Brain architecture of hearing, deaf people 'nearly identical'

A recent study has shown that the neural architecture in the auditory cortex, the part of the brain that processes sound, of profoundly deaf and hearing people is virtually identical.

Lead author Ella Striem-Amit from Harvard said, "One reason this is interesting is because we don't know what causes the brain to organize the way it does. How important is each person's experience for their brain development? In audition, a lot is known about (how it works) in hearing people, and in animals...but we don't know whether the same organization is retained in congenitally deaf people."

Those similarities between deaf and hearing brain architecture, Striem-Amit said, suggest that the organization of the auditory cortex doesn't critically depend on experience, but is likely based on innate factors. So in a person who is born deaf, the brain is still organized in the same manner.

But that's not to suggest experience plays no role in processing sensory information.

Evidence from other studies have shown that cochlear implants are far more successful when implanted in toddlers and young children, Striem-Amit said, suggesting that without sensory input during key periods of brain plasticity in early life, the brain may not process information appropriately.

To understand the organization of the auditory cortex, the team first obtained what are called "tonotopic" maps showing how the auditory cortex responds to various tones.

They then used the areas showing frequency preference in the tonotopic maps to study the functional connectivity profiles related to tone preference in the hearing and congenitally deaf groups and found them to be virtually identical.

"There is a balance between change and typical organization in the auditory cortex of the deaf," said senior researcher Yanchao Bi from Beijing Normal University, "but even when the auditory cortex shows plasticity to processing vision, its typical auditory organization can still be found".

The study also raises a host of questions that have yet to be answered.

"We know the architecture is in place - does it serve a function," Striem-Amit said. "We know, for example, that the auditory cortex of the deaf is also active when they view sign language and other visual information. The question is: What do these regions do in the deaf? Are they actually processing something similar to what they process in hearing people, only through vision?"

The study appears in Scientific Reports.