Figure 2. Voltage clamp recording and optogenetic silencing to isolate retinal excitation to SGS neurons.

a, Trial-averaged EPSC traces of an example SGS neuron to bars moving along 12 directions in the absence (left panel) or presence (right) of LED illumination (as indicated by the blue bar). The red dotted lines indicate the mean current level in the absence of visual stimulus. b, Direction tuning curves of this cell’s total EPSC (top panel, “tEPSC”) and retinal input (bottom, “rEPSC”). The dashed lines indicate the level that is 3 standard deviations above the mean current level as determined in the absence of visual stimulus. Data are presented as mean ± SEM, and n = 8, 7, 7, 7, 6, 7, 7, 7, 7, 7, 6, 6 trials in the top panel and n = 3 for all directions in the bottom panel. c, Scatter plot of this cell’s tEPSC versus its rEPSC. Peak rEPSC and tEPSC amplitudes are plotted for the responses to 12 directions of bars. The dotted line is the linear regression of the data points (R² = 0.95, F(1,10) = 192.7, p < 0.001, linear regression; r = 0.98, p < 0.001, Pearson correlation). d, Cumulative distributions of gDSI for tEPSC (n = 87 cells from 58 mice, red) and for V_m (n = 52 cells from 41 mice, black), indicating that tEPSC and V_m have nearly identical gDSI distributions (p = 0.30 K-S stat = 0.17, K-S test). e, Scatter plot of gDSI values for tEPSC and V_m in the same cells (n = 23 cells from 21 mice). They are well correlated (r = 0.99, p < 0.001, Pearson correlation) and similar in values (p = 0.18, W = 90, Wilcoxon test). Note that the plot is shown in log-log axis to better illustrate the cells with low gDSI. The dotted lines indicate gDSI levels of 0.1. f, Scatter plot of the preferred direction (“prefD”) for V_m versus EPSC. The diameter of each dot is scaled to the gDSI- V_m of that cell. Note that the preferred directions are similar for EPSC and V_m responses, especially for highly selective cells. The solid lines in both panel e and f are the lines of identity. g, Percentage of cells that receive direct retinal input in DS (n = 15/16) and non-DS (n = 26/32) SGS neurons. h, Distribution of amplification ratio of all cells that receive direct retinal input (n = 41). The red line indicates the mean of the distribution. i, Similar amplification ratio between DS (3.37 ±0.46, n = 15 cells from 13 mice) and non-DS (2.94 ± 0.26, n = 26 cells from 20 mice) SGS neurons (p = 0.41, U = 164, Mann-Whitney U test). Data are presented as mean ± SEM.