Figure 6: Optogenetic photo-stimulation with holographic spot patches.

(a) A pseudo-random projection image of spot patches (disk-like arrangement, 5 pixel diameter). Inset: zoomed image of a patch with speckle (left) and a patch after speckle was shift-averaged (right, 24 shifted copies of hologram projected sequentially). (b) Illustration of variable coverage of a cell’s soma by moving a patch around. (c,d) Peri-stimulus time histograms (PSTHs) showing effect of coverage (at 22.8 mW mm⁻²) and of illumination intensity (at 40–60% coverage) on the responses of a representative unit. (e,f) Spike latency and firing probability as a function of cell coverage (mean±s.e.m., n=31 units from two retinas). Latency plot is fit with inverse power fit (exponent, −0.77) and probability plot with an exponential saturation line. Time is relative to beginning of stimulation frame. (g) Optogenetic emulation of visual responses. Raster graphs of visually evoked neural activity in response to running cat (blue) and optogenetically emulated neural activity (red). PSTH graphs were calculated and overlaid to illustrate the resemblance between the two point processes. Scale bars, 10 μm.