A team at the University of Auckland have published a very interesting study exploring the neurological mechanisms that underpin why tinnitus can be temporarily reduced or silenced after patients have been exposed to masking noise.
The Acoustic Residual Inhibition (ARI) of tinnitus is a psychoacoustic effect that was first reported in the scientific literature almost fifty years prior (Feldmann 1971). It was noted as being a potential after effect that patients would report upon their tinnitus being masked with white noise. The partial or total inhibition of a subject’s tinnitus could last up to 30 mins with the majority of patients reporting that their tinnitus signal would gradually grow back to the pre-masked level. This phenomenon has historically been poorly researched and there is a large gap in the published literature between the late 1980’s until 2008.
We now have a basic understanding that the emergence of subjective tinnitus is linked to changes in activity levels within certain brain areas that are linked to auditory and emotional processing. These changes appear to be cultivated by a variety of factors including hearing loss, emotional health, genetics and somatic pain. In essence the neurological portion of the hearing system becomes more spontaneously active whilst higher centres of the brain become less adept at filtering unwanted auditory signals from conscious awareness. This emerging model has, in part, been formulated by observing how adults with bothersome tinnitus exhibit a different brain wave signature compared to individuals who do not perceive obvious internal noise. Brainwave patterns are assessed by monitoring the electrical or magnetic activity of the brain via electroencephalography (EEG) or magnetoencephalography (MEG).
This study examined changes in brainwave activity, via EEG recordings, for 30 tinnitus subjects who were exposed to noise that masked their tinnitus perception. The study was controlled by also evaluating how subject brainwave activity changed when patients were exposed to lower intensity noise that did not mask their tinnitus. Of the test subjects 13 successfully experienced their tinnitus, temporarily, reducing in volume after masking and this correlated with their brainwave patterns changing to a state that would be more akin to a subject without bothersome tinnitus. This observation was not repeated when the same patients were exposed to noise that did not effectively mask tinnitus awareness thus demonstrating that the changes recorded were being induced by the actual residual inhibition effect.
So why is this an interesting study? There are two main reasons; primarily this is an interesting phenomenon to any tinnitus clinician and, I believe, partially explains why bespoke sound therapies can be far more effective at controlling and reducing tinnitus related distress than simple generic noise or sound files. It is my clinical experience that sound therapy signals can induce the same effect when being perceived as just audible by patients if the frequency response of the signal is configured to their hearing loss region and tinnitus pitch. Secondly, it provides some evidence to suggest that this kind of imaging could have a clinical role in supporting how clinicians outcome the efficacy or tinnitus therapies so that we become less reliant on questionnaires or psychological acoustic outcome metrics.
A link to this very interesting paper is available below.
King ROC, Singh Shekhawat G, King C, Chan E, Kobayashi K, Searchfield GD. The Effect of Auditory Residual Inhibition on Tinnitus and the Electroencephalogram. Ear Hear. 2020 Aug 3;42(1):130-141. doi: 10.1097/AUD.0000000000000907. PMID: 32769434
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