updated 8/19/2009 9:10:46 AM ET 2009-08-19T13:10:46

Do your friends cover their ears when you sing along with the radio? Does the choir director ask you to lip-sync?

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If you're one of the unlucky people who is tone-deaf, it turns out your brain may have a wiring problem. That's what new research published Wednesday suggests.

People who are tone-deaf can't detect differences in musical pitch but usually have normal hearing and speech. Tone-deafness runs in families, and estimates of how many people have the problem range from 4 percent to 17 percent.

In the small study done in Boston, brain scans showed there was a difference in a particular brain circuit between those who were tone-deaf and those who weren't. Among the tone-deaf, researchers discovered there were fewer connections between two areas of the brain that perceive and produce sounds.

The study's lead author, Psyche Loui, likened the connection to a highway between two islands in the brain.

In tone-deaf people, "there's less traffic on the highway," said Loui, who studies music and the brain at Harvard Medical School and is also a musician.

Loui and her colleagues took brain scans of 20 people, half of them tone-deaf. Those who were tone-deaf had fewer nerve fibers between the frontal and temporal regions of the brain, or in some cases the fibers couldn't be detected at all.

The researchers reported their findings in Wednesday's issue of the Journal of Neuroscience.

"It's a new piece in our understanding of tone-deafness and the processes that are involved in the perception of pitch in general," said Nina Kraus of Northwestern University, who wasn't involved in the research.

Loui said the brain connection they examined was long known to be involved in language. "Now that we know which brain pathways to train," she said, there may be ways to help people with tone-deafness, and perhaps those with other language disorders.

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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