Figure 3. Superior ON direction-selective retinal ganglion cells (oDSGCs) receive similar inhibitory inputs but greater excitatory inputs compared to Inferior oDSGCs.

(A) Inhibitory currents measured from an exemplar Superior oDSGC under voltage-clamp at +10 mV in response to a bar drifting in eight directions. Mean peak inhibitory current is presented as the distance from the origin for each stimulus direction. Dashed line indicates the preferred direction of the peak inhibitory currents. Coordinates are in retinal space. (B) Same as (A) for an exemplar Inferior oDSGC. (C) Population responses for peak inhibitory currents across stimulus directions for Superior (magenta) and Inferior (gray) oDSGCs (mean ± SEM). Stimulus directions are aligned across cell types, where 0° indicates directly superior (for Superior oDSGCs) or inferior (for Inferior oDSGCs) motion. Positive directions are clockwise. (D) Distributions of the direction selectivity index for peak inhibitory currents in individual Superior and Inferior oDSGCs. (E) Excitatory currents measured from an exemplar Superior oDSGC under voltage-clamp at –60 mV in response to a bar drifting in eight directions. Same cell as in (A). (F) Same as (E) for an exemplar Inferior oDSGC. Same cell as in (B). (G) Population responses for peak excitatory currents across stimulus directions for Superior (magenta) and Inferior (gray) oDSGCs (mean ± SEM). (H) Distributions of the direction selectivity index for peak excitatory currents in individual Superior and Inferior oDSGCs. (I, J) The ratio of the peak excitatory current to the peak inhibitory current (E/I) was calculated for each stimulus direction for cells in which both metrics were recorded. (I) Distributions of the linear tuning curve area of E/I. (J) Distributions of the direction selectivity index for E/I. (K) Direction selectivity index for peak inhibitory (blue) and excitatory (yellow) currents collapsed across Superior and Inferior oDSGCs. For box plots, horizontal line represents median, box boundaries are IQR, and whiskers represent the most extreme observation within 1.5× IQR. *p<0.05, **p<0.01, ***p<0.001.

Figure 3—figure supplement 1. Superior ON direction-selective retinal ganglion cells (oDSGCs) receive more excitatory input, but are less intrinsically excitable, than Inferior oDSGCs.

(A, B) Linear tuning curve areas of the peak (A) inhibitory and (B) excitatory current measured in voltage-clamp recordings. Horizontal line represents median, box boundaries are IQR, and whiskers represent most extreme observation within 1.5× IQR. (C) Ratio of peak excitatory to peak inhibitory current (E/I) for each aligned stimulus direction (mean ± SEM), for cells in which both metrics were measured. 0° is directly superior (for Superior oDSGCs) or inferior (for Inferior oDSGCs) motion. Positive directions are clockwise. Statistical significance for each stimulus direction changes depending on how the tuning curves of Superior and Inferior oDSGCs are aligned (e.g., 180° rotation vs. reflection over the x-axis of the polar tuning curve). In general, E/I of Superior oDSGCs is greater than that of Inferior oDSGCs. (D–AA) For each bar direction, inhibition vs. spikes, excitation vs. spikes, and excitation vs. inhibition for cells in which both metrics were recorded (excitation and inhibition are peak values from voltage-clamp recordings, spikes are counts from cell-attached recordings). Dashed lines are least-squares linear regressions for Superior (magenta) and Inferior (gray) oDSGCs. R and p values are the Spearman’s rank correlation coefficient and associated two-sided significance, respectively. Large points represent univariate means ± SEM for each cell type taken from full data sets (i.e., small dots represent only a subset of cells in which both metrics were recorded, but full univariate datasets also consist of cells in which just one metric was recorded). Directions indicate aligned stimulus directions (as in [C]). For excitation vs. spikes, the fit line for Superior oDSGCs tends to fall below the fit line for Inferior oDSGCs, indicating lower intrinsic excitability. However, greater excitatory inputs to Superior oDSGCs outweigh the difference in intrinsic excitability, leading to more total spikes in Superior oDSGCs. Further, inhibition does not intuitively explain spike outputs since there is a positive correlation between inhibitory input and number of spikes across directions. This correlation is likely caused by an additional positive correlation between excitation and inhibition. Therefore, spikes are best explained by excitation. (BB) Preferred direction of inhibition vs. preferred direction of spikes recorded in the same cell. Dashed line represents the prediction for a 180° difference. (CC) Preferred direction of excitation vs. preferred direction of spikes recorded in the same cell. Dashed line represents prediction for 0° difference. (DD) Preferred direction of excitation vs. preferred direction of inhibition recorded in the same cell. Dashed line represents the prediction for 180° difference. Labels of T, D, N, and V correspond to temporal, dorsal, nasal, and ventral directions on the retina, respectively. *p<0.05, **p<0.01, ***p<0.001.

Figure 3—figure supplement 2. Full-field light increments elicit more spikes and excitation in Superior ON direction-selective retinal ganglion cells (oDSGCs).

(A, C) Example extracellular spike rasters from (A) a Superior and (C) an Inferior oDSGC in response to a 1 s light increment (405 nm). The schematic above shows the timing of the increment relative to the data. (B, D) Peristimulus time histograms (PSTHs) of average cell-attached light increment responses for each of (B) n = 124 Superior and (D) n = 165 Inferior oDSGCs. (E) Average PSTH across all cells shown in (B) and (D) (mean ± SEM). Highlighted region shows the first 150 ms after stimulus onset. (F) Distributions of each cell’s maximum firing rate throughout the entirety of the light increment. (G) Maximum firing rates during the first 150 ms after stimulus onset (i.e., highlighted region in [E]). (H) Mean firing rates ≥50 ms after stimulus offset. (I) Average inhibitory current in response to the 1 s light increment for Superior (magenta) and Inferior (gray) oDSGCs (mean ± SEM; voltage-clamp at +10 mV). (J) Peak inhibitory currents for the duration of the 1 s increment. (K) Total inhibitory charge transfers for the duration of the 3 s stimulus (i.e., including baseline and OFF response). (L) Peak inhibitory currents (as in [J]) versus maximum firing rate (as in [F]) for cells in which both metrics were recorded. (M) Average excitatory current in response to the 1 s light increment for Superior (magenta) and Inferior (gray) oDSGCs (mean ± SEM; voltage-clamp at –60 mV). (N) Peak excitatory currents for the duration of the 1 s increment. (O) Total excitatory charge transfers for the duration of the 3 s stimulus (i.e., including baseline and OFF response). (P) Peak excitatory current (as in [N]) versus maximum firing rate (as in [F]) for cells in which both metrics were recorded. The magenta line falls below the black line, indicating that Superior oDSGCs have a lower ratio of spike output to excitatory input. For scatter plots, large points and whiskers represent univariate medians and 95% confidence intervals (via bootstrapping). Dashed lines are least-squares linear regressions for Superior (magenta) and Inferior (gray) oDSGCs. R and p values are the Spearman’s rank correlation coefficient and associated two-sided significance, respectively. For box plots, the horizontal line represents median, box boundaries are IQR, and whiskers represent the most extreme observation within 1.5× IQR. *p<0.05, **p<0.01, ***P<0.001.