Broca’s area, located in the frontal lobe of the left hemisphere, is most involved in the processing of sign language, according to a new study.
- The researchers found that Broca’s area, located inside the cortex in the frontal lobe, was also involved in the analysis of sign language in people with hearing loss.
- This area of the brain, which is the motor area of spoken language, is not activated in the same way in them. Unlike hearing people, hand gestures and facial expressions make up the entire linguistic content.
What is the difference, for our brain, between spoken language and sign language? Scientists at the Max Planck Institute for Neurology and Cognitive Sciences in Leipzig, Germany, have just answered this question by pooling sign language processing data from several studies conducted around the world. Their work has just been published in the journal Human Brain Mapping. “A meta-study gives us the opportunity to get an overview of the neural basis of sign language, explains Emiliano Zaccarella, one of the authors of the article and group leader in the department of neuropsychology at the Max-Planck Institute. Thus, for the first time, we were able to statistically and robustly identify brain regions involved in sign language processing from all studies.” According to their results, the region of the brain that is most involved in the processing of sign language is Broca’s area, located in the frontal lobe of the left hemisphere.
Sign language and spoken language are different for the brain
For the brain, spoken language is different from sign language. It has its own organization, meaning and grammar. Previous studies of sign language processing in the human brain have highlighted similarities and differences between spoken and sign linguistics. But until now, researchers have been unable to analyze how the two forms of language are processed in the brain. Scientists from the Max-Planck Institute first verified that Broca’s area was also solicited by spoken language. For this, they compared their results with a database containing several thousand studies with brain scans. Thus, they believe that this region of the brain, Broca’s area, also plays an important role in spoken language, especially for grammar.
Broca’s area always activates in deaf people
The researchers also succeeded in showing that the right frontal lobe, that is to say the equivalent of Broca’s area but on the left side of the brain, was involved in sign language. The right frontal lobe was already known in previous studies because it makes it possible to process the non-linguistic aspects of language, such as the spatial or social information of one’s interlocutor. It is he, for example, who analyzes the movements of the hands, the expressions of the face or the body during a conversation. This new study also confirms the role of this area in sign language. However, the difference between hearing and deaf people is that the latter not only activate the right frontal lobe to understand the signs of their interlocutor but also Broca’s area. For them, the gestures constitute the entire linguistic content, which requires the activation of this Broca’s area in their brain to analyze them. While hearing people activate Broca’s area in oral language but do not activate it to analyze these gestures, their right frontal lobe takes care of it. The reason is that gestures, for hearing people, do not constitute the entire linguistic message. They are only additional movements, which bring a plus but do not determine the understanding of their interlocutor.
“The brain is therefore specialized in language itself, not just oral“
Broca’s area is activated for both spoken and oral language, but not in the same way. The researchers therefore believe that it is a central node in the linguistic network of the human brain, because it is also important for writing. But depending on the signal to be analyzed – sign, sound or written character – this zone works with other networks, which explains why it is always activated in deaf people, and less in hearing people. “The brain is therefore specialized in language itself, not just oral“, concludes Patrick C. Trettenbrein, one of the authors of the study and doctoral student at the Max-Planck Institute. Scientists are now working to determine whether Broca’s area is as involved in the grammar of sign language in deaf people as it is in hearing people.
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