Tinnitus From cortex to cochlea

Contents 1 Introduction to the thesis 7 2 Plasticity in tinnitus patients: a role for the efferent auditory system? 19 3 Asymmetry in primary auditory cortex activity in tinnitus patients 37 and controls 4 Contralateral suppression of otoacoustic emissions in tinnitus patients 55 5 Wavelet-analysis demonstrates no abnormality in contralateral 71 suppression of otoacoustic emissions in tinnitus patients 6 The effect of TMS on otoacoustic emissions: a pilot study probing 93 the efferent auditory system 7 General discussion and conclusion 109 8 Summary & Samenvatting 121 Dankwoord 131 Curriculum Vitae 135 Chapter 1 Introduction to the thesis Chapter 1 8 1.1 Tinnitus The word tinnitus comes from the Latin word " tinnire " , which means to ring. Tinnitus is the perception of a meaningless sound without an external source. It is described by patients in many ways, for example as a ringing, hissing or buzzing sound. Tinnitus can be lateralized to the left or right ear, or be perceived in the middle of the head. There are two types of tinnitus: objective and subjective tinnitus. Objective tinnitus is a sound that can be perceived by not only the patient, but also by an external observer. Objective tinnitus can be of vascular or muscular origin. Examples are a stenosis of the carotic artery, a sinodural fistula, a paraganglioma or a myoclonic contraction of the soft palate or the stapedial muscle (Chandler, 1983; Howsam et al., 2005; Sonmez et al., 2007). These conditions can give rise to a noticeable, pulsating sound, sometimes in synchrony with the heartbeat. The sound gives its auditory percept through the normal hearing mechanism, starting with perception in the cochlea. Because objective tinnitus has an identifiable source, treatment options are sometimes available, depending on the specific source. Objective tinnitus is rare, but because of potential treatment options or medical consequences, it needs to be assessed when a patient with tinnitus seeks medical attention. Subjective tinnitus cannot be heard by an external observer, but only by the patient. In this case there is no identifiable sound source, making subjective tinnitus a phantom percept. Subjective tinnitus is the most frequent form of tinnitus, and the subject of this thesis. Therefore we will not use the adjective " subjective " throughout this thesis anymore. Transient tinnitus is experienced by almost all adults at some point in their life. Permanent tinnitus is also a very frequently reported symptom, with prevalence ranging …