Development of tinnitus-related neuronal hyperactivity through homeostatic plasticity after hearing loss: a computational model

Deviant Dynamics of Resting State Electroencephalogram Microstate in Patients With Subjective Tinnitus

Given the importance of central reorganization and tinnitus, we undertook the current study to investigate changes to electroencephalogram (EEG) microstates and their association with the clinical symptoms in tinnitus. High-density (128 channel) EEG was used to explore changes in microstate features in 15 subjects with subjective tinnitus and 17 age-matched controls. Correlations between microstate parameters and subjective tinnitus symptoms were also analyzed. An increased presence of class A microstate and decreased presence of class D microstate were found in coverage and lifespan of microstate parameters in the tinnitus patients. Syntax analysis also demonstrated an aberrant pattern of activity, with reduced transitions from class D to class B in tinnitus patients. Moreover, a significant positive correlation of tinnitus loudness with increased lifespan of microstate class C was found. Significant differences in temporal characteristics and syntax of the EEG microstate classes were found at rest between tinnitus patients and the healthy subjects. Our study indicates that EEG microstates may provide a possible valuable method to study large-scale brain networks, which may in turn be beneficial to investigation of the neurophysiological mechanisms behind tinnitus.

Effects of Acoustic Environment on Tinnitus Behavior in Sound-Exposed Rats

Laboratory studies often rely on a damaging sound exposure to induce tinnitus in animal models. Because the time course and ultimate success of the induction process is not known in advance, it is not unusual to maintain sound-exposed animals for months while they are periodically assessed for behavioral indications of the disorder. To demonstrate the importance of acoustic environment during this period of behavioral screening, sound-exposed rats were tested for tinnitus while housed under quiet or constant noise conditions. More than half of the quiet-housed rats developed behavioral indications of the disorder. None of the noise-housed rats exhibited tinnitus behavior during 2 months of behavioral screening. It is widely assumed that the "phantom sound" of tinnitus reflects abnormal levels of spontaneous activity in the central auditory pathways that are triggered by cochlear injury. Our results suggest that sustained patterns of noise-driven activity may prevent the injury-induced changes in central auditory processing that lead to this hyperactive state. From the perspective of laboratory studies of tinnitus, housing sound-exposed animals in uncontrolled noise levels may significantly reduce the success of induction procedures. From a broader clinical perspective, an early intervention with sound therapy may reduce the risk of tinnitus in individuals who have experienced an acute cochlear injury.

Weak Middle-Ear-Muscle Reflex in Humans with Noise-Induced Tinnitus and Normal Hearing May Reflect Cochlear Synaptopathy

Chronic tinnitus is a prevalent hearing disorder, and yet no successful treatments or objective diagnostic tests are currently available. The aim of this study was to investigate the relationship between the presence of tinnitus and the strength of the middle-ear-muscle reflex (MEMR) in humans with normal and near-normal hearing. Clicks were used as test stimuli to obtain a wideband measure of the effect of reflex activation on ear-canal sound pressure. The reflex was elicited using a contralateral broadband noise. The results show that the reflex strength is significantly reduced in individuals with noise-induced continuous tinnitus and normal or near-normal audiometric thresholds compared with no-tinnitus controls. Due to a shallower growth of the reflex strength in the tinnitus group, the difference between the two groups increased with increasing elicitor level. No significant difference in the effect of tinnitus on the strength of the middle-ear muscle reflex was found between males and females. The weaker reflex could not be accounted for by differences in audiometric hearing thresholds between the tinnitus and control groups. Similarity between our findings in humans and the findings of a reduced middle-ear muscle reflex in noise-exposed animals suggests that noise-induced tinnitus in individuals with clinically normal hearing may be a consequence of cochlear synaptopathy, a loss of synaptic connections between inner hair cells (IHCs) in the cochlea and auditory-nerve (AN) fibers that has been termed hidden hearing loss.

10 Hz Amplitude Modulated Sounds Induce Short-Term Tinnitus Suppression

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.

Thalamic gamma band desynchronization in a computational model of the auditory pathway

Recent studies have focused on modeling the response of the early auditory processing stages to sound stimuli. However, the influence of sound on the higher stages like the auditory thalamus are not well identified. To understand how different sound stimuli affect the response of neurons in these higher stages, it is necessary to model the auditory pathway from the auditory nerve (AN) through the different stages up to the cortex. In this article we present a model of one of the paths through which sound travels from the AN to the cortex. The model presented is a compound of several sub models of different stages of the auditory pathway which offers a detailed resolution due to the subsequent simulation of processing stages. We consider neurons from the AN, the dorsal cochlear nucleus (DCN), the thalamus (specific and non-specific thalamic cells and reticular nucleus) and cortical columns simulating attended and unattended conditions. We use pure tone stimuli with different frequencies as an input and analyze the power spectra of the thalamic and cortical neurons. The main difference in the power spectra can be seen in the specific thalamic cells (STC), where a clear loss of power in the gamma band of the neurons responsible for processing the sound input occurred.

Continuous vs. intermittent neurofeedback to regulate auditory cortex activity of tinnitus patients using real-time fMRI - A pilot study

The emerging technique of real-time fMRI neurofeedback trains individuals to regulate their own brain activity via feedback from an fMRI measure of neural activity. Optimum feedback presentation has yet to be determined, particularly when working with clinical populations. To this end, we compared continuous against intermittent feedback in subjects with tinnitus.

Fourteen participants with tinnitus completed the whole experiment consisting of nine runs (3 runs × 3 days). Prior to the neurofeedback, the target region was localized within the auditory cortex using auditory stimulation (1 kHz tone pulsating at 6 Hz) in an ON-OFF block design. During neurofeedback runs, participants received either continuous (n = 7, age 46.84 ± 12.01, Tinnitus Functional Index (TFI) 49.43 ± 15.70) or intermittent feedback (only after the regulation block) (n = 7, age 47.42 ± 12.39, TFI 49.82 ± 20.28). Participants were asked to decrease auditory cortex activity that was presented to them by a moving bar. In the first and the last session, participants also underwent arterial spin labeling (ASL) and resting-state fMRI imaging. We assessed tinnitus severity using the TFI questionnaire before all sessions, directly after all sessions and six weeks after all sessions. We then compared neuroimaging results from neurofeedback using a general linear model (GLM) and region-of-interest analysis as well as behavior measures employing a repeated-measures ANOVA. In addition, we looked at the seed-based connectivity of the auditory cortex using resting-state data and the cerebral blood flow using ASL data.

GLM group analysis revealed that a considerable part of the target region within the auditory cortex was significantly deactivated during neurofeedback. When comparing continuous and intermittent feedback groups, the continuous group showed a stronger deactivation of parts of the target region, specifically the secondary auditory cortex. This result was confirmed in the region-of-interest analysis that showed a significant down-regulation effect for the continuous but not the intermittent group. Additionally, continuous feedback led to a slightly stronger effect over time while intermittent feedback showed best results in the first session. Behaviorally, there was no significant effect on the total TFI score, though on a descriptive level TFI scores tended to decrease after all sessions and in the six weeks follow up in the continuous group. Seed-based connectivity with a fixed-effects analysis revealed that functional connectivity increased over sessions in the posterior cingulate cortex, premotor area and part of the insula when looking at all patients while cerebral blood flow did not change significantly over time.

Overall, these results show that continuous feedback is suitable for long-term neurofeedback experiments while intermittent feedback presentation promises good results for single session experiments when using the auditory cortex as a target region. In particular, the down-regulation effect is more pronounced in the secondary auditory cortex, which might be more susceptible to voluntary modulation in comparison to a primary sensory region.

•

Comparison of continuous and intermittent fMRI neurofeedback in tinnitus patients

•

Both groups attempted down-regulation of the auditory cortex.

•

The continuous feedback group seemed to improve after multiple sessions.

•

Intermittent feedback worked best for a single session.

•

Down-regulation effect seems more pronounced in the secondary auditory cortex.

Stochastic Resonance Controlled Upregulation of Internal Noise after Hearing Loss as a Putative Cause of Tinnitus-Related Neuronal Hyperactivity

Subjective tinnitus is generally assumed to be a consequence of hearing loss. In animal studies it has been demonstrated that acoustic trauma induced cochlear damage can lead to behavioral signs of tinnitus. In addition it was shown that noise trauma may lead to deafferentation of cochlear inner hair cells (IHC) even in the absence of elevated hearing thresholds, and it seems conceivable that such hidden hearing loss may be sufficient to cause tinnitus. Numerous studies have indicated that tinnitus is correlated with pathologically increased spontaneous firing rates and hyperactivity of neurons along the auditory pathway. It has been proposed that this hyperactivity is the consequence of a mechanism aiming to compensate for reduced input to the auditory system by increasing central neuronal gain, a mechanism referred to as homeostatic plasticity (HP), thereby maintaining mean firing rates over longer timescales for stabilization of neuronal processing. Here we propose an alternative, new interpretation of tinnitus-related development of neuronal hyperactivity in terms of information theory. In particular, we suggest that stochastic resonance (SR) plays a key role in both short- and long-term plasticity within the auditory system and that SR is the primary cause of neuronal hyperactivity and tinnitus. We argue that following hearing loss, SR serves to lift signals above the increased neuronal thresholds, thereby partly compensating for the hearing loss. In our model, the increased amount of internal noise-which is crucial for SR to work-corresponds to neuronal hyperactivity which subsequently causes neuronal plasticity along the auditory pathway and finally may lead to the development of a phantom percept, i.e., subjective tinnitus. We demonstrate the plausibility of our hypothesis using a computational model and provide exemplary findings in human patients that are consistent with that model. Finally we discuss the observed asymmetry in human tinnitus pitch distribution as a consequence of asymmetry of the distribution of auditory nerve type I fibers along the cochlea in the context of our model.

Reductions in cortical alpha activity, enhancements in neural responses and impaired gap detection caused by sodium salicylate in awake guinea pigs

Tinnitus chronically affects between 10-15% of the population but, despite its prevalence, the underlying mechanisms are still not properly understood. One experimental model involves administration of high doses of sodium salicylate, as this is known to reliably induce tinnitus in both humans and animals. Guinea pigs were implanted with chronic electrocorticography (ECoG) electrode arrays, with silver-ball electrodes placed on the dura over left and right auditory cortex. Two more electrodes were positioned over the cerebellum to monitor auditory brainstem responses (ABRs). We recorded resting-state and auditory evoked neural activity from awake animals before and 2 h following salicylate administration (350 mg/kg; i.p.). Large increases in click-evoked responses (> 100%) were evident across the whole auditory cortex, despite significant reductions in wave I ABR amplitudes (in response to 20 kHz tones), which are indicative of auditory nerve activity. In the same animals, significant decreases in 6-10 Hz spontaneous oscillations (alpha waves) were evident over dorsocaudal auditory cortex. We were also able to demonstrate for the first time that cortical evoked potentials can be inhibited by a preceding gap in background noise [gap-induced pre-pulse inhibition (PPI)], in a similar fashion to the gap-induced inhibition of the acoustic startle reflex that is used as a behavioural test for tinnitus. Furthermore, 2 h following salicylate administration, we observed significant deficits in PPI of cortical responses that were closely aligned with significant deficits in behavioural responses to the same stimuli. Together, these data are suggestive of neural correlates of tinnitus and oversensitivity to sound (hyperacusis).

Zinc supplementation for tinnitus

BACKGROUND

Tinnitus is the perception of sound without external acoustic stimuli. Patients with severe tinnitus may have physical and psychological complaints and their tinnitus can cause deterioration in their quality of life. At present no specific therapy for tinnitus has been found to be satisfactory in all patients. In recent decades, a number of reports have suggested that oral zinc supplementation may be effective in the management of tinnitus. Since zinc has a role in cochlear physiology and in the synapses of the auditory system, there is a plausible mechanism of action for this treatment.

OBJECTIVES

To evaluate the effectiveness and safety of oral zinc supplementation in the management of patients with tinnitus.

SEARCH METHODS

The Cochrane ENT Information Specialist searched the ENT Trials Register; Central Register of Controlled Trials (CENTRAL 2016, Issue 6); PubMed; EMBASE; CINAHL; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished trials. The date of the search was 14 July 2016.

SELECTION CRITERIA

Randomised controlled trials comparing zinc supplementation versus placebo in adults (18 years and over) with tinnitus.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures recommended by Cochrane. Our primary outcome measures were improvement in tinnitus severity and disability, measured by a validated tinnitus-specific questionnaire, and adverse effects. Secondary outcomes were quality of life, change in socioeconomic impact associated with work, change in anxiety and depression disorders, change in psychoacoustic parameters, change in tinnitus loudness, change in overall severity of tinnitus and change in thresholds on pure tone audiometry. We used GRADE to assess the quality of the evidence for each outcome; this is indicated in italics.

MAIN RESULTS

We included three trials involving a total of 209 participants. The studies were at moderate to high risk of bias. All included studies had differences in participant selection criteria, length of follow-up and outcome measurement, precluding a meta-analysis. The participants were all adults over 18 years with subjective tinnitus, but one study conducted in 2013 (n = 109) included only elderly patients. Improvement in tinnitus severity and disabilityOnly the study in elderly patients used a validated instrument (Tinnitus Handicap Questionnaire) for this primary outcome. The authors of this cross-over study did not report the results of the two phases separately and found no significant differences in the proportion of patients reporting tinnitus improvement at four months of follow-up: 5% (5/93) versus 2% (2/94) in the zinc and placebo groups, respectively (risk ratio (RR) 2.53, 95% confidence interval (CI) 0.50 to 12.70; very low-quality evidence).None of the included studies reported any significant adverse effects. Secondary outcomesFor the secondary outcome change in tinnitus loudness, one study reported no significant difference between the zinc and placebo groups after eight weeks: mean difference in tinnitus loudness -9.71 dB (95% CI -25.53 to 6.11; very low-quality evidence). Another study also measured tinnitus loudness but used a 0- to 100-point scale. The authors of this second study reported no significant difference between the zinc and placebo groups after four months: mean difference in tinnitus loudness rating scores 0.50 (95% CI -5.08 to 6.08; very low-quality evidence).Two studies used unvalidated instruments to assess tinnitus severity. One (with 50 participants) reported the severity of tinnitus using a non-validated scale (0 to 7 points) and found no significant difference in subjective tinnitus scores between the zinc and placebo groups at the end of eight weeks of follow-up (mean difference (MD) -1.41, 95% CI -2.97 to 0.15; very low-quality evidence). A third trial (n = 50) also evaluated the improvement of tinnitus using a non-validated instrument (a 0 to 10 scale: 10 = severe and unbearable tinnitus). In this study, after eight weeks there was no difference in the proportion of patients with improvement in their tinnitus, 8.7% (2/23) treated with zinc versus 8% (2/25) of those who received a placebo (RR 1.09, 95% CI 0.17 to 7.10, very low-quality evidence).None of the included studies reported any of our other secondary outcomes (quality of life, change in socioeconomic impact associated with work, change in anxiety and depression disorders, change in psychoacoustic parameters or change in thresholds on pure tone audiometry).

AUTHORS' CONCLUSIONS

We found no evidence that the use of oral zinc supplementation improves symptoms in adults with tinnitus.

No change in the acoustic reflex threshold and auditory brainstem response following short-term acoustic stimulation in normal hearing adults

Unilateral auditory deprivation or stimulation can induce changes in loudness and modify the sound level required to elicit the acoustic reflex. This has been explained in terms of a change in neural response, or gain, for a given sound level. However, it is unclear if these changes are driven by the asymmetry in auditory input or if they will also occur following bilateral changes in auditory input. The present study used a cross-over trial of unilateral and bilateral amplification to investigate changes in the acoustic reflex thresholds (ARTs) and the auditory brainstem response (ABR) in normal hearing listeners. Each treatment lasted 7 days and there was a 7-day washout period between the treatments. There was no significant change in the ART or ABR with either treatment. This null finding may have occurred because the amplification was insufficient to induce experience-related changes to the ABR and ART. Based on the null findings from the present study, and evidence of a change in ART in previous unilateral hearing aid use in normal hearing listeners, the threshold to trigger adaptive changes appears to be around 5 days of amplification with real ear insertion gain greater than 13-17 dB.

Time course and frequency specificity of sub-cortical plasticity in adults following acute unilateral deprivation

Auditory deprivation and stimulation can change the threshold of the acoustic reflex, but the mechanisms underlying these changes remain largely unknown. In order to elucidate the mechanism, we sought to characterize the time-course as well as the frequency specificity of changes in acoustic reflex thresholds (ARTs). In addition, we compared ipsilateral and contralateral measurements because the pattern of findings may shed light on the anatomical location of the change in neural gain. Twenty-four normal-hearing adults wore an earplug continuously in one ear for six days. We measured ipsilateral and contralateral ARTs in both ears on six occasions (baseline, after 2, 4 and 6 days of earplug use, and 4 and 24 h after earplug removal), using pure tones at 0.5, 1, 2 and 4 kHz and a broadband noise stimulus, and an experimenter-blinded design. We found that ipsi- as well as contralateral ARTs were obtained at a lower sound pressure level after earplug use, but only when the reflex was elicited by stimulating the treatment ear. Changes in contralateral ARTs were not the same as changes in ipsilateral ARTs when the stimulus was presented to the control ear. Changes in ARTs were present after 2 days of earplug use, and reached statistical significance after 4 days, when the ipsilateral and contralateral ARTs were measured in the treatment ear. The greatest changes in ARTs occurred at 2 and 4 kHz, the frequencies most attenuated by the earplug. After removal of the earplug, ARTs started to return to baseline relatively quickly, and were not significantly different from baseline by 4-24 h. There was a trend for the recovery to occur quicker than the onset. The changes in ARTs are consistent with a frequency-specific gain control mechanism operating around the level of the ventral cochlear nucleus in the treatment ear, on a time scale of hours to days. These findings, specifically the time course of change, could be applicable to other sensory systems, which have also shown evidence of a neural gain control mechanism.

Reactive Neurogenesis and Down-Regulation of the Potassium-Chloride Cotransporter KCC2 in the Cochlear Nuclei after Cochlear Deafferentation

While many studies have been devoted to investigating the homeostatic plasticity triggered by cochlear hearing loss, the cellular and molecular mechanisms involved in these central changes remain elusive. In the present study, we investigated the possibility of reactive neurogenesis after unilateral cochlear nerve section in the cochlear nucleus (CN) of cats. We found a strong cell proliferation in all the CN sub-divisions ipsilateral to the lesion. Most of the newly generated cells survive up to 1 month after cochlear deafferentation in all cochlear nuclei (except the dorsal CN) and give rise to a variety of cell types, i.e., microglial cells, astrocytes, and neurons. Interestingly, many of the newborn neurons had an inhibitory (GABAergic) phenotype. This result is intriguing since sensory deafferentation is usually accompanied by enhanced excitation, consistent with a reduction in central inhibition. The membrane potential effect of GABA depends, however, on the intra-cellular chloride concentration, which is maintained at low levels in adults by the potassium chloride co-transporter KCC2. The KCC2 density on the plasma membrane of neurons was then assessed after cochlear deafferentation in the cochlear nuclei ipsilateral and contralateral to the lesion. Cochlear deafferentation is accompanied by a strong down-regulation of KCC2 ipsilateral to the lesion at 3 and 30 days post-lesion. This study suggests that reactive neurogenesis and down-regulation of KCC2 is part of the vast repertoire involved in homeostatic plasticity triggered by hearing loss. These central changes may also play a role in the generation of tinnitus and hyperacusis.

Non-Monotonic Relation between Noise Exposure Severity and Neuronal Hyperactivity in the Auditory Midbrain

The occurrence of tinnitus can be linked to hearing loss in the majority of cases, but there is nevertheless a large degree of unexplained heterogeneity in the relation between hearing loss and tinnitus. Part of the problem might be that hearing loss is usually quantified in terms of increased hearing thresholds, which only provides limited information about the underlying cochlear damage. Moreover, noise exposure that does not cause hearing threshold loss can still lead to “hidden hearing loss” (HHL), i.e., functional deafferentation of auditory nerve fibers (ANFs) through loss of synaptic ribbons in inner hair cells. While it is known that increased hearing thresholds can trigger increases in spontaneous neural activity in the central auditory system, i.e., a putative neural correlate of tinnitus, the central effects of HHL have not yet been investigated. Here, we exposed mice to octave-band noise at 100 and 105 dB SPL to generate HHL and permanent increases of hearing thresholds, respectively. Deafferentation of ANFs was confirmed through measurement of auditory brainstem responses and cochlear immunohistochemistry. Acute extracellular recordings from the auditory midbrain (inferior colliculus) demonstrated increases in spontaneous neuronal activity (a putative neural correlate of tinnitus) in both groups. Surprisingly, the increase in spontaneous activity was most pronounced in the mice with HHL, suggesting that the relation between hearing loss and neuronal hyperactivity might be more complex than currently understood. Our computational model indicated that these differences in neuronal hyperactivity could arise from different degrees of deafferentation of low-threshold ANFs in the two exposure groups. Our results demonstrate that HHL is sufficient to induce changes in central auditory processing, and they also indicate a non-monotonic relationship between cochlear damage and neuronal hyperactivity, suggesting an explanation for why tinnitus might occur without obvious hearing loss and conversely why hearing loss does not always lead to tinnitus.

Evidence of activity-dependent plasticity in the dorsal cochlear nucleus, in vivo, induced by brief sound exposure

The purpose of the present study was to investigate the immediate effects of acute exposure to intense sound on spontaneous and stimulus-driven activity in the dorsal cochlear nucleus (DCN). We examined the levels of multi- and single-unit spontaneous activity before and immediately following brief exposure (2 min) to tones at levels of either 109 or 85 dB SPL. Exposure frequency was selected to either correspond to the units' best frequency (BF) or fall within the borders of its inhibitory side band. The results demonstrate that these exposure conditions caused significant alterations in spontaneous activity and responses to BF tones. The induced changes have a fast onset (minutes) and are persistent for durations of at least 20 min. The directions of the change were found to depend on the frequency of exposure relative to BF. Transient decreases followed by more sustained increases in spontaneous activity were induced when the exposure frequency was at or near the units' BF, while sustained decreases of activity resulted when the exposure frequency fell inside the inhibitory side band. Follow-up studies at the single unit level revealed that the observed activity changes were found on unit types having properties which have previously been found to represent fusiform cells. The changes in spontaneous activity occurred despite only minor changes in response thresholds. Noteworthy changes also occurred in the strength of responses to BF tones, although these changes tended to be in the direction opposite those of the spontaneous rate changes. We discuss the possible role of activity-dependent plasticity as a mechanism underlying the rapid emergence of increased spontaneous activity after tone exposure and suggest that these changes may represent a neural correlate of acute noise-induced tinnitus.

Treatment of tinnitus

PURPOSE OF REVIEW

Tinnitus, the perception of sound in the absence of a corresponding external acoustic stimulus, is a highly prevalent and frequently severely impairing disorder with worldwide impact. In this article after a short overview about epidemiology and pathophysiology the currently available treatment options will be discussed with specific consideration of the available evidence, their mechanisms of action and their limitations.

RECENT FINDINGS

During the last decades, advances in neuroimaging methods and the development of animal models have contributed to an increasing understanding of the neuronal correlates of tinnitus and have motivated the development of innovative brain-based treatment approaches for directly targeting the neuronal correlates of tinnitus. A further important development has been the insight that there exist different forms of tinnitus that differ in their pathophysiology and their response to specific treatments.

SUMMARY

Treatment of tinnitus should be based on a comprehensive diagnosis of etiologic and concomitant aspects of an individual's tinnitus. Already today a large variety of therapeutic interventions are available, which can efficiently reduce tinnitus severity. Several innovative treatment approaches are currently under development.

Consensus on Hearing Aid Candidature and Fitting for Mild Hearing Loss, With and Without Tinnitus: Delphi Review

OBJECTIVES

In many countries including the United Kingdom, hearing aids are a first line of audiologic intervention for many people with tinnitus and aidable hearing loss. Nevertheless, there is a lack of high quality evidence to support that they are of benefit for tinnitus, and wide variability in their use in clinical practice especially for people with mild hearing loss. The aim of this study was to identify a consensus among a sample of UK clinicians on the criteria for hearing aid candidature and clinical practice in fitting hearing aids specifically for mild hearing loss with and without tinnitus. This will allow professionals to establish clinical benchmarks and to gauge their practice with that used elsewhere.

DESIGN

The Delphi technique, a systematic methodology that seeks consensus amongst experts through consultation using a series of iterative questionnaires, was used. A three-round Delphi survey explored clinical consensus among a panel of 29 UK hearing professionals. The authors measured panel agreement on 115 statements covering: (i) general factors affecting the decision to fit hearing aids, (ii) protocol-driven factors affecting the decision to fit hearing aids, (iii) general practice, and (iv) clinical observations. Consensus was defined as a priori ≥70% agreement across the panel.

RESULTS

Consensus was reached for 58 of the 115 statements. The broad areas of consensus were around factors important to consider when fitting hearing aids; hearing aid technology/features offered; and important clinical assessment to verify hearing aid fit (agreement of 70% or more). For patients with mild hearing loss, the greatest priority was given by clinicians to patient-centered criteria for fitting hearing aids: hearing difficulties, motivation to wear hearing aids, and impact of hearing loss on quality of life (chosen as top five by at least 64% of panelists). Objective measures were given a lower priority: degree of hearing loss and shape of the audiogram (chosen as top five by less than half of panelists). Areas where consensus was not reached were related to the use of questionnaires to predict and verify hearing aid benefit for both hearing and tinnitus; audiometric criteria for fitting hearing aids; and safety of using loud sounds when verifying hearing aid fitting when the patient has tinnitus (agreement of <70%).

CONCLUSIONS

The authors identified practices that are considered important when recommending or fitting hearing aid for a patient with tinnitus. More importantly perhaps, they identified practical issues where there are divided opinions. Their findings inform the design of clinical trials and open up debate on the potential impact of practice differences on patient outcomes.

Attentional Bias in Patients with Decompensated Tinnitus: Prima Facie Evidence from Event-Related Potentials

Tinnitus refers to the auditory perception of sound in the absence of external sound or electric stimuli. The influence of tinnitus on cognitive processing is at the cutting edge of ongoing tinnitus research. In this study, we adopted an objective indicator of attentional processing, i.e. the mismatch negativity (MMN), to assess the attentional bias in patients with decompensated tinnitus. Three kinds of pure tones, D1 (8,000 Hz), S (8,500 Hz) and D2 (9,000 Hz), were used to induce event-related potentials (ERPs) in the normal ear. Employing the oddball paradigm, the task was divided into two blocks in which D1 and D2 were set as deviation stimuli, respectively. Only D2 induced a significant MMN in the tinnitus group, while neither D1 nor D2 was able to induce MMN in the control group. In addition, the ERPs in the left hemisphere, which were recorded within the time window of 90-150 ms (ERP 90-150 ms), were significantly higher than those in the right hemisphere in the tinnitus group, while no significant difference was observed in the control group. Lastly, the amplitude of ERP 90-150 ms in the tinnitus group was significantly higher than that in the control group. These findings suggest that patients with decompensated tinnitus showed automatic processing of acoustic stimuli, thereby indicating that these patients allocated more cognitive resources to acoustic stimulus processing. We suggest that the difficulty in disengaging or facilitated attention of patients might underlie this phenomenon. The limitations of the current study are discussed.

Neural Hyperactivity of the Central Auditory System in Response to Peripheral Damage

It is increasingly appreciated that cochlear pathology is accompanied by adaptive responses in the central auditory system. The cause of cochlear pathology varies widely, and it seems that few commonalities can be drawn. In fact, despite intricate internal neuroplasticity and diverse external symptoms, several classical injury models provide a feasible path to locate responses to different peripheral cochlear lesions. In these cases, hair cell damage may lead to considerable hyperactivity in the central auditory pathways, mediated by a reduction in inhibition, which may underlie some clinical symptoms associated with hearing loss, such as tinnitus. Homeostatic plasticity, the most discussed and acknowledged mechanism in recent years, is most likely responsible for excited central activity following cochlear damage.

Hyperacusis Questionnaire as a Tool for Measuring Hypersensitivity to Sound in a Tinnitus Research Population

Hypersensitivity to external sounds is often comorbid with tinnitus and may be significant for adherence to certain types of tinnitus management. Therefore, a clear measure of sensitivity to sound is important. The aim of this study was to evaluate the validity and reliability of the Hyperacusis Questionnaire (HQ) for use as a measurement tool using data from a sample of 264 adults who took part in tinnitus research. We evaluated the HQ factor structure, internal consistency, convergent and discriminant validity, and floor and ceiling effects. Internal consistency was high (Cronbach's alpha = 0.88) and moderate correlations were observed between the HQ, uncomfortable loudness levels, and other health questionnaires. Confirmatory factor analysis revealed that the original HQ three-factor solution and a one-factor solution were both a poor fit to the data. Four problematic items were removed and exploratory factor analysis identified a two-factor (attentional and social) solution. The original three-factor structure of the HQ was not confirmed. All fourteen items do not accurately assess hypersensitivity to sound in a tinnitus population. We propose a 10-item (2-factor) version of the HQ, which will need to be confirmed using a new tinnitus and perhaps nontinnitus population.

Abnormal Auditory Gain in Hyperacusis: Investigation with a Computational Model

Hyperacusis is a frequent auditory disorder that is characterized by abnormal loudness perception where sounds of relatively normal volume are perceived as too loud or even painfully loud. As hyperacusis patients show decreased loudness discomfort levels (LDLs) and steeper loudness growth functions, it has been hypothesized that hyperacusis might be caused by an increase in neuronal response gain in the auditory system. Moreover, since about 85% of hyperacusis patients also experience tinnitus, the conditions might be caused by a common mechanism. However, the mechanisms that give rise to hyperacusis have remained unclear. Here, we have used a computational model of the auditory system to investigate candidate mechanisms for hyperacusis. Assuming that perceived loudness is proportional to the summed activity of all auditory nerve (AN) fibers, the model was tuned to reproduce normal loudness perception. We then evaluated a variety of potential hyperacusis gain mechanisms by determining their effects on model equal-loudness contours and comparing the results to the LDLs of hyperacusis patients with normal hearing thresholds. Hyperacusis was best accounted for by an increase in non-linear gain in the central auditory system. Good fits to the average patient LDLs were obtained for a general increase in gain that affected all frequency channels to the same degree, and also for a frequency-specific gain increase in the high-frequency range. Moreover, the gain needed to be applied after subtraction of spontaneous activity of the AN, which is in contrast to current theories of tinnitus generation based on amplification of spontaneous activity. Hyperacusis and tinnitus might therefore be caused by different changes in neuronal processing in the central auditory system.

Tinnitus: animal models and findings in humans

Chronic tinnitus (ringing of the ears) is a medically untreatable condition that reduces quality of life for millions of individuals worldwide. Most cases are associated with hearing loss that may be detected by the audiogram or by more sensitive measures. Converging evidence from animal models and studies of human tinnitus sufferers indicates that, while cochlear damage is a trigger, most cases of tinnitus are not generated by irritative processes persisting in the cochlea but by changes that take place in central auditory pathways when auditory neurons lose their input from the ear. Forms of neural plasticity underlie these neural changes, which include increased spontaneous activity and neural gain in deafferented central auditory structures, increased synchronous activity in these structures, alterations in the tonotopic organization of auditory cortex, and changes in network behavior in nonauditory brain regions detected by functional imaging of individuals with tinnitus and corroborated by animal investigations. Research on the molecular mechanisms that underlie neural changes in tinnitus is in its infancy and represents a frontier for investigation.

Tinnitus: Maladaptive auditory-somatosensory plasticity

Tinnitus, the phantom perception of sound, is physiologically characterized by an increase in spontaneous neural activity in the central auditory system. However, as tinnitus is often associated with hearing impairment, it is unclear how a decrease of afferent drive can result in central hyperactivity. In this review, we first assess methods for tinnitus induction and objective measures of the tinnitus percept in animal models. From animal studies, we discuss evidence that tinnitus originates in the cochlear nucleus (CN), and hypothesize mechanisms whereby hyperactivity may develop in the CN after peripheral auditory nerve damage. We elaborate how this process is likely mediated by plasticity of auditory-somatosensory integration in the CN: the circuitry in normal circumstances maintains a balance of auditory and somatosensory activities, and loss of auditory inputs alters the balance of auditory somatosensory integration in a stimulus timing dependent manner, which propels the circuit towards hyperactivity. Understanding the mechanisms underlying tinnitus generation is essential for its prevention and treatment. This article is part of a Special Issue entitled <Tinnitus>.

Cortical development and neuroplasticity in Auditory Neuropathy Spectrum Disorder

Cortical development is dependent to a large extent on stimulus-driven input. Auditory Neuropathy Spectrum Disorder (ANSD) is a recently described form of hearing impairment where neural dys-synchrony is the predominant characteristic. Children with ANSD provide a unique platform to examine the effects of asynchronous and degraded afferent stimulation on cortical auditory neuroplasticity and behavioral processing of sound. In this review, we describe patterns of auditory cortical maturation in children with ANSD. The disruption of cortical maturation that leads to these various patterns includes high levels of intra-individual cortical variability and deficits in cortical phase synchronization of oscillatory neural responses. These neurodevelopmental changes, which are constrained by sensitive periods for central auditory maturation, are correlated with behavioral outcomes for children with ANSD. Overall, we hypothesize that patterns of cortical development in children with ANSD appear to be markers of the severity of the underlying neural dys-synchrony, providing prognostic indicators of success of clinical intervention with amplification and/or electrical stimulation. This article is part of a Special Issue entitled <Auditory Synaptology>.

Thalamocortical Dysrhythmia: A Theoretical Update in Tinnitus

Tinnitus is the perception of a sound in the absence of a corresponding external sound source. Pathophysiologically it has been attributed to bottom-up deafferentation and/or top-down noise-cancelling deficit. Both mechanisms are proposed to alter auditory ­thalamocortical signal transmission, resulting in thalamocortical dysrhythmia (TCD). In deafferentation, TCD is characterized by a slowing down of resting state alpha to theta activity associated with an increase in surrounding gamma activity, resulting in persisting cross-frequency coupling between theta and gamma activity. Theta burst-firing increases network synchrony and recruitment, a mechanism, which might enable long-range synchrony, which in turn could represent a means for finding the missing thalamocortical information and for gaining access to consciousness. Theta oscillations could function as a carrier wave to integrate the tinnitus-related focal auditory gamma activity in a consciousness enabling network, as envisioned by the global workspace model. This model suggests that focal activity in the brain does not reach consciousness, except if the focal activity becomes functionally coupled to a consciousness enabling network, aka the global workspace. In limited deafferentation, the missing information can be retrieved from the auditory cortical neighborhood, decreasing surround inhibition, resulting in TCD. When the deafferentation is too wide in bandwidth, it is hypothesized that the missing information is retrieved from theta-mediated parahippocampal auditory memory. This suggests that based on the amount of deafferentation TCD might change to parahippocampocortical persisting and thus pathological theta–gamma rhythm. From a Bayesian point of view, in which the brain is conceived as a prediction machine that updates its memory-based predictions through sensory updating, tinnitus is the result of a prediction error between the predicted and sensed auditory input. The decrease in sensory updating is reflected by decreased alpha activity and the prediction error results in theta–gamma and beta–gamma coupling. Thus, TCD can be considered as an adaptive mechanism to retrieve missing auditory input in tinnitus.

Revisiting the cochlear and central mechanisms of tinnitus and therapeutic approaches

This short review aims at revisiting some of the putative mechanisms of tinnitus. Cochlear-type tinnitus is suggested to result from aberrant activity generated before or at the cochlear nerve level. It is proposed that outer hair cells, through their role in regulating the endocochlear potential, can contribute to the enhancement of cochlear spontaneous activity. This hypothesis is attractive as it provides a possible explanation for cochlear tinnitus of different aetiologies, such as tinnitus produced by acute noise trauma, intense low-frequency sounds, middle-ear dysfunction or temporomandibular joint disorders. Other mechanisms, namely an excitatory drift in the operating point of the inner hair cells and activation of NMDA receptors, are also briefly reported. Central-type tinnitus is supposed to result from aberrant activity generated in auditory centres, i.e. in these patients, the tinnitus-related activity does not pre-exist in the cochlear nerve. A reduction in cochlear activity due to hearing loss is suggested to produce tinnitus-related plastic changes, namely cortical reorganisation, thalamic neuron hyperpolarisation, facilitation of non-auditory inputs and/or increase in central gain. These central changes can be associated with abnormal patterns of spontaneous activity in the auditory pathway, i.e. hyperactivity, hypersynchrony and/or oscillating activity. Therapeutic approaches aimed at reducing cochlear activity and/or tinnitus-related central changes are discussed.

Relationship between tinnitus pitch and edge of hearing loss in individuals with a narrow tinnitus bandwidth

OBJECTIVE

Psychoacoustic measures of tinnitus, in particular dominant tinnitus pitch and its relationship to the shape of the audiogram, are important in determining and verifying pathophysiological mechanisms of the condition. Our previous study postulated that this relationship might vary between different groups of people with tinnitus. For a small subset of participants with narrow tinnitus bandwidth, pitch was associated with the audiometric edge, consistent with the tonotopic reorganization theory. The current study objective was to establish this relationship in an independent sample.

DESIGN

This was a retrospective design using data from five studies conducted between 2008 and 2013.

STUDY SAMPLE

From a cohort of 380 participants, a subgroup group of 129 with narrow tinnitus bandwidth were selected.

RESULTS

Tinnitus pitch generally fell within the area of hearing loss. There was a statistically significant correlation between dominant tinnitus pitch and edge frequency; higher edge frequency being associated with higher dominant tinnitus pitch. However, similar to our previous study, for the majority of participants pitch was more than an octave above the edge frequency.

CONCLUSIONS

The findings did not support our prediction and are therefore not consistent with the reorganization theory postulating tinnitus pitch to correspond to the audiometric edge.

Tinnitus-related changes in the inferior colliculus

Tinnitus is highly complex, diverse, and difficult to treat, in part due to the fact that the underlying causes and mechanisms remain elusive. Tinnitus is generated within the auditory brain; however, consolidating our understanding of tinnitus pathophysiology is difficult due to the diversity of reported effects and the variety of implicated brain nuclei. Here, we focus on the inferior colliculus (IC), a midbrain structure that integrates the vast majority of ascending auditory information and projects via the thalamus to the auditory cortex. The IC is also a point of convergence for corticofugal input and input originating outside the auditory pathway. We review the evidence, from both studies with human subjects and from animal models, for the contribution the IC makes to tinnitus. Changes in the IC, caused by either noise exposure or drug administration, involve fundamental, heterogeneous alterations in the balance of excitation and inhibition. However, differences between hearing loss-induced pathology and tinnitus-related pathology are not well understood. Moreover, variability in tinnitus induction methodology has a significant impact on subsequent neural and behavioral changes, which could explain some of the seemingly contradictory data. Nonetheless, the IC is likely involved in the generation and persistence of tinnitus perception.

Maladaptive neural synchrony in tinnitus: origin and restoration

Tinnitus is the conscious perception of sound heard in the absence of physical sound sources external or internal to the body, reflected in aberrant neural synchrony of spontaneous or resting-state brain activity. Neural synchrony is generated by the nearly simultaneous firing of individual neurons, of the synchronization of membrane-potential changes in local neural groups as reflected in the local field potentials, resulting in the presence of oscillatory brain waves in the EEG. Noise-induced hearing loss, often resulting in tinnitus, causes a reorganization of the tonotopic map in auditory cortex and increased spontaneous firing rates and neural synchrony. Spontaneous brain rhythms rely on neural synchrony. Abnormal neural synchrony in tinnitus appears to be confined to specific frequency bands of brain rhythms. Increases in delta-band activity are generated by deafferented/deprived neuronal networks resulting from hearing loss. Coordinated reset (CR) stimulation was developed in order to specifically counteract such abnormal neuronal synchrony by desynchronization. The goal of acoustic CR neuromodulation is to desynchronize tinnitus-related abnormal delta-band oscillations. CR neuromodulation does not require permanent stimulus delivery in order to achieve long-lasting desynchronization or even a full-blown anti-kindling but may have cumulative effects, i.e., the effect of different CR epochs separated by pauses may accumulate. Unlike other approaches, acoustic CR neuromodulation does not intend to reduce tinnitus-related neuronal activity by employing lateral inhibition. The potential efficacy of acoustic CR modulation was shown in a clinical proof of concept trial, where effects achieved in 12 weeks of treatment delivered 4–6 h/day persisted through a preplanned 4-week therapy pause and showed sustained long-term effects after 10 months of therapy, leading to 75% responders.

Cytoarchitectural and functional abnormalities of the inferior colliculus in sudden unexplained perinatal death

The inferior colliculus is a mesencephalic structure endowed with serotonergic fibers that plays an important role in the processing of acoustic information. The implication of the neuromodulator serotonin also in the aetiology of sudden unexplained fetal and infant death syndromes and the demonstration in these pathologies of developmental alterations of the superior olivary complex (SOC), a group of pontine nuclei likewise involved in hearing, prompted us to investigate whether the inferior colliculus may somehow contribute to the pathogenetic mechanism of unexplained perinatal death. Therefore, we performed in a wide set of fetuses and infants, aged from 33 gestational weeks to 7 postnatal months and died of both known and unknown cause, an in-depth anatomopathological analysis of the brainstem, particularly of the midbrain. Peculiar neuroanatomical and functional abnormalities of the inferior colliculus, such as hypoplasia/structural disarrangement and immunonegativity or poor positivity of serotonin, were exclusively found in sudden death victims, and not in controls. In addition, these alterations were frequently related to dysgenesis of connected structures, precisely the raphé nuclei and the superior olivary complex, and to nicotine absorption in pregnancy. We propose, on the basis of these results, the involvement of the inferior colliculus in more important functions than those related to hearing, as breathing and, more extensively, all the vital activities, and then in pathological conditions underlying a sudden death in vulnerable periods of the autonomic nervous system development, particularly associated to harmful risk factors as cigarette smoking.

Impact of noise on hearing in the military

Hearing plays a vital role in the performance of a soldier and is important for speech processing. Noise-induced hearing loss is a significant impairment in the military and can affect combat performance. Military personnel are constantly exposed to high levels of noise and it is not surprising that noise induced hearing loss and tinnitus remain the second most prevalent service-connected disabilities. Much of the noise experienced by military personnel exceeds that of maximum protection achievable with double hearing protection. Unfortunately, unlike civilian personnel, military personnel have little option but to remain in noisy environments in order to complete specific tasks and missions. Use of hearing protection devices and follow-up audiological tests have become the mainstay of prevention of noise-induced hearing loss. This review focuses on sources of noise within the military, pathophysiology and management of patients with noise induced hearing loss.

Suppression of putative tinnitus-related activity by extra-cochlear electrical stimulation

Studies on animals have shown that noise-induced hearing loss is followed by an increase of spontaneous firing at several stages of the central auditory system. This central hyperactivity has been suggested to underpin the perception of tinnitus. It was shown that decreasing cochlear activity can abolish the noise-induced central hyperactivity. This latter result further suggests that an approach consisting of reducing cochlear activity may provide a therapeutic avenue for tinnitus. In this context, extra-cochlear electric stimulation (ECES) may be a good candidate to modulate cochlear activity and suppress tinnitus. Indeed, it has been shown that a positive current applied at the round window reduces cochlear nerve activity and can suppress tinnitus reliably in tinnitus subjects. The present study investigates whether ECES with a positive current can abolish the noise-induced central hyperactivity, i.e., the putative tinnitus-related activity. Spontaneous and stimulus-evoked neural activity before, during and after ECES was assessed from single-unit recordings in the inferior colliculus of anesthetized guinea pigs. We found that ECES with positive current significantly decreases the spontaneous firing rate of neurons with high characteristic frequencies, whereas negative current produces the opposite effect. The effects of the ECES are absent or even reversed for neurons with low characteristic frequencies. Importantly, ECES with positive current had only a marginal effect on thresholds and tone-induced activity of collicular neurons, suggesting that the main action of positive current is to modulate the spontaneous firing. Overall, cochlear electrical stimulation may be a viable approach for suppressing some forms of (peripheral-dependent) tinnitus.

A review of hyperacusis and future directions: part II. Measurement, mechanisms, and treatment

PURPOSE

Hyperacusis can be extremely debilitating, and at present, there is no cure. In this detailed review of the field, we consolidate present knowledge in the hope of facilitating future research.

METHOD

We review and reference the literature on hyperacusis and related areas. This is the 2nd of a 2-part review.

RESULTS

Hyperacusis encompasses a wide range of reactions to sounds, which can be grouped into the categories of excessive loudness, annoyance, fear, and pain. Reasonable approaches to assessing the different forms of hyperacusis are emerging, including brain-imaging studies. Researchers are only beginning to understand the many mechanisms at play, and valid animal models are still evolving. There are many counseling and sound-therapy approaches that some patients find helpful, but well-controlled studies are needed to measure their long-term efficacy and to test new approaches.

CONCLUSIONS

Hyperacusis can make life difficult in this increasingly noisy world, forcing sufferers to dramatically alter their work and social habits. We believe this is an opportune time to explore approaches to better understand and treat hyperacusis.

Central gain control in tinnitus and hyperacusis

Sensorineural hearing loss induced by noise or ototoxic drug exposure reduces the neural activity transmitted from the cochlea to the central auditory system. Despite a reduced cochlear output, neural activity from more central auditory structures is paradoxically enhanced at suprathreshold intensities. This compensatory increase in the central auditory activity in response to the loss of sensory input is referred to as central gain enhancement. Enhanced central gain is hypothesized to be a potential mechanism that gives rise to hyperacusis and tinnitus, two debilitating auditory perceptual disorders that afflict millions of individuals. This review will examine the evidence for gain enhancement in the central auditory system in response to cochlear damage. Further, it will address the potential cellular and molecular mechanisms underlying this enhancement and discuss the contribution of central gain enhancement to tinnitus and hyperacusis. Current evidence suggests that multiple mechanisms with distinct temporal and spectral profiles are likely to contribute to central gain enhancement. Dissecting the contributions of these different mechanisms at different levels of the central auditory system is essential for elucidating the role of central gain enhancement in tinnitus and hyperacusis and, most importantly, the development of novel treatments for these disorders.

Gameplay as a source of intrinsic motivation in a randomized controlled trial of auditory training for tinnitus

Background

Previous studies of frequency discrimination training (FDT) for tinnitus used repetitive task-based training programmes relying on extrinsic factors to motivate participation. Studies reported limited improvement in tinnitus symptoms.

Purpose

To evaluate FDT exploiting intrinsic motivations by integrating training with computer-gameplay.

Methods

Sixty participants were randomly assigned to train on either a conventional task-based training, or one of two interactive game-based training platforms over six weeks. Outcomes included assessment of motivation, tinnitus handicap, and performance on tests of attention.

Results

Participants reported greater intrinsic motivation to train on the interactive game-based platforms, yet compliance of all three groups was similar (∼70%) and changes in self-reported tinnitus severity were not significant. There was no difference between groups in terms of change in tinnitus severity or performance on measures of attention.

Conclusion

FDT can be integrated within an intrinsically motivating game. Whilst this may improve participant experience, in this instance it did not translate to additional compliance or therapeutic benefit.

Trial Registration

ClinicalTrials.gov NCT02095262

Perceptual consequences of "hidden" hearing loss

Dramatic results from recent animal experiments show that noise exposure can cause a selective loss of high-threshold auditory nerve fibers without affecting absolute sensitivity permanently. This cochlear neuropathy has been described as hidden hearing loss, as it is not thought to be detectable using standard measures of audiometric threshold. It is possible that hidden hearing loss is a common condition in humans and may underlie some of the perceptual deficits experienced by people with clinically normal hearing. There is some evidence that a history of noise exposure is associated with difficulties in speech discrimination and temporal processing, even in the absence of any audiometric loss. There is also evidence that the tinnitus experienced by listeners with clinically normal hearing is associated with cochlear neuropathy, as measured using Wave I of the auditory brainstem response. To date, however, there has been no direct link made between noise exposure, cochlear neuropathy, and perceptual difficulties. Animal experiments also reveal that the aging process itself, in the absence of significant noise exposure, is associated with loss of auditory nerve fibers. Evidence from human temporal bone studies and auditory brainstem response measures suggests that this form of hidden loss is common in humans and may have perceptual consequences, in particular, regarding the coding of the temporal aspects of sounds. Hidden hearing loss is potentially a major health issue, and investigations are ongoing to identify the causes and consequences of this troubling condition.

Acute and long-term effects of noise exposure on the neuronal spontaneous activity in cochlear nucleus and inferior colliculus brain slices

Noise exposure leads to an immediate hearing loss and is followed by a long-lasting permanent threshold shift, accompanied by changes of cellular properties within the central auditory pathway. Electrophysiological recordings have demonstrated an upregulation of spontaneous neuronal activity. It is still discussed if the observed effects are related to changes of peripheral input or evoked within the central auditory system. The present study should describe the intrinsic temporal patterns of single-unit activity upon noise-induced hearing loss of the dorsal and ventral cochlear nucleus (DCN and VCN) and the inferior colliculus (IC) in adult mouse brain slices. Recordings showed a slight, but significant, elevation in spontaneous firing rates in DCN and VCN immediately after noise trauma, whereas no differences were found in IC. One week postexposure, neuronal responses remained unchanged compared to controls. At 14 days after noise trauma, intrinsic long-term hyperactivity in brain slices of the DCN and the IC was detected for the first time. Therefore, increase in spontaneous activity seems to develop within the period of two weeks, but not before day 7. The results give insight into the complex temporal neurophysiological alterations after noise trauma, leading to a better understanding of central mechanisms in noise-induced hearing loss.