DURHAM, N.C. -- An international consortium of 29 neuroscientists has proposed a drastic renaming of the structures of the bird brain to correctly portray birds as more comparable to mammals in their cognitive ability. The scientists assert that the century-old traditional nomenclature is outdated and does not reflect new molecular, genetic and behavioral studies that reveal the brainpower of birds.
For example, they identified behavioral studies demonstrating that pigeons can discriminate cubist from impressionistic styles of painting; that crows can make useful tools and pass on their skills to other birds, and that parrots can not only learn human words but use them to communicate with humans.
The researchers emphasize that the old view of evolution as progressive and linear is outdated, pointing out that so-called "primitive" animals such as birds evolved some 50 to 100 million years after mammals.
The Avian Brain Nomenclature Consortium published a report on the rationale for the proposed revised nomenclature in the February 2005 issue of Nature Reviews Neuroscience. A technical report detailing the revisions was published in the May 2004 issue of the Journal of Comparative Neurology. The consortium's efforts were supported by the National Institutes of Health and the National Science Foundation, including the NSF's Waterman Award for young researchers to the Nature Reviews Neuroscience paper's first author, Duke University Medical Center neurobiologist Erich Jarvis.
"We believe that names have a powerful influence on the experiments we do and the way in which we think," wrote the consortium members in their paper. "For this reason, and in the light of new evidence about the function and evolution of the vertebrate brain, the international consortium of neuroscientists has reconsidered the traditional 100-year-old terminology that is used to describe the avian cerebrum.
"Our current understanding of the avian brain -- in particular the neocortex-like cognitive functions of the avian pallium -- requires a new terminology that better reflects these functions and the homologies between avian and mammalian brains."
The consortium members asserted that the old terminology -- which implied that the avian brain was more primitive than the mammalian brain -- has hindered scientific understanding. They concluded that "The inaccurate evolution-based terminology for the vertebrate brain that was used throughout the twentieth century became a severe impediment to the communication of scientific discoveries and the generation of new insights."
The consortium's revision of the nomenclature for avian brains is aimed at replacing the century-old system developed in the 19th century by Ludwig Edinger, considered the father of comparative neuroanatomy. Edinger's system was based on the then-common practice of combining Darwin's recent theory of evolution and Aristotle's old concept that there exists a natural "scale" of creatures from lowest to highest. The result were the views that evolution was progressive from organisms with "lower" intelligence to those with "higher" intelligence and that evolution had a purpose -- the generation of humans.
The resulting nomenclature used prefixes such as palaeo- ("oldest") and archi- ("archaic") to designate structures in the avian brain and neo- ("new") to designate supposedly new structures, particularly in the mammalian brain.
"According to this theory, the avian cerebrum is almost entirely composed of basal ganglia, the basal ganglia is involved only in instinctive behavior, and the malleable behavior that is thought to typify mammals exclusively requires the so-called neocortex," wrote the researchers.
However, said Jarvis, "We have to get rid of the idea that mammals -- and humans in particular -- are the pinnacle of evolution. We have to stop using words like 'lower vertebrates' and 'higher vertebrates.' We also have to understand that evolution is not linear, but an intricate branching process. So, we can't automatically expect to track a structure in the human brain back to other current vertebrate species."
According to Jarvis, new research "debunks the theory that the brain evolved in stages, like the laying down of geological sediments layer by layer. There is no evidence to show that there was a primordial brain structure to which so-called higher brain structures were systematically added."
In the Nature Reviews Neuroscience paper, the authors described studies by other researchers and their own studies demonstrating that the so-called "primitive" regions of avian brains were actually sophisticated processing regions homologous to those in mammals.
Those studies, which included tracing of neural pathways and behavioral studies, showed that such avian brain regions carried out sensory processing, motor control and sensorimotor learning just as did the mammalian neocortex. Also, wrote the scientists, molecular studies have shown that the avian and mammalian brain regions are comparable in their genetic and biochemical machinery. The neocortex and related areas in the mammalian brain are derived from a region in the embryonic cerebrum called the pallium, which means mantle or covering. Edinger thought, however, that most of this region in the bird cerebrum was part of the basal ganglia. Accordingly, he gave them names that ended in the basal ganglia term "-striatum", a practice he also employed in naming the parts of the mammalian basal ganglia.
As a result of the recent studies, the consortium has recommended such changes as renaming the avian brain region called the "archistriatum" as the "arcopallium," (arched pallium); and renaming the region that includes part of the true basal ganglia in birds, the "palaeostriatum primitivum" and the "ventral palaeostriatum" which sits below the pallium as the "pallidum" (pallidal or pale domain).
The consortium's work began in 1997 and was organized by Jarvis, Anton Reiner of the University of Tennessee Health Science Center in Memphis, Martin Wild of the University of Auckland in New Zealand, and other neurobiologists, dubbing themselves the ThinkTank. Jarvis recalled that "there were people in the field of avian neurobiology who knew the real structures behind these names and knew the names were wrong. And as a member of the younger generation of neurobiologists, I just felt that it was against my conscience to continue to use terminology that I knew was wrong and would mislead scientists."
For example, said Jarvis, researchers not familiar with the growing body of scientific literature demonstrating the sophistication of the avian brain could not understand how birds could exhibit sophisticated cognitive abilities with brains that held only what the nomenclature designated as the equivalent of the human basal ganglia.
The result of the scientists' objections led to a seven-year effort, which steadily recruited new participants. This effort culminated in an intensive international scientific forum at Duke in 2002, in which the new nomenclature was developed.
"We knew that we were doing something that may have an impact, not only on the immediate conduct of research in neuroscience, but on neuroscience for the next hundred years," said Jarvis. "And, this nomenclature will help people understand that evolution has created more than one way to generate complex behavior -- the mammal way and the bird way. And they're comparable to one another. In fact, some birds have evolved cognitive abilities that are far more complex than in many mammals."
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