Individuals who are born deaf use the "hearing" part of their brain to feel touch and to see objects, suggests new research that highlights the plasticity of the human brain.
The new study, detailed online July 11 in The Journal of Neuroscience, shows that deaf people use the so-called auditory cortex to process both touch and visual stimuli much more than hearing individuals do.
"This research shows how the brain is capable of rewiring in dramatic ways," Dr. James Battey, Jr., director of the National Institute on Deafness and Other Communication Disorders, said in a statement. "This will be of greatinterest to other researchers who are studying multisensory processing in the brain."
Past research has suggested deaf people may use their brains differently than those born with hearing. For instance, researchers found when deaf individuals are signing, they rely on the same brain areas that interpret spoken language, suggesting that something about language is universal.
Another study has shown that those born deaf are better at processing peripheral vision and motion, the researchers noted. Perhaps, the researchers said, deaf individuals use several brain regions, particularly auditory ones, to process vision. But would deafness also affect how the brain processes touch and vision together? This has been a tough one to answer, say the researchers, because in the lab, it's tricky to produce precise tactile stimuli. [Top 10 Mysteries of the Mind]
In the new study, participants wore headphonelike devices developed by the researchers while inside a functional magnetic resonance imaging (MRI) scanner, a type of brain scan that reveals blood flow to active areas of the brain. Touch stimuli came in the form of soundless puffs of air delivered via flexible tubing to above the right eyebrow and to the cheek below the right eye; fiber-optic cables delivered brief pulses of light (visual stimuli).
The researchers measured this blood flow particularly in the Heschl's gyrus, a region in the primary auditory cortex where sound first reaches the brain.
"We designed this study because we thought that touch and vision might have stronger interactions in the auditory cortices of deaf people," study researcher Christina Karns, of the Brain Development Lab at the University of Oregon, said in a statement. "As it turns out, the primary auditory cortex in people who are profoundly deaf focuses on touch, even more than vision, in our experiment."
If, in fact, touch and vision interact more in the brains of deaf people, perhaps, the researchers say, touch could be used to help these students learn math or reading. In addition, if scientists could measure how much the auditory cortex has been hijacked for other sensory processing, they might be able to figure out how to retrain the brain to devote more capacity to auditory processing instead.
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