Tinnitus and its Residual Inhibition Using Tetanic Acoustic Stimulation

Abstract

Objectives: Tinnitus is a prevalent condition and for some individuals, highly debilitating. Although many strategies exist for the management of tinnitus, as of yet there are none clinically available which actually cure the problem. Most current treatments involve psychological treatment in combination with sound therapy. Treatment usually takes a long period of commitment before improvements are seen, and it is difficult to predict who will respond best to which strategy. Masking noise centred at the tinnitus pitch is effective at inducing residual inhibition (RI), a temporary suppression of tinnitus which occurs upon offset of a stimulus. If RI strength could be optimised and its effect sustained, highly successful methods of tinnitus treatment may be developed from it, with one major benefit over other treatment strategies being an essentially instant fix. Non-invasive induction of synaptic plasticity mechanisms potentially involved in RI in the human auditory system using tetanic acoustic stimuli motivated the current study. The main aim of this research was to investigate whether characteristics of RI differ when using constant acoustic stimuli compared to tetanic stimuli, and to identify relationships between annoyances to tinnitus and a stimulus used to elicit RI. Method: 17 participants aged 46-79 years with hearing between normal and moderately severe levels were recruited and underwent audiometric and tinnitus assessments. Participants were subjected to acoustic stimulation using three different types of narrowband noise (NBN) stimuli all centred at the tinnitus pitch: constant, fast-burst tetanic and slow-burst tetanic. Tinnitus loudness and pitch ratings were recorded during and after stimulation and annoyance ratings to tinnitus and to stimuli were also measured for various stimulus presentation levels. Findings: A relatively slow-burst rate tetanic stimulus generated greatest, longest lasting suppression of tinnitus when compared to fast-burst rate tetanic constant stimuli. Use of individually customised stimuli was advantageous over using the slow-burst rate tetanic stimulus generically for tinnitus suppression. Conclusions: Comparisons between use of constant stimuli and tetanic stimuli for the purpose of tinnitus suppression require further investigation in order to provide definitive conclusions about their efficacy. Fully ascertaining mechanisms behind RI will hopefully enable development of strong, long-lasting suppression of tinnitus.