Bird brains' cortex-like structure may be behind complex cognition, and even consciousness

Informing the century-long riddle of why some birds, despite having a radically different forebrain organization than mammals, demonstrate comparable cognitive abilities, two new 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 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 et al. 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 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. Suzana Herculano-Houzel discusses the papers further in a related Perspective.

Credit: 
American Association for the Advancement of Science