Figure 7. Stimulus contrast modulates the spike tuning curves of ON direction-selective retinal ganglion cells (oDSGCs).

(A) Cell-attached tuning curves from an exemplar Superior oDSGC at high (green) and low (tan, 20% relative) contrasts. Numbers on concentric circles indicate spike counts. Dashed lines represent preferred directions. Coordinates are in retinal space. (B) Linear tuning curve area and (C) direction selectivity index from spike responses to high-contrast (abscissa) and low-contrast (ordinate) bars drifting in eight directions. Differences between Superior (magenta) and Inferior (gray) oDSGCs persist under low contrast (see Figure 2). (D) Linear tuning curve area and (E) direction selectivity index from peak subthreshold voltage responses to high-contrast (abscissa) and low-contrast (ordinate) bars drifting in eight directions. (F) Residuals from the unity line of the direction selectivity index under high- and low-contrast conditions for simultaneously measured spikes and subthreshold voltages. Comparison is made between spikes and subthreshold voltages. For all scatter plots, the region of green (or tan) indicates the metric is greater under high-contrast (or low-contrast) conditions. Points on the line indicate equivalent metrics under the two conditions. Individual cells are represented by small dots. Large dots represent univariate medians (collapsed across cell type). Whiskers indicate 95% confidence intervals determined via bootstrapping. Significance values indicate whether the data tend to fall unevenly on one side of the unity line (two-sided signed-rank). *p<0.05, **p<0.01, ***p<0.001.

Figure 7—figure supplement 1. Stimulus contrast modulates spike tuning curve width but not the ratio of excitation to inhibition.

(A) Area of the normalized tuning curve from spike responses to high-contrast (abscissa) and low-contrast (ordinate) bars drifting in eight directions. Differences between Superior (magenta) and Inferior (gray) ON direction-selective retinal ganglion cells (oDSGCs) persist under low contrast (see Figure 2). (B) Area of the normalized tuning curve from subthreshold voltages in response to high-contrast (abscissa) and low-contrast (ordinate) bars drifting in eight directions. (C) Residuals from the unity line for simultaneously measured spikes (as in [A]) and subthreshold voltages (as in [B]). The dashed line indicates unity (i.e., no difference between high and low contrast). Comparison is made between spikes and subthreshold voltages. (D, E) Excitation-to-inhibition (E/I) ratios for high- and low-contrast bars drifting in (D) the preferred and (E) the null direction of each cell. (F) Direction selectivity index generated from a parallel conductance model of an oDSGC under different scale factors applied jointly to excitatory and inhibitory inputs (constant E/I). For all scatter plots, the region of green (or tan) indicates the metric is greater under high-contrast (or low-contrast) conditions. Points on the line indicate equivalent metrics under the two conditions. Individual cells are represented by small dots. Large dots represent univariate medians (collapsed across cell type). Whiskers indicate 95% confidence intervals determined via bootstrapping. Significance values indicate whether the data tend to fall unevenly on one side of the unity line (two-sided signed-rank). All data acquired following epifluorescence targeting. *p<0.05, **p<0.01, ***p<0.001.

Figure 7—figure supplement 2. Two-photon targeting confirms that ON direction-selective retinal ganglion cells (oDSGCs) are contrast sensitive.

(A) Tuning curve area, (B) direction selectivity index, and (C) normalized area of the spike tuning curve were measured in the cell-attached configuration in response to high- and low-contrast drifting bars following two-photon targeting of oDSGCs. As occurred following epifluorescence targeting (Figure 7, Figure 7—figure supplement 1), two-photon targeting revealed that the spike tuning curves of oDSGCs were smaller (A) and narrower (B, C) in response to low-contrast stimuli. For all plots, regions of green (or tan) indicate that the metric is greater for high-contrast (or low-contrast) stimuli. Points on the line indicate equivalent metrics under the two conditions. Individual cells are shown as small dots (Superior in magenta, Inferior in gray). Large red dots represent univariate medians collapsed across cell types. Whiskers indicate 95% confidence intervals determined via bootstrapping. Significance values indicate whether the data tend to fall unevenly on one side of the unity line (two-sided signed-rank). *p<0.05, **p<0.01, ***p<0.001.