Question
Can we use MMN in evaluation of tinnitus patients before and after retraining therapy?
Answer
In order to answer this question, we need to discuss MMN briefly. MMN is an auditory event-related potential that can be recorded as an automatic response of the auditory system to an oddball stimulus embedded in a train of standard stimuli. In other words our auditory system can detect a minute acoustical change when a different stimulus is introduced within a train of standard stimuli.
This paradigm possibly can be used in individuals with tinnitus. For instance, one may identify the tinnitus frequency match of a patient with tinnitus. Then, it is possible to record the mismatch negativity with the use of tone or frequency match of tinnitus as the oddball stimulus and a different tone as the standard stimulus. The recorded MMN will have electrophysiologic values such as latency, area, and amplitude. Then, after Tinnitus Retraining Therapy (TRT) we can repeat this procedure and look for the differences. We can assume that after TRT patient will demonstrate less consciousness about his/her tinnitus. Therefore, this lack of importance toward the oddball stimulus (i.e., the tinnitus frequency match) might result in a different MMN pattern, possibly with smaller amplitude and area, since the patient's auditory system may no longer identify tinnitus as an oddball stimulus. This may mean that the individual with tinnitus has created a habituation to the tinnitus signal that can be documented by MMN. This is one of the ways that evoked potentials can help clinicians in the determination of post-therapeutic aspects of tinnitus management.
Importantly, we are not sure yet if TRT generates any changes in the neural response in regard to tinnitus. However, it is possible to document changes in the neural response following tinnitus treatment using AERPs such as MMN.
Additionally, in the last few years the tinnitus research has employed neuroimaging studies such as fMRI and PET. These methods will help us to study the pre/post therapeutic differences in individuals with tinnitus in depth.
Ali A. Danesh, Ph.D., is an assistant professor and coordinator of Audiology at the Department of Communication Sciences and Disorders, Florida Atlantic University, Boca Raton, FL. He received his doctorate in audiology with an emphasis on auditory electrophysiology from the University of Memphis. His current research area is focused on electrophysiologic responses in individuals with tinnitus and auditory responses in children with autism spectrum disorders.
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