Why nail scraping makes you cringe

If the mere thought of fingernails scraping along a blackboard makes you cringe, your brain is to blame!

Scientists from Newcastle University, including one of Indian-origin, have discovered that primitive almond-shaped brain region - amygdala - is behind our aversion to high-pitched sounds.

They say our reaction to the sound of scraping nails – which is in the same frequency range as screams and babies’ cries – could be an ancient survival instinct.

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.

The study found that 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. It’s a possible distress signal from the amygdala to the auditory cortex,” said Dr Sukhbinder Kumar, the paper’s author.
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 found that the activity of the amygdala and the auditory cortex varied in direct relation to the ratings of perceived unpleasantness given by the subjects.

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 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,” Professor Tim Griffiths from Newcastle University, who led the study, said.