CHICAGO — Every time a large group sings “Happy Birthday,” there always seems to be someone who’s woefully off-key. If you’re unlucky, that person might even be you. People with congenital amusia are born unable to tell one note from another. And the problem, a new study finds, seems to stem from how the brain mistakenly processes pitch.
Many people like to say they are “tone-deaf” when they sing off-key. For most people, that isn’t true. They just haven’t practiced enough. But for a small group, no amount of training will help. This true amusia is rare, affecting only about one in every 25 people.
Samuel Norman-Haignere works at the Massachusetts Institute of Technology in Cambridge, where he studies how the brain processes sound. Scientists have never been sure why people with amusia can’t follow or identify a tune. Especially confusing: Most people with this condition hear other sounds perfectly well, he notes. So if the ears aren’t to blame, he says, the problem must rest with how the brain interprets sound.
To investigate that, he and his colleagues decided to study 11 people with amusia and 11 others who can easily distinguish differences in musical sounds. They used a technique called functional magnetic resonance imaging — or fMRI. This type of scan measures blood flow in the brain. Areas where it is highest highlight regions that are active during different tasks, such as listening to random sequences of music. The scientists were especially interested in the brain’s auditory cortex. It’s one of the first areas to process sound signals arriving from the ears.
A tone-deaf person’s auditory cortex can detect musical pitches, the new fMRI data showed. That brain region responded as well in the tone-deaf people as it did in those who can easily carry a tune.
Explains Norman-Haignere, “We tried everything we could think of” to find differences in the auditory cortex. Although this area of the brain seemed to register sounds well in the tone-deaf listeners, these people still couldn’t distinguish one note from another.
The results suggest that one or more other brain structures must take basic sound and interpret it into what most of us understand as music. Which parts of the brain? That’s still a mystery.
Norman-Haignere presented his team’s results October 19 here at the Society for Neuroscience annual meeting.
This might seem like a failed study. After all, the scientists still don’t know where the tune is getting lost. But knowing what parts of a tone-deaf brain work well will allow scientists to focus their searches elsewhere, says Kirill Nourski. He works at the University of Iowa in Iowa City. There he studies auditory neuroscience, or how the brain processes sound.
Understanding what’s behind tone-deafness might one day help amusic people appreciate tunes after all, says Adam Greenberg. He works at the University of Wisconsin in Milwaukee. There he studies brain functioning. The best way to figure out how a machine works is to compare it with one that’s partially broken, he says. It takes “detective work to understand what is broken.” Now that scientists know the auditory cortex isn’t the problem, they can look elsewhere to find out where the brain is dropping the melody.
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amusia Commonly called tone-deafness, this is a brain disorder where people are unable to tell one note from another, to recognize tunes or to remember music they have heard before.
auditory An adjective referring to something that can be heard or that has to do with the process of hearing.
auditory cortexA part of the brain in humans and other animals that processes sound.
brain scan The use of an imaging technology, typically using X rays or a magnetic resonance imaging (or MRI) machine, to view structures inside the brain. With MRI technology — especially the type known as functional MRI (or fMRI) — the activity of different brain regions can be viewed during an event, such as viewing pictures, computing sums or listening to music.
congenital A term that refers to conditions that are present from birth, either because they were inherited or occurred as a fetus developed in the womb.
neuroscience Science that deals with the structure or function of the brain and other parts of the nervous system. Researchers in this field are known as neuroscientists.
fMRI (functional magnetic resonance imaging) A special type of machine used to study brain activity. It uses a strong magnetic field to monitor blood flow in the brain. Tracking the movement of blood can tell researchers which brain regions are active. (See also, MRI or magnetic resonance imaging)