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Processing Sign Language in the Brain

By: Inas Essa

How our brain processes language has always been a rich field for research since it manifests how we learn, speak, and generally communicate. Sign Language (SL) may seem extremely different from spoken and written languages (SWL) in communication form, grammar, etc., and this may lead to a way of thinking that each of them triggers a different area in the brain. However, previous research shows that both of them access similar brain structures. The point that was yet unclear and needed more identification was the brain regions that process both forms of language and to what extent linguistic similarities between SL and SWL are in the recruitment of similar neural resources during language comprehension.

Previous research suggests that SL may rely more on right hemispheric neural components, which are different from the left-lateralized neural response to SWL. But new research from the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany, has shown that Broca's area in the left hemisphere, which plays an important role in speech production and is central for spoken languages, is also crucial for sign languages. This area is where the grammar and meaning are processed whether it is spoken or signed language.



Autonomous Languages

Research in the cognitive science field has highlighted that sign languages are autonomous with complex organization of grammar, meaning, and other linguistic levels. Therefore, their processing in the brain has some similarities and also differences from spoken languages. Yet, these differences in language processing had remained unidentified until this new research highlighted how it works and which areas in the brain are actually involved in this complicated process.

In the recent meta-study published in the Human Brain Mapping journal, researchers worked on this point by analyzing different studies on sign language, processing experiments conducted globally to find an answer and identify how large the overlap is with brain regions that hearing people use in spoken language processing. "A meta-study gives us the opportunity to get an overall picture of the neural basis of sign language. So, for the first time, we were able to statistically and robustly identify the brain regions that were involved in sign language processing across all studies," says Emiliano Zaccarella, last author of the paper and group leader in the Department of Neuropsychology at the MPI CBS.


Broca’s Area is Involved

Broca’s area in the frontal brain of the left hemisphere has been known for its essential role in language processing. By analyzing the previous different studies, researchers found that it is also involved in the processing of sign language.

Through this analysis, researchers could confirm the existence of the overlap between spoken and signed language in Broca's area besides showing the role of the right frontal brain, which is the counterpart of Broca’s area and is responsible for processing non-linguistic parts like spatial and social information, in the process.

This means that facial expressions, hand movements, and body language used in sign language are perceived in the same way by hearing and deaf people. The difference remains, in the case of deaf people, in activating the language network in the left hemisphere of the brain while receiving these signs. So, they perceive gestures as gestures with linguistic content, not as something separate from language as hearing people do.

These findings suggest that the human brain evolved a lateralized language network in Broca’s area, which computes linguistic information independent of speech, and that this area is central in the language network in the brain. It works together with other networks whether the language used is spoken, signed, or even abstract linguistic information, in general, is received.

"The brain is therefore specialized in language per se, not in speaking." explains Patrick C. Trettenbrein, first author of the publication and doctoral student at the MPI CBS.


How The Brain Processes Sign Language