Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Neuroscience

Supervisor

Butler, Blake E.

Abstract

Misophonia is a condition characterized by an extreme aversion to certain ordinary sounds, such as chewing or breathing. These sounds are typically innocuous but elicit strong feelings of anger, anxiety, and disgust as well as physiological stress in people with misophonia. This misophonic reaction to “trigger” sounds is also marked by increased activity in regions of the brain that process sound, ascribe salience, and regulate emotion (Kumar et al., 2017; Schroder et al., 2019). It has therefore been theorized that aberrant connectivity between these brain regions (particularly the anterior insula, auditory cortex, amygdala, and hippocampus) may underlie the experience of misophonia. The current work addressed two hypotheses related to this overarching theory. In the first study, we examined resting-state connectivity in people with varying degrees of sound sensitivity and demonstrate that people with clinical misophonia may have reduced functional connectivity within this network in comparison to those with sub-clinical sensitivity to sound. In the second study, we show preliminary evidence of reduced phonemic perceptual narrowing in misophonics. Since perceptual narrowing is thought to be a behavioural correlate of synaptic pruning during development, this trending result provides indirect evidence for atypical neural connectivity in misophonia. Taken together, the studies implicate a potential developmental mechanism of abnormal salience attribution in misophonia and highlight the importance of studying individual differences in the misophonic experience. These findings also inform the neural and perceptual characterization of misophonia, and since misophonia is not yet listed as a psychological disorder in diagnostic manuals, such findings are an important step towards understanding and classifying misophonia.

Summary for Lay Audience

People experience sound differently from one another. For instance, the sound of rainfall may be calming to one person while irritating to another. Misophonia is an extreme example of such individual differences in sound-emotion processing, where certain ordinary sounds (like chewing and breathing) elicit a stress response. When someone with misophonia hears their “trigger” sound, they experience feelings of intense anger, anxiety, and disgust as well as physiological symptoms such as increased heart rate and muscle contraction. This reaction to trigger sounds is reflected in differences in brain activity between misophonics and those without sensitivity to specific sounds. More specifically, in response to trigger sounds (but not other types of sounds), people with misophonia have heightened activity in brain regions that process sound, ascribe salience, and regulate emotion. However, it is unclear if these atypical patterns of brain activity reflect differences in connectivity between these regions. This thesis addressed this question through two separate studies. In the first study, we examined patterns of resting brain connectivity in people with varying degrees of sound sensitivity severity. Here, we demonstrated that, indeed, people with misophonia may have altered connectivity in a brain network associated with sound-salience processing, and that connectivity in this network may be distinct from those with sub-clinical irritation to sound. In the second study, we indirectly examined brain connectivity using a perceptual measure that is thought to be associated with the refinement and stabilization of neural connections. The results from this study are inconclusive, but trends in the data suggest that misophonia may be characterized by atypical brain connectivity that is shaped during development. Overall, these findings progress our understanding of the neural and perceptual components of misophonia. This is especially important because misophonia is currently under-researched, largely uncharacterized, and yet to be represented in clinical diagnostic manuals, so these findings inform how misophonia should be classified and motivate future research directions.

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