Tracking down motion perception
Neurobiologists have determined the number of circuits needed to see movements
Surely, everybody knows this phenomenon: an animal doesn't stand out against its background and becomes visible to us only when it moves. The reason behind this is that we depend strongly on our eyesight for navigation, and the perception of motion is particularly well developed. But what exactly happens in the brain during this process? How must the nerve cells be interconnected for movements to be recognized as such? Scientists at the Max Planck Institute of Neurobiology in Martinsried have now established that two different motion detectors are required for this process in the fly brain.
Such a task seems almost too complicated just for two nerve cell detectors. However, the construction and maintenance of four circuits is much more elaborate than that of two. In other words, from the evolutionary point of view, two motion detectors are expected to be preferable to four. To establish whether this is the case, the neurobiologists recorded the electrical responses of those nerve cells that reacted to motion while the flies saw how the stripes changed contrast in the fly cinema. In addition, the scientists also conducted diverse computer simulations to predict and analyze the results. All these investigations came to the clear conclusion that the information about ON- and OFF-contrast changes is relayed to two motion detectors only.
The cells behind the detector
"This amounts to a scientific breakthrough", says Hubert Eichner, commenting the results of his study. "For over 50 years now, the scientific world has been trying to work out how many detectors are necessary in order to perceive motion". Now that the number of motion detectors has been determined, the neurobiologists can set about tracking down the cells that constitute these two detectors. Chances are good that the brain analysis of these tiny flies will help us to understand also our own motion perception in the future.