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No one enjoys hearing the sound of someone else chewing their food. Most of the time, though, it’s not that big a deal — gross, maybe, but a minor annoyance.

But for a small group of people with a condition called misophonia, the sound can be torturous, provoking extreme anger and deep discomfort. The most ordinary sounds can turn an otherwise benign situation into a minefield: chewing, knuckle-cracking, even breathing are common triggers. Past attempts to explain the causes of misophonia have suggested everything from obsessive-compulsive disorder to an irritable personality — but according to a study published yesterday in the journal Current Biology and highlighted by Tiffany O’Callaghan in New Scientist, the true culprit may be the structure of the brain.

For the study, a team of researchers led by Newcastle University neuroscientist Sukhbinder Kumar recruited 42 volunteers, around half of whom had extreme misophonia (the other half served as the control group), and played them several different noises: some neutral; some jarring, like the sound of a person screaming; and some that were neutral for the control group but known to be aggravating for people with misophonia, like the sound of breathing. As the participants listened, the study authors monitored them for signs of distress, both physical symptoms and behavioral cues, and observed their brain activity using fMRI scans.

The only significant difference in reaction between the two groups happened, unsurprisingly, during the misophonia-specific sounds, when those with the condition showed physical changes that suggested they were entering fight-or-flight mode (a result consistent with earlier research). Their brain scans, O’Callaghan wrote, also showed an interesting pattern of activity:

[M]isophonics had heightened activity in the anterior insular cortex (AIC), an area known to play a central role in the system that determines which things we should pay attention to. When the trigger sounds were played, there was not only more activity in this region but also abnormally high levels of connectivity to other regions. “The AIC is hyperconnected to structures that are involved in emotion regulating and memory,” says Kumar.



There was also increased connectivity to regions involved in the default mode network, which helps summon memories and processes internally generated thoughts.



Misophonia, in other words, may be a result of misplaced attention — the brain of a misophonic is wired to focus on things that other people normally tune out, and to have a more emotional reaction to those focal points. On a related note, on behalf of misophonics and manners-minded moms everywhere: Please, chew with your mouth closed.