On the trail of amazing bird intelligence: Two studies now shed light on why the brain performance of some bird species can compete with that of primates. According to this, the bird’s brains are more similar to our thinking organs than expected: Researchers have uncovered neuronal structures in the bird’s brain that are similar to those in the neocortex of mammals. A second team of researchers was able to link these areas with conscious sensory perceptions in corvids.
“You sparrow brain!” For a long time, birds were thought to have had little brains. The reason: Their brains appear small and they do not seem to have the structures responsible for the higher cognitive abilities of mammals. But modern research has now impressively shown that birds are anything but stupid: representatives of parrots and corvids in particular understand highly complex relationships, use tools and can empathize with other living beings. Their brain performance can be compared with that of the most intelligent mammals.
Neurological studies have also already provided indications as to why bird brains can produce such high levels of performance: They have a particularly high nerve density. What remained unclear, however, was the apparent lack of the typical structures of the cerebral cortex (neocortex) in birds, which are responsible for the higher cognitive abilities of mammals. This area of our brain is made up of six layers and arranged in columns perpendicular to these layers. At first glance, however, it seems that there are only collections of neurons in the bird’s brain. But the researchers led by Onur Güntürkün from the Ruhr University Bochum have now been able to show that there are organizational structures in bird brains that are similar to those of mammalian brains.
Organized in a similarly complex manner
In their sights was a forebrain region of birds called the pallium, which is believed to be most similar to the mammalian neocortex. The scientists first examined this area using polarized light imaging. It makes it possible to show individual nerve fibers and their alignment. As the researchers report, the examination of the brains of pigeons and owls revealed an organization that is similar to that in the mammalian brain: In the pallium, too, the fibers run horizontally and vertically in a similar way to the neocortex.
In further experiments, the researchers examined thin sections of the brain using tiny crystals, which are transported into the finest branches of the nerve cells in brain slices. In this way, they were able to record the networking of cells in the bird’s brain more precisely than ever before. “Here, too, there was a structure in columns in which signals are passed on from top to bottom and vice versa, and horizontal long fibers,” reports Güntürkün. The results therefore show that there is a similar neuro-architecture that explains why birds are cognitively similarly gifted to mammals, the researchers sum up.
Crows looked into their brains
This is exactly what the second current study makes clear: the researchers working with Andreas Nieder from the University of Tübingen were able to demonstrate by measuring brain signals that the conscious sensory perception in crows (Corvus corone) is based on processing by nerve cells in the pallium. It is the first neuroscientific evidence of the processes on which the amazing abilities of these feathered shrews are based.
For the study, the scientists trained two crows: in order to get delicacies, they should press their head to indicate whether they had seen a stimulus on a screen or not. At first, the decisions were easy: the birds were presented with either clear points of light or no stimuli at all. But then it got tricky: the researchers made some stimuli so weak that they were within the range of the birds’ perception limit. Sometimes the crows indicated that they had seen the weak stimulus, in other cases they opted for the negative statement. Thus, the subjective perception of the crows was asked – this is a process of consciousness, the researchers explain.
Signature of subjective perception
They then recorded what was happening in the brain using implanted electrodes: while the crows reacted to the optical stimuli, the researchers recorded the activity of individual nerve cells in the brain. It was shown that if the crows thought they had seen something, nerve cells of the pallium were active in the period between the stimulus presentation and the behavioral response. Based on the activity of the nerve cells, it was thus possible to predict which subjective experience the crows felt with regard to the stimulus. “Nerve cells that represent visual impressions without subjective components should always respond the same to a constant visual stimulus,” explained Nieder: “Our results, on the other hand, only allow the conclusion that nerve cells at higher processing levels of the crow’s brain are influenced by subjective experience, or more precisely , produce subjective experiences, ”says Nieder.
Both studies now raise the question of how the similar structures and processes that underlie cognition in mammals and birds have evolved. It seems possible that the basic elements were already present in the last common ancestors of both lines of development about 320 million years ago, say the scientists. In addition, however, a parallel development is also an option, which has independently led to similar structures and skills. “In any case, the ability to consciously experience can be achieved with differently constructed brains,” Nieder concludes.
Source: Research Center Jülich, University of Tübingen,
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Science, doi: 10.1126 / science.abc5534