Fig. 7.

A disinhibitory circuit of amacrine cells is responsible for distant activation. a Responses of ganglion cells to a randomly moving bar, similar representation than Fig. 1c. Ellipse indicates responses of distant cells. b Same as a after application of strychnine. c Distant response amplitude (see Methods section) for normal (blue) and strychnine (red) condition (n = 16 cells). The three stars indicate that the p-value of a two-sample t-test was lower than 0.001. d Response to a bar flashed inside the receptive field center is not altered by the addition of strychnine. Single-cell responses to repeated presentations of the dark bar (shaded gray indicates the time window where the bar was presented); each dot is a spike, each row corresponds to a stimulus repeat. Black: control. Red: after addition of 1 μM strychnine to the bath. Green: after washing out strychnine. Bottom: PSTHs computed from the rasters. e Same as a for a bar flashed far from the receptive field center. f Single-cell responses to repeated presentations of the dark bar, same representation as in d. Black raster: control. Purple raster: after addition of 10  μM picrotoxin to the bath. Bottom: PSTHs computed from the rasters. g Same as f for a bar flashed far from the receptive field center. h Left histogram: percentage of cells responding to a central flash (left) and to a distant flash (right) before and after strychnine application, and after the drug wash-out. Same colors as d, e. Data are represented as mean ± SEM. Right histogram: same for picrotoxin. The three stars indicate that the p-value of a two-sample t-test was lower than 0.001. i Schematic showing a putative circuit for distant activation. When a distant stimulus is present, excitation of GABAergic amacrine cells (blue), through ON bipolar cells, inhibits subsequent glycinergic amacrine cells (red), which, in turn, disinhibits bipolar cells and ganglion cells. Similar glycinergic cells relay the output of ON bipolar cell inside the receptive field center to create a balance between ON and OFF inputs (see text). ONL: outer nuclear layer. INL: inner nuclear layer. GCL: ganglion cell layer