Two studies published in the journal Science last September address the centuries-old mystery of why some birds have comparable cognitive abilities despite a radically different forebrain organization than mammals.
The studies report that a neuron-dense part of the bird’s brain, the pallium, can help birds achieve these cognitive functions, including consciousness. Instead of the typical stratification in the cerebral cortex of mammals, the pallium in birds is characterized by a high density of neurons.
Martin Stacho from the Ruhr University Bochum and colleagues in Germany used 3D polarized light imaging and techniques to track neural circuits to characterize the anatomy of the pallium in pigeons and owls, which enabled them to visualize the neural structure of the region in detail. Stacho discovered that the structure and circuitry of the pallial fibers in each of the distantly related bird species are strikingly similar to the layered architecture of the mammalian cortex. This organization can be the basis for the birds’ exceptional cognitive abilities.
Andreas Nieder from the University of Tübingen in Germany and colleagues observed the neural reaction in trained carrion crows when they reacted to visual stimuli. The results showed that, like the primate prefrontal cortex, the crow’s pallium exhibits neural activity that appears to match the animal’s perception of what it has seen, which the authors suggest could be a marker of awareness.
The two studies make an interesting suggestion – could the mammalian cortex-like neural hardware that enables complex cognitive abilities such as consciousness have existed 320 million years ago in the last common ancestor of birds and mammals? Or perhaps it arose in both classes independently, despite very different forebrain organizations, through convergent evolution.
A version of this article appears in Birding Briefs in the March / April 2021 issue of BirdWatching. Subscribe here
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