A tethered fruit fly, seen from below, inside of an LED illuminated drum which displays moving visual patterns. The fly flaps it’s wings in an attempt to steer such that the moving pattern is stabilized. 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 green fluorescent proteins in the muscles of a genetically modified fly. The green fluorescence is picked up by the same microscope optics, through a special filter which blocks reflecting blue light.