Why chewing, clicking pens annoy us decoded

London: Irritated by the sound of chewing or repeated pen clicking? Your brain may be wired to go into overdrive on hearing such trigger noises, researchers
including one of Indian-origin have found.

Researchers from Newcastle University in the UK found the physical basis for people suffering from a condition called misophonia, a disorder where they have a hatred of sounds such as eating, chewing or repeated pen clicking. Called "trigger sounds" by the misophonia community, the response can be an immediate and intense fight or flight feeling.

The researchers report the first evidence of clear changes in the structure of the brain's frontal lobe in sufferers of misophonia and also report changes in the brain activity. Brain imaging showed that people with the condition have an abnormality in the emotional control mechanism which causes their brains to go into overdrive on hearing trigger sounds.

Researchers also found brain activity originated from a different connectivity pattern to the frontal lobe. This is normally responsible for suppressing the abnormal reaction to sounds. The researchers also found that trigger sounds evoked a heightened physiological response with increased heart rate and sweating in people with misophonia.

"For many people with misophonia, this will come as welcome news as for the first time we have demonstrated a difference in brain structure and function in sufferers," said Sukhbinder Kumar from the Newcastle University. "Patients with misophonia had strikingly similar clinical features and yet the syndrome is not recognised in any of the current clinical diagnostic schemes," said Kumar.

"This study demonstrates the critical brain changes as further evidence to convince a sceptical medical community that this is a genuine disorder," Kumar added. Using brain scans carried out with Magnetic resonance imaging (MRI) the team showed a physical difference in the frontal lobe between the cerebral hemispheres of people with misophonia - with higher myelination in the grey matter of ventromedial prefrontal cortex (vmPFC).

The study also used functional MRI to measure the brain activity of people with and without misophonia while they were listening to a range of sounds such as - neutral, unpleasant and trigger sounds. This showed abnormal connections between this frontal-lobe area and an area called the anterior insular cortex (AIC).

This area is in the grey matter of the brain but buried in a deep fold at the side of the brain and is known to be involved in processing emotions and integrating signals both from the body and outside world. When presented with trigger sounds activity goes up in both areas in misophonic subjects, whilst in normal subjects the activity goes up in the AIC but down in the frontal area. The study was publishing in the journal Current Biology.