The sound of nails on a chalkboard or screams may send shivers down the spine for a good reason.
A new study shows annoying sounds trigger a highly emotional response in the brain.
Researchers found the part of the brain that regulates emotions, the amygdala, appears to take over the hearing part of the brain when people hear an extremely annoying sound.
"It appears there is something very primitive kicking in," says researcher Sukhbinder Kumar of the Institute of Neuroscience at Newcastle University in Newcastle upon Tyne, U.K. "It’s a possible distress signal from the amygdala to the auditory cortex."
The results suggest that a heightened emotional response in the brain to certain unpleasant sounds may alter people’s perception of them.
The Most Annoying Sounds
Using functional magnetic resonance imaging (fMRI), researchers looked at activity in the brains of 13 healthy volunteers when they heard a range of 74 different sounds.
The participants rated each sound from most annoying or unpleasant to pleasant.
The results, published in the Journal of Neuroscience, show the top 10 most unpleasant sounds (and you can click on the first five to hear the sound):
6. Female scream
7. Disc grinder
8. Squealing brakes on a bicycle
9. Baby crying
10. Electric drill
On the other end of the spectrum, though, are the least unpleasant sounds among the group. They are:
1. Applause
2. Baby laughing
3. Thunder
4. Water flowing
What Makes Sounds Unpleasant
The study shows that activity in the amygdala and auditory complex varies according to the perceived unpleasantness of the sound.
When listeners heard an annoying sound, activity in the amygdala increased and took over regulation of the auditory part of the brain.
Researchers say this spike in emotional activity heightened people's perception of annoying sounds compared with soothing ones, like bubbling water or a baby laughing.
The study also shows that sounds in the higher-frequency range of around 2,000 to 5,000 Hz were rated as most unpleasant.
"This is the frequency range where our ears are most sensitive," says Kumar. "Although there's still much debate as to why our ears are most sensitive in this range, it does include sounds of screams, which we find intrinsically unpleasant."
Researchers say the results should help scientists better understand how the brain reacts to noise as well as disorders that affect people's perception of sound.
"This work sheds new light on the interaction of the amygdala and the auditory cortex," says researcher Tim Griffiths of Newcastle University. "This might be a new inroad into emotional disorders and disorders like tinnitus and migraine in which there seems to be heightened perception of the unpleasant aspects of sounds."
SOURCES: Kumar, S. Journal of Neuroscience, Oct. 10, 2012.News release, New Castle University.
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