Fruit fly (Drosophila melanogaster) tethered in LED illuminated chamber which stimulates moving visual patterns. Behind the fly is a camera, which is used to record its wing beat amplitude  a rough measure of whether it is trying to turn to the left or right. At the top of the image is the microscope objective, which focuses bright blue light onto the fly. The blue light excites fluorescent proteins in the flyˇs muscles, which emit green light. The green fluorescence is picked up by the same microscope optics, through a special filter which blocks the blue light. California Institute of Technology, USA, December 2016.