The hearing parts of the brain, known as auditory cortex, are involved in processing and understanding sounds. In our latest study, we show that in deaf people the auditory cortex changes its role: it becomes involved in what we call working memory. Working memory can be thought of as a mental workspace where we mentally store, manipulate and update information to help us with ‘cognitive’ tasks like problem solving and decision making. This is very exciting, because it shows that regions of the brain can change from their usual role of processing sounds (sensory processing) to a new role of storing and updating information (cognitive processing). This means that the brain has a bigger and better ability to change how it works than we previously thought.
Studying deafness and the brain
One of the reasons we are interested in studying the deaf brain is that we can contribute evidence to guide and improve health and education for deaf people, and to promote Deaf Awareness. Studying deafness can also tell us a lot about how the brain works, and what the brain has the potential to do. So why is this?
We use our brain to make sense of all the information that we get through our eyes, ears and through touch. For example, all the images that reach our eyes are processed in what we call the visual cortex. The part of the brain that is involved in understanding sounds is called the auditory cortex. But what happens to the auditory cortex in deaf people? Does is not get used at all? Or does it do something else, and if so what? These are the kinds of questions that the deaf brain can help us to answer.
“Auditory cortex” and the deaf brain
Previous research, from our group and others, shows that in deaf people the auditory cortex helps them to process vision and touch. But how does this happen? What changes happen in the brain so that this region (that’s usually involved in hearing) starts to process these other senses?
One idea is that, well… not much is changed. I know this seems a bit strange, so I’ll give you an example. We know that there are specific parts of the brain that process different aspects of a sensory signal – for example, certain parts of the brain are involved in understanding the location of sounds, others in processing sound movement. Research has shown that, in deaf people, the parts of the brain that usually process the location and movement of sounds are involved in processing the location and movement of visual images. This means that the auditory cortex still keeps its usual role (location and movement), but now it does it for vision instead of hearing. In short, the sense changes (vision instead of hearing), but brain function is preserved (location and movement).
How could this be the case? An everyday analogy could be that of a food processor. In a food processor, whenever you put in carrots or tomatoes, it will give you slices. A food processor doesn’t care about what food it is, it will treat it as something that needs to be sliced. You could think the same way about nerve cells in the brain (neurons): they do not care what electrical signals or information gets put in (sound or vision), they will see it all as electrical signals and give you information about their location and movement.
Can the brain change its function?
So it seems that parts of the brain can maintain their usual role, but change so that they can now use this for different senses. But this may only be part of the story. Our research team want to understand how the deaf brain processes ‘higher-level functions’ or tasks, such as working memory.
What we did
In our study, we used a brain scanning technique (functional magnetic resonance imaging, fMRI) to look at how people’s brains responded while they performed some tasks. Twelve deaf people who used British Sign Language to communicate took part, and so did sixteen people who did not have a hearing loss but who could sign. Everyone did a working memory task and we looked at how their brain responded while they were doing this. They also did a colour task so that we could use this as a ‘control’ or comparison.
What did we find?
We saw that the auditory cortex responded during the working memory task in deaf people, but not in hearing people. This means that deaf people were using the hearing parts of their brain to perform the working memory task. Interestingly, this did not happen for the control colour task. This is very exciting because it shows that, rather than staying the same, regions of the brain may shift from their usual role of processing sounds (sensory processing) to a new role of storing and updating information (cognitive processing).
What does this mean?
Let’s use again our food processor analogy. A change in function means that the food processor makes slices when we put in tomatoes, but when we put carrots, it doesn’t make slices anymore; it makes something else entirely, let’s say soup. The only way this can happen is by either using a different blade or a different processor altogether. In the same way, if a brain region changes what it does from processing sound to working memory, then something has to change – either the way the neurons work, or the type of neurons that are involved.
These results are exciting because it means that the brain has a bigger and better ability to change how it works than we previously thought. However, these results are just the first step, and we still need to conduct more research to check that these brain areas do indeed change the role that they’re playing. We are now trying to understand if the hearing parts of the brain really are involved in working memory and other cognitive tasks. We are also looking at whether regions of the brain can maintain, as well as change, their function at the same time, or whether these two things can only happen separately from each other. Get in touch if you want to volunteer to take part in this research, and stay tuned for further results!
How to take part
If you are severely or profoundly deaf from birth or early infancy, and would like to take part in this research, please contact Dr Velia Cardin firstname.lastname@example.org, or visit her website for details about her research https://deafbrainplasticity.com/
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The original research paper was published recently in the journal Cerebral Cortex. Please visit Dr Cardin’s website (external link, opens in new window).
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