It had been assumed that primary, or sensory, consciousness is only possessed by humans and a few of our primate cousins that share similarly sharp brains. However, a new study has shown for the first time that crows also possess some degree of subjective experience and sensory consciousness.
Perhaps most intriguing of all, the research indicates that these brainiac birds are able to display consciousness despite lacking a cerebral cortex, the brain structure that was previously thought to be responsible for this feat of higher intelligence. The new discovery is reported in the journal Science.
So, first things first: what is consciousness? It’s a question that philosophers have argued about for centuries, but it loosely refers to an awareness of one's own internal experience and external existence. Although scientists have previously shown that crows and other corvids are anything but bird-brained, they have never definitively proven they have true sensory consciousness, the ability to have a subjective experience that can be explicitly accessed and then responded to.
By recording behavior and brain activity at the same time, scientists at the University of Tübingen in Germany were able to show that the birds were capable of conscious perception.
To test this out, they trained two carrion crows (Corvus corone) to reliably move their heads in response to seeing different colored marks on a screen. Meanwhile, the researchers recorded the activity of individual neurons using electrodes implanted in the crows’ brains. Some colors were vibrant and clear to see, and the crows picked up on them, but others were so faint and fleeting they skirted the edge of perception. For the faint stimulus, the crows sometimes indicated that they had seen it, but in other cases, they reported there was no stimulus. By looking at the brain activity during this, the researchers were able to show that the nerve cells of the crows' brains were being influenced by subjective experience in reporting their answers because they were consciously perceiving sensory input from the stimulus. It appears their brains were not simply reacting to the brightness of the color in an instinctive fashion, but rather responding to their own internal assessment.
“Nerve cells that represent visual input without subjective components are expected to respond in the same way to a visual stimulus of constant intensity,” Professor Andreas Nieder, a neurobiologist at the University of Tübingen, said in a statement. “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.”
Interestingly, conscious experience is thought to take place in the cerebral cortex among humans and other non-primates. However, birds do not have this brain structure. According to the researchers, this challenges many old assumptions about consciousness. In doing so, it opens up the intriguing possibility that the evolutionary origins of consciousness might be far older and more widespread in the animal kingdom than previously thought.
"I think the results of our study open up a new way of looking at the evolution of awareness and its neurobiological constraints," Professor Nieder told IFLScience. "It becomes more likely that also other animals on different branches of the tree of life, and with brains that strikingly differ from ours, also have sensory consciousness."
In another study published in Science last week, a separate team of researchers from Ruhr-University Bochum in Germany closely studied the brains of birds with known cognitive abilities, owls and pigeons, and discovered they contain sensory connections that were similar to those found in the mammalian neocortex. Essentially, it was these connections, as opposed to structure, that gave birds their brainy abilities.