Wired for Language -- Balter 2008 (324): 2 -- ScienceNOW

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Wired for Language
By Michael Balter
ScienceNOW Daily News
24 March 2008
We humans can do all sorts of things other animals
can't. Take language, for example--an ability
researchers have long chalked up to our big andspecialized brains. But size isn't everything, according
to a new study, which suggests that important changes
in the brain's wiring played a key role in language
evolution.

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Back in the 19th century, neuroanatomists identified
small regions of the human brain--such as Broca's areain the frontal cortex and Wernicke's area in theWell connected.
temporal cortex--and linked them to language. (Other,The arcuate fasciculus (red andsmaller-brained primates have regions that roughly
green in MRI image above andcorrespond to these areas, but they appear to serve
schematic below) links key
other functions.) More recently, scientists have foundlanguage areas in the humanthat language ability is not just isolated in discrete brainbrain.
areas but requires close communication between them.
For example, patients with damage to the brain's
CREDIT: JAMES RILLING AND
arcuate fasciculus, which consists of multiple bundles
MATTHEW GLASSER
of nerve fibers that connect Broca's and Wernicke's
areas, have severe difficulty speaking andunderstanding others. And a number of recent studies suggest that the brains of humans
are wired somewhat differently than those of other primates (Science, 2 March 2007, p.
1208 ).
To see whether the arcuate fasciculus had been rewired over the course of human
evolution, a team led by anthropologist James Rilling of Emory University in Atlanta,Georgia, turned to a relatively new technique called diffusion tensor imaging. This type of
MRI visualizes tissues by detecting the flow of water within them, allowing scientists totrace the long nerve fibers that connect parts of the brain. The researchers scanned thebrains of 10 live human subjects as well as three deceased chimpanzees and two
deceased macaque monkeys. They also looked at one live chimpanzee and one live
macaque, to be sure that any differences they saw were not due to the chemicals used topreserve the dead brains.
The scans showed dramatic differences between humans and the other primates.
Although the arcuate fasciculus in all three species was hooked up to the frontal cortex-including with Broca's area in humans--only in humans did the arcuate fasciculus extend
deeply into language-associated areas of the temporal cortex, such as Wernicke's area. In
chimps, the arcuate fasciculus made only very limited connections with temporal cortex
regions homologous to Wernicke's area, and there was little evidence of such connections
in macaques, the team reports online this week in Nature Neuroscience.
The authors conclude that the evolution of specialized language areas in the human brain
was accompanied by the addition of major new wiring via the arcuate fasciculus. The net
effect was that Wernicke's area, which is associated with understanding word meaning,
became strongly connected with Broca's area, which plays an important role in themhtml:file://C:\Users\Kuni\Documents\HomePage\Sakai_Lab_files\News\Wired_for_Langua...

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Wired for Language -- Balter 2008 (324): 2 -- ScienceNOW

Page 2 of 2construction and understanding of sentences.
The findings demonstrate "the uniqueness of the human brain, because it has been widelyassumed that the basic brain structures are essentially similar between humans andapes," says Kuniyoshi Sakai, a language researcher at the University of Tokyo in Japan.
Thomas Schoenemann, an anthropologist at James Madison University in Harrisonburg,
Virginia, says diffusion tensor imaging is a promising approach to understanding how ourbrains are wired, but he cautions that the approach should be repeated with more samples
before drawing firm conclusions.
Related sites
Visualizing the arcuate fasciculus
 Language and the brain, with more on Broca's and Wernicke's areaMagazine | News | Signaling | Careers | Multimedia | Collections | Help | Site Map | RSS
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