There’s nothing quite like a karaoke night to best demonstrate how delusional some are in regards to their singing ability. But don’t blame your tone-deaf friends for their off-key renditions of “Love Is A Battlefield” or “Total Eclipse of the Heart.” Truly tone-deaf people can blame their brains, finds a small new study.
Estimated to affect 4% of the population, tone-deaf individuals can neither perceive nor produce musical sequences accurately. “The best way to think of amusia…is to think of it as an auditory-motor disorder,” says Gottfried Schlaug, PhD, of Harvard Medical Center.
“There are [several] components that could be impaired or dysfunctional. The most likely component is that [which] receives auditory feedback of vocal output,” says Schlaug. In other words, we misinterpret the sounds we hear coming from our mouths.
A paper published in a recent issue of Brain by Philippe Albouy and colleagues at INSERM in France found that the deficits seen in such individuals originate in a region of the brain called the auditory cortex.
In the study, nine congenital amusics (meaning individuals who are tone-deaf from birth, not due to brain injury) and nine control subjects performed two melodic short-term memory tasks.
The first task had individuals listen to two six-tone musical melody and indicate whether the sequence of notes was the same or different. The second task simply transposed one of the six-tone sequences into a different key.
While listening to the various melodies (192, to be exact), the participants sat very still with a large device covering their heads. The technique, called magnetoencephalography, maps brain activity in real time by recording magnetic fields produced by electrical currents in the brain.
The researchers focused on a particular electrical current called “N100m,” a large, negatively-charged signal that can be detected in everybody roughly 100 milliseconds after a stimulus (in this case, the sound of the melody).
The researchers found that tone-deaf individuals performed poorly on the melody task. They were more likely to incorrectly identify two sequences as being the same or different compared to control subjects, suggesting a deficit in their short-term memory.
Interestingly, the N100m current was abnormally recruited in the tone-deaf brain while listening to the melodies.
Overall, tone-deaf individuals, compared to controls, had fewer connections in the auditory cortex, the portion of the brain that processes sound.
A 3D MRI also revealed altered ratios of white matter (fiber tracts) and gray matter (neural cell bodies) between amusics and controls in two brain regions: the right inferior frontal gyrus and the right superior temporal gyrus, implicated in language production and sound processing, respectively.
So what causes this altered anatomy? Is it learned? Genetic? Abnormal prenatal or childhood brain development? The answer, so far, is unknown. But the next time you groan at your friends’ cringe-worthy vocal renditions, simply blame the early brain responses of their auditory cortices.
First published June 4 2013, 5:59 AM