The human thinking organ has to work in a very special way, if only gestures convey information, one might think. But an overview study now shows that the brain specializes in language and not necessarily in speaking. It is becoming apparent that a region in the left hemisphere processes sign language, which is also responsible for spoken language. It is apparently a general node in the voice network. The gestures, which the hearing perceive as pure movement sequences, evoke the same neural effects in the deaf as sounds.
Language is a key concept for the success of our species – thanks to our highly developed communication skills, we can convey complex information to our fellow human beings. However, one has to state that language is not necessarily the same as speaking. Over 70 million people around the world use complex movements of hands, face and body as a fully-fledged communication system. The more than 200 different sign languages also convey information on several linguistic levels such as grammar and meaning. From the point of view of brain research, the question arises of how our thinking organ deals with this communication system.
Do you need special brain activity?
Various studies have already revealed some aspects of this question. But so far there has been no uniform picture from the research field, report the researchers working with Emiliano Zaccarella from the Max Planck Institute for Cognitive and Neurosciences in Leipzig (MPI CBS). That is why they have now worked out from all relevant studies which brain regions are relevant in sign language and how big the overlap with spoken language processing is in the hearing. “This meta-study enabled us to get an overall picture of the neural basis of sign language. For the first time, we were able to reliably identify the brain regions that were involved in the processing of sign language across all studies, ”explains Zaccarella.
The scientists found: In almost all of the studies evaluated, researchers reported a function of the so-called Broca area in the frontal lobe of the left hemisphere in the processing of sign language. It is already known that this region of the brain also plays a central role in spoken language as well as in the perception of writing and is used in the processing of grammar and meaning. In order to further substantiate the results from the meta-study and classify them more comprehensively, the scientists then compared their results with a database containing information from several thousand studies with brain scans.
A node in the voice network
For the first time, they were able to clearly show that there is an overlap between spoken and sign language in the Broca area. As they further report, it also became apparent what significance the counterpart to Broca’s area in the right frontal lobe has, which also plays a role in many of the studies on sign language evaluated. As the researchers explain, this area of the human brain usually records spatial movements. This means that the deaf and hearing people perceive the movements of hands, face and body in the same way. In the deaf, however, they also activate the voice network in the left hemisphere, including Broca’s area. They perceive the gestures as gestures with linguistic content – instead of pure movement sequences, as would be the case with hearing people, the results suggest.
As the scientists sum up, their study shows the central role of Broca’s area as a node in the language network of the human brain. This left-sided brain region apparently generally processes abstract linguistic information in any form of language. To this end, she works together with other special networks – depending on whether people use language in the form of signs, sounds or writing, the meta-analysis shows. “The brain specializes in language per se, not in speaking,” says first author Patrick Trettenbrein from the MPI CBS.
The scientists are now planning to investigate the significance of Broca’s area in more detail: Among other things, they want to find out whether, similar to hearing people, the different parts of this brain region also specialize in grammar or the meaning of elements of sign language in the deaf.
Source: Max Planck Institute for Human Cognitive and Brain Sciences, specialist article: Human Brain Mapping, doi: 10.1002 / hbm.25254