September 18, 2013
New Map Of Bird Brains Finds Fundamental Similarities To Mammalian Brains
Brett Smith for redOrbit.com - Your Universe Online
Using state-of-the-art genetic and diagnostic tools, researchers from Duke University and the University of California, San Diego have re-contextualized the map of the avian brain, as described to two separate papers published in the Journal of Comparative Neurology.
The 10-year exploration of the brains of eight species of birds was based on a computational analysis of the action of 52 genes across 23 areas of the bird brain.
Duke neuroscientist and study author Erich Jarvis said the genetic research suggested the existence of columnar organization in the bird brain.
“Columnar organization is a rule, rather than an exception found only in mammals," Jarvis said. "One way I visualize this view is that the avian brain is one big, giant (brain structure) folding around a ventricle space, functioning like what you'd find in the mammalian brain.”
To activate different genetic responses in the bird brains being studied, the birds were subjected to several different environmental stimuli such as darkness or light, silence or bird song, and a magnetic field that stimulated the navigational circuits of migratory birds.
The reworking of the map builds on a 2004 model that officially altered a century-old theory based on the idea that the avian brain is made of mostly primitive regions. Formulated by the Avian Brain Nomenclature Consortium, the game-changing model argued that the avian brain contains many forebrain regions similar to those found in mammals but organized in a different manner.
"The change in terminology is small this time, but the change in concept is big," said Jarvis, who led the 2004 effort.
One of the major changes posited by the new study is that two groups of cells on either side of the ventricle, a structural gap in the brain, are the same cell types with parallel patterns of gene expression. Previous studies have found that the ventricle is a physical barrier separating cell types. However, the Duke researchers demonstrated that dividing brain cells spread and flow around the ventricle as they multiply.
The new map reduces the bird cortex from seven populations of cells down to four major populations. By comparison, humans have five populations of cells structured in six layers.
Study researchers said the new findings could eventually be a useful model for answering questions about the human brain.
"Where does the mammalian brain come from?" asked Harvey Karten, a professor of neurosciences at the University of California-San Diego who was one of the first to re-think the brain structure of birds in the late 1960s. "And what's the origin of these structures at the cellular and molecular level?"
Some neuroscientists have said that the mammalian cortex is separate from that of other vertebrates. However, Jarvis and Karten are currently arguing that vertebrate brains have more in common than they have differences – which would make birds an even more useful model for investigating the human brain.
For example, “there are very few animal models where you can learn – at the molecular level – what's going on in vocal learning," Karten said.