Birds like this homing pigeon may have the necessary neural anatomy for thinking.
Never before has “bird brain” been such a compliment: In recent years, birds have been found to make tools, understand abstract concepts, and even recognize paintings by Monet and Picasso. But their lack of a neocortex—the area of the mammalian brain where working memory, planning, and problem solving happen—has long puzzled scientists. Now, researchers have found a previously unknown arrangement of microcircuits in the avian brain that may be analogous to the mammalian neocortex. And in a separate study, other researchers have linked this same region to conscious thought.
The two papers are already being hailed as groundbreaking. “It’s often assumed that birds’ alien brain architecture limits thought, consciousness, and most advanced cognition,” says John Marzluff, a wildlife biologist and specialist on crows at the University of Washington, Seattle, who was not involved with either study. Researchers who have “demonstrated the cognitive abilities of birds won’t be surprised by these results,” he adds, “but they will be relieved.”
Indeed, it was because of birds’ and mammals’ similar cognitive abilities that Martin Stacho, a neuroanatomist at Ruhr-University Bochum, decided to investigate the avian forebrain, which controls perception. A gross comparison of mammalian and avian brains suggests “they have nothing in common,” he says. “Yet birds and mammals have many of the same cognitive skills.”
To find out how bird brains support these mental talents, Stacho and his colleagues examined microscopic slices of three homing pigeon brains using 3D polarized light imaging. This high-resolution technique let them analyze the circuitry of a forebrain region called the pallium, considered most similar to the mammalian neocortex. Although the pallium lacks the cortex’s six layers, it has distinctive structures connected by long fibers.
The scientists compared the images of the birds’ pallia with those of rat, monkey, and human cortices. Their analysis revealed the fibers in the birds’ pallia are organized in a manner strikingly similar to those of fibers in mammal cortexes.
Researchers also visualized the connections among neurons in the brains of two distantly related avian species: pigeons and owls. After removing the brains of deeply anesthetized birds, scientists injected crystals into the dissected brains and discovered circuits in the sensory regions that were similar to those found in the mammalian neocortex. It is this neuroarchitecture—the connections between structures, rather than the structures themselves—that explains why birds are as cognitively talented as mammals, they report today in Science.
“This research confirms the old adage that looks can be deceiving,” Marzluff says. Although bird and mammalian brains “look very different, this study shows us they are actually wired in very complementary ways.”
But do birds have conscious experiences? Are they aware of what they see and do? To find out, Andreas Nieder, a neurophysiologist at the University of Tübingen, observed the brains of carrion crows (Corvus corrone) as they responded to cues. Known as “feathered apes” for their intelligence, these crows and their cousins have even been shown to reason causally. But inferring consciousness from such experiments is challenging, Nieder says.
So, he and colleagues used a test similar to one that probes primates for signs of consciousness—a state of mind thought to arise with the sudden activation of certain neurons. They trained two lab-raised, 1-year-old carrion crows to move or stay still in response to a faint cue displayed on a monitor. When correct, the birds were rewarded. The scientists then implanted electrodes in the crows’ brains to record their neuronal signals as they responded. When the crows reacted, their neurons fired, suggesting they had consciously perceived the cue; but when they didn’t, their neurons were silent. The neurons that fired in agreement with the crows’ action were located in the pallia, the researchers report today, also in Science. Nieder calls this “an empirical marker of sensory consciousness in birds’ brains,” similar to that seen in primates.
That’s certain to stir debate, as “some researchers argue that consciousness is uniquely human,” says Irene Pepperberg, a comparative psychologist at Harvard University known for her work with Alex, an African gray parrot who communicated in English about abstract concepts. Pepperberg was not involved in these new studies but finds them “really exciting.”
Stacho and Nieder add that the building blocks for mammalian and avian cognition may have been present in their last common ancestor, some 320 million years ago. “Of course, mammal and bird brains evolved differently,” Stacho says. “What is surprising is how similar they still are in their perceptual and cognitive abilities.”
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