Study Reveals Why React to Unpleasant Sounds

Ever realized why your hands crawl up to your ears on hearing the unpleasant sound of the chalk on the blackboard or a knife on a bottle. The researchers from the Newcastle University have presented an explanation that highlight the heightened activity between the emotional and auditory parts of the brain.

The study that was funded by the Wellcome Trust reveal the interaction between the region of the brain that processes sound, the auditory cortex, and the amygdala, which is active in the processing of negative emotions when we hear unpleasant sounds.

With the help of brain imaging it was shown that on hearing unpleasant sound the amygdala modulates the response of the auditory cortex heightening activity. And this instigates the immediate negative reaction.

"It appears there is something very primitive kicking in," says Dr Sukhbinder Kumar, the paper's author from Newcastle University. "It's a possible distress signal from the amygdala to the auditory cortex."

With the help of the functional magnetic resonance the researchers at the Wellcome Trust Centre for Neuroimaging at UCL examined the activity of brain in 13 volunteers. They analyzed how the brain responded to a range of sounds..

Listening to the noises inside the scanner they rated them from the most unpleasant such as the sound of knife on a bottle to pleasing ones such as bubbling water.  With this the researchers were able to study the brain responses to each type of sound.

On analyzing the responses the researchers noticed that the activity of the amygdala and the auditory cortex varied in direct relation to the ratings of perceived unpleasantness given by the subjects.

It is the amygdale the emotional part of the brain that takes control and modulates the activity of the auditory part of the brain. This is done so that our awareness of a highly unpleasant sound, such as a knife on a bottle, is sharp as compared to a soothing sound, such as bubbling water.

Whereas on focusing on the acoustic features of the sounds they noticed that anything in the frequency range of around 2,000 to 5,000 Hz was rated as unpleasant

Dr Kumar explains: "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."

According to the researchers 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 and autism when there is sensitivity to noise.

The top ten unpleasant sound people reported was the 'Knife on a bottle', 'Fork on a glass', 'Chalk on a blackboard', 'Ruler on a bottle', 'Nails on a blackboard', 'Female scream', 'Anglegrinder', 'Brakes on a cycle squealing', 'Baby crying', 'Electric drill'.

While the least unpleasant sound is given to that of 'applause', 'Baby Laughing', 'Thunder', 'Water flowing'.

Professor Tim Griffiths from Newcastle University, who led the study, says: "This work sheds new light on the interaction of the amygdala and the auditory cortex. 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."

This study was published in the journal of Neuroscience.