Scientists have long known that the birds navigate using the earth's magnetic field. Now, a new study has found subtle mechanics in the brain of pigeons that allow them to find their way.
A team at Baylor College of Medicine in the US identified a group of 53 cells in a pigeon's
brain that record detailed information on the Earth's magnetic field, a kind of internal global positioning system (GPS).
However, the study, published in journal Science, leaves open the question of how these"GPS neurons" actually help the birds sense the magnetic field.
"People had reported in the past, establishing that birds do not seem to respond to the polarity of the magnetic field, yet here we have neurons that are in fact doing that," study author Prof David Dickman said.
"That's one of the beautiful aspects of what we have identified,because it shows how single brain cells can record multiple properties or complex qualities in a simple way," he told BBC News.
For their study, Prof Dickman and his colleague Le-Qing Wu set up an experiment in which pigeons were held in a dark room and used a 3D coil system to cancel out the planet's natural geomagnetic field and generate a tunable, artificial magnetic field inside theroom.
While they adjusted the elevation angles and magnitude of their artificial magnetic field, they simultaneously recorded the activity of the 53 neurons in the pigeons' brain which had already been identified as candidates for such sensors.
So, they measured the electrical signals from each one as the field was changed and found that every neuron had its own characteristic response to the magnetic field, each giving a sort of 3D compass reading along the familiar north-south directions as well as pointing directly upward or downward.
In life, this could help the bird determine not only its heading just as acompass does, but would also reveal its approximate position, the researchers said.
Each cell also showed a sensitivity to field strength, with the maximum sensitivity corresponding to the strength of the Earth's natural field, they added.
And like a compass, the neurons had opposite responses to different field "polarity", the magnetic north and south of a field, that surprised the researchers most of all.
Several hypotheses hold that birds' magnetic navigation arises in cells that contain tiny chunks of metal in their noses or beaks, or possibly in an inner ear organ.
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