Scientists identify why nails scraping down a blackboard is such an unpleasant sound

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If the mere thought of  fingernails scraping along a blackboard makes you cringe, blame your amygdala.

Scientists have discovered that this primitive almond-shaped brain region 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.have found an answer to why the sound of nails scraping down a blackboard is so unpleasant it makes us wince.

Scientists have discovered the reason why nails scraping down a blackboard is such an unpleasant sound to the human ear

The study scanned the brains of 13 volunteers while they listened to a range of sounds before rating how much they liked them.

The more unpleasant a sound, the greater the amygdala – one of the first brain structures to evolve – lit up. 

It then activated the auditory cortex, which processes sound, leading the volunteers to perceive the noise more keenly.

The sound of a knife on a glass bottle was rated the most unpleasant, followed by a fork on a glass. 

Chalk on blackboard came third, a ruler on a bottle fourth and nails on a blackboard fifth, the Journal of Neuroscience reports.

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

MOST ANNOYING NOISES

Out of 74 sounds, volunteers rated the five most unpleasant as:

1. Knife on a bottle

2. Fork on a glass

3. Chalk on a blackboard

4. Ruler on a bottle

5. Nails on a blackboard

Further analysis found that these high-pitched sounds were more easily picked up by the ear.

Researcher Dr Sukhbinder Kumar, of Newcastle University, said: ‘It appears there is something very primitive kicking in. 

‘It’s a possible distress signal from the amygdala to the auditory cortex.

‘There is a frequency range where our ears are the most sensitive.

 

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‘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.’

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