Figure 8. Rod and cone systems generate a smooth transition in ganglion cell temporal kinetics across light levels and drive similarly robust responses.

A. There is a gradual speeding of the response (shortened zero-cross time) over a 2.5 log-unit increase in photoisomerization rate. Rod-mediated responses are shown for the Gnat2^cpfl3 retina. Cone-mediated responses are shown for the Gnat1^−/− retina and for the wild-type retina after saturating or bleaching the rods. A mixed rod- and cone-mediated response is shown for the wild-type retina before bleaching or saturating, and for these points, we indicate the range of R* rates with a horizontal bar (rod R* rate on the left, cone R* rate on the right). There is a smooth transition in the kinetics between the rod- and cone-mediated responses. Gnat1^−/− ganglion cell responses were slower than wild-type cone-mediated responses, consistent with previous cone recordings (Nikonov et al., 2006). The dashed line was fit by eye to the wild-type and Gnat2^cpfl3 cells. Error bars indicated ± 1 SD across cells.

B. The firing rate was relatively stable over a 2.5 log-unit increase in photoisomerization rate. Plotted is the maximum firing rate in the nonlinear function minus the estimated firing rate at 0% contrast [i.e., firing rate at f(x)=0 of the nonlinear function]. Despite having a small percentage of cone photoreceptors (~3%), firing rate increases slightly in the range of cone-mediated responses. Error bars indicated ± 1 SD across cells.

C. Temporal tuning extends to higher frequencies under cone-mediated conditions. Functions show the average, normalized responses of light-adapted rod-mediated responses (Gnat2^cpfl3, 520 R*/rod/s mean; from Figure 5D) and cone-mediated responses (wild-type, 12,000 R*/cone/s mean after the bleaching stimulus; from Figure 7H). Error bars indicated ± 1 SEM across cells.