|The human ear. (Fotolia.com)
By the sound of it, humans own a remarkable repulsion system.
Though science still isn't sure why we become so alarmed by certain noises.
A new study published in the Journal of Neuroscience has found our ears and a section of our brain are specifically designed to make us recoil when we hear certain annoying frequencies.
When finger nails scrape across a blackboard or metal runs across glass or even certain missed musical notes, the study has charted a complicated interaction between the area of the brain that processes sound -- the auditory cortex -- and the amygdala region that registers an emotionally charged "I can't stand that sound" response.
"The way the ear is structured is very important to this," Dr. Sukhbinder Kumar, the paper's author and a research fellow at the U.K.'s Newcastle University, told QMI Agency.
Kumar, who has studied our reaction to certain annoying noises for years, used brain imaging on 13 volunteers to chart how different sounds reach and react with the amygdala.
Kumar notes of certain ones: "It appears there's something very primitive kicking in."
While it may be a distress signal, scientists are not certain why it activates. Some suggest the frequencies are close to screams of distress or even warning calls from animals.
But the human ear, and brain, may be uniquely tuned to certain sounds.
Kumar points out a recent study by another researcher found monkeys don't seem to share the same list of sucky sounds.
In his work, Kumar watched what physically took place in the brains of subjects, while having them listen to universally annoying noises -- a knife across a bottle -- as well as pleasing sounds -- water bubbling.
The amygdala, the team found, takes charge during times of certain annoying sounds -- anything around 2,000 to 5,000 Hz -- and modulates the auditory part of the brain so our perception is suddenly heightened.
Though among the notorious sounds he had to leave out was of someone throwing up. He figures our repulsion to that may be clouded by our imagination or knowledge of what we may soon smell.
Knowing why we react as we do could someday help doctors treat those who are hypersensitive to noise.
The work helps to chart what takes place in our heads. But so far, as well as not knowing exactly why our brain reacts as it does, the researcher points out we can't even be sure the same alarming frequencies have stayed constant since our species first came equipped with ears.
That, Kumar notes, sounds like an interesting question that we may never know the answer to.