RETURN TO THE WORLD SCIENCE HOME PAGE

New language area in brain found

Discovery could reveal facts about the origins of language, researchers say

A study using a powerful new brain scanning technique has confirmed suspicions that the brain has a third language circuit beside the two known to science, researchers say. The finding could reveal new facts about the origins of language, they add.

The language network of the brain seemed simpler in the past. One brain area was recognized to be critical for the production of language, another for its comprehension. A dense bundle of nerve fibers connected the two.

But there have always been naysayers who pointed to evidence that failed to fit this tidy picture. The new study, published in the December 13, 2004 online edition of the research journal Annals of Neurology, bears this out, the researchers said.

“We were surprised that the two classical language areas were densely connected to a third area, whose presence had already been suspected but whose connections with the classical network were unknown,” said Marco Catani, a psychiatrist at King’s College London and lead author of the study. 

The authors dubbed this language area “Geschwind’s territory” in honor of the American neurologist Norman Geschwind who championed its linguistic significance decades ago.

Language is generated and understood in the cortex, the outermost covering of the brain. Paul Broca and Carl Wernicke, 19th Century neurologists, noted that damage to specific cortical areas, which came to bear their names, produced primarily language production or language processing disorders, but not both. A large bundle of nerve fibers was found to connect Broca’s and Wernicke’s areas, and damage to this pathway also produced language disorders.

However, even in the 19th Century, there were bits of evidence that other brain areas play some role in language, though these have remained enigmatic, as scientists could not use animals to probe language networks in the same way they could visual or movement networks in the brain.

In the last few decades, advanced brain imaging techniques have allowed scientists to begin studying these areas in living humans. One of the more recent techniques, Magnetic Resonance Imaging (MRI), allows researchers to identify which areas are being used during different tasks, including producing and comprehending language.

A new variant of this technique, called Diffusion tensor MRI, reveals in greater detail the nerve fiber connections through which different brain regions form communication networks, researchers say. Using this new method, Catani and his colleagues found a separate, roundabout route that connects Broca’s and Wernicke’s areas via a region in the parietal lobe of the cortex, the region at the top of the brain. Geschwind had pointed this out as an important language region already in the 1960s.

“There are clues that the parallel pathway network we found is important for the acquisition of language in childhood,” said Catani. “Geschwind’s territory is the last area in the brain to mature, the completion of its maturation coinciding with the development of reading and writing skills. An important future line of study will be to examine the maturation of this area and its connections in the context of autism and dyslexia.”

These pathways appear to exist – in more rudimentary forms – in the brains of monkeys, the researchers said, which may have bearing on the search for the evolutionary origins of language. “These data suggest that language evolved, in part, from changes in pre-existing networks, not through the appearance of new brain structures,” said Catani.

“This method provides another example of the remarkable versatility of MRI technology,” said Marsel Mesulam of Northwestern University in Chicago, Illinois, who has written an editorial scheduled to accompany the print publication of the article. One could theoretically combine the new type of MRI with other types to “reveal the connectivity of brain areas with identified specializations,” he added. “This method can be applied anywhere in the brain.”

* * *