Appendix 7—figure 2. Testing R1-R8 photoreceptors sensitivity to deep-red illumination by electroretinogram (ERG) recordings.

(A) ERGs were recorded in intact Drosophila, placed inside a conical holder, to 1 s long very bright green (545 nm), red (740 nm) and deep-red (740 nm LED with 720 nm high-performance long-pass filter) pulses. A normal ERG contains a large but slow photoreceptor (DC) component and the faster on- and off-transients (Heisenberg, 1971), which signal histaminergic transmission to lamina interneurons. (B) The very small ERG response (wine) to the deep-red pulse indicated very little R1-R8 photoreceptor activation. Mean ± SD shown, n = 6–7 wild-type flies.