An international team, led by University of Zurich, has used a neurologger to record the brain activity of the birds, in this case pigeons, in flight, the Current Biology journal reported. According to the researchers, the study is the first to simultaneously record electrical brain activity integrated with large-scale navigational movements of free-flying birds.
Lead researcher Alexei Vyssotski said: Weve successfully applied electrophysiological methods, previously used for investigation of brain functions in the lab, to a freely flying bird in nature. The approach revealed places of interest for the pigeons and the pattern of their brain activation at such locations.
Over familiar landscapes, pigeons depend on visual cues to get around, earlier studies have shown. To learn more about how the birds respond to what they see in the current study, the team devised a miniature neurologger device, designed to record and store EEG signals.
Those signals reflect the firing of neurons within the brain. Vyssotski said that a recording session with the device, which weighs a mere two grams, can last up to several days, during which time the birds flight paths were also tracked with GPS.
The researchers got some baseline information by recording the brain activity of birds in the lab and of birds flying over the relatively featureless open sea. They then followed pigeons donning the neurologgers as they flew over a landscape including familiar and other relevant landmarks.
When pigeons pass over visual landmarks, their brains show a
bi-phase activation pattern, consisting of high-frequency oscillations followed by middle-frequency activity, they said.
The middle-frequency activity was the most reliable indicator of visual stimulation. When a pigeon looked at something with attention, this activity increased, Vyssotski said.
High-frequency brain waves showed an even more intriguing pattern, he said. That kind of activity seemed to reflect the birds flight history and their recognition of places they had visited before. In other words, activation of these oscillations may be associated with some memory processing or some other high-level brain functions.
Interestingly, the brain recordings revealed that the pigeons took unusual interest in a couple of locations that did not seem to be relevant to finding their way home.