Tinnitus, physical activity and improved quality of life: investigation of the neural correlates of tinnitus and potential treatment options

Objectives. The objectives of the dissertation are to (1) identify the neural correlates of tinnitus distress and successful habituation, and (2) investigate any relationship between physical activity and tinnitus distress. Subjective tinnitus, commonly referred to as ringing in the ears, is the perception of a sound without an external sound source. It affects approximately 50 million adults in the United States of America, of whom 16 million seek medical attention and 2 million experience catastrophic tinnitus distress. The driving factor of tinnitus distress is not the loudness of tinnitus, but rather the negative emotional reaction to the percept. This reaction is associated with impaired quality of life, anxiety and depression. The limbic system is the focal region of the brain involved in the emotional reaction to stimuli. However, few studies have directly targeted this system to understand neural mechanisms of tinnitus distress or successful habituation. Physical activity has been correlated with improved quality of life and lower levels of anxiety and depression, but, this has not been established in the tinnitus population. Therefore, we investigated the association between physical activity and tinnitus distress. Design. To complete our objectives, we conducted three interconnected studies. In the first study, we examined functional and behavioral differences in those recently diagnosed with tinnitus compared to those who had tinnitus for a long period of time. Note that those with chronic tinnitus of long standing in our study reported lower distress levels than those with recently-diagnosed tinnitus. Second, we conducted a cross-sectional survey study to examine any relationship between physical activity and tinnitus severity. Lastly, we built upon the first two studies to investigate functional and behavioral differences in those with higher levels of tinnitus distress compared to those with lower levels of tinnitus distress, while accounting for physical activity levels. In studies 1 and 3, neural correlates of tinnitus distress were evaluated by comparing those with higher levels of tinnitus distress to those with lower levels of tinnitus distress, while they were listening to affective sounds. The reverse comparison was used to identify regions that may be associated with successful habituation. Results. In the first study, heightened response in the emotional processing system, particularly the insula, was observed in those with higher tinnitus distress compared to those with lower tinnitus severity when listening to affective sounds. Increased response in the middle frontal gyrus was observed in the reverse comparison. In the third study, we found increased response in the amygdala, another region of the emotional processing system, for the higher distress group compared to the lower distress group, and increased response in the superior and middle frontal gyrus for the opposite comparison. Those in the lower tinnitus severity group were also more active, on average, compared to those in the higher tinnitus severity group. Note that in study three, there was a more pronounced difference in tinnitus severity between groups than in study one. In the survey study, increased levels of physical activity were found to be correlated with lower levels of tinnitus severity and higher quality of life, while controlling for other demographic variables. Conclusion. The specific region of the limbic system recruited during emotional processing may determine the severity of tinnitus. Those with mild forms of tinnitus distress appeared to show enhanced engagement of the insula, whereas increased response from the amygdala may be specific to those with more severe forms of tinnitus. Successful habituation to tinnitus was associated with elevated response of frontal cortex, which may reduce amygdala response improve emotional control and lead to habituation to tinnitus. Our results suggest that physical activity may act as therapy to individuals with tinnitus by providing them with a sense of control over the percept and enhanced engagement of the frontal regions