Two studies published last September in the journal Science address the century-long riddle of why some birds, despite having a radically different forebrain organization than mammals, demonstrate comparable cognitive abilities.
The studies report that a neuron-dense part of the avian brain, the pallium, may help birds achieve these cognitive feats, including conscious awareness. Instead of the hallmark layering found in the cerebral cortex of mammals, the pallium in birds is characterized by high neuron density.
Using 3D-polarized light imaging and neural circuit tracing techniques, Martin Stacho of German’s Ruhr-University Bochum and colleagues characterized the anatomy of the pallium in pigeons and owls, which allowed them to visualize the region’s neuronal structure in great detail. Stacho discovered that the pallial fibers’ structure and circuitry in each of the distantly related bird species are strikingly similar to the layered architecture of the mammalian cortex. This organization may be the foundation of birds’ exceptional cognitive abilities.
Andreas Nieder of the University of Tübingen in Germany and colleagues observed the neuronal response in trained Carrion Crows as they responded to visual stimuli. The results revealed that, like the prefrontal cortex of primates, the pallium of crows exhibits neural activity that seemingly corresponds to the animal’s perception about what it has seen, which may be a marker for consciousness, according to the authors.
The two studies raise an interesting suggestion – could the mammalian cortex-like neural hardware that allows for complex cognitive abilities, such as consciousness, have already existed in the last common ancestor of birds and mammals 320 million years ago? Or, perhaps, it arose independently in both classes, despite very different forebrain organizations, by way of convergent evolution.
A version of this article appears in “Birding Briefs” in the March/April 2021 issue of BirdWatching. Subscribe here