Chuck Bednar for redOrbit.com – @BednarChuck
While scientists have known for well over a century which part of the brain is responsible for producing speech, new research published Tuesday in the journal Proceedings of the National Academy of Sciences reveals the details of this process for the first time.
Researchers from the Johns Hopkins University School of Medicine examined the brain region known as Broca’s area, which was found to play a key role in speech production more than 150 years ago, to learn exactly what that key role was.
By studying recordings from the surface of the brain, made between surgical procedures to treat epileptic seizures, they found that it is active early in the process of sentence formation and ends its task before even a single word is spoken – far earlier than experts had predicted.
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Senior author Dr. Nathan E. Crone, an associate professor of neurology at Johns Hopkins, explained that Broca’s area (which is located in the frontal cortex, above and behind the left eye) “mediates a cascade of activation from sensory representations of words in temporal cortex to their corresponding articulatory gestures in motor cortex.”
However, it remains largely inactive during the actual process of articulation, and is not involved in the actual production of individual word. Rather, the authors said that Broca’s area coordinates the transformation of information processing across cortical networks involved in the production of spoken words. Their findings may help treat stroke or injury-related language issues.
“We were interested in studying how information flows through the brain during speech, and in this study, for the first time, we were able to record very precisely the timing of activation of different centers of the brain during different language tasks,” Crone said in a statement Tuesday.
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“Broca’s area has always been viewed as very important for the articulation of speech, but until now its precise role was unclear,” he added. “We found that rather than carrying out the articulation of speech, Broca’s area is developing a plan for articulation, and then monitoring what is said to correct errors and make adjustments in the flow of speech.”
Conducting the research
Crone’s team conducted their research with the help of seven patients receiving treatment for epilepsy seizures at Johns Hopkins. While those individual were undergoing brain mapping to locate the source of their seizures, doctors recorded the electrical activity from Broca’s area and other parts of the brain using electrodes placed directly on the frontal cortex.
Since patients are awake and alert during this process, the researchers asked each of them to read or listen to a one-syllable word and repeat it out loud. They found that Broca’s area was the most active part of the brain just before the words were spoken, but its activity levels declined as the patients started speaking. The study also found that the region of the brain was most active when the patients were presented with unfamiliar, nonsense words instead of actual ones.
Based on their observations, Crone and his colleagues believe that Broca’s area serves as a sort of intermediary between the temporal cortex (where incoming sensory information is organized) and the motor cortex (which triggers the movements of the mouth).
While the area shuts down during speech delivery, it may remain active during a conversation, helping to plan future words and full sentences, said lead author Adeen Flinker, a postdoctoral researcher at New York University.
Flinker explained that neuroscientists previously believed that the brain’s language center was divided into two main areas: one that perceived speech, and one that produced it. The new study, however, reveals that Broca’s area “is not simply a center for speech production but rather a critical area for integrating and coordinating information across brain regions.”
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