Peering Inside a Bird's Brain

A device tracks pigeons' brain activity as they find their way home.

Ever wonder what goes through a bird's mind as it flaps across the sky? Scientists are now a step closer to finding out. A study published today in Current Biology used a small device to record the brain activity of homing pigeons as they made training flights; by pairing the device with GPS, the scientists could determine how the birds' brains reacted to different landmarks along their journey. It is the first time such a technology has been used in free-flying birds, and it opens up a new view into how animals respond to their environment outside the laboratory.

Brain box: A small "neurologger" device affixed to a pigeon's head provides a window into its brain activity as it flies home. Credit: Current Biology

Homing pigeons, which are trained to return to their home loft, can make the journey back even when released from unfamiliar places hundreds of miles away. But how they manage this feat has puzzled scientists for decades. Earlier research relied on simply watching where the birds were headed, but recent studies with GPS have created a more detailed picture. When pigeons are far away, they seem to use a combination of cues to determine the location of home: the position of the sun, the planet's magnetic field, and even smells in the air. But when closer to home, the birds seem to rely on familiar landmarks and roads to guide their way.

For the new study, 26 birds were anesthetized, and electrodes were placed on the surface of their brains through small holes in the skull. A small electroencephalography (EEG) device was affixed to each bird's head and attached to the electrodes. The birds were also given backpacks carrying a GPS monitor that recorded their position over time. Alexei Vyssotski, a behavioral neuroscientist at University of Zurich who led the study, says that his team decided to release the birds from the sea, about 30 kilometers from their home loft, so that they had to traverse a relatively featureless environment before passing over familiar land.

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EEG measures the electrical activity of neurons in the brain, revealing different patterns depending on the animal's state of consciousness. When the scientists analyzed the EEG data from a series of flights, they were able to identify at least three bands of brain-wave frequencies that seemed to be important in flying behavior. They could then plot out how these frequency bands changed at different positions along the journey.

Vyssotski says that lower-frequency brain waves seemed strongest when something commanded the birds' attention: when they passed over landmarks or other sites of interest. These frequencies were weak when the birds began their journey over water but strengthened dramatically as they passed over land. The researchers were even able to correlate brain activity to specific landmarks. For instance, one striking visual feature to the left of the birds--a large open-pit mine--caused some birds to veer briefly off course. As they did, the researchers saw a jump in activity in the right hemisphere of the brain--consistent with the fact that birds process visual information from each eye in the opposite hemisphere. In another instance, the pigeons attended to two seemingly uninteresting spots on land, which puzzled the researchers until they visited the sites and realized that the interest wasn't navigational: they were sites where flocks of feral pigeons hung out.