Our understanding of the human brain is always changing—much like the brain itself, which is constantly forming new pathways in the phenomenon known as neuroplasticity. Now we know that the brain responds to even slight diminishment in sensory perception.
New research is suggesting that the brain actually reorganizes itself in response to the loss of one of the five senses. Like a company that closes a division but keeps the employees on the payroll, it reassigns neurons to other functions. It does this even when the sensory loss is fairly minor.
Dr. Anu Sharma of the University of Colorado unveiled research in May showing that, in people with hearing loss, the parts of the brain that process visual patterns and touch will “recruit” areas of the brain where hearing is normally processed. That happens both when the hearing impairment is severe (as in deafness) and when it’s minor (in the early stages of age-related hearing loss).
Dr. Robert Sweetow, an audiologist and professor at the UC–San Francisco School of Medicine, puts it like this: “Twenty-five years ago the brain was thought to be a fixed entity—that if you were blind, the visual cortex wasn’t getting stimulated anymore.
“If you’re deaf or blind, that is affecting the peripheral organs—the eye and the ear,” he continues. “But the brain itself, those neurons designed for hearing and vision, they want to be doing something. So they take on other roles.”
Audiologists are trying to figure out what this means for people with hearing loss. Can it be reversed? Can those former “employees” of the brain’s hearing processing center ever get their old jobs back? And if they can’t, what is the prognosis for patients recovering their ability to process sound with the aid of technology?
It depends on whom you ask. Sharma warns that such “cross-modal cortical reorganization” could spell bad news for people who are suddenly reintroduced to sound—as happens when people get cochlear implants, which bypass damaged auditory organs and send signals directly to the brain.
“We find that this kind of compensatory adaptation may significantly decrease the brain’s available resources for processing sound and can affect a deaf patient’s ability to effectively perceive speech with their cochlear implants,” said Sharma.
This being science, there is a competing view. “Other researchers have taken the idea that if certain areas of brain—like the frontal lobe, which controls a lot of logic and rational thinking—if that starts to take over for some of the hearing functions, then maybe that is a good compensation,” says Sweetow.
The jury’s out on this one for now. But be it known: this writer would gladly trade a little hearing for some extra smarts, in case anybody’s asking. —Traci Hukill