How pigeons pick up Earth's magnetic field
Scientists have detected the parts of a pigeon's brain that enable it to use the Earth's magnetic field to navigate.
That birds such as pigeons, as well as a host of other animals, are sensitive to magnetic fields and might use them like a cognitive compass to find their way around has been known for some time; but how they detect and then process this information neurologically has remained a grey area.
Now, working with homing pigeons, two researchers from Baylor School of Medicine in Texas, Le-Qing Wu and David Dickson, have identified the parts of the bird brain responsible.
Writing in Science, the duo first exposed pigeons to a changing magnetic field and then looked in the animal's brains for nerve cells that had increased their expression of a gene called c-Fos which is linked to neural activation.
Four areas lit up: the lateral hyperpallium, hippocampus, dorsal thalamus, and caudal vestibular nuclei. These regions are are all known to be involved in navigation functions and in spatial orientation.
Next the researchers used electrodes to record nerve activity in one of these regions, the vestibular nuclei, in seven pigeons.
The animals were tested in the dark to avoid giving them light-related cues. A set of coils were used to generate a magnetic field that cancelled out the planet's natural field and then applied its own.
The researchers varied the orientation of this field, which was equivalent in strength to the Earth's own magnetic field, in 10 degree steps. They were able to show that the cells displayed a "tuning curve" of activity, responding most in some orientations and least in others.
How the birds actually detect the magnetic field in the first place isn't known for sure, but the researchers have so far homed in on a structure called the lagena in the inner ear, which they plan to look at next, although the beak and retina could also be involved.