Abstracts

Rationale: Tinnitus incidence is rising due to an aging population and an increase in day-to-day noise exposure. These phantom auditory sensations have typically been viewed as having an exclusively auditory origin, mainly because it is an auditory percept and is often triggered by specific auditory conditions, such as noise trauma causing hearing loss. This said, experts estimate that only a third of those with hearing loss will go on to develop tinnitus. Although many theories on its neurological underpinning exist, no studies have identified why tinnitus only occurs in specific individuals. According to Rauschecker and collaborators (2010), dysfunctional limbic noise cancelling mechanisms could be responsible for tinnitus perception after hearing loss. To test this hypothesis, we investigated the prevalence of tinnitus in a population of patients with a dysfunction of the amygdala in a case control study. Methods: A group of 166 patients who had undergone unilateral medial temporal lobe removal (including the amygdala) for the relief of medically intractable epilepsy took part in this study. Specifically, data were collected regarding the patients' general health and audition. These data were compared with data from a group of paired healthy (n=332) and a group of self-reported epileptic (n=332) controls taken from the French Nutrinet-Sant頣ohort (n=93 756; Hercberg et al., 2010). Results: As predicted, we found that 23.5% of epileptic patients who underwent median temporal lobe resection including the amygdala reported experiencing tinnitus. This prevalence is significantly different from the paired healthy (OR 278, 95% CI 167-462, p < 0001) and self-reported epileptic (OR 231, 95% CI 141-377, p < 0001) controls, although it increases with age in all groups. Conclusions: The present findings support the idea that a compromised neural noise-cancellation mechanism could be responsible for tinnitus perception, and provides convincing evidence for the involvement of the limbic system in this phenomenon. According to our results, it appears that a unilateral medial temporal lobe surgery including the amygdala increases the risk for a patient to develop tinnitus. Funding: Canadian Institutes of Health Research