Computation of motion by T4 cells in the fly brain is more complex than previously believed. As indicated by their name, photoreceptor cells in the eye respond to light: is an image point bright or dark? They do not indicate the direction of a movement. This perception only arises in the brain through the comparative computations of light signals coming from adjacent image points. Engineers, physicists and neurobiologists have been debating the exact nature of these computations for around 50 years.
Scientists from the Max Planck Institute of Neurobiology have now combined two theories about these computations, which were previously considered to be alternative hypotheses – and discovered that they are carried out in a single neuron.Flies are usually very difficult to catch. No wonder – they invest around ten percent of their brain in the detection and processing of image motion. For the fly, a hand approaches in slow motion and the fly’s evasive manoeuvre has long been triggered before any real danger arises. Scientists have been researching for decades how the fly brain can perceive and process movements so quickly and accurately. “Our goal is slowly coming into view, and we are close to completely decoding the neuronal circuit of motion perception in the fly,” says Alexander Borst, who has been working on this problem with his Department at the Max Planck Institute of Neurobiology for quite some time. The scientists have now come one step closer to the answer: They have provided experimental data that combine two theories previously considered as alternatives. More