Researchers Identify Brain Regions Involved in Conversation

Having a conversation takes high-level coordination: listening, processing, formulating responses, often rapidly amid a back-and-forth dialogue. It’s all happening so fast that people are often planning their responses while listening.

A recent NIDCD study mapped the brain during speech planning. The findings may lead to a better understanding of speech disorders such as stuttering. Results appeared in Nature.

Earlier studies identified several brain regions likely involved in the speech planning process, but the exact neural circuits responsible for planning replies weren’t well understood. 

A research team, led by Dr. Michael Long of the NYU Grossman School of Medicine, measured brain activity in eight volunteers undergoing brain surgery to remove tumors or treat epilepsy. Brain surgery patients are initially kept conscious to avoid damaging speech centers in the brain.

To precisely monitor brain activity, the team used electrocorticography (ECoG), a technology in which electrodes are placed directly on the brain’s surface. Hundreds of electrodes were placed on each patient’s left-brain hemisphere, which is involved in speech and language.

While using ECoG, the researchers posed a series of structured questions to the volunteers, changing the word order of the same question to help researchers determine when speech planning began. Researchers found that brain activity during speech planning was distinct from perception and speech production. The patterns suggested the brain networks for each function are largely separate.

The team then mapped the location of the circuits involved. Most of the electrodes that responded during planning were in two regions: the caudal inferior frontal gyrus (cIFG) and the caudal middle frontal gyrus (cMFG). The cIFG, or “Broca’s region,” has long been known as an important language processing center. But the involvement of cMFG in speech planning was unexpected.

Further tests showed that the planning networks identified during the task were also active during natural conversations. These results shed light on the brain circuitry that enables quick verbal exchanges. 

“Our study pinpoints brain networks behind the planning that makes this back and forth possible which have been elusive until now,” said Long.—adapted from NIH Research Matters