Changes in spontaneous neural activity immediately after an acoustic trauma: implications for neural correlates of tinnitus

Probe into the treatment of tinnitus by acupuncture combined with medicine under the mechanism of pathophysiology: A review

Tinnitus is a common medical disorder. The risk factors include hearing loss, ototoxic medications, head injuries, and depression. Therefore, ear disorders, anxiety, and depression should be considered in the treatment of tinnitus. Although considerable research has been conducted on the pathogenesis and treatment of tinnitus, there is currently no effective treatment. Traditional Chinese medicine (TCM) has a certain effect on tinnitus and a large number of clinical trials have been conducted. Its treatment methods vary and include TCM, acupuncture, and music therapy. TCM treatment of tinnitus usually takes the method of comprehensive treatment, not only relying on drugs but also safety. Therefore, this review explores the treatment of tinnitus using acupuncture combined with medicine, based on the new pathophysiological mechanism of tinnitus.

Cortical region-specific recovery of auditory temporal processing following noise-induced hearing loss

Noise-induced hearing loss (NIHL) studies have focused on the lemniscal auditory pathway, but little is known about how NIHL impacts different cortical regions. Here we compared response recovery trajectories in the auditory and frontal cortices (AC, FC) of mice following NIHL. We recorded EEG responses from awake mice (male n = 15, female n = 14) before and following NIHL (longitudinal design) to quantify event related potentials and gap-in-noise temporal processing. Hearing loss was verified by measuring the auditory brainstem response (ABR) before and at 1-, 10-, 23-, and 45-days after noise-exposure. Resting EEG, event related potentials (ERP) and auditory steady state responses (ASSR) were recorded at the same time-points after NIHL. The inter-trial phase coherence (ITPC) of the ASSR was measured to quantify the ability of AC and FC to synchronize responses to short gaps embedded in noise. Despite the absence of click-evoked ABRs up to 90 dB SPL and up to 45-days post-exposure, ERPs from the AC and FC showed full recovery in ∼ 50 % of the mice to pre-NIHL levels in both AC and FC. The ASSR ITPC was reduced following NIHL in AC and FC in all the mice on day 1 after NIHL. The AC showed full recovery of ITPC over 45-days. Despite ERP amplitude recovery, the FC does not show recovery of ASSR ITPC. These results indicate post-NIHL plasticity with similar response amplitude recovery across AC and FC, but cortical region-specific trajectories in temporal processing recovery.

Cochlear implant induced changes in cortical networks associated with tinnitus severity

Objective.We investigated tinnitus-related cortical networks in cochlear implant users who experience tinnitus and whose perception of tinnitus changes with use of their implant. Tinnitus, the perception of unwanted sounds which are not present externally, can be a debilitating condition. In individuals with cochlear implants, use of the implant is known to modulate tinnitus, often improving symptoms but worsening them in some cases. Little is known about underlying cortical changes with use of the implant, which lead to changes in tinnitus perception. In this study we investigated whether changes in brain networks with the cochlear implant turned on and off, were associated with changes in tinnitus perception, as rated subjectively.Approach.Using functional near-infrared spectroscopy, we recorded cortical activity at rest, from 14 cochlear implant users who experienced tinnitus. Recordings were performed with the cochlear implant turned off and on. For each condition, participants rated the loudness and annoyance of their tinnitus using a visual rating scale. Changes in neural synchrony have been reported in humans and animal models of tinnitus. To assess neural synchrony, functional connectivity networks with the implant turned on and off, were compared using two network features: node strength and diversity coefficient.Main results.Changes in subjective ratings of loudness were significantly correlated with changes in node strength, averaged across occipital channels (r=-0.65, p=0.01). Changes in both loudness and annoyance were significantly correlated with changes in diversity coefficient averaged across all channels (r=-0.79,p<0.001 and r=-0.86,p<0.001). More distributed connectivity with the implant on, compared to implant off, was associated with a reduction in tinnitus loudness and annoyance.Significance.A better understanding of neural mechanisms underlying tinnitus suppression with cochlear implant use, could lead to their application as a tinnitus treatment and pave the way for effective use of other less invasive stimulation-based treatments.

Effects of tinnitus retraining therapy on patients with tinnitus: a systematic review of randomized controlled trials

PURPOSE

This review aims to explore the influences of tinnitus retraining therapy (TRT) on patients with tinnitus.

METHODS

PubMed, MEDLINE, EMBASE, CINAHL, PEDro, SCOPUS, and Web of Science were screened for randomized controlled trials (RCTs) that explored the effects of TRT on patients with tinnitus from inception to June 30, 2024. The methodological quality of the included RCTs was evaluated using the physiotherapy evidence database (PEDro) scale.

RESULTS

Fifteen studies met our eligibility criteria. A total of 2069 patients with tinnitus (mean age 52.93 years; 66% male) were involved in the present review. The quality of the selected studies ranged from 5 to 8 on the PEDro scale, with a median score of 7. TRT did not provide superior effects in treating patients with tinnitus compared to tinnitus masking (TM), tinnitus educational counselling (TED), TRT with open ear hearing aids, Tailor-made notched music training (TMNMT), partial TRT, usual care, and smart TRT.

CONCLUSIONS

TRT intervention is considered a treatment option for patients with tinnitus. Combining TRT with other interventions, such as cognitive-behavioral therapy, pharmacotherapy, or tDS, may show even greater efficacy. Additional studies are strongly required to recognize the long-term effects of TRT on tinnitus, determine who most likely would benefit from the intervention regarding tinnitus type and severity, and identify the optimal treatment protocol.

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.

Subcortical auditory system in tinnitus with normal hearing: insights from electrophysiological perspective

PURPOSE

The mechanism of tinnitus remains poorly understood; however, studies have underscored the significance of the subcortical auditory system in tinnitus perception. In this study, our aim was to investigate the subcortical auditory system using electrophysiological measurements in individuals with tinnitus and normal hearing. Additionally, we aimed to assess speech-in-noise (SiN) perception to determine whether individuals with tinnitus exhibit SiN deficits despite having normal-hearing thresholds.

METHODS

A total 42 normal-hearing participants, including 22 individuals with chronic subjective tinnitus and 20 normal individuals, participated in the study. We recorded auditory brainstem response (ABR) and speech-evoked frequency following response (sFFR) from the participants. SiN perception was also assessed using the Matrix test.

RESULTS

Our results revealed a significant prolongation of the O peak, which encodes sound offset in sFFR, for the tinnitus group (p < 0.01). The greater non-stimulus-evoked activity was also found in individuals with tinnitus (p < 0.01). In ABR, the tinnitus group showed reduced wave I amplitude and prolonged absolute wave I, III, and V latencies (p ≤ 0.02). Our findings suggested that individuals with tinnitus had poorer SiN perception compared to normal participants (p < 0.05).

CONCLUSION

The deficit in encoding sound offset may indicate an impaired inhibitory mechanism in tinnitus. The greater non-stimulus-evoked activity observed in the tinnitus group suggests increased neural noise at the subcortical level. Additionally, individuals with tinnitus may experience speech-in-noise deficits despite having a normal audiogram. Taken together, these findings suggest that the lack of inhibition and increased neural noise may be associated with tinnitus perception.

Mendelian randomization analyses support causal relationships between tinnitus of different stages and severity and structural characteristics of specific brain regions

This study aims to delineate the causal relationships between idiopathic tinnitus in different stages and severity and the morphological properties in specific brain regions. We utilized a two-sample bidirectional Mendelian randomization (MR) analysis to ascertain the causal effects of brain structural attributes on varying severities and stages of tinnitus. Our approach involved harnessing genetic variables derived from extensive genome-wide association studies as instrumental variables, centered mainly on pertinent single-nucleotide polymorphisms associated with tinnitus. Subsequently, we integrated this data with brain structural imaging inputs to facilitate the MR analysis. We also applied reverse MR analysis to pinpoint the critical brain regions implicated in the onset of tinnitus. Our analysis revealed a demonstrable causal relationship between tinnitus and brain structural alterations, including changes primarily within the auditory cortex and hub regions of the limbic system, as well as portions of the frontal-temporal-occipital circuit. We found that individuals exhibiting cortical thickness alterations in the bilateral peri-calcarine and right superior occipital gyrus might have previously experienced tinnitus. Changes in the cortical areas of the right rectus, left inferior frontal gyrus, and right pars-orbitalis appeared unrelated to tinnitus. Furthermore, moderate tinnitus patients showed more pronounced structural alterations. This study substantiates that tinnitus could instigate substantial structural alterations mainly within the auditory-limbic-frontal-visual system, while the reciprocal causality was not supported. Moreover, the data underscores that moderate, rather than severe, tinnitus precipitates the most significant structural changes. Morphological alterations in several specific brain areas either indicate a history of tinnitus or bear no relation to it.

Synaptic reorganization of synchronized neuronal networks with synaptic weight and structural plasticity

Abnormally strong neural synchronization may impair brain function, as observed in several brain disorders. We computationally study how neuronal dynamics, synaptic weights, and network structure co-emerge, in particular, during (de)synchronization processes and how they are affected by external perturbation. To investigate the impact of different types of plasticity mechanisms, we combine a network of excitatory integrate-and-fire neurons with different synaptic weight and/or structural plasticity mechanisms: (i) only spike-timing-dependent plasticity (STDP), (ii) only homeostatic structural plasticity (hSP), i.e., without weight-dependent pruning and without STDP, (iii) a combination of STDP and hSP, i.e., without weight-dependent pruning, and (iv) a combination of STDP and structural plasticity (SP) that includes hSP and weight-dependent pruning. To accommodate the diverse time scales of neuronal firing, STDP, and SP, we introduce a simple stochastic SP model, enabling detailed numerical analyses. With tools from network theory, we reveal that structural reorganization may remarkably enhance the network's level of synchrony. When weaker contacts are preferentially eliminated by weight-dependent pruning, synchrony is achieved with significantly sparser connections than in randomly structured networks in the STDP-only model. In particular, the strengthening of contacts from neurons with higher natural firing rates to those with lower rates and the weakening of contacts in the opposite direction, followed by selective removal of weak contacts, allows for strong synchrony with fewer connections. This activity-led network reorganization results in the emergence of degree-frequency, degree-degree correlations, and a mixture of degree assortativity. We compare the stimulation-induced desynchronization of synchronized states in the STDP-only model (i) with the desynchronization of models (iii) and (iv). The latter require stimuli of significantly higher intensity to achieve long-term desynchronization. These findings may inform future pre-clinical and clinical studies with invasive or non-invasive stimulus modalities aiming at inducing long-lasting relief of symptoms, e.g., in Parkinson's disease.

Map plasticity following noise exposure in auditory cortex of rats: implications for disentangling neural correlates of tinnitus and hyperacusis

Introduction

Both tinnitus and hyperacusis, likely triggered by hearing loss, can be attributed to maladaptive plasticity in auditory perception. However, owing to their co-occurrence, disentangling their neural mechanisms proves difficult. We hypothesized that the neural correlates of tinnitus are associated with neural activities triggered by low-intensity tones, while hyperacusis is linked to responses to moderate- and high-intensity tones.

Methods

To test these hypotheses, we conducted behavioral and electrophysiological experiments in rats 2 to 8 days after traumatic tone exposure.

Results

In the behavioral experiments, prepulse and gap inhibition tended to exhibit different frequency characteristics (although not reaching sufficient statistical levels), suggesting that exposure to traumatic tones led to acute symptoms of hyperacusis and tinnitus at different frequency ranges. When examining the auditory cortex at the thalamocortical recipient layer, we observed that tinnitus symptoms correlated with a disorganized tonotopic map, typically characterized by responses to low-intensity tones. Neural correlates of hyperacusis were found in the cortical recruitment function at the multi-unit activity (MUA) level, but not at the local field potential (LFP) level, in response to moderate- and high-intensity tones. This shift from LFP to MUA was associated with a loss of monotonicity, suggesting a crucial role for inhibitory synapses.

Discussion

Thus, in acute symptoms of traumatic tone exposure, our experiments successfully disentangled the neural correlates of tinnitus and hyperacusis at the thalamocortical recipient layer of the auditory cortex. They also suggested that tinnitus is linked to central noise, whereas hyperacusis is associated with aberrant gain control. Further interactions between animal experiments and clinical studies will offer insights into neural mechanisms, diagnosis and treatments of tinnitus and hyperacusis, specifically in terms of long-term plasticity of chronic symptoms.

Sound-Evoked Neural Activity in Normal-Hearing Tinnitus: Effects of Frequency and Stimulated Ear Side

Tinnitus is a common phantom auditory percept believed to be related to plastic changes in the brain due to hearing loss. However, tinnitus can also occur in the absence of any clinical hearing loss. In this case, since there is no hearing loss, the mechanisms that drive plastic changes remain largely enigmatic. Previous studies showed subtle differences in sound-evoked brain activity associated with tinnitus in subjects with tinnitus and otherwise normal hearing, but the results are not consistent across studies. Here, we aimed to investigate these differences using monaural rather than binaural stimuli. Sound-evoked responses were measured using functional magnetic resonance imaging (MRI) in participants with and without tinnitus. All participants had clinically normal audiograms. The stimuli were pure tones with frequencies between 353 and 8000 Hz, presented monaurally. A Principal Component Analysis (PCA) of the response in the auditory cortex revealed no difference in tonotopic organization, which confirmed earlier studies. A GLM analysis showed hyperactivity in the lateral areas of the bilateral auditory cortex. Consistent with the tonotopic map, this hyperactivity mainly occurred in response to low stimulus frequencies. This may be related to hyperacusis. Furthermore, there was an interaction between stimulation side and tinnitus in the parahippocampus. This may reflect an interference between tinnitus and spatial orientation.

Sodium salicylate improves detection of amplitude-modulated sound in mice

Salicylate is commonly used to induce tinnitus in animals, but its underlying mechanism of action is still debated. We therefore tested its effects on the firing properties of neurons in the mouse inferior colliculus (IC). Salicylate induced a large decrease in the spontaneous activity and an increase of ∼20 dB SPL in the minimum threshold of single units. In response to sinusoidally modulated noise (SAM noise) single units showed both an increase in phase locking and improved rate coding. Mice also became better at detecting amplitude modulations, and a simple threshold model based on the IC population response could reproduce this improvement. The responses to dynamic random chords (DRCs) suggested that the improved AM encoding was due to a linearization of the cochlear output, resulting in larger contrasts during SAM noise. These effects of salicylate are not consistent with the presence of tinnitus, but should be taken into account when studying hyperacusis.

Tinnitus-related increases in single-unit activity in awake rat auditory cortex correlate with tinnitus behavior

Tinnitus is known to affect 10-15 % of the population, severely impacting 1-2 % of those afflicted. Canonically, tinnitus is generally a consequence of peripheral auditory damage resulting in maladaptive plastic changes in excitatory/inhibitory homeostasis at multiple levels of the central auditory pathway as well as changes in diverse nonauditory structures. Animal studies of primary auditory cortex (A1) generally find tinnitus-related changes in excitability across A1 layers and differences between inhibitory neuronal subtypes. Changes due to sound-exposure include changes in spontaneous activity, cross-columnar synchrony, bursting and tonotopic organization. Few studies in A1 directly correlate tinnitus-related changes in neural activity to an individual animal's behavioral evidence of tinnitus. The present study used an established condition-suppression sound-exposure model of chronic tinnitus and recorded spontaneous and driven single-unit responses from A1 layers 5 and 6 of awake Long-Evans rats. A1 units recorded from animals with behavioral evidence of tinnitus showed significant increases in spontaneous and sound-evoked activity which directly correlated to the animal's tinnitus score. Significant increases in the number of bursting units, the number of bursts/minute and burst duration were seen for A1 units recorded from animals with behavioral evidence of tinnitus. The present A1 findings support prior unit recording studies in auditory thalamus and recent in vitro findings in this same animal model. The present findings are consistent with sensory cortical studies showing tinnitus- and neuropathic pain-related down-regulation of inhibition and increased excitation based on plastic neurotransmitter and potassium channel changes. Reducing A1 deep-layer tinnitus-related hyperactivity is a potential target for tinnitus pharmacotherapy.

Application of functional near-infrared spectroscopy (fNIRS) in tinnitus research: contemporary insights and perspectives

Tinnitus, characterized by phantom sound perception, is a highly disruptive condition lacking clearly effective treatments. Its complex neural mechanisms are not fully elucidated. Functional near-infrared spectroscopy (fNIRS) is a promising neuroimaging tool well-suited for assessing tinnitus due to its quietness, portability, and ability to directly measure cortical hemodynamic responses. This study timely summarizes the recent applications of fNIRS in investigating tinnitus pathology, correlating neuroimaging biomarkers with symptom severity, and evaluating treatment efficacy. Further studies with larger samples are warranted to reproduce existing findings. Thus, fNIRS appears to be a promising tool in tinnitus research. Addressing technical limitations, optimizing control groups, advancing data analysis, integrating standardized, and individualized experimental protocols can facilitate the extended and robust utilization of fNIRS in tinnitus research.

Heterogeneous correlate and potential diagnostic biomarker of tinnitus based on nonlinear dynamics of resting-state EEG recordings

Tinnitus is a heterogeneous condition of hearing a rattling sound when there is no auditory stimulus. This rattling sound is associated with abnormal synchronous oscillations in auditory and non-auditory cortical areas. Since tinnitus is a highly heterogeneous condition with no objective detection criteria, it is necessary to search for indicators that can be compared between and within participants for diagnostic purposes. This study introduces heterogeneous though comparable indicators of tinnitus through investigation of spontaneous fluctuations in resting-state brain dynamics. The proposed approach uses nonlinear measures of chaos theory, to detect tinnitus and cross correlation patterns to reflect many of the previously reported neural correlates of tinnitus. These indicators may serve as effective measures of tinnitus risk even at early ages before any symptom is reported. The approach quantifies differences in oscillatory brain dynamics of tinnitus and normal subjects. It demonstrates that the left temporal areas of subjects with tinnitus exhibit larger lyapunov exponent indicating irregularity of brain dynamics in these regions. More complex dynamics is further recognized in tinnitus cases through entropy. We use this evidence to distinguish tinnitus patients from normal participants. Besides, we illustrate that certain anticorrelation patterns appear in these nonlinear measures across temporal and frontal areas in the brain perhaps corresponding to increased/decreased connectivity in certain brain networks and a shift in the balance of excitation and inhibition in tinnitus. Additionally, the main correlations are lost in tinnitus participants compared to control group suggesting involvement of distinct neural mechanisms in generation and persistence of tinnitus.

Evidence of cochlear neural degeneration in normal-hearing subjects with tinnitus

Tinnitus, reduced sound-level tolerance, and difficulties hearing in noisy environments are the most common complaints associated with sensorineural hearing loss in adult populations. This study aims to clarify if cochlear neural degeneration estimated in a large pool of participants with normal audiograms is associated with self-report of tinnitus using a test battery probing the different stages of the auditory processing from hair cell responses to the auditory reflexes of the brainstem. Self-report of chronic tinnitus was significantly associated with (1) reduced cochlear nerve responses, (2) weaker middle-ear muscle reflexes, (3) stronger medial olivocochlear efferent reflexes and (4) hyperactivity in the central auditory pathways. These results support the model of tinnitus generation whereby decreased neural activity from a damaged cochlea can elicit hyperactivity from decreased inhibition in the central nervous system.

An MR spectroscopy study of temporal areas excluding primary auditory cortex and frontal regions in subjective bilateral and unilateral tinnitus

Previous studies indicate changes in neurotransmission along the auditory pathway in subjective tinnitus. Most authors, however, investigated brain regions including the primary auditory cortex, whose physiology can be affected by concurrent hearing deficits. In the present MR spectroscopy study we assumed increased levels of glutamate and glutamine (Glx), and other Central Nervous System metabolites in the temporal lobe outside the primary auditory cortex, in a region involved in conscious auditory perception and memory. We studied 52 participants with unilateral (n = 24) and bilateral (n = 28) tinnitus, and a control group without tinnitus (n = 25), all with no severe hearing losses and a similar hearing profile. None of the metabolite levels in the temporal regions of interest were found related to tinnitus status or laterality. Unexpectedly, we found a tendency of increased concentration of Glx in the control left medial frontal region in bilateral vs unilateral tinnitus. Slightly elevated depressive and anxiety symptoms were also shown in participants with tinnitus, as compared to healthy individuals, with the bilateral tinnitus group marginally more affected. We discuss no apparent effect in the temporal lobes, as well as the role of frontal brain areas, with respect to hearing loss, attention and psychological well-being in chronic tinnitus. We furthermore elaborate on the design-related and technical obstacles of MR spectroscopy.

Role of insula and its subregions in progression from recent onset to chronic idiopathic tinnitus

We determined the structural and functional alterations in the insula and its subregions in patients with idiopathic tinnitus in order to identify the neural changes involved in the progression from recent onset to chronic tinnitus. We recruited 24 recent-onset tinnitus patients, 32 chronic tinnitus patients and 36 healthy controls. We measured the grey matter volume and fractional amplitude of low-frequency fluctuation of the insula and its subregions and the functional connectivity within the insula and between the insula and the rest of the brain. Relationships between MRI and clinical characteristics were estimated using partial correlation analysis. Both recent-onset and chronic tinnitus patients showed decreased fractional amplitude of low-frequency fluctuation in the insula and its subregions, but only chronic tinnitus patients showed bilateral grey matter atrophy in the ventral anterior insula. Abnormal functional connectivity was detected in recent-onset and chronic tinnitus patients relative to the healthy controls, but functional connectivity differences between recent-onset and chronic tinnitus patients were found in only the auditory-related cortex, frontal cortex and limbic system. Functional alterations (fractional amplitude of low-frequency fluctuation and functional connectivity of the left ventral anterior insula), but not structural changes, were correlated with clinical severity. Bilateral grey matter atrophy in the ventral anterior insula decreased regional activities in the left ventral anterior insula and left posterior insula, and abnormal functional connectivity of the insula subregions with auditory and non-auditory areas were implicated in the progression from recent onset to chronic tinnitus. This suggests that tinnitus generation and development occur in a dynamic manner and involve aberrant multi-structural and functional (regional brain activity and abnormal functional connectivity) reorganization of the insula.

Evaluating the Efficacy and Underlying Mechanisms of Acupuncture for Chronic Subjective Tinnitus Using Functional Near-Infrared Spectroscopy: Study Protocol for a Randomized Controlled Trial

Objective

This study aims to evaluate the efficacy and safety of acupuncture for chronic subjective tinnitus and explore the central mechanism underlying acupuncture for chronic subjective tinnitus using functional near-infrared spectroscopy (fNIRS).

Methods

We will randomly assign 60 tinnitus patients to either an acupuncture group or a waiting-list control group. The acupuncture group will undergo 12 treatment sessions over 4 weeks, whereas the waiting-list control group will receive no intervention concurrently. Clinical outcome measures include the Tinnitus Handicap Inventory (THI) score, tinnitus loudness assessed by 11-point NRS, average pure-tone threshold, and Hamilton Anxiety Scale (HAM-A) score. Neuroimaging outcomes assessed by fNIRS included blood oxygen concentration and resting-state functional connectivity (RSFC). All outcome measurements will be assessed at the baseline, after 4-week treatment, and at 3-month follow-ups.

Results

Our investigation will determine if significant differences exist between the two groups regarding THI, NRS, average pure-tone threshold, and HAM-A scores. Moreover, the analysis will reveal whether the acupuncture group demonstrates significant change in blood oxygen concentration and RSFC between specific brain regions compared to the waiting-list control group.

Conclusion

With the novel technique of fNIRS, in addition to efficacy evaluation of acupuncture, this study's findings are anticipated to partly elucidate the neural mechanisms underlying acupuncture treatment for subjective tinnitus and offer an objective assessment method for its therapeutic impact, thereby contributing to filling the research gap.

Trial Registration

Clinicaltrials registry (identification code NCT05829278).

Targeting the Limbic System: Insights into Its Involvement in Tinnitus

Tinnitus is originally derived from the Latin verb tinnire, which means "to ring". Tinnitus, a complex disorder, is a result of sentient cognizance of a sound in the absence of an external auditory stimulus. It is reported in children, adults, and older populations. Patients suffering from tinnitus often present with hearing loss, anxiety, depression, and sleep disruption in addition to a hissing and ringing in the ear. Surgical interventions and many other forms of treatment have been only partially effective due to heterogeneity in tinnitus patients and a lack of understanding of the mechanisms of tinnitus. Although researchers across the globe have made significant progress in understanding the underlying mechanisms of tinnitus over the past few decades, tinnitus is still deemed to be a scientific enigma. This review summarises the role of the limbic system in tinnitus development and provides insight into the development of potential target-specific tinnitus therapies.

Transcriptional Profile Changes after Noise-Induced Tinnitus in Rats

Tinnitus is an unpleasant symptom characterized by detective hearing without the actual sound input. Despite numerous studies elucidating a variety of pathomechanisms inducing tinnitus, the pathophysiology of tinnitus is not fully understood. The genes that are closely associated with this subtype of the auditory hallucination that could be utilized as potential treatment targets are still unknown. In this study, we explored the transcriptional profile changes of the auditory cortex after noise-induced tinnitus in rats using high throughput sequencing and verification of the detected genes using quantitative PCR (qPCR). Tinnitus models were established by analyzing startle behaviors through gap pre-pulse inhibition (PPI) of the acoustic startle. Two hundred and fifty-nine differential genes were identified, of which 162 genes were up-regulated and 97 genes were down-regulated. Analysis of the pathway enrichment indicated that the tinnitus group exhibited increased gene expression related to neurodegenerative disorders such as Huntington’s disease and Amyotrophic lateral sclerosis. Based on the identified genes, networks of protein–protein interaction were established and five hub genes were identified through degree rank, including Fos, Nr4a1, Nr4a3, Egr2, and Egr3. Therein, the Fos gene ranked first with the highest degree after noise exposure, and may be a potential target for the modulation of noise-induced tinnitus.

Tinnitus Prevalence in the Adult Population-Results from the Gutenberg Health Study

Background and Objectives: Tinnitus is a common symptom in medical practice, although data on its prevalence vary. As the underlying pathophysiological mechanism is still not fully understood, hearing loss is thought to be an important risk factor for the occurrence of tinnitus. The aim of this study was to assess tinnitus prevalence in a large German cohort and to determine its dependence on hearing impairment. Materials and Methods: The Gutenberg Health Study (GHS) is a population-based cohort study and representative for the population of Mainz and its district. Participants were asked whether they suffer from tinnitus and how much they are burdened by it. Extensive audiological examinations using bone- and air-conduction were also performed. Results: 4942 participants (mean age: 61.0, 2550 men and 2392 women) were included in the study. The overall prevalence of tinnitus was 26.1%. Men were affected significantly more often than women. The prevalence of tinnitus increased with age, peaking at ages 75 to 79 years. Considering only annoying tinnitus, the prevalence was 9.8%. Logistic regression showed that participants with severe to complete hearing loss (>65 dB) were more likely to have tinnitus. Conclusions: Tinnitus is a common symptom, and given demographic changes, its prevalence is expected to increase.

Comparing tinnitus, pain, psychosocial and cognitive factors between patients with tinnitus and pain: A systematic review

OBJECTIVE

Tinnitus is a multifactorial symptom, which shows similarities with the involved mechanisms in chronic pain. The aim of this systematic review is to provide an overview of studies comparing patients with only tinnitus to patients with pain (headache, temporomandibular joint (TMJ) pain or neck pain) with or without tinnitus, regarding tinnitus-related, pain-related, psychosocial and cognitive factors.

METHODS

This systematic review was written following the PRISMA guidelines. To identify relevant articles, PubMed, Web of Science and Embase databases were searched. The risk of bias was rated using the Newcastle Ottawa scale for case-control studies.

RESULTS

Ten articles were included in the qualitative analysis. The risk of bias ranged from low to moderate. Low to moderate evidence shows that patients with tinnitus experience higher mean symptom intensity, but lower psychosocial and cognitive distress, compared to patients with pain. Inconsistent results were found for tinnitus-related factors. Low to moderate evidence points to a higher severity of hyperacusis and psychosocial distress in patients with both pain and tinnitus, compared to patients with tinnitus only, as well as for positive associations between tinnitus-related factors and the presence or intensity of pain.

CONCLUSION

This systematic review shows that psychosocial dysfunctions are more clearly present in patients with pain only, compared to patients with tinnitus only and the co-occurrence of tinnitus and pain increases psychosocial distress as well as hyperacusis severity. Some positive associations were identified between tinnitus-related and pain-related factors.

Tinnitus and Its Relation to Depression, Anxiety, and Stress-A Population-Based Cohort Study

Tinnitus is a common symptom reported in otolaryngologic practice. Although the pathophysiology of tinnitus has not been fully understood, clinical studies suggest that psychological symptoms of depression, anxiety, and somatization are increased in tinnitus patients. However, patients seeking medical treatment for tinnitus may be especially vulnerable. Population-based studies reporting on the association between tinnitus and psychological distress are still lacking. The aim of this study was to investigate the correlation of tinnitus with depression, anxiety, or somatization in a large population-based cohort. The Gutenberg Health Study is a population-based cohort study. Participants were asked about the occurrence of tinnitus (yes/no) and how much they were bothered by it. In addition, they completed the PHQ-9, GAD-7, and SSS-8 questionnaires to assess depressive symptoms, anxiety, and somatic symptom disorders. A total of 8539 participants were included in the study cohort. Tinnitus prevalence was 28.0% (2387). The prevalence of depression/anxiety/somatic symptom disorders was significantly higher among participants with tinnitus than among participants without tinnitus (7.9%/5.4%/40.4% participants with tinnitus vs. 4.6%/3.3%/26.9% participants without tinnitus, p-value < 0.0001). Logistic regression results showed that participants with tinnitus were more likely to suffer from depression (OR = 2.033, 95% CI [1.584; 2.601], p-value < 0.0001), anxiety (OR = 1.841, 95% CI [1.228; 2.728], p-value = 0.0027), or somatic symptom disorders (OR = 2.057, 95% CI [1.799; 2.352], p-value < 0.0001). Symptoms of depression, anxiety, and somatic symptom disorders were increased in participants with tinnitus. This must be taken into account when treating these patients.

Loud noise-exposure changes the firing frequency of subtypes of layer 5 pyramidal neurons and Martinotti cells in the mouse auditory cortex

Introduction

Loud noise-exposure can generate noise-induced tinnitus in both humans and animals. Imaging and in vivo studies show that noise exposure affects the auditory cortex; however, cellular mechanisms of tinnitus generation are unclear.

Methods

Here we compare membrane properties of layer 5 (L5) pyramidal cells (PCs) and Martinotti cells expressing the cholinergic receptor nicotinic alpha 2 subunit gene (Chrna2) of the primary auditory cortex (A1) from control and noise-exposed (4-18 kHz, 90 dB, 1.5 h, followed by 1.5 h silence) 5-8 week old mice. PCs were furthermore classified in type A or type B based on electrophysiological membrane properties, and a logistic regression model predicting that afterhyperpolarization (AHP) and afterdepolarization (ADP) are sufficient to predict cell type, and these features are preserved after noise trauma.

Results

One week after a loud noise-exposure no passive membrane properties of type A or B PCs were altered but principal component analysis showed greater separation between type A PCs from control and noise-exposed mice. When comparing individual firing properties, noise exposure differentially affected type A and B PC firing frequency in response to depolarizing current steps. Specifically, type A PCs decreased initial firing frequency in response to +200 pA steps (p = 0.020) as well as decreased steady state firing frequency (p = 0.050) while type B PCs, on the contrary, significantly increased steady state firing frequency (p = 0.048) in response to a + 150 pA step 1 week after noise exposure. In addition, L5 Martinotti cells showed a more hyperpolarized resting membrane potential (p = 0.04), higher rheobase (p = 0.008) and an increased initial (p = 8.5 × 10^-5) and steady state firing frequency (p = 6.3 × 10^-5) in slices from noise-exposed mice compared to control.

Discussion

These results show that loud noise can cause distinct effects on type A and B L5 PCs and inhibitory Martinotti cells of the primary auditory cortex 1 week following noise exposure. As the L5 comprises PCs that send feedback to other areas, loud noise exposure appears to alter levels of activity of the descending and contralateral auditory system.

Effectiveness and cost effectiveness of digital hearing aids in patients with tinnitus and hearing loss: a randomised feasibility trial (THE HUSH Trial)

Background

Education and advice is provided for tinnitus management in all UK audiology clinics. Sound therapy, including provision of hearing aids may be offered, but this is often dependent on a clinician’s decision rather than UK policy. This inconsistent management reflects a lack of evidence around the effectiveness of hearing aids for tinnitus. This open-label, two-arm multicentre randomised controlled feasibility trial gathered data around recruitment, acceptability and outcome assessments to determine the feasibility of conducting a large randomised controlled trial investigating the effectiveness of hearing aids for tinnitus management.

Methods

Adults referred to audiology for tinnitus, with an aidable hearing loss were recruited at five UK audiology clinics. They were randomised 1:1 to either education and advice (treatment as usual (TAU), n = 41) or TAU plus hearing aids (n = 42). Outcomes were collected by questionnaires 12 weeks after randomisation. After participation, interviews were conducted with a subset of both participants and clinicians from each trial centre.

Results

Eighty three participants from five sites were randomised. Non-aidable hearing loss was the main reason for ineligibility to participate in the trial reported by the sites. Seventy three percent of participants returned the 12-week questionnaires, with return rates by site ranging from 61 to 100%. Fifteen out of 33 participants (45%) reported using hearing aids for the clinician-recommended time, or longer, during the day. The Tinnitus Functional Index (TFI) was the outcome measure most responsive to change. The majority of participants also agreed it was relevant to their tinnitus and hearing loss. Qualitative data demonstrated that the trial was acceptable to participants. Feedback from clinicians revealed a potential lack of equipoise. It also highlighted the differences in referral and treatment pathways between departments and differences in audiometric criteria for fitting hearing aids. Health economic measures were well completed for those returned. No change in health-related quality of life was observed. Costs were higher in the intervention arm, but self-reports of healthcare service use indicated participant confusion in treatment pathways.

Conclusions

This feasibility trial is the first step towards obtaining high quality evidence to determine potential clinical effectiveness and cost effectiveness of hearing aids for tinnitus versus usual care. A definitive trial was deemed to be feasible, with some modifications based on feasibility findings and using the TFI as the primary outcome.

This trial was funded by the National Institute for Health Research, Research for Patient Benefit Programme (PB-PG-0816–20,014) and registered with ISRCTN (ISRCTN14218416).

Supplementary Information

The online version contains supplementary material available at 10.1186/s40814-022-01188-9.

Surface-based functional metrics and auditory cortex characteristics in chronic tinnitus

Abnormal auditory cortex (AC) neuronal activity is thought to be a primary cause of the auditory disturbances perceived by individuals suffering from tinnitus. The present study was designed to test that possibility by evaluating auditory cortical characteristics (volume, curvature, surface area, thickness) and surface-based functional metrics in chronic tinnitus patients. In total, 63 chronic tinnitus patients and 36 age-, sex- and education level-matched healthy control (HC) patients were enrolled in this study. Hearing levels in these two groups were comparable, and following magnetic resonance imaging (MRI) of these individuals, the DPABISurf software was used to compute cerebral cortex curvature, thickness, and surface area as well as surface-based functional metrics. The Tinnitus Handicap Inventory (THI), Tinnitus Handicap Questionary (THQ), and Visual Analogue Scales (VAS) were used to gauge participant tinnitus severity, while correlation analyses were conducted to evaluate associations between these different analyzed parameters. A significant increase in the regional homogeneity (ReHo) of the right secondary AC was detected in the tinnitus group relative to the HC group. There were also significant reductions in the cortical volume and surface area of the right secondary AC in the tinnitus group relative to the HC group (all P < 0.05). In addition, significant negative correlations between tinnitus pitch and the cortical area and volume of the right secondary AC were observed in the tinnitus group.

Comparison of Different Therapeutic Effects of T-MIST for Chronic Idiopathic Tinnitus

Objective. Tinnitus, as a common clinical symptom, has the characteristics of high incidence and great heterogeneity among different patients. As one of the common treatment strategies for tinnitus, this study is aimed at exploring the factors influencing tinnitus sound therapy and the correlation between different tinnitus acoustic characteristics. Methods. 315 patients with chronic tinnitus were enrolled and divided into three groups according to the tinnitus multielement integration sound therapy (T-MIST): (1) vanishing, (2) remission, and (3) unchanged. The general characteristics, psychoacoustic scores (tinnitus handicap inventory (THI) and visual analog scale (VAS)), residual inhibition (RI), degree of hearing loss, and tinnitus characteristics of each group were compared. Finally, we analyze the predictive significance of different features for acoustic effects. Results. The frequency of tinnitus in the vanishing group was higher than that in the remission and unchanged groups ( $P<0.05$ ). There were no differences in age, initial onset time, course of the disease, and VSAD between the vanishing group and the unchanged group ( $P>0.05$ ). High-frequency tinnitus may predict the vanishing of tinnitus after treatment ( $P<0.05$ ), but the degree of hearing loss, tinnitus characteristics (loudness and frequency), and psychoacoustic score (THI and VAS) were only weakly correlated ( $P<0.05$ ). Residual inhibition test (RI) was an independent risk factor for the efficacy of acoustic therapy ( $P<0.001$ ). Conclusion. The patients were divided into three groups by T-MIST treatment effect; Kruskal-Wallis test and chi-square test were used to compare the baseline information of each group. Then, we analyzed the correlation between patient characteristics and psychoacoustic scores. Finally, logistic regression was performed to explore predictors that might influence the treatment effect. High-frequency tinnitus may have a better therapeutic effect; age, disease course, and other factors can not be stable explanation factors for a poor therapeutic effect of tinnitus. The residual inhibition (RI) test was an independent factor in predicting the efficacy of T-MIST.

Long-Term Effects of Repetitive Transcranial Magnetic Stimulation on Tinnitus in a Guinea Pig Model

The auditory phantom sensation of tinnitus is associated with neural hyperactivity. Modulating this hyperactivity using repetitive transcranial magnetic stimulation (rTMS) has shown beneficial effects in human studies. Previously, we investigated rTMS in a tinnitus animal model and showed that rTMS over prefrontal cortex (PFC) attenuated tinnitus soon after treatment, likely via indirect effects on auditory pathways. Here, we explored the duration of these beneficial effects. Acoustic trauma was used to induce hearing loss and tinnitus in guinea pigs. Once tinnitus developed, high-frequency (20 Hz), high-intensity rTMS was applied over PFC for two weeks (weekdays only; 10 min/day). Behavioral signs of tinnitus were monitored for 6 weeks after treatment ended. Tinnitus developed in 77% of animals between 13 and 60 days post-trauma. rTMS treatment significantly reduced the signs of tinnitus at 1 week on a group level, but individual responses varied greatly at week 2 until week 6. Three (33%) of the animals showed the attenuation of tinnitus for the full 6 weeks, 45% for 1–4 weeks and 22% were non-responders. This study provides further support for the efficacy of high-frequency repetitive stimulation over the PFC as a therapeutic tool for tinnitus, but also highlights individual variation observed in human studies.

A Narrative Review of Auditory Categorisation and Its Potential Role in Tinnitus Perception

Auditory categorisation is a phenomenon reflecting the non-linear nature of human perceptual spaces which govern sound perception. Categorisation training paradigms may reduce sensitivity toward training stimuli, decreasing the representation of these stimuli in auditory perceptual maps. Reduced cortical representation may have clinical implications for conditions that arise from disturbances in cortical activation, such as tinnitus. This review explores the categorisation of sound, with a particular focus on tinnitus. The potential of categorisation training as a sound-based tinnitus therapy is discussed. A narrative review methodological framework was followed. Four databases (PubMed, Google Scholar, Scopus, and ScienceDirect) were extensively searched for the following key words: categorisation, categorical perception, perceptual magnet effect, generalisation, and categorisation OR categorical perception OR perceptual magnet effect OR generalisation AND sound. Given the exploratory nature of the review and the fact that early works on categorisation are crucial to the understanding and development of auditory categorisation, all study types were selected for the period 1950–2022. Reference lists of articles were reviewed to identify any further relevant studies. The results of the review were catalogued and organised into themes. In total, 112 articles were reviewed in full, from which 59 were found to contain relevant information and were included in the review. Key themes identified included categorical perception of speech stimuli, warping of the auditory perceptual space, categorisation versus discrimination, the presence of categorisation across several modalities, and categorisation as an innate versus learned feature. Although a substantial amount of work focused on evaluating the effects of categorisation training on sound perception, only two studies investigated the effects of categorisation training on tinnitus. Implementation of a categorisation-based perceptual training paradigm could serve as a promising means of tinnitus management by reversing the changes in cortical plasticity that are seen in tinnitus, in turn altering the representation of sound within the auditory cortex itself. In the instance that the categorisation training is successful, this would likely mean a decrease in the level of activity within the auditory cortex (and other associated cortical areas found to be hyperactive in tinnitus) as well as a reduction in tinnitus salience.

Prognostic Factors Influencing the Tinnitus Improvement After Idiopathic Sudden Sensorineural Hearing Loss Treatment

PURPOSE

Logistic regression analysis was used to explore the factors that influence tinnitus improvement after idiopathic sudden sensorineural hearing loss (ISSNHL) treatment.

MATERIALS AND METHODS

In this retrospective study, 137 ISSNHL patients with tinnitus were recruited at the Sun Yatsen Memorial Hospital of Sun Yat-sen University, China. They underwent audiological examinations, vestibular assessments, tinnitus examinations, a Tinnitus Handicap Inventory (THI) assessment and ISSNHL treatments. Logistic regression analysis was performed to investigate factors that affected tinnitus improvement.

RESULTS

Participants were divided into an effective group (73 patients) and noneffective group (64 patients) according to THI scores before and after treatment. The effective group had better averaged hearing threshold than the noneffective group (effective group vs. noneffective group: 74.47 vs. 87.66 dB HL; t = 3.03, p < 0.05). Additionally, before intervention there were significant difference in profound audiogram configuration (effective group vs. noneffective group: 17.81% vs. 46.88%, x2 = 23.63; p < 0.001), mid tinnitus pitch (effective group vs. noneffective group: 19.18% vs. 35.94%, x2 = 6.58; p = 0.037) and mean THI scores (effective group vs. noneffective group: 57.07 ± 22.27 vs. 36.78 ± 24.41, t = -5.09, p < 0.001) between the effective and noneffective tinnitus groups. Logistic regression analysis showed that audiogram configurations (profound audiogram: OR = 0.10, 95% CI 0.01-0.72, p = 0.022), tinnitus pitch (mid tinnitus pitch: OR = 0.16, 95% CI 0.05-0.57, p = 0.004) and THI scores (OR = 1.05, 95% CI 1.03-1.07, p < 0.001) were independent factors associated with tinnitus improvement.

CONCLUSION

Audiogram configuration, tinnitus pitch, and THI scores before intervention appear to be predictive of the effectiveness of acute tinnitus improvement following ISSNHL treatment.

The Effectiveness of Targeted Electrical Stimulation via Cochlear Implant on Tinnitus-Perceived Loudness

Introduction

The cause of tinnitus improvement in cochlear implant (CI) users is not understood. On the basis that a spatially limited dysfunction in the auditory pathway could cause tinnitus, we used single-channel stimulation to evaluate any variation of tinnitus-perceived loudness and identify the cochlear regions involved.

Materials and Methods

It was an observational prospective case-crossover study. After the first mapping, 21 adults with unilateral CI and chronic tinnitus expressed their tinnitus loudness based on the Visual Analog Scale (VAS) score (0–10) at baseline (L⁰), during a 10 s single-channel stimulation with C-level of electric current (L¹) and 30 min after CI activation (L²). Tinnitus reduction [R^T = (L⁰ – L¹) × 100/L⁰] > 50% was considered significant. VAS outcomes were compared between baseline (L0) and (each) single-channel stimulation (L1) to find the channel with the greatest R^T (suppressive channel-SC), whose frequency range revealed the cochlear region involved. Seven patients with asymmetric hearing loss underwent the pitch-matching test to identify the actual frequency evoked by the SC. We compared selective (L¹) and non-selective (L²) intracochlear stimulation using paired t-test. Preoperative Tinnitus Handicap Inventory (THI) score was compared with those at 1, 6, and 12 months with paired t-tests to evaluate long-term tinnitus perception.

Results

We observed a significant reduction of tinnitus loudness during the experimental procedure [L⁰ (6.4 ± 2.4) vs. L¹ (1.7 ± 2.7), p = 0.003]. A total of 15/21 patients (71.4%) had a significant (R^T > 50%) and selective improvement, reporting a mean L¹ of 0.4 ± 2.0 (p = 0.0001). In 10/15 (66.6%) patients, the SC was in the apical turn, within 1,000 Hz; in 5/15 patients (33.4%) within 4,000 Hz. The cochlear region 125–313 Hz was the most affected by tinnitus improvement (p = 0.0074). Targeted stimulation was more effective than non-selective stimulation [L¹ vs. L² (4.3 ± 2.5), p = 0.0022]. In 3/7 patients, the perceived pitch did not fall within the SC frequency ranges. All patients with selective attenuation described tinnitus as monotone. Patients with non-selective attenuation had polyphonic tinnitus and better THI results after 1 year.

Conclusion

Targeted intracochlear electrical stimulation improved chronic tinnitus perception, especially in monotone tinnitus, and the apical region was mainly involved. Our results provide new insights into the pathophysiological mechanisms of tinnitus and targets for innovative therapeutic strategies.

Does Listening to Tinnitus Frequency-Filtered Music Relieve Tinnitus?

Background and Objectives

Tinnitus frequency-filtered music therapy aims to restore lateral inhibition to reverse tonotopic reorganization in the auditory cortex. Although the tinnitus-relieving effect of this therapy has been investigated, the results remain controversial. We performed a prospective, randomized, controlled double-blind study to determine the tinnitus-suppressing effect of tinnitus frequency-filtered music therapy.

Subjects and Methods

The study included 90 participants who were randomly categorized into an experimental group that listened to tinnitus frequency-filtered music and a control group that listened to music from which a random frequency was removed. The Tinnitus Handicap Inventory (THI) score and measures of tinnitus loudness, daily awareness, and tinnitus-induced annoyance were evaluated at the initial visit and at 3 and 6 months (final follow-up). The rates of improvement in THI scores in the two groups were also recorded.

Results

All measured variables showed significant improvement in both groups, except the matched tinnitus loudness and minimal masking level. However, no significant intergroup differences were observed in the amount of improvement in THI scores and any other variable. The rates of improvement in THI scores were higher in the control group at 3 and 6 months.

Conclusions

Listening to tinnitus frequency-filtered music reduced tinnitus-induced handicaps; however, this approach was not significantly better than listening to music from which a random frequency was removed.

Definition of Tinnitus

Tinnitus is generally defined as the perception of sound in the absence of vibration of an external elastic body. If this definition appears useful to differentiate tinnitus from somatosounds, it is not suitable for distinguishing it from psychiatric hallucinations. Nor does this solution define a temporal limit of duration of the perception, which is important for distinguishing pathological tinnitus from those occasional noises that we all perceive from time to time. A complete definition appears necessary not only to achieve homogeneity in epidemiological studies but also to set up correct and personalized therapeutic schemes. An analogy with neuropsychiatric studies and, in particular, the concept of auditory hallucinosis are proposed by the authors to define tinnitus. According to the authors, tinnitus is auditory hallucinosis, and similarly, vertigo is spatial hallucinosis.

Tinnitus: at a crossroad between phantom perception and sleep

Sensory disconnection from the environment is a hallmark of sleep and is crucial for sleep maintenance. It remains unclear, however, whether internally generated percepts—phantom percepts—may overcome such disconnection and, in turn, how sleep and its effect on sensory processing and brain plasticity may affect the function of the specific neural networks underlying such phenomena. A major hurdle in addressing this relationship is the methodological difficulty to study sensory phantoms, due to their subjective nature and lack of control over the parameters or neural activity underlying that percept. Here, we explore the most prevalent phantom percept, subjective tinnitus—or tinnitus for short—as a model to investigate this. Tinnitus is the permanent perception of a sound with no identifiable corresponding acoustic source. This review offers a novel perspective on the functional interaction between brain activity across the sleep–wake cycle and tinnitus. We discuss characteristic features of brain activity during tinnitus in the awake and the sleeping brain and explore its effect on sleep functions and homeostasis. We ask whether local changes in cortical activity in tinnitus may overcome sensory disconnection and prevent the occurrence of global restorative sleep and, in turn, how accumulating sleep pressure may temporarily alleviate the persistence of a phantom sound. Beyond an acute interaction between sleep and neural activity, we discuss how the effects of sleep on brain plasticity may contribute to aberrant neural circuit activity and promote tinnitus consolidation. Tinnitus represents a unique window into understanding the role of sleep in sensory processing. Clarification of the underlying relationship may offer novel insights into therapeutic interventions in tinnitus management.

Phenotypic Profiling of People With Subjective Tinnitus and Without a Clinical Hearing Loss

Our objective was to study the characteristics of patients with subjective tinnitus and normal hearing and to investigate whether the features correlated to different shapes on audiograms. In this retrospective study, 313 patients with subjective tinnitus and clinically normal hearing were enrolled from the tinnitus outpatient department of the Eye and ENT Hospital of Fudan University. The following phenotypic variables were collected: age, dominant tinnitus pitch (TP), tinnitus loudness, tinnitus duration, tinnitus severity, sex, education, hearing thresholds, tinnitus position, and tinnitus condition. The dominant TPs of patients with normal hearing were mostly high-pitched, with a mean of 4866.8 ± 2579.6 Hz; thus, we speculated that the condition is related to high-frequency hearing threshold elevations. We further divided the patients into four subgroups based on the matched TP: (i) TP ≤ 500 Hz (n = 34), (ii) 500 Hz < TP ≤ 3,000 Hz (n = 15), (iii) 3,000 Hz < TP ≤ 8,000 Hz (n = 259), and (iv) TP > 8,000 Hz (n = 5). We studied the phenotypic profiling of different audiograms and found that the group with TP of ≤500 Hz had an average “inverted-U” shaped audiogram, and the group with TP between 500 and 3,000 Hz had a slowly ascending slope audiogram below 2,000 Hz, followed by a drastically descending slope audiogram ranging from 2,000 to 8,000 Hz; further, the high-frequency (3,000–8,000 Hz) and ultra-high-frequency (>8,000 Hz) groups had flat curves below 2,000 Hz and steeper slope audiograms over 2,000 Hz. Our findings confirmed a consistency ratio between the distributions of dominant TPs and the frequencies of maximum hearing thresholds in both ears. The dominant TP was positively correlated with the maximum hearing threshold elevation frequency (left ear: r = 0.277, p < 0.05; right ear: r = 0.367, p < 0.001). Hearing threshold elevations, especially in high frequency, might explain the appearance of dominant high-frequency TP in patients without clinically defined hearing loss. This is consistent with the causal role of high-frequency coding in the generation of tinnitus.

The Road Traveled and Journey Ahead for the Genetics and Genomics of Tinnitus

The feasibility to unravel genetic and genomic signatures for disorders affecting the auditory system has accelerated since arriving in the post-genomics era roughly 20 years ago. Newly emerging studies have provided initial landmarks signaling heritability and thus, a genetic link, to severe tinnitus. Tinnitus, the phantom perception of ringing in the ears, is experienced by at least 15% of the adult population and can be extremely disabling. Despite its ubiquity, there is no cure for tinnitus and modalities offering relief are often of limited success. Because tinnitus is frequently reported in patients with acquired conductive or sensorineural hearing impairment, it has been widely accepted that tinnitus is secondary to and a symptom arising from hearing impairment. However, tinnitus has also been identified in the absence of auditory dysfunction and in young individuals, resulting in a debate about its origins. Genetics studies have identified severe tinnitus as a complex disorder arising from gene and environment interactions, refining its classification as a neurological disorder and, in at least a subset of patients, it appears not as a symptom of another health issue. This current opinion summarizes several recent studies that have challenged a long-accepted dogma and postulates how this information could eventually be used in the future to help patients. It is with great hope that this knowledge opens translational paths to provide relief for the many who suffer from the burden of tinnitus on a daily basis.

[Principles of diagnosis and treatment of tinnitus]

Tinnitus is one of the most common otological symptoms and can be defined as the conscious perception of sound lasting more than 5 minutes in the absence of an external auditory stimulus. Based on the review of articles, a comparative analysis of modern methods of diagnosis and treatment of tinnitus was carried out in order to substantiate the most effective and promising algorithms for providing care to patients. Diagnosis of tinnitus includes taking anamnesis, assessing the severity of tinnitus using questionnaires, otoscopy, hearing examination, and performing additional tests. In case of secondary murmur, etiotropic therapy should be started as soon as possible to prevent hearing loss and other complications. For primary noise, the most effective treatments are cognitive-behavioral therapy, tinnitus maskers and sound therapy, transcutaneous electrical stimulation, and biofeedback. Magnetic stimulation, invasive neuromodulation, drug therapy have a lower level of effectiveness and evidence base.

Changes in the spatiotemporal pattern of spontaneous activity across a cortical column after noise trauma

In the auditory modality, noise trauma has often been used to investigate cortical plasticity as it causes cochlear hearing loss. One limitation of these past studies, however, is that the effects of noise trauma have been mostly documented at the granular layer, which is the main cortical recipient of thalamic inputs. Importantly, the cortex is composed of six different layers each having its own pattern of connectivity and specific role in sensory processing. The present study aims at investigating the effects of acute and chronic noise trauma on the laminar pattern of spontaneous activity in primary auditory cortex of the anesthetized guinea pig. We show that spontaneous activity is dramatically altered across cortical layers after acute and chronic noise-induced hearing loss. First, spontaneous activity was globally enhanced across cortical layers, both in terms of firing rate and amplitude of spike-triggered average of local field potentials. Second, current source density on (spontaneous) spike-triggered average of local field potentials indicates that current sinks develop in the supra- and infragranular layers. These latter results suggest that supragranular layers become a major input recipient and that the propagation of spontaneous activity over a cortical column is greatly enhanced after acute and chronic noise-induced hearing loss. We discuss the possible mechanisms and functional implications of these changes.

Randomised controlled trial of interventions for bothersome tinnitus: DesyncraTM versus cognitive behavioural therapy

OBJECTIVE

Compare the relative efficacy of Desyncra^TM and Cognitive Behavioural Therapy (CBT).

DESIGN AND STUDY SAMPLE

Sixty-one participants were randomly assigned to receive either Desyncra^TM (n = 29) or CBT (n = 32). Randomisation included stratification regarding current hearing aid (HA) use. Depending on group assignment, participants attended approximately 7-12 visits. Tinnitus distress was measured using the Tinnitus Questionnaire (TQ).

RESULTS

Mean TQ scores decreased post-baseline from 5-15 points across treatment arms and strata. Model-based findings for the no-HA stratum showed a difference of -2.0 TQ points favouring Desyncra at 24-weeks, with a 90% posterior interval varying from -5.4 points favouring Desyncra to 0.8 TQ points favouring CBT. For the HA stratum, results show a difference of -1.0 TQ points favouring Desyncra, with a 90% posterior interval ranging from -4.7 points favouring Desyncra to 2.9 points favouring CBT.

CONCLUSIONS

The difference between Desyncra and CBT on average showed greater improvement with Desyncra in the no-HA stratum by about 2 TQ points. To the extent that the study sample represents a clinical population and recognising the assumptions in the design and analysis, these results suggest Desyncra is just as effective or more so than CBT in reducing tinnitus distress.

The Role of Eye Color in the Emergence of Tinnitus in Silence

Introduction  Previous research suggests that African Americans are less likely than Caucasians to perceive tinnitus in sustained silence.

Objective  To evaluate the association between non-cutaneous melanin as indicated by eye color and the emergence of temporary tinnitus during a brief period of silence.

Methods  A cross-section of adults grouped according to their eye color were exposed to silence. A total of 62 adults, aged 18 to 35 years (10 males, 52 females) were required to sit in silence for 10 minutes, after which they filled out a questionnaire to report their eye color and any perception of sounds in the ears or head.

Results  In total, 63% of the participants perceived tinnitus while sitting in silence, and, of these 95% perceived the tinnitus sounds within 5 minutes of sitting in silence. Though African Americans were less likely to perceive tinnitus in silence, this difference was not significant ( p  = 0.6). After a period of silence, 69% of the subjects with light-colored eyes and 58% of the dark-eyed subjects perceived tinnitus. This difference was not statistically significant (χ ² (1) = 0.77; p  = 0.38).

Conclusion  When exposed to reduced auditory stimulation, 3 out of 5 normal-hearing people are likely to experience tinnitus. However, there was no relationship between eye color and the perception of tinnitus in silence. Although melanin has been shown to play a role in the protection of the ear against noise trauma and the effects of age-related hearing loss, its role in the emergence of tinnitus needs further investigation.

Temporal Alterations to Central Auditory Processing without Synaptopathy after Lifetime Exposure to Environmental Noise

People are increasingly exposed to environmental noise through the cumulation of occupational and recreational activities, which is considered harmless to the auditory system, if the sound intensity remains <80 dB. However, recent evidence of noise-induced peripheral synaptic damage and central reorganizations in the auditory cortex, despite normal audiometry results, has cast doubt on the innocuousness of lifetime exposure to environmental noise. We addressed this issue by exposing adult rats to realistic and nontraumatic environmental noise, within the daily permissible noise exposure limit for humans (80 dB sound pressure level, 8 h/day) for between 3 and 18 months. We found that temporary hearing loss could be detected after 6 months of daily exposure, without leading to permanent hearing loss or to missing synaptic ribbons in cochlear hair cells. The degraded temporal representation of sounds in the auditory cortex after 18 months of exposure was very different from the effects observed after only 3 months of exposure, suggesting that modifications to the neural code continue throughout a lifetime of exposure to noise.

Bayesian brain in tinnitus: Computational modeling of three perceptual phenomena using a modified Hierarchical Gaussian Filter

Recently, Bayesian brain-based models emerged as a possible composite of existing theories, providing an universal explanation of tinnitus phenomena. Yet, the involvement of multiple synergistic mechanisms complicates the identification of behavioral and physiological evidence. To overcome this, an empirically tested computational model could support the evaluation of theoretical hypotheses by intrinsically encompassing different mechanisms. The aim of this work was to develop a generative computational tinnitus perception model based on the Bayesian brain concept. The behavioral responses of 46 tinnitus subjects who underwent ten consecutive residual inhibition assessments were used for model fitting. Our model was able to replicate the behavioral responses during residual inhibition in our cohort (median linear correlation coefficient of 0.79). Using the same model, we simulated two additional tinnitus phenomena: residual excitation and occurrence of tinnitus in non-tinnitus subjects after sensory deprivation. In the simulations, the trajectories of the model were consistent with previously obtained behavioral and physiological observations. Our work introduces generative computational modeling to the research field of tinnitus. It has the potential to quantitatively link experimental observations to theoretical hypotheses and to support the search for neural signatures of tinnitus by finding correlates between the latent variables of the model and measured physiological data.

Excitatory Repetitive Transcranial Magnetic Stimulation Over Prefrontal Cortex in a Guinea Pig Model Ameliorates Tinnitus

Tinnitus, a phantom auditory perception that can seriously affect quality of life, is generally triggered by cochlear trauma and associated with aberrant activity throughout the auditory pathways, often referred to as hyperactivity. Studies suggest that non-auditory structures, such as prefrontal cortex (PFC), may be involved in tinnitus generation, by affecting sensory gating in auditory thalamus, allowing hyperactivity to reach the cortex and lead to perception. Indeed, human studies have shown that repetitive transcranial magnetic stimulation (rTMS) of PFC can alleviate tinnitus. The current study investigated whether this therapeutic effect is achieved through inhibition of thalamic hyperactivity, comparing effects of two common clinical rTMS protocols with sham treatment, in a guinea pig tinnitus model. Animals underwent acoustic trauma and once tinnitus developed were treated with either intermittent theta burst stimulation (iTBS), 20 Hz rTMS, or sham rTMS (10 days, 10 min/day; weekdays only). Tinnitus was reassessed and extracellular recordings of spontaneous tonic and burst firing rates in auditory thalamus made. To verify effects in PFC, densities of neurons positive for calcium-binding proteins, calbindin and parvalbumin, were investigated using immunohistochemistry. Both rTMS protocols significantly reduced tinnitus compared to sham. However, spontaneous tonic firing decreased following 20 Hz stimulation and increased following iTBS in auditory thalamus. Burst rate was significantly different between 20 Hz and iTBS stimulation, and burst duration was increased only after 20 Hz treatment. Density of calbindin, but not parvalbumin positive neurons, was significantly increased in the most dorsal region of PFC indicating that rTMS directly affected PFC. Our results support the involvement of PFC in tinnitus modulation, and the therapeutic benefit of rTMS on PFC in treating tinnitus, but indicate this is not achieved solely by suppression of thalamic hyperactivity.

Non-stimulus-evoked activity as a measure of neural noise in the frequency-following response

BACKGROUND

The frequency-following response, or FFR, is a neurophysiologic response that captures distinct aspects of sound processing. Like all evoked responses, FFR is susceptible to electric and myogenic noise contamination during collection. Click-evoked auditory brainstem response collection standards have been adopted for FFR collection, however, whether these standards sufficiently limit FFR noise contamination is unknown. Thus, a critical question remains: to what extent do distinct FFR components reflect noise contamination? This is especially relevant for prestimulus amplitude (i.e., activity preceding the evoked response), as this measure has been used to index both noise contamination and neural noise.

NEW METHOD

We performed two experiments. First, using >1000 young-adult FFRs, we ran regressions to determine the variance explained by myogenic and electrical noise, as indexed by artifact rejection count and electrode impedance, on each FFR component. Second, we reanalyzed prestimulus amplitude differences attributed to athletic experience and socioeconomic status, adding covariates of artifact rejection and impedance.

RESULTS

We found that non-neural noise marginally contributed to FFR components and could not explain group differences on prestimulus amplitude.

COMPARISON WITH EXISTING METHOD

Prestimulus amplitude has been considered a measure of non-neural noise contamination. However, non-neural noise was not the sole contributor to variance in this measure and did not explain group differences.

CONCLUSIONS

Results from the two experiments suggest that the effects of non-neural noise on FFR components are minimal and do not obscure individual differences in the FFR and that prestimulus amplitude indexes neural noise.

Effect of Unilateral Acoustic Trauma on Neuronal Firing Activity in the Inferior Colliculus of Mice

Neural hyperactivity induced by sound exposure often correlates with the development of hyperacusis and/or tinnitus. In laboratory animals, hyperactivity is typically induced by unilateral sound exposure to preserve one ear for further testing of hearing performance. Most ascending fibers in the auditory system cross into the superior olivary complex and then ascend contralaterally. Therefore, unilateral exposure should be expected to mostly affect the contralateral side above the auditory brain stem. On the other hand, it is well known that a significant number of neurons have crossing fibers at every level of the auditory pathway, which may spread the effect of unilateral exposure onto the ipsilateral side. Here we demonstrate that unilateral sound exposure causes development of hyperactivity in both the contra and ipsilateral inferior colliculus in mice. We found that both the spontaneous firing rate and bursting activity were increased significantly compared to unexposed mice. The neurons with characteristic frequencies at or above the center frequency of exposure showed the greatest increase. Surprisingly, this increase was more pronounced in the ipsilateral inferior colliculus. This study highlights the importance of considering both ipsi- and contralateral effects in future studies utilizing unilateral sound exposure.

The thalamus and tinnitus: Bridging the gap between animal data and findings in humans

The neuronal mechanisms underlying tinnitus are yet to be revealed. Tinnitus, an auditory phantom sensation, used to be approached as a purely auditory domain symptom. More recently, the modulatory impact of non-auditory brain regions on the percept and burden of tinnitus are explored. The thalamus is uniquely situated to facilitate the communication between auditory and non-auditory subcortical and cortical structures. Traditionally, animal models of tinnitus have focussed on subcortical auditory structures, and research with human participants has been concerned with cortical activity in auditory and non-auditory areas. Recently, both research fields have investigated the connectivity between subcortical and cortical regions and between auditory and non-auditory areas. We show that even though the different fields employ different methods to investigate the activity and connectivity of brain areas, there is consistency in the results on tinnitus between these different approaches. This consistency between human and animals research is observed for tinnitus with peripherally instigated hearing damage, and for results obtained with salicylate and noise-induced tinnitus. The thalamus integrates input from limbic and prefrontal areas and modulates auditory activity via its connections to both subcortical and cortical auditory areas. Reported altered activity and connectivity of the auditory, prefrontal, and limbic regions suggest a more systemic approach is necessary to understand the origins and impact of tinnitus.

Direct and Transcutaneous Vagus Nerve Stimulation for Treatment of Tinnitus: A Scoping Review

Recent animal research has shown that vagus nerve stimulation (VNS) paired with sound stimuli can induce neural plasticity in the auditory cortex in a controlled manner. VNS paired with tones excluding the tinnitus frequency eliminated physiological and behavioral characteristics of tinnitus in noise-exposed rats. Several clinical trials followed and explored the effectiveness of VNS paired with sound stimuli for alleviating tinnitus in human subjects. Transcutaneous VNS (tVNS) has received increasing attention as a non-invasive alternative approach to tinnitus treatment. Several studies have also explored tVNS alone (not paired with sound stimuli) as a potential therapy for tinnitus. In this review, we discuss existing knowledge about direct and tVNS in terms of applicability, safety, and effectiveness in diminishing tinnitus symptoms in human subjects. This review includes all existing clinical and neuroimaging studies of tVNS alone or paired with acoustic stimulation in tinnitus patients and outlines the present limitations that must be overcome to maximize the potential of (t)VNS as a therapy for tinnitus.

Low Thyroid-stimulating Hormone Levels Are Associated With Annoying Tinnitus in Adult Women: Korea National Health and Nutrition Examination Surveys

OBJECTIVE

This study aimed to investigate the relationship between thyroid function and tinnitus.

STUDY DESIGN

A cross-sectional study.

SETTING

The Korean National Health and Nutrition Examination Survey from 2013 was used.

PATIENTS AND INTERVENTIONS

A total of 1,165 participants ≥ 40 years old who were surveyed for the presence of tinnitus and underwent thyroid function tests were included. The presence of discomfort from tinnitus was defined as annoying tinnitus. The control group included participants with "no tinnitus" or "no discomfort from tinnitus." The participants were divided into the annoying tinnitus group and the control group.

MAIN OUTCOME MEASURES

The associations of free thyroxine and thyroid-stimulating hormone (TSH) with annoying tinnitus were analyzed using logistic regression with complex sampling methods. Subgroup analyses were performed according to sex.

RESULTS

The low TSH level group had 2.35-fold greater odds of annoying tinnitus than the control group (95% confidence interval  = 1.10-5.12, p = 0.027). Even in patients with a normal free thyroxine level, a low TSH level was related to 2.78-fold higher odds of annoying tinnitus (95% confidence interval  = 1.21-6.38, p = 0.016). In subgroup analyses, this association was apparent in the female subgroup. The male subgroup did not show a relationship between low TSH levels and annoying tinnitus.

CONCLUSIONS

Subclinical hyperthyroidism was related to an increased risk of annoying tinnitus. This relationship was apparent in the female subgroup.