[www.keralites.net] Unpleasant irritating sounds ?

Nasty noises: Why do we recoil at unpleasant sounds?

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.

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.

---

www.keralites.net