Brain sees what it can’t hear, study finds

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Brain sees what it can’t hear, study finds

October 10, 2010

ph Hall

Health Reporter

People born deaf can see with parts of their brain that normally process sound,

a new University of Western Ontario study says.

The research helps explain why the congenitally deaf often exhibit enhancements

in their vision and other senses, says Western neuroscientist Lomber.

“There is a very large region of the brain that normally processes auditory

input,†says Lomber, the lead study author.

“When that area is (permanently) denied auditory input . . . the brain is a

fairly efficient structure and usually doesn’t let processing power go to

waste.â€

The study, which looked at the brains of congenitally deaf cats, showed that key

auditory processing segments of the organ had been reassigned to visual tasks.

In particular, the auditory centres responsible for peripheral hearing and the

recognition of sound direction allowed for more acute peripheral sight and a

keener perception of visual motion, Lomber says.

The study appears Monday in the journal Nature Neuroscience.

Lomber’s team made its findings by temporarily freezing segments of auditory

tissue in the deaf cats’ brains.

When the segments devoted to peripheral hearing were deactivated the creatures

lost their peripheral vision advantage.

Likewise, when brain segments responsible for picking up the direction a sound

was moving in were shut down, the cats could no longer pick up movements.

“There appears to be these kinds of functions that every sense has to do,â€

Lomber says. “And the area that would normally localize where sound was coming

from actually reorganized and was now processing where visual stimulus is.â€

It has long been noted that people born deaf had enhancements in other senses

like sight and touch.

But the Western study, conducted out of the university’s Schulich School of

Medicine & Dentistry, is the first to show that those heightened senses are

being run from the brain’s vacant hearing centres.

“It seems this area of auditory cortex actually gets reassigned to other

senses whether that be vision, or touch,†Lomber says.

The study helps explain why people born deaf often find it hard to accept

cochlear implants that can restore hearing, Lomber says.

He says the areas of the brain that would normally welcome the new auditory

input are busily processing vision or some other sense and can’t recognize the

new sound stimuli.