Hate the sound of chewing? Here’s why
A new study reveals the motor basis for misophonia, a condition that causes exceptionally negative responses to sounds such as chewing, providing an insight into new potential treatments.
Sitting down to eat with your family or a friend is a pleasant experience for most. Good food, company and perhaps a drink; it’s the simple pleasures that can deliver the most precious moments. But for some – between 6 and 20% of people – this utopian scene can lead to inexplicable rage and, at its worst, the urge to lean across the table and deliver a right hook so powerful it knocks the food flying straight out of your unwitting compatriot’s mouth.
The cause of this fury stems from a condition known as misophonia, which is stimulated by ‘trigger’ sounds typically originating from facial activity, most famously the sound of chewing. Misophonia can be experienced so severely that it can affect relationships and prevent sufferers from engaging in social situations. Until recently, the mechanism for this condition was poorly understood.
A mechanism for misophonia
A recent study from researchers at Newcastle University (UK) has identified a neurological link – the first to be associated with the condition – that provides a clear hypothesis for the mechanism of misophonia. Led by Sukhbinder Kumar, the findings provide a new avenue for therapies to treat and control the condition.
To explore the neurological connections responsible for misophonia, the research team used fMRI to monitor the responses, when exposed to triggers, of several sites in the brains of controls and misophonia sufferers.
Ask the Experts: Alzheimer’s fabrication controversy
Recently, Science revealed that an Alzheimer’s research paper from 2006, detailing the toxicity of an amyloid fragment, may have contained fabricated images. We asked three experts to provide insight into what this allegation means for Alzheimer’s disease research, drug development, scientific publication and the public.
Surprisingly, the team found that response to trigger sound caused no noticeable difference between the response of the auditory cortex in both controls and misophonia sufferers. Instead, they identified increased connectivity between the auditory and ventral pre-motor cortex in the brains of people with the condition, both in general and especially in response to trigger sounds.
The ventral pre-motor cortex is responsible for orofacial movements (movements of the mouth and face) suggesting the involvement of the ‘mirror system’ in misophonia. The mirror system allows humans to interpret the actions of others by stimulating their own brain in a similar way, mimicking the neural processes that control the actions.
Kumar explained how this could tie into misophonia, stating “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.”
An established technique for controlling misophonia is for people to copy the action that is triggering them. Previously unaware of why this technique works, the team now believes that by copying the action it returns a sense of agency and control, lessening the feeling of violation that can lead to rage.
The team plan to continue their exploration of misophonia to uncover further avenues for new treatments. “The study provides new ways to think about the treatment options for misophonia. Instead of focussing on sound centers in the brain, which many existing therapies do, effective therapies should consider motor areas of the brain as well,” Kumar noted.
So, if you experience these responses, know that you don’t need to reach for a boxing glove at dinner and try copying the sound that so infuriates you.
The power of comics and art as a vehicle for science
Science, technology, engineering, and mathematics (STEM) are the backbone of innovations, inform our understanding of the world and influence how it is governed. As such, STEM communication conveyed in clear and engaging ways is imperative.
Different regions for different triggers?
In a subsequent paper, a team of researchers from Ohio State University (OH, USA) built on this initial study, delving into the mechanisms of other triggers. Misophonia does not just relate to chewing and facial sounds, as was examined in the study from Kumar et al; finger tapping and clicking can also trigger this response, which is less easily explained by the increased connectivity observed between the auditory and the orofacial motor cortex.
To explore this further, the team also assembled 19 participants who ranked between no and mild misophonia. The participants’ brains were monitored using fMRI while they vocalized specific syllables, when they repeatedly tapped their fingers on their legs and when they did nothing.
The first vocalization test enabled the fMRI scan to identify the regions of the brain activated during the production of speech, which significantly coincides with orofacial movements such as chewing.
The results demonstrated that the mild misophonia participants had stronger connections between the auditory cortex and the motor control area identified in the previous study, than the no misophonia participants. While this was consistent with the previous study, the region of the brain identified as active while the participants moved their mouths and formed speech differed from the area identified as the orofacial motor cortex in the first study.
What’s more, there was no stronger connection observed between this newly identified area and the auditory cortex. Heather Hansen, lead author of the study, highlighted that this may mean that what the “previous research identified as the orofacial region … may not actually be the orofacial region.”
Noting the foundations provided by the original paper in conversation with BioTechniques, Hansen noted that, “Kumar and colleagues have largely inspired my venture into neuroimaging misophonia and I’m grateful for the starting point they provided.”
However, when they examined the differences observed between mild and no misophonia participants while they were finger tapping, the researchers observed a stronger connection between the region of the brain associated with finger movement and the insular cortex. The insular cortex is involved in a host of functions from sensory processing to the representation of emotions, including disgust.
“We have actual evidence in the brain of people disliking sounds that aren’t just from the mouth and face. It is an important step forward in understanding misophonia,” Hansen stated. This study indicates that there is more at play than the original mechanism identified by the Newcastle University team, highlighting the disparate triggers involved and that there may be differences in the areas of the brain associated with them.
When asked to comment on the article and the potential conflicts between the two, Kumar highlighted that “We think that the study adds to our understanding of misophonia in that it highlights the non-dominant triggers within the misophonia population, and that this population may have a different underlying brain network that uses the same mechanism of ‘mirroring’ as suggested in our work. The study in that sense does not conflict with our findings.”
Ultimately, this study adds more color to the condition of misophonia, indicating that its causes may be more complex than first thought and bringing attention to the other triggers for the condition. “This takes us one step closer to understanding the multitude of ways that misophonia might present itself. It is affirming to people who don’t experience misophonia from chewing but do have it for other repetitive noises,” Hansen concluded.
For more information and advice with misophonia, check out: https://www.healthline.com/health/misophonia .
This article was originally published on 21 May 2021 and was updated on 30 September 2022 to include the information in the study conducted by Hansen et al and the quotes from both authors.