Fig. 7. Laser-evoked responses in the absence of fluorescent dye.

a Schematic cross-section of the retina illustrating scan size and focal planes (both for 2P imaging and light stimulation) relative to the recorded ganglion cell. b Spiking responses of two unidentified ganglion cells (extracellular recordings) to opening/closing of the laser shutter and to switching the laser between mode lock (ML) and continuous wave (CW) (scan area: 141×141 µm, 128×128 pixels/frame, at 2 ms/line; stimulator background intensity I_Bkg=21×10³ photons·s⁻¹·µm⁻²). c Spiking response of an ON ganglion cell (extracellular recording) to the laser (in ML mode) when varying the z position of the focal plane (as illustrated in a) (scan area and resolution as in b; I_Bkg=84×10³ photons·s⁻¹·µm⁻²) d Spiking response of an ON/OFF ganglion cell to a bright spot stimulus (200 µm in diameter) for increasing I_Bkg before (d₁) and during (d₂) laser scanning. Bars above traces indicate when spot was presented and when laser shutter was opened/closed. Spiking frequency as function of I_Bkg (d₃) for different time windows as indicated by the brackets below the traces (contrast (I_spot –I_bkg)/(I_spot + I_bkg) between stimulus spot and background: 32%, 39%, 36%, 33%, 27%, 16%, 13%, 10%, and 4%. Scan area: 23×23 µm, 256×256 pixels at 2 ms/line) e Spiking response of an ON ganglion cell; same conditions as in d except that the spot diameter was 800 µm and the scan area (zoom) was varied. Only traces for two different I_Bkg are shown. Laser: tuned to ~925 nm; mode locked (ML) except in b; power: b, c, e ~12 mW; d ~7 mW; focal plane in the GCL except in c. Stimulator LED: yellow, band pass-filtered (578 BP 10) and used for both stimulus and background