Why Nails Scraping Down A Blackboard Is Such An Unpleasant Sound

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.

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.

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.