Final Report Summary - CEMOMAGNETO (The Cellular and Molecular Basis of Magnetoreception) Each year millions of animals migrate across the globe guided by the Earth's magnetic field. Yet the mechanisms that underlie this mysterious sixth sense are unknown. One idea, known as the magnetite theory of magnetosensation, predicts that animals possess an intracellular compass made of iron. In this project we tested this hypothesis exploiting a broad range of methods to identify magnetic cells in pigeons. We attempted to find magnetite based on it's chemical composition, it's magnetic properties, and the light it emits when excited by X-rays. Our inability to identify sensory cells with a magnetic compass compelled us to reconsider an alternative hypothesis forgotten by time. In 1882 a French scientist, Viguier, proposed that animals detect magnetic fields by relying on the generation of small currents within the inner ear, as the animal moves through the Earth's fixed magnetic field. In support of this "inductive" hypothesis we have shown that it is feasible at a theoretical and experimental level, and that pigeons possess highly sensitive electroreceptors in the inner ear. Moreover, we have confirmed that regions of the brain that are directly connected to the inner ear are activated by magnetic stimuli. In short, we have made important advances in understanding how the magnetic sense works.
