Researchers trained crows to move their heads when they perceived a visual stimuli projected on a screen. Photo courtesy of Tobias Machts, University of Tübingen
Sept. 25 (UPI) -- For the first time, scientists have observed conscious processes in the brains of crows. Until now, the neural origins of subjective experience have only been observed in humans and other primates.
"The results of our study opens up a new way of looking at the evolution of awareness and its neurobiological constraints," lead researcher Andreas Nieder, professor of animal physiology at the University of Tübingen in Germany, said in a news release.
Previous brain imaging studies have shown the ability of humans and the primates to consciously perceive sensory input is located in the cerebral cortex.
But the brains of most animals are structured quite differently than those of humans and nonhuman primates. Most animals don't have a cerebral cortex.
For the latest study, researchers in Germany wanted to determine whether conscious processes could originate brains without cerebral cortexes. To find out, scientists recorded the neural patterns of two trained crows as they responded to stimuli.
The crows were trained to move their heads to confirm whether or not they observed stimuli on a screen. When the crows witnessed visual stimuli, they moved their heads. When nothing appeared, they remained still.
During the initial test, researchers used unambiguous stimuli. For humans and birds, it was obvious whether a signal appeared on the screen, and the crows responded as expected.
In a second test, researchers used fainter signals. The signals were so faint, they were straddling the threshold of perception. Sometimes, the crows moved their head to show they had seen the stimuli. Other times, the signals flashed on the screen and disappeared without registering.
The neural signals recorded during the tests showed that when the crows observed the visual stimuli, nerve cells fired between the presentation of the stimulus and the behavioral response, the movement of the head. When the crows saw nothing and kept their heads still, the nerve cells remained silent.
In essence, the firing of the nerve cells predicted the subjective experience of the crows.
"Nerve cells that represent visual input without subjective components are expected to respond in the same way to a visual stimulus of constant intensity," Nieder said. "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."
The latest findings, published Friday in the journal Science, suggest consciousness may be more widespread throughout the animal kingdom and its origins farther back on the evolutionary timeline than previously thought.
The oldest common relative between humans and crows lived some 320 million years ago. It's possible consciousness arose then, during the geologic period known was the Carboniferous. It's also possible consciousness developed independently in a variety of animal lineages.
"In any case, the capability of conscious experience can be realized in differently structured brains and independently of the cerebral cortex," Nieder said.