Objectives: Creative approaches to improve access to evidence-based tinnitus interventions are required. The purpose of this thesis was to address this need by developing an Internet-based cognitive behavioural therapy intervention (iCBT) specifically for those with tinnitus in the United Kingdom (UK). A unique aspect was providing audiological, instead of psychological guidance for those undertaking the intervention. Further objectives were to evaluate whether audiologist-guided iCBT could reduce tinnitus distress and tinnitus-associated comorbidities in a UK population. Method: Initially an innovative iCBT tinnitus intervention adapted for a UK population was developed. The intervention was assessed for functionality and acceptability by both tinnitus professionals (n = 5) and adults with tinnitus (n = 29). A three-phase audiologist-guided clinical trial followed to evaluate feasibility (n = 39), efficacy (n = 146) and effectiveness (n = 92). In addition, the longer-term outcomes and unwanted effects were investigated (n = 104). A process evaluation was conducted parallel to the efficacy trial. Standardised self-reported assessment measures for tinnitus distress, insomnia, anxiety, depression, hearing disability hyperacusis, cognitive failures and life satisfaction were included. Results: The developed intervention was rated as acceptable by both professionals and adults experiencing tinnitus. In Phase I, feasibility was established in terms of recruitment potential, attrition and adherence rates. In Phase II, efficacy was evident as undertaking iCBT led to a significant reduction in tinnitus distress and tinnitus-related comorbidities (insomnia, depression, hyperacusis, cognitive failures and increase in life satisfaction). These results remained stable up to 1 year post-intervention. Unwanted treatment effects were reported by 11% of participants. Process evaluation identified intervention aspects that facilitated and hampered the outcomes obtained. Phase III results were comparable regardless of receiving iCBT or individualised face-to-face care. Conclusion: An acceptable iCBT tinnitus intervention was developed for a UK population. Original research has been undertaken, which has indicated the acceptability, feasibility, efficacy and effectiveness of audiologist-guided iCBT in reducing tinnitus distress and tinnitus-associated comorbidities in a UK population.

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Tinnitus is a phantom auditory perception characterized by a ringing sound in either one or both ears. It is a common disorder most often associated with hearing loss and can have a severe impact on a person's quality of life. There is currently no cure and no efficient therapeutic options. There is little known about the neural mechanisms underlying the generation of tinnitus but a better understanding of its neural basis could greatly benefit the development of efficient treatment methods. This literature study aims to explore the neural mechanisms of tinnitus in terms of generation, perpetuation, and perception. Cochlear dysfunction, changes in neuronal firing rates and oscillatory properties, hyperactivity, lack of inhibitory activity and plasticity in auditory-limbic structures have been associated with tinnitus and may be a part of a crossmodal network involved in generating, perpetuating and perceiving tinnitus, through maladaptive CNS plasticity. New developing treatment methods aim to modulate and re-route tinnitus-related plasticity, however, this leads to treatment difficulties due to the crossmodal nature of the tinnitus pathophysiology. These difficulties will be further examined in the discussion.

This work sought to characterise neurochemical and neurophysiological processes underlying tinnitus in humans. The first study involved invasive brain recordings from a neurosurgical patient, along with experimental manipulation of his tinnitus, to map the cortical system underlying his tinnitus. Widespread tinnitus-linked changes in low- and high-frequency oscillations were observed, along with inter-regional and cross-frequency patterns of communication. The second and third studies compared tinnitus patients to controls matched for age, sex and hearing loss, measuring auditory cortex spontaneous oscillations (with magnetoencephalography) and neurochemical concentrations (with magnetic resonance spectroscopy) respectively. Unlike in previous studies not controlled for hearing loss, there were no group differences in oscillatory activity attributable to tinnitus. However, there was a significant correlation between gamma oscillations (>30Hz) and hearing loss in the tinnitus group, and between delta oscillations (1-4Hz) and perceived tinnitus loudness. In the neurochemical study, tinnitus patients had significantly reduced GABA concentrations compared to matched controls, and within this group there was a positive correlation between choline concentration (potentially linked to acetylcholine and/or neuronal plasticity) and both hearing loss, and subjective tinnitus intensity and distress. In light of present and previous findings, tinnitus may be best explained by a predictive coding model of perception, which was tested in the final experiment. This directly controlled the three main quantities comprising predictive coding models, and found that delta/theta/alpha oscillations (1-12Hz) encoded the precision of predictions, beta oscillations (12-30Hz) encoded changes to predictions, and gamma oscillations represented surprise (unexpectedness of stimuli based on predictions). The work concludes with a predictive coding model of tinnitus that builds upon the present findings and settles unresolved paradoxes in the literature. In this, precursor processes (in varying combinations) synergise to increase the precision associated with spontaneous activity in the auditory pathway to the point where it overrides higher predictions of ‘silence’.

Tinnitus is defined as an auditory stimulus that is unrelated to external stimulation. There are many theories as to what causes tinnitus, therefore, there are many treatment options for tinnitus. This paper attempts to increase the audiologist's knowledge of the etiology, as well as, the most appropriate treatment for tinnitus. There are two types of tinnitus, objective and subjective. Subjective tinnitus is more common, although it is more difficult to treat than objective tinnitus. There are many theories as to what causes tinnitus. Several disorders that have tinnitus as a symptom, such as, Meniere's disease, acoustic neuroma, and dysfunction of serotonin levels, are discussed. Before treatment of tinnitus, the patient must undergo a medical and audiologic evaluation. Tests of tinnitus pitch, loudness, residual masking, and minimal masking are included. The implications of these tests on treatment are also discussed. There are many treatment options available for tinnitus, such as, electrical stimulation, medications, stress and psychological therapy, tinnitus maskers, and hearing aids. This paper focuses on mainly the treatments that are most feasible for an audiologist. In addition, included is an empirical study that was conducted to examine the effects of hearing aids and circuit type on tinnitus relief. To conclude, this paper will summarize the steps to follow in order to manage a patient that exhibits tinnitus. Although there are some treatments that seem to be more appropriate for an audiologist to utilize, (i.e., hearing aids, maskers, and Tinnitus Retraining Therapy, none have been proven to be effective in every patient. Research is still needed in this area.

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The purpose of the present study was to determine whether the perceived severity of chronic tinnitus in a geriatric population increased, decreased, or remained constant with the passage of time. A questionnaire was designed to ascertain the subjects' perceived severity at time of onset and the perceived severity of their current tinnitus. The subjects were asked to rate their past and present tinnitus severity according to how much it bothered them. They were also asked questions pertaining to noise exposure history, hearing aid use, and tinnitus sound parameters for purposes of comparison with other groups previously studied.

Tinnitus is the phantom perception of a sound heard in the absence of a physical sound source. One framework that attempts to explain tinnitus is called the deafferentation model, which asserts that hearing damage precipitates compensatory neural plasticity in the central auditory system, leading to hyperactivity perceived as tinnitus. While considerable evidence supports this view, the role of deafferentation and its effects on central auditory processing are not fully understood. This thesis addresses two questions raised within the model. First, audiometric hearing loss is not always present in tinnitus subjects, so is there evidence of deafferentation in these individuals? The second question concerns the effect of tinnitus with audiometric hearing loss on central auditory processing. Specifically, is auditory attention affected in tinnitus, and if so, how? Following a background review in Chapter 1, Chapter 2 describes a study addressing the first issue, which found evidence for previously undetected hearing loss in tinnitus subjects that distinguishes them from individuals with normal hearing. Chapter 3 addresses the second question, describing an investigation that found that top-down attention appears to operate normally in tinnitus, but the tinnitus-affected region of auditory cortex is insensitive to the influence of attention because it is busy encoding the tinnitus. Chapter 4 describes a background study using non-tinnitus individuals to test this latter conclusion, finding evidence that auditory cortical neurons reacting to stimulus change are concurrently sensitive to top-down attention. This procedure can be used to assess if tinnitus-affected auditory cortical neurons are generally insensitive to input. Chapter 5 discusses the implications of the above empirical findings for understanding the role of deafferentation in tinnitus and tinnitus-related changes that occur in central auditory processing. / Dissertation / Doctor of Philosophy (PhD)