LMU neurobiologists have identified a neural pathway for processing magnetic information that originates in the inner ear.

In 1882, the French Naturalist Camille Viguier was amongst the first to propose the existence of a magnetic sense. His speculation proved correct, many animals – from bats, to migratory birds and sea turtles use the Earth’s magnetic field to navigate. Yet despite decades of research, scientists still know surprisingly little about the magnetic sense. How do animals detect magnetic fields? Which brain circuits process the information? And where in the body is this sensory system located?

Viguier audaciously proposed that magnetic sensing might occur in the inner ear relying on the generation of small electric currents. This idea was ignored and then forgotten; a historical musing lost with the passage of time. Now more than a century later it has been resurrected by neuroscientists at LMU in a paper published in Science. A team led by Professor David Keays took an unbiased approach studying pigeon brains exposed to magnetic fields.

“State-of-the-art microscopy allowed us to identify specialized circuits that process magnetic information. Moreover, it provided a critical clue to the location of the primary magnetic sensors”. PhD students Grégory Nordmann and Spencer Balay observed robust activation in a brain region called the vestibular nucleus, which is connected to the inner ear. Genetic analysis of inner ear tissue revealed cells with highly sensitive electric sensors, the same ones used by sharks to detect their prey.

“The cells we describe are ideally equipped to detect magnetic fields using electromagnetic induction – enabling pigeons to find their way home using the same physical principle which permits the wireless charging of phones.” In both cases, a magnetic pulse is converted into an electrical signal. For the pigeon, this powers their natural GPS.

The researchers emphasize that it is likely not the only magnetic sensing strategy in nature. “Our data suggests that there’s a ‘dark compass’ in the inner ear, while other studies point to a light-dependent compass in the visual system,” explains Keays. “In all likelihood, magnetoreception has evolved convergently in different organisms. Much remains to be discovered!”