Abstract
Objectives: Acoustic stimulation or sound therapy is proposed as a main treatment option for chronic subjective tinnitus. To further probe the field of acoustic stimulations for tinnitus therapy, this exploratory study compared 10 Hz amplitude modulated (AM) sounds (two pure tones, noise, music, and frequency modulated (FM) sounds) and unmodulated sounds (pure tone, noise) regarding their temporary suppression of tinnitus loudness. First, it was hypothesized that modulated sounds elicit larger temporary loudness suppression (residual inhibition) than unmodulated sounds. Second, with manipulation of stimulus loudness and duration of the modulated sounds weaker or stronger effects of loudness suppression were expected, respectively.Methods: We recruited 29 participants with chronic tonal tinnitus from the multidisciplinary Tinnitus Clinic of the University of Regensburg. Participants underwent audiometric, psychometric and tinnitus pitch matching assessments followed by an acoustic stimulation experiment with a tinnitus loudness growth paradigm. In a first block participants were stimulated with all of the sounds for 3 min each and rated their subjective tinnitus loudness to the pre-stimulus loudness every 30 s after stimulus offset. The same procedure was deployed in the second block with the pure tone AM stimuli matched to the tinnitus frequency, manipulated in length (6 min), and loudness (reduced by 30 dB and linear fade out). Repeated measures mixed model analyses of variance (ANOVA) were calculated to assess differences in loudness growth between the stimuli for each block separately.Results: First, we found that all sounds elicit a short-term suppression of tinnitus loudness (seconds to minutes) with strongest suppression right after stimulus offset [F(6, 1331) = 3.74, p < 0.01]. Second, similar to previous findings we found that AM sounds near the tinnitus frequency produce significantly stronger tinnitus loudness suppression than noise [vs. Pink noise: t(27) = −4.22, p < 0.0001]. Finally, variants of the AM sound matched to the tinnitus frequency reduced in sound level resulted in less suppression while there was no significant difference observed for a longer stimulation duration. Moreover, feasibility of the overall procedure could be confirmed as scores of both tinnitus loudness and questionnaires were lower after the experiment [tinnitus loudness: t(27) = 2.77, p < 0.01; Tinnitus Questionnaire: t(27) = 2.06, p < 0.05; Tinnitus Handicap Inventory: t(27) = 1.92, p = 0.065].Conclusion: Taken together, these results imply that AM sounds, especially in or around the tinnitus frequency, may induce larger suppression than unmodulated sounds. Future studies should thus evaluate this approach in longitudinal studies and real life settings. Furthermore, the putative neural relation of these sound stimuli with a modulation rate in the EEG α band to the observed tinnitus suppression should be probed with respective neurophysiological methods.
Highlights
Subjective tinnitus is defined as “the perception of sound(s) in the absence of an external sound source” (Eggermont and Roberts, 2004; Erlandsson and Dauman, 2013) and is deemed chronic after 12 months since first occurrence (Mazurek et al, 2010)
Post hoc contrasts between each of the 7 stimuli elicited significant differences (p < 0.05) for AMMusic vs. AMTinnitus [t(27) = 4.42, p < 0.0001], Pink noise vs. AMTinnitus [t(27) = 4.22, p = 0.001], AMLow vs. AMTinnitus [t(27) = 3.70, p = 0.004], AMFM vs. AMMusic [t(27) = −3.31, p = 0.016], and AMFM vs. Pink Noise [t(27) = −3.12, p = 0.031], respectively. These results are indicative of a pattern of enhanced tinnitus suppression of AMTinnitus and AMFM compared to Pink Noise, AMMusic, and AMLow [except AMFM vs. AMLow with t(27) = −2.60, p = 0.127]
Feasibility of the overall procedure could be confirmed as scores of both tinnitus questionnaires as well as the visual analog scale (VAS) for tinnitus loudness were lower after the experiment
Summary
Subjective tinnitus is defined as “the perception of sound(s) in the absence of an external sound source” (Eggermont and Roberts, 2004; Erlandsson and Dauman, 2013) and is deemed chronic after 12 months since first occurrence (Mazurek et al, 2010). Tinnitus is considered to be caused by either objective (Eggermont and Roberts, 2004; Schaette and Kempter, 2006; Mazurek et al, 2010) or hidden hearing loss (Weisz et al, 2006; Schaette and McAlpine, 2011; Adjamian et al, 2012; Xiong et al, 2013), where loss of cochlear hair cells in objective hearing loss has been shown to lead to maladaptive plasticity throughout the auditory pathway and brain. Tinnitus pitch seems to average near the frequency of maximal hearing loss, especially in sufferers with pure-tone tinnitus (Schecklmann et al, 2012). Related to this maladaptive plasticity, a similarity of tinnitus to phantom limb or general phantom (pain) perception following sensory deafferentation has been proposed (De Ridder et al, 2011). Models of pathogenesis and physiology are still being debated and are limited by an underlying inherent heterogeneity of the disorder, it can be stated with confidence that both the inner ear and the brain are involved (Jastreboff, 1990; Eggermont and Roberts, 2004; Adjamian et al, 2009; De Ridder et al, 2011, 2014; Vanneste and De Ridder, 2012; Elgoyhen et al, 2015)
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