A smell of home
The ability to sense the earth's magnetic field appears to be widespread in the animal kingdom. The big question has always been how exactly this perception occurs. Now researchers in New Zealand have found the physical basis of magnetotaxis - at least in one species. The rainbow trout (Oncorhynchus mykiss) smells its way north, so to speak: its magnetic compass is in the olfactory epithelium of its snout. Michael M. Walker and his colleagues at the University of Auckland, New Zealand, have demonstrated how rainbow trout responded behaviorally to changes in the strength of magnetic fields (Nature, November 27, 1997). They also located the area in the snout of these fish where the magnetic receptors are found. The scientists identified the receptor, which contains the magnetic mineral magnetite, and traced the route of nerves from the receptor cells to the brain. The investigations also showed that this system interacts with a learned response to magnetic fields.
The researchers tried to teach the fish how to find food in their tank at the locations marked by magnetic fields. They found out that the trout can distinguish different field strengths, but not the direction of the magnetic fields. While this may seem like a rather odd way to emulate a compass, it is quite a viable method for navigating over longer distances. The strength of the Earth's magnetic field varies with latitude, being strongest at the poles and weakest at the equator. When navigating over long distances, this latitude detector is able to provide a magnetic map of the world.
Joseph L. Kirschvink of the California Institute of Technology in Pasadena wrote a comment in the same issue of Nature, explaining that humans also have the same nerve branches and the ability to sense magnetism. Magnetite has also been found in human brains. He states that Polynesian navigators are still able to find the right direction even when all obvious aids such as sun, moon or stars are not available. In his opinion the last word on the existence of human perception of magnetic fields has not yet been given.
The Heidelberger Verlag Spektrum der Wissenschaft is the operator of this portal. Its online and print magazines, including "Spektrum der Wissenschaft", "Gehirn&Geist" and "Spektrum – Die Woche", report on current research findings.
