Courtesy of Anton Reiner
Schematic line drawings of transverse sections of the cerebrum in pigeon (first and last) and rat (middle), showing the outdated interpretation of cerebral organization and the outdated nomenclature for birds, the established interpretation of mammalian cerebral organization and nomenclature, and the current interpretation of the organization of avian cerebrum and new nomenclature. In each schematic, the yellow region represents pallium, the turquoise region represents striatum, and the orange region represents globus pallidus.
Everybody in avian neuroscience endures jokes about "bird brains." But the business of bird brains is quite serious. A profound understanding of learning and memory development has emerged from studies showing how male songbirds learn the mating songs of their species. Unfortunately, the birds may be communicating better with their peers than are the neuroscientists who study them.
The problem is nomenclature. Ill-conceived terms create false analogies with mammalian brains that bedevil...
Avian neuroscientists would spend the next three decades beginning their presentations by saying, "Despite what this area is called ..." Finally, in the late 1990s, an international team organized by Reiner and Jarvis began online discussions about implementing an updated nomenclature. In July 2002, the concerned researchers met at Duke to decide what the appropriate modern terms should be.
At one point it was argued that new names might become the basis for a fresh nomenclature that could extend across all species. But this seemingly elegant idea is almost impossibly complicated by reptiles, according to Reiner. Because the brains of different groups of reptiles are so different, each one has its own nomenclature. "Lizard people can talk to lizard people, turtle people can talk to turtle people, but for lizard people to talk to turtle people, they've both got to do their homework," says Reiner. More importantly, he explains, "To have a uniform terminology, we'd have to be sure we're correctly identifying area A in a mammal, area A in a crocodile, and area A in a bird ...."
Nevertheless, changing nomenclature in even just one field leaves the challenge of "before" and "after" terms. Would the time come when old papers would need a vocabulary key? The group suggested a compromise: Make sure the new terms would still shorten to the same acronyms as the old ones.
The final results of intense research and arguments will be published this spring in the
The new terms could ultimately result in a new understanding of the way that cortical structure leads to higher cognitive abilities, according to Jarvis. The neocortical-like area now called the hyperpallium in birds is a nucleated structure, rather than a layered one. "The behaviors that birds can do without a layered organization are just as complex and in some species more complex than most mammals," says Jarvis. "What layering seems to do is not give you the ability to 'become smarter,' but [it] allows you to grow a bigger body with a big brain, [since] with layering you allow more folding."
The new terms have already proved useful. Jarvis and several collaborators, as well as a University of California, Los Angeles, team led by Stephanie White, have just published back-to-back papers in the
Despite the consensus, controversy continues. Luis Puelles, head of the human anatomy and psychobiology department at the University of Murcia, Spain, was a part of the original nomenclature consortium, but he withdrew his support. Expressing his objections through E-mail, he writes, "Some meeting participants ... were in the paradoxical situation of wanting to correct the conceptual errors of their elders, but not wanting to correct their emerging own ones."
Puelles feels his colleagues' claims may be premature and overreaching. Much of the argument between the two sides turns on homologies. Karten's side would see a large area as homologous to mammalian neocortex. Basing his research on molecular markers with homeobox genes, Puelles contends that "the mammalian isocortex (neocortex) exclusively develops out of the dorsal pallium portion ... the lateral and ventral portions instead produce olfactory allocortex and the underlying claustroamygdaloid pallial nuclei." Both sides concede that more data are necessary, and will, of course, prove their own theories correct.
Even though scientists spar over the latest data, the new nomenclature has already made an impact, for it coincides with the cloning of the chicken genome and BAC clone libraries of the zebra finch already available. "The timing is really critical," White says. "We need to get this discussion and these parallels explicit now."