The sound of other people chewing, slurping, and swallowing can be pretty annoying, but some people find such noises to be utterly unbearable. The intense discomfort brought about by these audible triggers is known as misophonia, and new research has finally revealed the neural mechanism underlying this hatred of certain sounds.
Appearing in the Journal of Neuroscience, the study indicates that misophonia arises when irritating noises activate parts of the brain that control the movement of the face, rather than the auditory processing regions.
To conduct their research, the study authors used functional magnetic resonance imaging (fMRI) to scan the brains of people with misophonia while they listened to their specific “trigger sounds”. In the vast majority of cases, the offending noises were related to movements of the face and throat, and include actions such as chewing, breathing, and speaking.
Compared to people without misophonia, those with the condition displayed no unusual activity with their motor cortices – the part of the brain that controls voluntary movement – even when presented with their trigger sounds. However, hearing these irritating noises did produce greater activation in neurons that connect the auditory cortex to the orofacial motor cortex, which controls the movement of the face and throat.
This means that hearing certain noises actually produced the sensation of facial movement in certain individuals, as if they themselves were carrying out the action that produces the sound. According to the study authors, this generates a sense of having one’s faculties invaded, which is what makes the experience so intolerable.
“We also found a similar pattern of communication between the visual and motor regions, which reflects that misophonia can also occur when triggered by something visual,” explained study author Dr Sukhbinder Kumar in a statement. In other words, just watching someone eat can generate the same sense of disgust as hearing them.
“This lead us to believe that this communication activates something called the ‘mirror system’, which helps us process movements made by other individuals by activating our own brain in a similar way - as if we were making that movement ourselves,” says Kumar.
Mirror neurons play an important role in social interactions, as they allow us to imagine what other people are experiencing, yet the discovery of their role in misophonia is a somewhat unexpected finding.
“We think that in people with misophonia involuntary overactivation of the mirror system leads to some kind of sense that sounds made by other people are intruding into their bodies, outside of their control,” explains Kumar.
Based on these findings, the study authors conclude that “misophonia is therefore not an abreaction to sounds, per se, but a manifestation of activity in parts of the motor system involved in producing those sounds.” As such, they claim that future treatments for the condition should focus not only on the brain’s sound processing centers but on the motor cortex as well.