Figure 7. Amplitude and kinetics of paired-flash depression can predict background-dependent gain changes.

(A) Schematic of probe stimuli delivered every 800 ms in darkness and on a background of 1 Rh*/rod/s (top panel). Poisson train of single photon events for probe and background photons (bottom panel). (B) Predicted gain values for each photon absorption, obtained from paired-flash depression of a single photon (1 Rh*/rod bipolar). (C) Responses to probe flashes (arrows) in an AII amacrine cell in darkness (first 5 responses) and on the background (last 5 responses). Average responses in darkness are shown in gray for comparison. (D) Overlaid individual trials (thin lines) and average (thick lines) responses in darkness (gray) and on the background (black). Gain at simulated background normalized to gain in darkness is 0.47 ± 0.08 (mean ± s.e.m; n = 5). (E) Background-dependent gain changes for ON ganglion cells (black circles). Results and fit shown previously in (Dunn et al., 2006). Overlaid in gray is the gain change prediction made by paired-flash depression induced by a single photon. Prediction was for backgrounds dimmer than at which rod photoreceptor adaptation began.