NIH study shows the deaf brain processes touch differently
People who are born deaf process the sense of touch differently than people who are born with normal hearing according to NIH-funded research.
Akinso: A recent study suggests that since the auditory cortex of profoundly deaf people is not exposed to sound stimuli, it adapts and takes on additional sensory processing tasks.
Karns: In any scientific study we’re asking a specific question, and the question we were trying to answer is what happens to the hearing regions of the brain when a person is born deaf.
Akinso: Dr. Christina Karns is a NIH postdoctoral research associate in the Brain Development Lab at the University of Oregon.
Karns: The reason that we want to know the answer to this question is it tell us something about how the brain develops. We know that the basic instruction for how a brain is built based on genes, but carrying out these instructions is highly influenced by experience that tells the development is plastic—meaning flexible and multiple opposed to sort of hard and brittle. And because the experience of someone who’s born deaf is really different than the typical experience that can tell us how flexible is the brain development of the auditory system.
Akinso: Deaf people may process vision using many different brain regions, especially auditory areas, including the primary auditory cortex. However, no one has tackled whether vision and touch together are processed differently in deaf people, primarily because in experimental settings, it's more difficult to produce the kind of precise tactile stimuli needed to answer this question. Dr. Karns and her colleagues developed an apparatus that could be worn like head-phones while subjects were in a MRI scanner.
Karns: So we scanned the brain of hearing people and people born profoundly deaf while they did a task in the MRI scanner. We compared the brain signal measures between these two groups. While the people were in the scanner they do a task, where they detect dim lights or feel gentle touches to the face. So we had to develop this kind of crazy headphone apparatus that they can wear inside this kind of tight tube. And the tubes deliver both ear puffs and then they have a little fiber optic cable that presents a dim light so that we can present touch and vision right at the same time, right in about the same place. Our volunteers ended up looking a bit like a cyborg wearing this headset with all these tubes kind of attached aiming at their face but it was pretty comfortable for them.
Akinso: The researchers have been able to show that deaf people use the auditory cortex to process touch stimuli and visual stimuli to a much greater degree than occurs in hearing people.
Karns: And what we found was that in deaf participants Heschl's gyrus, which is primary auditory cortex, had a much stronger response to touch and vision than in the hearing participants. So in hearing participants just like you might expect that part of the brain is specialized for hearing. So it’s not going to be as responsive to these other senses. But in the deaf people the brain has reorganized or organized in a way that’s not typical so that they're responding to these other senses. And in fact the response to touch was about twice as strong as for vision. And touch and vision seem to interact with each other more in the deaf participants.
Akinso: The study adds to a growing list of discoveries that confirm the impact of experiences and outside influences in molding the developing brain.
Karns: One of the really cool findings was that in some deaf participants the way that touch and vision in auditory cortex interacted was so strong that a single flash of light appeared to be two flashes when it was paired with two air puffs. So feeling two touches made them think they saw two lights. And what was really cool was that those deaf participants with the largest response in the primary auditory cortex saw this illusion more often than others.
Akinso: Dr. Karns says there are several ways the finding may help deaf people.
Karns: We've learn something new about the deaf brain and how sensitive the hearing areas are the touch and the deaf and also to vision. And there's a lot more work to do, but this discovery might support the use of new approaches for education of deaf people. The more we know about the way that the brain might adapt the better that we can tailor education and therapeutic intervention to deaf folks.
Akinso: She adds that the primary auditory cortex in people who are profoundly deaf focuses on touch even, more than vision. For more information on this study, visit www.nidcd.nih.gov. For NIH Radio, this is Wally Akinso— NIH...Turning Discovery Into Health®
About This Audio Report
Reporter: Wally Akinso
Sound Bite: Dr. Christina Karns
Topic: deaf, brain, deafness, auditory, cortex, hearing
Additional Info: NIH study shows the deaf brain processes touch differently