Many scientists believe we only use one side of our brain for speech and language. Now, a new study from the US shows that as far as speech is concerned, we use both sides.
The study poses a significant challenge to current thinking about brain activity and could have important implications for developing treatment and rehabilitation to help people recover speech after stroke or injury, say the researchers from New York University (NYU) and NYU Langone Medical Center.
Senior author Bijan Pesaran, an associate professor in the Center for Neural Science at NYU, says:
"Our findings upend what has been universally accepted in the scientific community - that we use only one side of our brains for speech. In addition, now that we have a firmer understanding of how speech is generated, our work toward finding remedies for speech afflictions is much better informed."
Speech rarely studied separately from language
As well as listening and speaking, speech involves language for constructing and understanding sentences. Thus most studies conclude that speech, like language, happens on one side of the brain. And these studies rely on indirect measurement of brain activity, explain the researchers.
For their study, they took a different approach and examined the link between speech and brain processes directly.
The data for the study came from a group of patients being treated for epilepsy. They had electrodes implanted directly inside and on the surface of their brains as they performed sensory and thinking tasks.
Co-author Thomas Thesen, director of the NYU ECog Center where the data was collected, and an assistant professor at NYU Lagone, says:
"Recordings directly from the human brain are a rare opportunity. As such, they offer unparalleled spatial and temporal resolution over other imaging technologies to help us achieve a better understanding of complex and uniquely human brain functions, such as language."
To record what happens in the brain during speech alone that is separate from language, the patients were asked to repeat "non-words," like "kig" and "pob."
Study shows speech is a bilateral brain process
The recordings showed that both sides of the brain were involved during speech - suggesting that speech is a "bilateral" brain process, as the researchers conclude in their study report:
"Using a non-word transformation task, we show that bilateral sensory-motor responses can perform transformations between speech-perception- and speech-production-based representations. These results establish a bilateral sublexical speech sensory-motor system."
Prof. Pesaran adds:
"Now that we have greater insights into the connection between the brain and speech, we can begin to develop new ways to aid those trying to regain the ability to speak after a stroke or injuries resulting in brain damage. With this greater understanding of the speech process, we can retool rehabilitation methods in ways that isolate speech recovery and that don't involve language."
Meanwhile, US researchers - who discovered how accurately we respond to a beat is tied to how effectively our brains respond to speech - suggest in The Journal of Neuroscience that musical training could improve our brains' response to language.