Why some noises send shivers down my spine?

We posed this question to Trevor Cox, Professor of Acoustic Engineering at the University of Salford....

Trevor - I’m Trevor Cox.  I’m Professor of Acoustic Engineering at the University of Salford.  Now when we drag fingernails down the blackboard, some people have a really strong reaction.  It sends shivers down the spine and actually, it’s a really similar reaction to very emotional music - you know when you get to that really heightened emotional point and you can feel the hair stand up in the back of your neck. 

So I suppose that we can guess that maybe fingernails down the blackboard is exciting the same parts of the brain and the parts of the brain that get excited by music is actually the reward sense of the brain which deals things or stuff we get when we take drugs. 

So I think we can know which part of the brain that are likely to be involved but then why does it get triggered from this scraping sound?  Well I think what the clue might be is if you listen to the sound quality, if you can bare to listen to the sound quality because the sound of scraping fingernails is actually a bit similar to a screen.  It’s high pitched, it’s very rough.  And so I think what's happening is your brain is misinterpreting the sound as being a threat signal, someone’s in distress and of course, this is something you're going to have a strong  emotional response to because you might need to protect someone or you might yourself need to runaway because you're in danger.  So I think it might be a rather overreaction to what we think is distress call.

Diana - It may be that the pitch of the sound of nails trailing down a blackboard matches that of a scream or similar distress signal and that our bodies are programmed to experience the same level of tension and fear at it.  It’s an emotional response which some people are more likely to feel than others.