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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.

Most unpleasant sounds

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.”