(PP1405) The Use of Late Auditory Evoked Potentials as Potential Biomarkers of Tinnitus

Tinnitus, or the perception of sound without an external acoustic stimulus, affects approximately 10% of the US population. Despite this prevalence, the mechanisms of tinnitus are not completely understood, and there is no objective test that can diagnose tinnitus. Previous studies have examined auditory evoked potentials to identify differences in tinnitus and non-tinnitus populations; however, none have incorporated the pitch matched tinnitus frequency in multiple paradigms. This study was designed to elicit auditory late responses, mismatch negativity, and P300 responses using the tinnitus frequency in subjects with and without tinnitus, in an attempt to identify potential biomarkers of tinnitus.


Summary: 

Objective

 The purpose of this study is to identify an auditory electrophysiological test battery that would potentially lead to biomarkers which can be utilized to differentiate between individuals with and without tinnitus.

Rationale/Purpose

Subjective tinnitus is a condition that is not fully understood, and as a result there are no diagnostic tests or completely efficacious treatments that can be used. The financial implications of this are particularly evident in the VA, where tinnitus is one of the top two service-connected disabilities, behind hearing loss, costing hundreds of millions of dollars annually. The test battery utilized in this study examines both exogenous and endogenous potentials to search for differences between tinnitus and matched non-tinnitus controls. This allows for a more complete evaluation of the auditory system, starting with the early evoked cortical potential, P1, and ending with the endogenous P300 potential. Identification of differences along the central auditory pathway, beginning at the cortical level, could also inspire research for treatment methods that target the cortical regions where differences exist. We hypothesize that individuals with tinnitus, compared to their matched controls without tinnitus, will exhibit differences in their ALR, MMN responses, and P300 responses when their pitch matched tinnitus frequency is incorporated into the test paradigm due to their inability to completely disengage from their perceived tinnitus. Specifically, an inability to completely disengage from their tinnitus is expected to result in reduced amplitudes due to the allocation of attentional resources focused on the internal tinnitus signal, thereby leaving fewer resources available for the processing of the paradigms utilized.

Methods

The subject pool consists of 10 tinnitus participants that have chronic, bilateral, tonal tinnitus that has been present for at least 6 months and 10 control non-tinnitus participants that are matched for age, gender, and hearing status. The test battery administered to both groups consists of: Case history, the Tinnitus Reaction Questionnaire, the Tinnitus Handicap Inventory, tympanograms, extended high frequency pure tone testing, loudness discomfort levels, tinnitus pitch matching and loudness matching (for tinnitus participants only), and late auditory evoked potentials that are evoked using the pitch matched tinnitus frequency.

Results and conclusions

Data analyses is still ongoing, but preliminary results indicate differences in P1 and N1 in the ALR paradigm, with controls exhibiting larger peak amplitudes. The data also indicates differences in MMN amplitudes between tinnitus and non-tinnitus controls in the central midline and frontal electrode channels, with the tinnitus group exhibiting a smaller MMN amplitude than the control group. Furthermore, the tinnitus group showed a decrease in P300 amplitude compared to the control group. This would suggest that individuals with tinnitus have fewer pre-attentional and attentional resources to devote towards identification of the deviant stimulus. These results thus far implicate that tinnitus is a complex phenomenon that can be best evaluated using a combination of evoked potential paradigms.