Nasty noises: why we recoil at unpleasant sounds
10 October 2012
Heightened activity between the emotional and auditory parts of the brain explains why the sound of chalk on a blackboard, or a knife on a bottle, is so unpleasant.
In a study published today in the Journal of Neuroscience UCL and Newcastle University scientists 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.
Brain imaging has shown that when we hear an unpleasant noise the amygdala modulates the response of the auditory cortex heightening activity and provoking our negative reaction.
"It appears there is something very primitive kicking in," says author Dr Sukhbinder Kumar, who has a joint appointment at the Wellcome Trust Centre for Neuroimaging at UCL and Newcastle University. "It's a possible distress signal from the amygdala to the auditory cortex."
The researchers used functional magnetic resonance imaging (fMRI) to examine how the brains of 13 volunteers responded to a range of sounds. Listening to the noises inside the scanner they rated them from the most unpleasant - the sound of knife on a bottle - to pleasing - babbling water. Researchers were then able to study the brain response to each type of sound.
The study found that the activity of the amygdale and the auditory cortex varied in direct relation to the ratings of perceived unpleasantness given by the subjects. The emotional part of the brain, the amygdala, in effect takes charge and modulates the activity of the auditory part of the brain so that our perception of a highly unpleasant sound, such as a knife on a bottle, is heightened in comparison to a soothing sound, such as babbling water.
Analysis of the acoustic features of the sounds found that anything in the frequency range of around 2,000 to 5,000 Hz was found to be 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."
Scientifically, 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.
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."
The work was funded by the Wellcome Trust.
Media contact: David Weston
Image caption: A bottle being scraped with a knife, from Fritish on Flickr