Frenetic activity between the emotional and auditory parts of the brain explains why the sound of a knife on a bottle is so unpleasant, say University of Newcastle (UK) researchers who have been examining fMRI brain scans of subjects listening to different sounds.
Their study, published in the Journal of Neuroscience, reveals 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.
Study author Sukhbinder Kumar explained 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,” he said. “It’s a possible distress signal from the amygdala to the auditory cortex.”
Kumar has produced two lists ranking the sounds that were included in the study:
Most Unpleasant Sounds
- Knife on a bottle
- Fork on a glass
- Chalk on a blackboard
- Ruler on a bottle
- Nails on a blackboard
- Female scream
- Brakes on a cycle squealing
- Baby crying
- Electric drill
Most Pleasant Sounds
- Baby laughing
- Water flowing
Kumar’s findings showed that the activity of the amygdala and the auditory cortex varied in direct relation to the ratings of perceived unpleasantness. “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 as compared to a soothing sound, such as bubbling water,” he explained.
An 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. “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,” he noted.
The findings may help our understanding of medical conditions where people have a decreased tolerance to sound, such as migraine, hyperacusis, tinnitus, misophonia (literally a “hatred of sound”), and autism.
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