Tinnitus Issues

There is a wealth of information available on subjective responses and by these measures tinnitus has many features in common with pain, i.e. it may be very distressing. However, only the individual affected by it can attest to how severe are the symptoms.

There has been lengthy debate about what aspects of tinnitus are important and these basically split into two areas, the notion of a peripheral trigger for tinnitus, and the central manifestation of how the individual responds to such a trigger, and whether once established, a trigger plays any major continuing role. Needless to say there are two camps fairly strongly divided into physiological and psychological areas of interest. Tinnitus literature is dominated by clinical papers because of the social size of the problem of tinnitus and because there is no truly objective method of quantifying it. It is true that it has been quantified with via intracranial magnetic fields using SQUID technology (Hoke et al), but these are studies using extraordinary research tools. So-called objective methods which attempt to match internal percepts and external sounds still rely upon behavioural responses, are only objective within the conceptual models used thus far to explain psychophysical descriptors.

It is my expectation that a joint consideration of both psychological and physiological offers a rich field for investigation. We are not disintereted in the clinical aspects of tinnitus, but we have to start somewhere, and that is with the physiological mechanisms which give rise to tinnitus. This is for two reasons. The first is that study of the classes and characteristics of tinnitus may give new insight into methods of treatment or management. The second, is that the subjective responses do give quite strong clues as to physiological mechanisms, and these may give additional insight into the study of auditory physiology directly.

In 1991 I attended a meeting of the Australian Audiologists in Private Practice, in Melbourne, at which Jack Vernon was the keynote speaker. I went to talk about our research into otoacoustic emissions, but as I heard Jack give his talk, I went through a process of completely reworking my talk. Jack spoke about his and Mary Meikle’s data on tinnitus and I came to see almost every symptom as having meaningful correlations with not just the cochlear mechanical data I had been collecting for the previous 20 years, but also with my own considerable experience of tinnitus. My new found interest in tinnitus also seemed to fit with much of my recent work in Germany looking at the motor properties of outer hair cells. Jack subsequently invited me to contribute a chapter to his planned book, and specifically instructed authors to freely speculate about possible mechanisms. It became a real dilemma about how much of my own subjective experience to report in the chapter. On the one hand it was only one person’s experience, but on the other, I could describe my subjective experience with more than average precision. Unlike many tinnitus patients I have seen at NAL, who could only describe their tinnitus in the vaguest qualitative terms, likening their experience to everyday sounds, I could specify what I was hearing with the languages of an audio-engineer, scientist and musician.

My chapter “A Model For Cochlear Origin Of Subjective Tinnitus: Excitatory Drift In Operating Point Of Inner Hair Cells” (also available to download as a pdf) was nearly three years from concept to completion and I used as the approach a correlation of many of the symptoms and features of tinnitus which Jack initially outlined with many behaviours being considered in cochlear mechanics. Much has been made since of the central aspects of clinical practice, and in some instances this has been virtually dismissive of the auditory periphery as having an important role. I saw this chapter as providing me an opportunity to contribute almost more towards understanding of cochlear physiology than an understanding of the clinical aspects. In particular, my primary contribution to the study of cochlear mechanics was not just the confirmation of nonlinear mechanical behaviour, but the association of the nonlinearity with baseline shifts of the basilar membrane. Such baseline shifts provide a natural and novel explanation of high frequency tinnitus and this chapter is the development of this idea.

One of the key ideas in the chapter was the notion that transient tinnitus displayed apparently exponential decays and this strongly fits with the notion of a baseline shift affecting the operating points of the outer hair cells. These transient ‘pings’, as we have come to term them, provide compelling reasons to regard at least this class of tinnitus behaviour as being generated in the cochlea. As a musician I have been acutely aware of hearing these pings since I was a teenager, and at one point I kept a diary of them and their characteristics. Now I regard these non-traumatic events not just with musical curiosity, but with considerable excitement as auditory scientists’ interest in the processes of cochlear homeostasis grows (see for example an early report LePage, 1989, Hear.Res. qv).

Last year (2003) I was delighted to hear of an Australian Hearing audiologist (Kim Ter-Horst) was interested to conduct a survey about the prevalence of ping tinnitus and hence invoked immediate interest in the light of its relevance to physiological mechanisms. I supported her to run the tinnitus questionnaire amongst Australian Hearing audiologists and this Internet Survey On Ping Tinnitus is the logical extension of that project. Please take a few minutes to tell us of your experiences of ping tinnitus. A follow up survey is planned to delve into more precise details of the phenomenon from people who have similar backgrounds. Please indicate if you would like to participate in that survey too.

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