitivity within the receptive field centre of ON- and OFF-centre ganglion cells. 2. The functions describing response versus test luminance were similar in shape for all test and adaptation configurations. This assured that, using a fixed criterion response, sensitivity determinations could be made just as well in any receptive field location and under any of the experimental conditions. 4. A concentric surround, antagonistic to the receptive field centre, was readily apparent only under conditions of light adaptation. Experiments on the local effects of small adapting spots, conducted with selective surround adaptation, showed that the non-uniform spread of adaptation within the receptive field centre was not linked to surround intrusion. 5. The possibility that the photopic mechanism intruded to contaminate these results was considered and rejected. 6. When a suprathreshold spot was alternated between two 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, thus demonstrating, in another way, the non-uniform spread of adaptation within the receptive field centre. 7. It is concluded that significant pooling of adaptation effects occurs prior to the combination of influences which contribute to the centre response of a ganglion cell.