Buzz
The screech of nails scraping a chalkboard is so unbearable that most people instantly react: A chill runs down their spine, and their hands instinctively cover their ears. What is it about such unpleasant sounds that triggers such a strong response?
Researchers at Newcastle University believe they've identified the cause. In a recent study, they placed 13 participants inside functional Magnetic Resonance Imaging (fMRI) machines, which monitor brain activity by detecting shifts in blood flow. As the researchers played a variety of 74 different sounds, they observed the brain's response.
Their findings reveal that we react strongly to unpleasant sounds due to the interaction between two key brain areas: the auditory cortex, which processes sound, and the amygdala, which is involved in processing negative emotions. When we hear a scream or a baby cry, the amygdala becomes more active, amplifying the auditory response and generating a negative feeling. This heightened activity does not occur with soothing sounds.
Through acoustic analysis, the researchers discovered that sounds ranging from 2000 to 5000 Hertz were universally unpleasant to the study participants. They hope that by better understanding how the brain responds to noise, they can help those who are sensitive to loud sounds, such as individuals with certain types of autism, as well as people suffering from tinnitus and migraines.
One of the more unexpected findings from this study was that the participants ranked nails on a chalkboard as only the fifth most irritating sound—coming behind other sounds like a knife on a bottle, a fork on a glass, chalk on a blackboard, and a ruler on a bottle.
