Australasian Science: Australia's authority on science since 1938

Wired for Sound?

Credit: Scott Griessel/Adobe

Credit: Scott Griessel/Adobe

By Tim Hannan

A new study proposes a biological cause for misophonia – the pathological hatred of sounds.

Many of us display a degree of discomfort when exposed to certain sounds, such as fingernails being scraped down a blackboard, the grinding of teeth, or fellow diners chewing their kale too loudly. For some people, however, these and certain other sounds trigger an intense emotional reaction involving increased physiological arousal, a feeling of disgust and the desire to flee.

While acknowledging that some people find certain sounds unpleasant, and that this may have an impact on one’s emotional state, health professionals have largely been skeptical as to whether this constitutes a discrete condition, and unpersuaded that a neurobiological basis could be identified. Now, a study by researchers in the UK has found that those who are observed to display this reaction have different patterns of brain activation when exposed to certain sounds. The researchers argue that this is proof for a genuine medical disorder.

Termed misophonia, meaning “hatred of sound”, the condition is proposed to comprise an unusually adverse reaction to certain auditory stimuli. The sounds that trigger the reaction vary among individuals, but often relate to bodily functions such as chewing, slurping, snorting or snuffling. Other reportedly problematic sounds are associated with perceived potential injury, such as knuckles cracking or fingernails on blackboards. However, sufferers also report being distressed by repetitive environmental sounds, such as those of leaf blowers, chainsaws and ticking clocks, as well as some sounds that many non-sufferers find benign, such as dogs barking, plastic bags or bottles being crushed, or balloons being stroked.

Misophonia is argued to be more than just a strong dislike of such sounds: sufferers report experiencing significant and persisting physical and emotional symptoms, including increased physiological arousal, headaches and other pains, and feelings of nausea. Some have been documented to fly into a rage at exposure to triggering sounds; these responses have been interpreted as a fight-or-flight response, implying that misophonics are experiencing a primal defensive reaction to a perceived threat.

Yet critics of the concept have noted the lack of theoretical explanation for the heightened sensitivity to sound and the proposed automaticity of a strong emotional response. With only a few studies in this field, there remains no clear theory, no evidence of pathology, no established diagnostic criteria, no estimates of prevalence, and no reports of effective treatments.

In the study published in Current Biology, researchers from Newcastle University in the UK described the reactions of 20 people with misophonia to a range of sounds, and compared their physiological responses and brain activity to those of 22 non-sufferers. Participants first rated how distressing they found a range of sounds, as either neutral (e.g. rain), unpleasant (e.g. a baby crying) or a trigger for an intense reaction (e.g. sounds of eating, breathing etc.). Heart rate and sweating were measured upon presentation of each type of sound, and brain scans were conducted to explore patterns of neural activity.

The researchers found that, when presented with “merely unpleasant” sounds, those with misophonia displayed similar physiological responses to those without the condition. However, in response to the trigger sounds, the misophonics displayed increased physiological signs of anxiety, and they also exhibited markedly increased activity in the anterior insular cortex, a region associated with the experience and regulation of emotions.

The findings may be interpreted as evidence for a causal role for a neurobiological abnormality in the development of misophonia: that due to some unspecified cause, a region of the brain of a sufferer is not functioning in the same way as it does in other people, and that this gives rise to a greater sensitivity to sound and an intense, adverse experience.

However, it must be noted that the observation of an association between a pattern of brain activity and an emotional response does not prove that the former causes the latter: it may equally be speculated that misophonia is simply a learned, exaggerated psychological reaction to unpleasant stimuli, and that the neural patterns observed simply represent the strong emotional reaction.

Despite the enthusiasm of the researchers, and the desire of sufferers for recognition of their condition as a medical condition, further research is required to establish misophonia as a valid diagnosis.

A/Prof Tim Hannan is Head of the School of Psychology at Charles Sturt University, and the Past President of the Australian Psychological Society.