A rattle in the dashboard, a fork scraping a plate, the squeak of Styrofoam – these are the sounds of our undoing. Why do they so annoy?

A team of neuroscientists set out to answer questions about the matter by conducting a study of human responses to unpleasant sounds. Using event-related functional magnetic resonance imaging (fMRI) to measure the brain’s responses to a set of 74 sounds, they were able to develop a model of how the brain processes the noises that annoy.

The conclusion? “The stimulus is first processed to a high level in the auditory cortex (STG), which portends the assignment of valence in the amygdala. The amygdala, in turn, modulates the auditory cortex in accordance with the valence of sounds.”

The stuff of excitement for neuroscientists. But for the rest of us, in the process of mapping out "the how," they also ended up with a list of "the what."

Although the unfortunate sound of nails being dragged along a chalkboard has long held the dishonorable distinction of Worst Sound in the World, the study found two other sounds even more intolerable. Here's the breakdown (with sound files for the top five, click if you dare):

10. An electric drill

9. A crying baby

8. Squealing brakes on a bicycle

7. A disc grinder 

6. A female scream

5. Nails on a blackboard

4. A ruler on a bottle
3. Chalk on a blackboard
2. A fork on a glass

1. A knife on a bottle

Of interest was the finding that along with activity seen in the auditory cortex (the part of the brain that processes sounds), there was also activity in the amygdala (the part of the brain that produces emotions). The MRIs revealed that the amygdala communicated with signals coming from the auditory cortex, increasing the degree of unpleasantness conveyed by the most annoying sounds.

“It appears there is something very primitive kicking in,” says Sukhbinder Kumar, the study’s lead author. “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.”

Which would make sense, given our instinct for safety and survival and such. According to Smithsonian.com, some theories have suggested that we have an innate sensitivity to the “alarm calls” that annoying sounds might signify. Yet recent research may discount that theory and replace it with a more physiological one: The actual shape of the human ear amplifies some frequencies to a degree that they actually cause physical pain, and thus, the Pavlov’s dogs that we are, we begin to automatically consider them to be unpleasant by association.

Whatever the case may be, there is little debate about the rankle factor of the sounds determined most unpleasant. But how about nice noises? The researchers found that the sounds of flowing water, thunder, and a baby laughing were the least unpleasant, with the sound of applause being the number one pleasant sound.

The paper was published in The Journal of Neuroscience.

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