Spatial and temporal response properties of individual RGCs were calculated from 24 different drifting sine-wave grating stimuli (6 different spatial scales × 4 different temporal frequencies, see Methods and
Figs. 2A,
2B; population data are presented in
Supplementary Figs. S1–S8). We measured the response strength of individual RGCs for each of the 24 different grating stimuli. For example,
Figure 2A
1 shows the raw response of a single RGC (from an 18-month Opa1
enu/+ retina recorded in scotopic conditions) to the 200-μm grating drifting at 2 Hz.
Figure 2A
2 shows the corresponding Fourier transform, from which we extracted the response strength to this stimulus (arrow). The raster in
Figure 2B shows the color-coded response strengths of the same cell to all 24-grating stimuli. Spatial and temporal tuning for this cell was then calculated by taking the median of the response strengths along the space and time dimensions of this response raster, as indicated in
Figure 2B. Such measurements were performed for all RGCs and the results were grouped separately for the four age groups, three brightness levels, and two genotypes. Examples of the resulting distributions of spatial tuning are shown in
Figure 2C where we compare the response strengths of 18-month-old WT (blue) and Opa1
enu/+ (orange) RGCs measured in scotopic (left) and photopic (right) conditions. We applied Wilcoxon rank sum tests to these distributions to assess if they differed between Opa1
enu/+ and WT retinas. A summary of these tests for each age group and brightness condition is shown in
Figure 2D as color-coded
P values (red if a parameter was enhanced in Opa1
enu/+ compared with WT retinas, blue if it was decreased in Opa1
enu/+). Similarly,
Figure 2E shows the summary for the temporal tuning differences between Opa1
enu/+ and WT RGCs. The underlying raw data for the
P values depicted in
Figures 2D and
2E are shown in
Supplementary Figures S1 through S8. It is striking that most differences between WT and Opa1
enu/+ response properties only emerge in the oldest age group (18 months). Secondly, the specific difference in spatial and temporal tuning was not fixed, but depended on the stimulus conditions. Under scotopic conditions, responses to gratings with small spatial periods were enhanced in old Opa1
enu/+ retinas compared with WT (
Fig. 2C left, red squares in
Fig. 2D), while the responses did not differ at the other spatial scales. Under photopic conditions, on the other hand, the responses of WT RGCs were stronger than in Opa1
enu/+ retinas at medium spatial scales (
Fig. 2C right, blue squares in
Fig. 2D). Similarly to spatial tuning, we found opposite effects under scotopic and photopic stimulus conditions for temporal frequency tuning: While old Opa1
enu/+ RGCs tended to respond more strongly to 4-Hz stimuli under scotopic luminance conditions, RGCs in WT retinas had stronger responses under photopic conditions (
Fig. 2E).