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Nasty noises: Why do we recoil at unpleasant sounds?

Oct. 14, 2012
Courtesy of Newcastle University
and World Science staff

Nails screech­ing on a black­board. A knife scrap­ing against a bot­tle. These sounds are sin­gular­ly annoy­ing to many—but why? Height­ened ac­ti­vity be­tween the brain’s emo­tion­al and au­di­to­ry parts is to blame, new re­search says.

MOST UNPLEASANT SOUNDS
Rating 74 sounds in a new study, people found the most unpleasant to be as follows (click on links for samples):

1. Knife on a bottle 
2. Fork on a glass
3. Chalk on a blackboard 
4. Ruler on a bottle
5. Nails on a blackboard
6. Female scream
7. Anglegrinder (power tool)
8. Brakes on a cycle squealing
9. Baby crying
10. Electric drill

LEAST UNPLEASANT SOUNDS
1. Applause
2. Baby laughing
3. Thunder
4. Water flowing

In a study pub­lished Oct. 10 in The Jour­nal of Neu­ro­sci­ence, sci­en­tists re­port an in­ter­ac­tion be­tween the re­gion of the brain that pro­cesses sound, the au­di­to­ry cor­tex, and the amyg­da­la, ac­tive in the pro­cess­ing of neg­a­tive emo­tions. 

When we hear an un­pleas­ant noise, the re­search­ers said, the amyg­da­la mod­u­lates the au­di­to­ry cor­tex re­sponse, height­en­ing its ac­ti­vity and pro­vok­ing a neg­a­tive re­ac­tion.

“It ap­pears there is some­thing very prim­i­tive kick­ing in,” said Sukh­bin­der Ku­mar, a co-au­thor of the re­port, from New­cas­tle Uni­vers­ity in the U.K. “It’s a pos­si­ble dis­tress sig­nal from the am­yg­da­la to the au­di­to­ry cor­tex.”

The re­search­ers used a scan­ning meth­od known as func­tion­al mag­net­ic res­o­nance im­ag­ing to ex­am­ine how 13 vol­un­teers re­sponded to a range of sounds. Lis­ten­ing to the noises while in­side a brain scan­ner, they rat­ed the sounds from most un­pleas­ant—the sound of knife scrap­ing against a bot­tle—to pleas­ing: bub­bling wa­ter.

Re­search­ers then stud­ied the brain re­sponse to each type of sound.

They found that the ac­ti­vity of the amyg­da­la and the au­di­to­ry cor­tex var­ied in di­rect rela­t­ion to the rat­ings giv­en by the sub­jects. The emo­tion­al brain struc­ture, the amyg­da­la, in ef­fect takes charge and mod­u­lates the ac­ti­vity of the au­di­to­ry re­gion so that our pe­r­cep­tion of a dis­turb­ing sound, such as a knife scrap­ing on a bot­tle, is height­ened, the sci­en­tists ex­plained.

An anal­y­sis al­so found that an­y­thing in the fre­quen­cy range of around 2,000 to 5,000 Hz (vibra­t­ions per sec­ond) was con­sid­ered un­pleas­ant. “This is the fre­quen­cy range where our ears are most sen­si­tive. 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,” said Ku­mar.

A bet­ter un­der­stand­ing of the brain’s re­ac­tion to noise could help our un­der­stand­ing of med­i­cal con­di­tions where peo­ple have a de­creased sound tol­er­ance such as hype­racusis, miso­pho­nia (lit­er­ally a “ha­tred of sound”) and au­tism when there is sen­si­ti­vity to noise, sci­en­tists added.

“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,” said Tim Grif­fiths of New­cas­tle, who led the stu­dy.

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Heightened activity between the brain’s emotional and auditory parts explains why the sound of chalk on a blackboard or a knife on a bottle is so annoying, new research said. In a study published Oct. 10 in the Journal of Neuroscience, scientists report an interaction between the region of the brain that processes sound, the auditory cortex, and the amygdala, active in the processing of negative emotions. When we hear an unpleasant noise, the researchers said, the amygdala modulates the auditory cortex response, heightening its activity and provoking a negative reaction. “It appears there is something very primitive kicking in,” said Sukhbinder Kumar, the paper’s author from Newcastle University in the U.K. “It’s a possible distress signal from the amygdala to the auditory cortex.” The researchers used a scanning method known as functional magnetic resonance imaging to examine how 13 volunteers responded to a range of sounds. Listening to the noises while inside a brain scanner, they rated the sounds from most unpleasant—the sound of knife scraping against a bottle—to pleasing: bubbling water. Researchers then studied the brain response to each type of sound. They found that the activity of the amygdala and the auditory cortex varied in direct relation to the ratings given by the subjects. The emotional brain structure, the amygdala, in effect takes charge and modulates the activity of the auditory region so that our perception of a highly unpleasant sound, such as a knife on a bottle, is heightened, the scientists explained. An analysis also found that anything in the frequency range of around 2,000 to 5,000 Hz (vibrations per second) was considered unpleasant. “This is the frequency range where our ears are most sensitive. 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,” said Kumar. A better understanding of the brain’s reaction to noise could help our understanding of medical conditions where people have a decreased sound tolerance such as hyperacusis, misophonia (literally a “hatred of sound”) and autism when there is sensitivity to noise, scientists added. “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,” said Tim Griffiths of Newcastle, who led the study.