Sensory and Cognitive Components of Auditory Processing in Individuals With Tinnitus

Tinnitus mechanisms and the need for an objective electrophysiological tinnitus test

Tinnitus, the perception of sound with no external auditory stimulus, is a complex, multifaceted, and potentially devastating disorder. Despite recent advances in our understanding of tinnitus, there are limited options for effective treatment. Tinnitus treatments are made more complicated by the lack of a test for tinnitus based on objectively measured physiological characteristics. Such an objective test would enable a greater understanding of tinnitus mechanisms and may lead to faster treatment development in both animal and human research. This review makes the argument that an objective tinnitus test, such as a non-invasive electrophysiological measure, is desperately needed. We review the current tinnitus assessment methods, the underlying neural correlates of tinnitus, the multiple tinnitus generation theories, and the previously investigated electrophysiological measurements of tinnitus. Finally, we propose an alternate objective test for tinnitus that may be valid in both animal and human subjects.

Objective Detection of Tinnitus Based on Electrophysiology

Tinnitus, a common disease in the clinic, is associated with persistent pain and high costs to society. Several aspects of tinnitus, such as the pathophysiology mechanism, effective treatment, objective detection, etc., have not been elucidated. Any change in the auditory pathway can lead to tinnitus. At present, there is no clear and unified mechanism to explain tinnitus, and the hypotheses regarding its mechanism include auditory plasticity theory, cortical reorganization theory, dorsal cochlear nucleus hypothesis, etc. Current theories on the mechanism of tinnitus mainly focus on the abnormal activity of the central nervous system. Unfortunately, there is currently a lack of objective diagnostic methods for tinnitus. Developing a method that can detect tinnitus objectively is crucial, only in this way can we identify whether the patient really suffers from tinnitus in the case of cognitive impairment or medical disputes and the therapeutic effect of tinnitus. Electrophysiological investigations have prompted the development of an objective detection of tinnitus by potentials recorded in the auditory pathway. However, there is no objective indicator with sufficient sensitivity and specificity to diagnose tinnitus at present. Based on recent findings of studies with various methods, possible electrophysiological approaches to detect the presence of tinnitus have been summarized. We analyze the change of neural activity throughout the auditory pathway in tinnitus subjects and in patients with tinnitus of varying severity to find available parameters in these methods, which is helpful to further explore the feasibility of using electrophysiological methods for the objective detection of tinnitus.

Tinnitus Affects Endogenous But Not Exogenous Auditory Attention Orienting

Purpose:

Previous studies have demonstrated that people with tinnitus show attention dysfunctions. In this study, we investigated the influence of tinnitus on attention orienting, especially whether the ability of attention orienting could be modulated by the degree of tinnitus.

Method:

Fifty-nine and 54 unilateral tinnitus participants were included in Experiment 1 and Experiment 2, respectively. All participants reported subjective tinnitus for at least 3 months and were divided into a mild tinnitus group (Tinnitus Handicap Inventory [THI] < 37) or a moderate to severe tinnitus group (THI ≥ 37) according to the THI score. An auditory exogenous attention task and an auditory endogenous attention task were adopted. In the exogenous task, a target sound following a cue sound was presented on either the left or right side. Participants were required to discriminate whether the target was pure tone or white noise. In the endogenous task, participants were required to pay attention to the stimuli on one side and judge the pitch of a target sound. Mixed-design analyses of variance were conducted for the mean reaction times and accuracy across the experimental conditions.

Results:

Our results showed that in the endogenous attention task, compared with the mild tinnitus group, moderate to severe tinnitus participants had better performance for stimuli presented on the tinnitus side but not on the nontinnitus side. In contrast, in the exogenous attention task, no differences were found between mild and moderate to severe tinnitus groups.

Conclusion:

The results suggest that the degree of tinnitus influences the performance of auditory endogenous attention but not auditory exogenous attention orienting.

Cortical Reorganization Following Psychoeducational Counselling and Residual Inhibition Therapy (RIT) in Individuals with Tinnitus

Introduction Psychoeducational counselling and residual inhibition therapy (RIT) are traditional approaches used in many clinics to manage tinnitus. However, neurophysiological studies to evaluate posttreatment perceptual and functional cortical changes in humans are scarce.

Objectives The present study aims to explore whether cortical auditory-evoked potentials (CAEPs; N1 and P3) reflect the effect of modified RIT and psychoeducational counselling, and whether there is a correlation between the behavioral and electrophysiological measures.

Methods Ten participants with continuous and bothersome tinnitus underwent a session of psychoeducational counselling and modified RIT. Perceptual measures and CAEPs were recorded pre- and posttreatment. Further, the posttreatment measures were compared with age and gender-matched historical control groups.

Results Subjectively, 80% of the participants reported a reduction in the loudness of their tinnitus. Objectively, there was a significant reduction in the posttreatment amplitude of N1 and P3, with no alterations in latency. There was no correlation between the perceived difference in tinnitus loudness and the difference in P3 amplitude (at Pz).

Conclusion The perceptual and functional (as evidenced by sensory, N1, and cognitive, P3 reduction) changes after a single session of RIT and psychoeducational counselling are suggestive of plastic changes at the cortical level. The current study serves as preliminary evidence that event-related potentials (ERPs) can be used to quantify the physiological changes that occur after the intervention for tinnitus.

Systematic review and meta-analysis on the effect of continuous subjective tinnitus on attention and habituation

Background

Attention and habituation are two domains known to play key roles in the perception and maintenance of tinnitus. The heterogeneous nature of tinnitus and the methodologies adopted by various studies make it difficult to generalize findings. The current review aims at assessing and synthesizing evidence on the possible roles of attention and habituation in continuous subjective tinnitus.

Methodology

The literature search included five databases (PubMed, Scopus, Web of Sciences, CINAHL and ProQuest) that resulted in 1,293 articles, published by July 2019. Studies on attention and/or habituation in individuals with tinnitus using either behavioural or electrophysiological tests were included in the review after a quality assessment.

Results

Seventeen studies on attention in tinnitus were included in the narrative synthesis. Two meta-analyses were performed to assess the role of attention in tinnitus using a behavioural methodology (z = 4.06; p < 0.0001) and P300 amplitude (z = 2.70; p = 0.007) with 531 participants. With respect to habituation, the review indicates the lack of quality articles for habituation inclusion in the narrative synthesis.

Conclusions

The review highlights that selective domains of attention were consistently impaired in individuals with tinnitus. Habituation, on the other hand, needs further exploration.