Newly Discovered Brain Structure May Grant Birds Impressive Intelligence
Birds are capable of some extraordinary cognitive feats. New Caledonian crows can make and use tools. Grey parrots can learn various human words and complete certain tests of intelligence at the level of four to six-year-old human children. Pigeons can remember large numbers of images for several years. But how birds accomplish these tasks despite having brains the size of walnuts has long eluded our own comprehension.
Now, in two tandem studies, researchers in Germany have imaged a structure in the avian brain that might just endow birds with their impressive abilities, and maybe even grant them rudimentary consciousness.
In the first study, scientists used 3D-Polarized Light Imaging, a rising technique that came to prominence in the past decade or so, to map the nerve fibers of barn owls' and pigeons' forebrains, specifically the pallium, layers of grey and white matter that cover the upper surface.
They found that the structure and circuitry of both bird species' pallia are strikingly similar to the pallia of mice, monkeys, and humans.
"If the bird pallium as a whole is organized just like the mammalian pallium, then it follows that the part of the bird pallium that is demonstrably functionally connected like the mammalian prefrontal pallium should also function like it," Vanderbilt neuroscientist Suzana Herculano-Houzel wrote of the studies.
"Corvids and parrots have upwards of half a billion neurons in their pallia and can have as many as 1 or 2 billion—like monkeys," she added. "So far, it appears that the more neurons there are in the pallium as a whole... the more cognitive capacity is exhibited by the animal."
In the second study, scientists at the University of Tübingen observed the neuronal response in trained crows as they pecked a screen in response to visual stimuli. The experiment suggested that the pallium of crows functioned similarly to the prefrontal cortex in primates, exhibiting neural activity that seemingly corresponds to the animal’s perception about what it has seen. Scientists have described the prefrontal cortex as a "mental sketch pad", representing knowledge and information not in the immediate physical environment.
"Concluding that birds do have what it takes to display consciousness— patterns of neuronal activity that represent mental content that drives behavior—now appears inevitable," Herculano-Houzel wrote of the second study.
The broader, speculative implication of the research is that the last common ancestor of birds and mammals, which existed 320 million years ago, may also have had the same cognitive machinery and thus been similarly capable of formidable thinking abilities.