Figure 3: Neuronal responses to full-field flashes.

(a) Response Raster plots of three units (colour coded) from a ChR2-expressing mouse. The second-long illumination flashes (solid blue line) initially evoke normal visual responses (top) which are blocked by a pharmacological cocktail (middle). Responses (putatively to direct ChR2 excitation) are restored at a higher illumination level (bottom). (b) In wild-type retinas, normal visual responses are evoked, but not seen in pharmacologically blocked retinas even at much higher illumination levels. (c) Summary statistics for neurons from ChR2-expressing (n=51) and wild-type retinas (n=14). Intensities:↓low (0.1–0.15 mW mm⁻²),↑ high (~2.6 mW mm⁻²), ↑↑ very high (<30 mW mm⁻²). Error bars represent s.e.m. values. Significantly different responses are marked by asterisks (two-tailed Student’s t-test, P<0.0001). (d,e) Normalized responses and latencies (mean±s.e.m., n=52 units from single retina) for flashes with varying illumination levels. (f) Comparison of mean extracellular spike waveforms measured in two representative ChR2 units in response to low-intensity (normal vision) and high-intensity (pharmacologically blocked) illumination flashes.