Brain signal measurements have shown that crows possess the ability to think consciously - something previously thought to be restricted to humans and primates.
It means that the birds are aware of themselves, and the world around them, and ‘know that they know’ - just like human beings.
Until now, this sort of consciousness has only been witnessed in primates, which have completely different brain structures to birds.
Professor Andreas Nieder says, “The results of our study opens up a new way of looking at the evolution of awareness and its neurobiological constraints.”
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For humans, and our nearest relatives, nonhuman primates, the ability to be aware of things consciously is located in the cerebral cortex.
Until now there’s been no evidence to show that birds (who lack a cerebral cortex) can think in this way.
In terms of evolutionary history it means the origins of consciousness could be far older and more widespread in the animal kingdom than previously thought.
“The last common ancestors of humans and crows lived 320 million years ago,” says Nieder.
“It is possible that the consciousness of perception arose back then and has been passed down ever since.”
Different trials presented either bright figures or no stimulus at all, and the crows reliably signaled the presence or absence of these stimuli, respectively.
Some stimuli were so faint that they were at the threshold of perception: for the same faint stimulus, the crows sometimes indicated that they had seen it, whereas in other cases they reported that there was no stimulus.
While the crows responded to the visual stimuli, the researchers simultaneously recorded the activity of individual nerve cells in the brain.
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When the crows reported having seen something, the nerve cells were active in the period between presentation of the stimulus and the bird’s response - showing that it was ‘processing’ the experience.
If they did not perceive a stimulus, the nerve cells remained silent.
Nieder says, “Nerve cells that represent visual input without subjective components are expected to respond in the same way to a visual stimulus of constant intensity.”
“Our results however conclusively show that nerve cells at higher processing levels of the crow’s brain are influenced by subjective experience, or more precisely produce subjective experiences.”
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