Tinnitus: Models and mechanisms

The efficacy of transcranial random noise stimulation in treating tinnitus: a systematic review

PURPOSE

This review aims to examine the effects of transcranial random noise stimulation (tRNS) on tinnitus and to determine the optimal treatment parameters, if possible.

METHODS

A comprehensive search, including MEDLINE, PubMed, EMBASE, CINAHL, SCOPUS, and PEDro, was conducted to determine experiments studying the effects of tRNS on tinnitus from inception to March 1, 2024. The Physiotherapy Evidence Database (PEDro) scale was used to evaluate the quality of the included studies.

RESULTS

Seven studies met the eligibility criteria. A total of 616 patients with non-pulsatile tinnitus (mean age 50.93 years; 66% males) were included in this review. The included studies ranged from 3 to 8 out of 10 (median = 7) on the PEDro scale. The results showed that tRNS is an effective intervention in reducing tinnitus symptoms.

CONCLUSIONS

The evidence for the effects of tRNS on people with chronic non-pulsatile tinnitus is promising. Administering tRNS with an intensity of 1-2 mA, high-frequency (101-650 Hz), using a 35 cm² electrode size over the auditory cortex and DLPFC, for 20 min with eight sessions may demonstrate the desired tRNS effects. The tRNS stimulation should be contralateral for unilateral tinnitus and bilaterally for bilateral tinnitus. Combining tRNS with other concurrent interventions may show superior effects in reducing tinnitus compared to tRNS alone. Further high-quality studies with larger sample sizes are strongly needed.

Abnormal static and dynamic brain network connectivity associated with chronic tinnitus

In order to comprehensively understand the changes of brain networks in patients with chronic tinnitus, this study combined static and dynamic analysis methods to explore the abnormalities of brain networks. Thirty-two patients with chronic tinnitus and 30 age-, sex- and education-matched healthy controls (HC) were recruited. Independent component analysis was used to identify resting-state networks (RSNs). Static and dynamic functional network connectivity (FNC) were performed. The temporal properties of brain network including mean dwell time (MDT), fraction time (FT) and numbers of transitions (NT) were calculated. Two-sample t test and Spearman's correlation were used for group compares and correlation analysis. Four RSNs showed abnormal FNC including auditory network (AUN), default mode network (DMN), attention network (AN) and sensorimotor network (SMN). For static analysis, tinnitus patients showed significantly decreased FNC in AUN-DMN, AUN-AN, DMN-AN, and DMN-SMN than HC [p < 0.05, false discovery rate (FDR) corrected]. For dynamic analysis, tinnitus patients showed significantly decreased FNC in DMN-AN in state 3 (p < 0.05, FDR corrected). MDT in state 3 was significantly decreased in tinnitus patients (t = 2.039, P = 0.046). In the tinnitus group, the score of tinnitus functional index (TFI) was negatively correlated with MDT and FT in state 4, and the duration of tinnitus was positively correlated with FT in state 1 and NT. Chronic tinnitus causes abnormal brain network connectivity. These abnormal brain networks help to clarify the mechanism of tinnitus generation and chronicity, and provide a potential basis for the treatment of tinnitus.

Exploring the interplay of depression, sleep quality, and hearing in tinnitus-related handicap: insights from polysomnography and pure-tone audiometry

BACKGROUND

Tinnitus affects approximately 740 million adults globally, involving hearing, emotion, and sleep systems. However, studies using polysomnography and pure-tone audiometry (PTA) are limited. We aimed to assess the correlation between tinnitus and hearing, sleep quality, characteristics, and depression using polysomnography and PTA.

METHODS

In this cross-sectional study, we divided participants into tinnitus and non-tinnitus groups. We included 100 outpatients (65 with tinnitus, 35 without) from a medical center in Taiwan, who underwent polysomnography and completed rating scales including the Patient Health Questionnaire-9 (PHQ-9), Chinese version of the Pittsburgh Sleep Quality Index (PSQI), and Chinese-Mandarin version of the Tinnitus Handicap Inventory (THI-CM). We analyzed correlations, conducted group comparisons, assessed factors related to THI-CM scores, constructed ROC curves to predict depression in the tinnitus group, and performed multinomial and logistic regression to explore associations.

RESULTS

Descriptive statistics identified a cohort with mean age 53.9 ± 12.80 years, 63% exhibited PHQ-9 scores ≥ 10, and 66% had Apnea-Hypopnea Index (AHI) > 5. The ratio of rapid eye movement and deep sleep to stage 1 + 2 sleep was relatively low and non-significant. Likewise, leg movements was higher in the tinnitus group but not statistically significant. In the tinnitus group, 63.08% had depression, and 81.54% had AHI > 5. Univariate logistic regression linked tinnitus to AHI > 5 (Odds ratio (OR) 2.67, p = 0.026) and male sex (OR 2.49, p = 0.034). A moderate positive correlation was found between the THI-CM score and PHQ-9 score (rs = 0.50, p < 0.001). Further adjustment for obstructive sleep apnea showed associations between PHQ-9 (total score) or depression and THI-CM Grade 3-5 (OR = 1.28; OR = 8.68). Single- and multifactor regression analyses highlighted significant associations of PSQI scores > 13 (OR 7.06, p = 0.018) and THI-CM scores > 47 (OR 7.43, p = 0.002) with depression.

CONCLUSIONS

Our study recruited tinnitus participants with slight or mild hearing loss and mild tinnitus handicap. Depression was identified as a predominant factor in tinnitus-related handicap. The mild tinnitus handicap in tinnitus participants may explain the lack of significant differences in depression, sleep quality, and polysomnographic sleep characteristics between tinnitus and non-tinnitus groups. Further extensive and prospective studies are needed to elucidate the complex links among depression, sleep, and tinnitus.

Glycine is a transmitter in the human and chimpanzee cochlear nuclei

Introduction

Auditory information is relayed from the cochlea via the eighth cranial nerve to the dorsal and ventral cochlear nuclei (DCN, VCN). The organization, neurochemistry and circuitry of the cochlear nuclei (CN) have been studied in many species. It is well-established that glycine is an inhibitory transmitter in the CN of rodents and cats, with glycinergic cells in the DCN and VCN. There are, however, major differences in the laminar and cellular organization of the DCN between humans (and other primates) and rodents and cats. We therefore asked whether there might also be differences in glycinergic neurotransmission in the CN.

Methods

We studied brainstem sections from humans, chimpanzees, and cats. We used antibodies to glycine receptors (GLYR) to identify neurons receiving glycinergic input, and antibodies to the neuronal glycine transporter (GLYT2) to immunolabel glycinergic axons and terminals. We also examined archival sections immunostained for calretinin (CR) and nonphosphorylated neurofilament protein (NPNFP) to try to locate the octopus cell area (OCA), a region in the VCN that rodents has minimal glycinergic input.

Results

In humans and chimpanzees we found widespread immunolabel for glycine receptors in DCN and in the posterior (PVCN) and anterior (AVCN) divisions of the VCN. We found a parallel distribution of GLYT2-immunolabeled fibers and puncta. The data also suggest that, as in rodents, a region containing octopus cells in cats, humans and chimpanzees has little glycinergic input.

Discussion

Our results show that glycine is a major transmitter in the human and chimpanzee CN, despite the species differences in DCN organization. The sources of the glycinergic input to the CN in humans and chimpanzees are not known.

Eavesdropping on Tinnitus Using MEG: Lessons Learned and Future Perspectives

Tinnitus has been widely investigated in order to draw conclusions about the underlying causes and altered neural activity in various brain regions. Existing studies have based their work on different tinnitus frameworks, ranging from a more local perspective on the auditory cortex to the inclusion of broader networks and various approaches towards tinnitus perception and distress. Magnetoencephalography (MEG) provides a powerful tool for efficiently investigating tinnitus and aberrant neural activity both spatially and temporally. However, results are inconclusive, and studies are rarely mapped to theoretical frameworks. The purpose of this review was to firstly introduce MEG to interested researchers and secondly provide a synopsis of the current state. We divided recent tinnitus research in MEG into study designs using resting state measurements and studies implementing tone stimulation paradigms. The studies were categorized based on their theoretical foundation, and we outlined shortcomings as well as inconsistencies within the different approaches. Finally, we provided future perspectives on how to benefit more efficiently from the enormous potential of MEG. We suggested novel approaches from a theoretical, conceptual, and methodological point of view to allow future research to obtain a more comprehensive understanding of tinnitus and its underlying processes.

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.

The Effect of Tinnitus and Related Characteristics on Subcortical Auditory Processing

OBJECTIVES

The primary aim of this study was to evaluate whether individuals with tinnitus exhibited evidence of reduced inhibition and increased excitation at the subcortical auditory processing level. Based on the proposed mechanism of tinnitus generation, including peripheral auditory insult that triggers reduced inhibition and subcortical hyperactivity, it was hypothesized that a tinnitus group would yield reduced amplitudes for the most peripheral auditory brainstem response (ABR) component (wave I) and larger amplitudes for the most central ABR component (wave V) relative to controls matched on factors of age, sex, and hearing loss. Further, this study assessed the relative influence of tinnitus presence versus other related individual characteristics, including hearing loss, age, noise exposure history, and speech perception in noise on these ABR outcomes.

DESIGN

Subcortical processing was examined using click-evoked ABR in an independent groups experimental design. A group of adults who perceived daily unilateral or bilateral tinnitus were matched with a control group counterpart without tinnitus by age, hearing, and sex (in each group n = 18; 10 females, 8 males). Amplitudes for ABR waves I, III, V, and the V/I ratio were compared between groups by independent t-tests. The relative influence of tinnitus (presence/absence), age (in years), noise exposure history (subjective self-report), hearing loss (audiometric thresholds), and speech perception in noise (SNR-50) was determined based on the proportional reduction in error associated with accounting for each variable of interest using multiple regression.

RESULTS

Between-group trends were consistent with smaller amplitudes for all ABR components in individuals with tinnitus. Contrary to our hypotheses, however, none of the tinnitus compared with control group differences in ABR outcomes were statistically significant. In the multiple regression models, none of the factors including tinnitus presence, age, noise exposure history, hearing loss, and speech perception in noise significantly predicted ABR V/I ratio outcomes.

CONCLUSIONS

The presence of reduced inhibition and subcortical hyperactivity in the tinnitus group was not supported in the current study. There were trends in ABR outcomes consistent with reduced peripheral to central brainstem auditory activity in the tinnitus group, but none of the group differences reached significance. It should also be noted that the tinnitus group had poorer extended high-frequency thresholds compared with controls. Regardless, neither tinnitus presence nor any of the proposed related characteristics were found to significantly influence the ABR V/I ratio. These findings suggest that either reduced subcortical inhibition was not a primary underlying mechanism for the tinnitus perceived by these subjects, or that ABR was not a reliable indicator of reduced subcortical inhibition possibly due to characteristics of the sample including a skewed distributions toward young and normal hearing individuals with little tinnitus distress.

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.

Speech Perception in Ménière Disease

Introduction  Ménière disease (MD) affects the inner ear, comprising the cochlea and semicircular canals. Symptoms include severe incapacitating vertigo, nausea, vomit, aural fullness, and sensorineural hearing loss - in which speech discrimination and intelligibility are impaired and can be quantified with speech audiometry. Objective  To investigate the influence of the stimuli presentation level in speech audiometry and the quality of life in adults with and without a diagnosis of MD. Method  Two groups were formed with nine individuals each - one with and the other without MD. The Speech Recognition Percentage Index was researched with stimuli presented above the self-reported comfort level or 5 dB below the discomfort level. Dizziness Handicap and Tinnitus Handicap Inventories were administered to individuals with tinnitus and vertigo complaints. Results  Speech recognition was better in the study group with higher presentation levels, as 75% of the sample improved their performance. The presence of vertigo significantly impacted the quality of life of individuals in the study group. Conclusion  Speech recognition improves with higher presentation levels. Also, MD impacts the quality of life, especially regarding limitations caused by vertigo.

[Functional neuroimaging options for tinnitus]

BACKGROUND

The pathophysiology behind tinnitus is still not well understood. Different imaging methods help in the understanding of the complex relationships that lead to the perception of tinnitus.

OBJECTIVE

Herein, different functional imaging methods that can be used in the study of tinnitus are presented.

MATERIALS AND METHODS

Considering the recent literature on the subject, the relevant imaging methods used in tinnitus research are discussed.

RESULTS AND CONCLUSION

Functional imaging can reveal correlates of tinnitus. Due to the still limited temporal and spatial resolution of current imaging modalities, a conclusive explanation of tinnitus remains elusive. With increasing use of functional imaging, additional important insights into the explanation of tinnitus will be gained in the future.

Auditory cortex hyperconnectivity before rTMS is correlated with tinnitus improvement

INTRODUCTION

Repetitive transcranial magnetic stimulation (rTMS) has been used as a potential treatment for tinnitus; however, its effectiveness is variable and unpredictable. We hypothesized that resting-state functional connectivity before rTMS may be correlated with rTMS treatment effectiveness.

METHODS

We applied 1-Hz rTMS to the left primary auditory (A1) and dorsolateral prefrontal cortices (DLPFC) of 10 individuals with tinnitus and 10 age-matched controls. Resting-state functional magnetic resonance imaging (fMRI) studies were performed approximately one week before rTMS. Seed-based connectivity analyses were conducted for each individual, with seed regions as rTMS target areas.

RESULTS

Compared to controls, the left superior temporal areas showed significantly increased positive connectivity with the left A1 and negative connectivity with the left DLPFC in the tinnitus group. The left frontoparietal and right cerebellar areas showed significantly increased negative connectivity with the left A1 and positive connectivity with the left DLPFC. Seed-based hyperconnectivity was correlated with tinnitus improvement (pre-rTMS vs. 2-week post-rTMS Tinnitus Handicap Inventory scores). Tinnitus improvement was significantly correlated with left A1 hyperconnectivity; however, no correlation was observed with left DLPFC connectivity. Positive rTMS outcomes were associated with significantly increased positive connectivity in bilateral superior temporal areas and significantly increased negative connectivity in bilateral frontal areas.

CONCLUSIONS

Our results suggest that oversynchronisation of left A1 connectivity before rTMS of the left A1 and DLPFC is associated with treatment effectiveness.

Increased pyramidal and VIP neuronal excitability in rat primary auditory cortex directly correlates with tinnitus behaviour

Tinnitus affects roughly 15%-20% of the population while severely impacting 10% of those afflicted. Tinnitus pathology is multifactorial, generally initiated by damage to the auditory periphery, resulting in a cascade of maladaptive plastic changes at multiple levels of the central auditory neuraxis as well as limbic and non-auditory cortical centres. Using a well-established condition-suppression model of tinnitus, we measured tinnitus-related changes in the microcircuits of excitatory/inhibitory neurons onto layer 5 pyramidal neurons (PNs), as well as changes in the excitability of vasoactive intestinal peptide (VIP) neurons in primary auditory cortex (A1). Patch-clamp recordings from PNs in A1 slices showed tinnitus-related increases in spontaneous excitatory postsynaptic currents (sEPSCs) and decreases in spontaneous inhibitory postsynaptic currents (sIPSCs). Both measures could be correlated to the rat's behavioural evidence of tinnitus. Tinnitus-related changes in PN excitability were independent of changes in A1 excitatory or inhibitory cell numbers. VIP neurons, part of an A1 local circuit that can control the excitation of layer 5 PNs via disinhibitory mechanisms, showed significant tinnitus-related increases in excitability that directly correlated with the rat's behavioural tinnitus score. That PN and VIP changes directly correlated to tinnitus behaviour suggests an important role in A1 tinnitus pathology. Tinnitus-related A1 changes were similar to findings in studies of neuropathic pain in somatosensory cortex suggesting a common pathology of these troublesome perceptual impairments. Improved understanding between excitatory, inhibitory and disinhibitory sensory cortical circuits can serve as a model for testing therapeutic approaches to the treatment of tinnitus and chronic pain. KEY POINTS: We identified tinnitus-related changes in synaptic function of specific neuronal subtypes in a reliable animal model of tinnitus. The findings show direct and indirect tinnitus-related losses of normal inhibitory function at A1 layer 5 pyramidal cells, and increased VIP excitability. The findings are similar to what has been shown for neuropathic pain suggesting that restoring normal inhibitory function at synaptic inputs onto A1 pyramidal neurons (PNs) could conceptually reduce tinnitus discomfort.

Comparative analysis of acoustic therapies for tinnitus treatment based on auditory event-related potentials

Introduction

So far, Auditory Event-Related Potential (AERP) features have been used to characterize neural activity of patients with tinnitus. However, these EEG patterns could be used to evaluate tinnitus evolution as well. The aim of the present study is to propose a methodology based on AERPs to evaluate the effectiveness of four acoustic therapies for tinnitus treatment.

Methods

The acoustic therapies were: (1) Tinnitus Retraining Therapy (TRT), (2) Auditory Discrimination Therapy (ADT), (3) Therapy for Enriched Acoustic Environment (TEAE), and (4) Binaural Beats Therapy (BBT). In addition, relaxing music was included as a placebo for both: tinnitus sufferers and healthy individuals. To meet this aim, 103 participants were recruited, 53% were females and 47% were males. All the participants were treated for 8 weeks with one of these five sounds, which were moreover tuned in accordance with the acoustic features of their tinnitus (if applied) and hearing loss. They were electroencephalographically monitored before and after their acoustic therapy, and wherefrom AERPs were estimated. The sound effect of acoustic therapies was evaluated by examining the area under the curve of those AERPs. Two parameters were obtained: (1) amplitude and (2) topographical distribution.

Results

The findings of the investigation showed that after an 8-week treatment, TRT and ADT, respectively achieved significant neurophysiological changes over somatosensory and occipital regions. On one hand, TRT increased the tinnitus perception. On the other hand, ADT redirected the tinnitus attention, what in turn diminished the tinnitus perception. Tinnitus handicapped inventory outcomes verified these neurophysiological findings, revealing that 31% of patients in each group reported that TRT increased tinnitus perception, but ADT diminished it.

Discussion

Tinnitus has been identified as a multifactorial condition highly associated with hearing loss, age, sex, marital status, education, and even, employment. However, no conclusive evidence has been found yet. In this study, a significant (but low) correlation was found between tinnitus intensity and right ear hearing loss, left ear hearing loss, heart rate, area under the curve of AERPs, and acoustic therapy. This study raises the possibility to assign acoustic therapies by neurophysiological response of patient.

Onset-offset cortical auditory evoked potential amplitude differences indicate auditory cortical hyperactivity and reduced inhibition in people with tinnitus

OBJECTIVE

The current study investigates evidence of hypothesized reduced central inhibition and/or increased excitation in individuals with tinnitus by evaluating cortical auditory onset versus offset responses.

METHODS

Cortical auditory evoked potentials (CAEPs) were recorded to the onset and offset of 3-second white noise stimuli in tinnitus and control groups matched in pairs by age, hearing, and sex (n = 26 total). Independent t-tests and 2-way mixed model ANOVA were used to evaluate onset-offset differences in amplitude, area, and latency of CAEP components by group. The predictive influence of tinnitus presence and associated participant characteristics on CAEP outcomes was assessed by multiple regression proportional reduction in error.

RESULTS

The tinnitus group had significantly larger onset minus offset P2 amplitudes (ΔP2 amplitudes) than control group participants. No other component variables differed significantly. ΔP2 amplitude was best predicted by tinnitus status and not significantly influenced by other variables such as hearing loss or age.

CONCLUSIONS

Hypothesized reduced central inhibition and/or increased excitation in tinnitus participants was partially supported by a group difference in ΔP2 amplitude.

SIGNIFICANCE

This was the first study to evaluate CAEP onset minus offset differences to investigate changes in central excitation/inhibition in individuals with tinnitus versus controls in matched groups.

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.

The association between stress, emotional states, and tinnitus: a mini-review

Extensive literature supporting the view of tinnitus induced stress in patients is available. However, limited evidence has been produced studying the opposite, that is, does stress cause tinnitus? The hypothalamus pituitary adrenal axis, one of the main neuroendocrine systems involved in stress response, is commonly disturbed in tinnitus patients. Patients with chronic tinnitus have been shown to develop abnormal responses to psycho-social stress, where the hypothalamus pituitary adrenal axis response is weaker and delayed, suggesting chronic stress contributes to the development of chronic tinnitus. The sympathetic branch of the autonomic nervous system also plays a major role in stress response and its chronic hyperactivity seems to be involved in developing tinnitus. Psycho-social stress has been shown to share the same probability of developing tinnitus as occupational noise and contributes to worsening tinnitus. Additionally, exposure to high stress levels and occupational noise doubles the likelihood of developing tinnitus. Interestingly, short-term stress has been shown to protect the cochlea in animals, but chronic stress exposure has negative consequences. Emotional stress also worsens pre-existing tinnitus and is identified as an important indicator of tinnitus severity. Although there is limited body of literature, stress does seem to play a vital role in the development of tinnitus. This review aims to highlight the association between stress, emotional states, and the development of tinnitus while also addressing the neural and hormonal pathways involved.

Tinnitus characteristics in patients with hyperacusis and vertigo (including Ménière's disease) vs. hyperacusis alone

INTRODUCTION AND OBJECTIVES

To compare clinical and psychoacoustic tinnitus characteristics in patients with the comorbidity of hyperacusis, hyperacusis and vertigo, and with Ménière's disease (MD).

MATERIALS AND METHODS

Three hundred and twenty-nine tinnitus patients underwent audiological and otoneurological evaluation. Records of 94 individuals younger than 65 years, 40 women and 54 men (mean age 41.8, range 24-64 years), who complained of tinnitus and hyperacusis, were analyzed. One hundred and thirty-one ears with tinnitus were identified: 67 in the group of patients with tinnitus and hyperacusis (group 1; 41 patients); 28 in the group fulfilling criteria of MD diagnosis (group 2; 28); and 36 in the group with tinnitus, hyperacusis and typical symptoms of vertigo (group 3; 25).

RESULTS AND CONCLUSIONS

Mean value of interaural difference in canal paresis in group 1 was 6.3%; in group 2: 23.7%; and in group 3: 25.9%; p<.001. Mean tinnitus pitch value was significantly lower in group 3 (1679Hz; SD=1139) and group 2 (2250Hz; SD=1162) compared to group 1 (4538Hz; SD=3123; p=.012). Values of tinnitus intensity and other characteristics did not significantly differ between the groups. Tinnitus and hyperacusis were most frequently preceded by acoustic trauma. Tinnitus coinciding with hyperacusis and vertigo was observed in patients after head trauma. Mean tinnitus pitch was lower in the groups of patients with hyperacusis and peripheral labyrinthine lesion than in tinnitus sufferers with hyperacusis alone. Tinnitus sufferers with low tinnitus pitch should undergo vestibular system evaluation. Hyperacusis and vertigo are likely comorbidities in tinnitus patients after head trauma. Hyperacusis may coincide in tinnitus patients after head trauma.

Comparison of two behavioral tests for tinnitus assessment in mice

Animal research focused on chronic tinnitus associated with noise-induced hearing loss can be expensive and time-consuming as a result of the behavioral training required. Although there exist a number of behavioral tests for tinnitus; there have been few formal direct comparisons of these tests. Here, we evaluated animals in two different tinnitus assessment methods. CBA/CaJ mice were trained in an operant conditioning, active avoidance (AA) test, and a reflexive, gap-induced pre-pulse inhibition of acoustic startle (GPIAS) test, or both. Tinnitus was induced in awake mice by unilateral continuous sound exposure using a 2-kHz- or 12 octave-wide noise centered at 16 kHz and presented at 113- or 116-dB SPL. Tinnitus was assessed 8 weeks after sound overexposure. Most mice had evidence of tinnitus behavior in at least one of the two behaviors. Of the mice evaluated in AA, over half (55%) had tinnitus positive behavior. In GPIAS, fewer animals (13%) were positive than were identified using the AA test. Few mice were positive in both tests (10%), and only one was positive for tinnitus behavior at the same spectral frequency in both tests. When the association between tinnitus behavior and spontaneous activity recorded in the inferior colliculus was compared, animals with tinnitus behavior in AA exhibited increased spontaneous activity, while those positive in GPIAS did not. Thus, it appears that operant conditioning tests, like AA, maybe more reliable and accurate tests for tinnitus than reflexive tests.

Topographic and widespread auditory modulation of the somatosensory cortex: potential for bimodal sound and body stimulation for pain treatment

OBJECTIVE

There has been growing interest in understanding multisensory integration in the cortex through activation of multiple sensory and motor pathways to treat brain disorders, such as tinnitus or essential tremors. For tinnitus, previous studies show that combined sound and body stimulation can modulate the auditory pathway and lead to significant improvements in tinnitus symptoms. Considering that tinnitus is a type of chronic auditory pain, bimodal stimulation could potentially alter activity in the somatosensory pathway relevant for treating chronic pain. As an initial step towards that goal, we mapped and characterized neuromodulation effects in the somatosensory cortex (SC) in response to sound and/or electrical stimulation of the body.

APPROACH

We first mapped the topographic organization of activity across the SC of ketamine-anesthetized guinea pigs through electrical stimulation of different body locations using subcutaneous needle electrodes or with broadband acoustic stimulation. We then characterized how neural activity in different parts of the SC could be facilitated or suppressed with bimodal stimulation.

MAIN RESULTS

The topography in the SC of guinea pigs in response to electrical stimulation of the body aligns consistently to that shown in previous rodent studies. Interestingly, auditory broadband noise stimulation primarily excited SC areas that typically respond to stimulation of lower body locations. Although there was only a small subset of SC locations that were excited by acoustic stimulation alone, all SC recording sites could be altered (facilitated or suppressed) with bimodal stimulation. Furthermore, specific regions of the SC could be modulated by stimulating an appropriate body region combined with broadband noise.

SIGNIFICANCE

These findings show that bimodal stimulation can excite or modulate firing across a widespread yet targeted population of SC neurons. This approach may provide a non-invasive method for altering or disrupting abnormal firing patterns within certain parts of the SC for chronic pain treatment.

Lower glutamate and GABA levels in auditory cortex of tinnitus patients: a 2D-JPRESS MR spectroscopy study

We performed magnetic resonance spectroscopy (MRS) on healthy individuals with tinnitus and no hearing loss (n = 16) vs. a matched control group (n = 17) to further elucidate the role of excitatory and inhibitory neurotransmitters in tinnitus. Two-dimensional J-resolved spectroscopy (2D-JPRESS) was applied to disentangle Glutamate (Glu) from Glutamine and to estimate GABA levels in two bilateral voxels in the primary auditory cortex. Results indicated a lower Glu concentration (large effect) in right auditory cortex and lower GABA concentration (medium effect) in the left auditory cortex of the tinnitus group. Within the tinnitus group, Glu levels positively correlated with tinnitus loudness measures. While the GABA difference between groups is in line with former findings and theories about a dysfunctional auditory inhibition system in tinnitus, the novel finding of reduced Glu levels came as a surprise and is discussed in the context of a putative framework of inhibitory mechanisms related to Glu throughout the auditory pathway. Longitudinal or interventional studies could shed more light on interactions and causality of Glu and GABA in tinnitus neurochemistry.

Aberrant Resting-State Functional Connectivity of the Dorsal Attention Network in Tinnitus

Previous functional magnetic resonance imaging (fMRI) analyses have shown that the dorsal attention network (DAN) is involved in the pathophysiological changes of tinnitus, but few relevant studies have been conducted, and the conclusions to date are not uniform. The purpose of this research was to test whether there is a change in intrinsic functional connectivity (FC) patterns between the DAN and other brain regions in tinnitus patients. Thirty-one patients with persistent tinnitus and thirty-three healthy controls were enrolled in this study. A group independent component analysis (ICA), degree centrality (DC) analysis, and seed-based FC analysis were conducted. In the group ICA, the tinnitus patients showed increased connectivity in the left superior parietal gyrus in the DAN compared to the healthy controls. Compared with the healthy controls, the tinnitus patients showed increased DC in the left inferior parietal gyrus and decreased DC in the left precuneus within the DAN. The clusters within the DAN with significant differences in the ICA or DC analysis between the tinnitus patients and the healthy controls were selected as regions of interest (ROIs) for seeds. The tinnitus patients exhibited significantly increased FC from the left superior parietal gyrus to several brain regions, including the left inferior parietal gyrus, the left superior marginal gyrus, and the right superior frontal gyrus, and decreased FC to the right anterior cingulate cortex. The tinnitus patients exhibited decreased FC from the left precuneus to the left inferior occipital gyrus, left calcarine cortex, and left superior frontal gyrus compared with the healthy controls. The findings of this study show that compared with healthy controls, tinnitus patients have altered functional connections not only within the DAN but also between the DAN and other brain regions. These results suggest that it may be possible to improve the disturbance and influence of tinnitus by regulating the DAN.

Potential inflammatory biomarkers for tinnitus in platelets and leukocytes: a critical scoping review and meta-analysis

OBJECTIVE

To explore the association between platelets or leukocytes and tinnitus.

DESIGN

A meta-analysis and scoping review examining the association between tinnitus and platelets and leukocytes. All 11 studies included were critically appraised using the Joanna Briggs Institute (JBI) checklist (2017a). A random effects model was used to pool the results of the studies examining mean platelet volume (MPV) and tinnitus.

STUDY SAMPLE

1935 studies were identified in the initial search, 11 of which were included in the scoping review. 6 of the 11 studies had their MPV values pooled in the meta-analysis.

RESULTS

Pooled results of 818 subjects from 6 studies indicated that MPV was significantly higher in those with tinnitus compared to a comparison group without tinnitus. The overall mean difference was 0.43 fL with a 95% confidence interval (CI) from 0.31 to 0.55 and a p value of < 0.0001 which was statistically significant. MPV is the only haematological parameter which is reliably associated with tinnitus.

CONCLUSIONS

MPV could be a useful biomarker for tinnitus. Further studies should aim to standardise methodology with more rigorous exclusion criteria to reproduce and define this association. NLR, PLR, WBC count, RDW and PDW do not show a reliable association with tinnitus.

Strain Comparison in Rats Differentiates Strain-Specific from More General Correlates of Noise-Induced Hearing Loss and Tinnitus

Experiments in rodent animal models help to reveal the characteristics and underlying mechanisms of pathologies related to hearing loss such as tinnitus or hyperacusis. However, a reliable understanding is still lacking. Here, four different rat strains (Sprague Dawley, Wistar, Long Evans, and Lister Hooded) underwent comparative analysis of electrophysiological (auditory brainstem responses, ABRs) and behavioral measures after noise trauma induction to differentiate between strain-dependent trauma effects and more consistent changes across strains, such as frequency dependence or systematic temporal changes. Several hearing- and trauma-related characteristics were clearly strain-dependent. Lister Hooded rats had especially high hearing thresholds and were unable to detect a silent gap in continuous background noise but displayed the highest startle amplitudes. After noise exposure, ABR thresholds revealed a strain-dependent pattern of recovery. ABR waveforms varied in detail among rat strains, and the difference was most prominent at later peaks arising approximately 3.7 ms after stimulus onset. However, changes in ABR waveforms after trauma were small compared to consistent strain-dependent differences between individual waveform components. At the behavioral level, startle-based gap-prepulse inhibition (gap-PPI) was used to evaluate the occurrence and characteristics of tinnitus after noise exposure. A loss of gap-PPI was found in 33% of Wistar, 50% of Sprague Dawley, and 75% of Long Evans rats. Across strains, the most consistent characteristic was a frequency-specific pattern of the loss of gap-PPI, with the highest rates at approximately one octave above trauma. An additional range exhibiting loss of gap-PPI directly below trauma frequency was revealed in Sprague Dawley and Long Evans rats. Further research should focus on these frequency ranges when investigating the underlying mechanisms of tinnitus induction.

Understanding Factors That Cause Tinnitus: A Mendelian Randomization Study in the UK Biobank

OBJECTIVES

To investigate the causal role of established risk factors and associated conditions to tinnitus and tinnitus severity in the UK Biobank.

DESIGN

The prospective cohort study with large dataset of >500,000 individuals. The analytical sample of 129,731 individuals in the UK Biobank of European descent. Participants were recruited from National Health Service registries, baseline age range between 37 and 73 years, response rate to baseline survey 6%. Participants were asked subjective questions about tinnitus and its severity. Previously observed associations (n = 23) were confirmed in the UK Biobank using logistic and ordinal regression models. Two-sample Mendelian randomization approaches were then used to test causal relationships between the 23 predictors and tinnitus and tinnitus severity. The main outcome measures were observational and genetic association between key demographics and determinants and two tinnitus outcomes (current tinnitus and tinnitus severity).

RESULTS

Prevalence of tinnitus was 20% and severe tinnitus 3.8%. The observational results are consistent with the previous literature, with hearing loss, older age, male gender, high BMI, higher deprivation, higher blood pressure, smoking history, as well as numerous comorbidities being associated with higher odds of current tinnitus. Mendelian randomization results showed causal correlations with tinnitus. Current tinnitus was predicted by genetically instrumented hearing loss (odds ratio [OR]: 8.65 [95% confidence interval (CI): 6.12 to 12.23]), major depression (OR: 1.26 [95% CI: 1.06 to 1.50]), neuroticism (OR: 1.48 [95% CI: 1.28 to 1.71]), and higher systolic blood pressure (OR: 1.01 [95% CI:1.00 to 1.02]). Lower odds of tinnitus were associated with longer duration in education (OR: 0.74 [95% CI: 0.63 to 0.88]), higher caffeine intake (OR: 0.89 [95% CI: 0.83 to 0.95]) and being a morning person (OR: 0.94 [95% CI: 0.90 to 0.98]). Tinnitus severity was predicted by a higher genetic liability to neuroticism (OR: 1.15 [95% CI: 1.06 to 1.26]) and schizophrenia (OR: 1.02 [95% CI: 1.00 to 1.04]).

CONCLUSIONS

Tinnitus data from the UK Biobank confirm established associated factors in the literature. Genetic analysis determined causal relationships with several factors that expand the understanding of the etiology of tinnitus and can direct future pathways of clinical care and research.

Age-related central gain compensation for reduced auditory nerve output for people with normal audiograms, with and without tinnitus

Central gain compensation for reduced auditory nerve output has been hypothesized as a mechanism for tinnitus with a normal audiogram. Here, we investigate if gain compensation occurs with aging. For 94 people (aged 12-68 years, 64 women, 7 tinnitus) with normal or close-to-normal audiograms, the amplitude of wave I of the auditory brainstem response decreased with increasing age but was not correlated with wave V amplitude after accounting for age-related subclinical hearing loss and cochlear damage, a result indicative of age-related gain compensation. The correlations between age and wave I/III or III/V amplitude ratios suggested that compensation occurs at the wave III generator site. For each one of the seven participants with non-pulsatile tinnitus, the amplitude of wave I, wave V, and the wave I/V amplitude ratio were well within the confidence limits of the non-tinnitus participants. We conclude that increased central gain occurs with aging and is not specific to tinnitus.

Behavioral Outcomes and Neural Network Modeling of a Novel, Putative, Recategorization Sound Therapy

The mechanisms underlying sound's effect on tinnitus perception are unclear. Tinnitus activity appears to conflict with perceptual expectations of "real" sound, resulting in it being a salient signal. Attention diverted towards tinnitus during the later stages of object processing potentially disrupts high-order auditory streaming, and its uncertain nature results in negative psychological responses. This study investigated the benefits and neurophysiological basis of passive perceptual training and informational counseling to recategorize phantom perception as a more real auditory object. Specifically, it examined underlying psychoacoustic correlates of tinnitus and the neural activities associated with tinnitus auditory streaming and how malleable these are to change with targeted intervention. Eighteen participants (8 females, 10 males, mean age = 61.6 years) completed the study. The study consisted of 2 parts: (1) An acute exposure over 30 min to a sound that matched the person's tinnitus (Tinnitus Avatar) that was cross-faded to a selected nature sound (Cicadas, Fan, Water Sound/Rain, Birds, Water and Bird). (2) A chronic exposure for 3 months to the same "morphed" sound. A brain-inspired spiking neural network (SNN) architecture was used to model and compare differences between electroencephalography (EEG) patterns recorded prior to morphing sound presentation, during, after (3-month), and post-follow-up. Results showed that the tinnitus avatar generated was a good match to an individual's tinnitus as rated on likeness scales and was not rated as unpleasant. The five environmental sounds selected for this study were also rated as being appropriate matches to individuals' tinnitus and largely pleasant to listen to. There was a significant reduction in the Tinnitus Functional Index score and subscales of intrusiveness of the tinnitus signal and ability to concentrate with the tinnitus trial end compared to baseline. There was a significant decrease in how strong the tinnitus signal was rated as well as ratings of how easy it was to ignore the tinnitus signal on severity rating scales. Qualitative analysis found that the environmental sound interacted with the tinnitus in a positive way, but participants did not experience change in severity, however, characteristics of tinnitus, including pitch and uniformity of sound, were reported to change. The results indicate the feasibility of the computational SNN method and preliminary evidence that the sound exposure may change activation of neural tinnitus networks and greater bilateral hemispheric involvement as the sound morphs over time into natural environmental sound; particularly relating to attention and discriminatory judgments (dorsal attention network, precentral gyrus, ventral anterior network). This is the first study that attempts to recategorize tinnitus using passive auditory training to a sound that morphs from resembling the person's tinnitus to a natural sound. These findings will be used to design future-controlled trials to elucidate whether the approach used differs in effect and mechanism from conventional Broadband Noise (BBN) sound therapy.

Auditory cortex hyperconnectivity before rTMS is correlated with tinnitus improvement

INTRODUCTION

Repetitive transcranial magnetic stimulation (rTMS) has been used as a potential treatment for tinnitus; however, its effectiveness is variable and unpredictable. We hypothesized that resting-state functional connectivity before rTMS may be correlated with rTMS treatment effectiveness.

METHODS

We applied 1-Hz rTMS to the left primary auditory (A1) and dorsolateral prefrontal cortices (DLPFC) of 10 individuals with tinnitus and 10 age-matched controls. Resting-state functional magnetic resonance imaging (fMRI) studies were performed approximately one week before rTMS. Seed-based connectivity analyses were conducted for each individual, with seed regions as rTMS target areas.

RESULTS

Compared to controls, the left superior temporal areas showed significantly increased positive connectivity with the left A1 and negative connectivity with the left DLPFC in the tinnitus group. The left frontoparietal and right cerebellar areas showed significantly increased negative connectivity with the left A1 and positive connectivity with the left DLPFC. Seed-based hyperconnectivity was correlated with tinnitus improvement (pre-rTMS vs. 2-week post-rTMS Tinnitus Handicap Inventory scores). Tinnitus improvement was significantly correlated with left A1 hyperconnectivity; however, no correlation was observed with left DLPFC connectivity. Positive rTMS outcomes were associated with significantly increased positive connectivity in bilateral superior temporal areas and significantly increased negative connectivity in bilateral frontal areas.

CONCLUSIONS

Our results suggest that oversynchronisation of left A1 connectivity before rTMS of the left A1 and DLPFC is associated with treatment effectiveness.

The Neural Mechanisms of Tinnitus: A Perspective From Functional Magnetic Resonance Imaging

Tinnitus refers to sound perception in the absence of external sound stimulus. It has become a worldwide problem affecting all age groups especially the elderly. Tinnitus often accompanies hearing loss and some mood disorders like depression and anxiety. The comprehensive adverse effects of tinnitus on people determine the severity of tinnitus. Understanding the mechanisms of tinnitus and related discomfort may be beneficial to the prevention and treatment, and then getting patients out of tinnitus distress. Functional magnetic resonance imaging (fMRI) is a powerful technique for characterizing the intrinsic brain activity and making us better understand the tinnitus neural mechanism. In this article, we review fMRI studies published in recent years on the neuroimaging mechanisms of tinnitus. The results have revealed various neural network alterations in tinnitus patients, including the auditory system, limbic system, default mode network, attention system, and some other areas involved in memory, emotion, attention, and control. Moreover, changes in functional connectivity and neural activity in these networks are related to the perception, persistence, and severity of tinnitus. In summary, the neural mechanism of tinnitus is a complex regulatory mechanism involving multiple networks. Future research is needed to study these neural networks more accurately to refine the tinnitus models.

Noise-induced neurophysiological alterations in the rat medial geniculate body and thalamocortical desynchronization by deep brain stimulation

The thalamic medial geniculate body (MGB) is uniquely positioned within the neural tinnitus networks. Deep brain stimulation (DBS) of the MGB has been proposed as a possible novel treatment for tinnitus, yet mechanisms remain elusive. The aim of this study was to characterize neurophysiologic hallmarks in the MGB after noise exposure and to assess the neurophysiological effects of electrical stimulation of the MGB. Fourteen male Sprague-Dawley rats were included. Nine subjects were unilaterally exposed to a 16-kHz octave-band noise at 115 dB for 90 min, five received sham exposure. Single units were recorded from the contralateral MGB where spontaneous firing, coefficient of variation, response type, rate-level functions, and thresholds were determined. Local field potentials and electroencephalographical (EEG) recordings were performed before and after high-frequency DBS of the MGB. Thalamocortical synchronization and power were analyzed. In total, 214 single units were identified (n = 145 in noise-exposed group, n = 69 in control group). After noise exposure, fast-responding neurons become less responsive or nonresponsive without change to their spontaneous rate, whereas sustained- and suppressed-type neurons exhibit enhanced spontaneous activity without change to their stimulus-driven activity. MGB DBS suppressed thalamocortical synchronization in the β and γ bands, supporting suppression of thalamocortical synchronization as an underlying mechanism of tinnitus suppression by high frequency DBS. These findings contribute to our understanding of the neurophysiologic consequences of noise exposure and the mechanism of potential DBS therapy for tinnitus.NEW & NOTEWORTHY Separate functional classes of MGB neurons might have distinct roles in tinnitus pathophysiology. After noise exposure, fast-responding neurons become less responsive or nonresponsive without change to their spontaneous firing, whereas sustained and suppressed neurons exhibit enhanced spontaneous activity without change to their stimulus-driven activity. Furthermore, results suggest desynchronization of thalamocortical β and γ oscillations as a mechanism of tinnitus suppression by MGB DBS.

The Acceptability and Influencing Factors of an Internet-Based Tinnitus Multivariate Integrated Sound Therapy for Patients With Tinnitus

OBJECTIVE

To explore the acceptability and influencing factors of an Internet-based Tinnitus Multivariate Integrated Sound Therapy (iT-MIST). The individually tailored sound therapy used narrowband noise centered on the patient's tinnitus frequency in combination with natural sounds and relaxing music.

DESIGN

Patients with tinnitus were given a 1-week trial of iT-MIST. Semistructured interviews were then carried out and a thematic analysis used to analyze, identify, organize, and report factors discovered in the data.

STUDY SAMPLE

Semistructured interviews were carried out with 11 participants, 2 women and 9 men, mean age 39.82 years.

RESULTS

The first theme identified from patient interview analysis was their motivation to undertake and expectations of iT-MIST. Nearly half of the participants indicated that advice from the physician was considered very important and professional. Benefits acknowledged by most participants from their iT-MIST experience were accessibility, convenience, time- and cost-effectiveness, and emotional benefit. However, a few participants with poor understanding of tinnitus and iT-MIST showed a negative acceptability with doubtful thoughts and complaints about technical issues such as being easily interrupted by messages and phone calls.

CONCLUSION

Patients with tinnitus in this study were not universally accepting of the iT-MIST therapy. Concerns about their tinnitus and ability to comply with doctor's recommendations were the main influencing factors. Attitude or willingness to explore new therapies facilitated its use. Emotional benefits, for example, relaxation and comfort, were seen to sustain motivation, while doubtful thoughts and technical problems negatively affected acceptability.

Tinnitus and hyperacusis: Central noise, gain and variance

Tinnitus is a phantom auditory sensation in the absence of external sounds, while hyperacusis is an atypical sensitivity to external sounds that leads them to be perceived as abnormally loud or even painful. Both conditions may reflect the brain's over-compensation for reduced input from the ear. The present work differentiates between two compensation models: The additive central noise compensates for hearing loss and is likely to generate tinnitus, whereas the multiplicative central gain compensates for hidden hearing loss and is likely to generate hyperacusis. Importantly, both models predict increased variance in central representations of sounds, especially a nonlinear increase in variance by the central gain. The increased central variance limits the amount of central compensation and reduces temporal synchrony, which can explain the insufficient central gain reported in the literature. Future studies need to collect trial-by-trial firing variance data so that the present variance-based model can be falsified.

Novel Risk Loci in Tinnitus and Causal Inference With Neuropsychiatric Disorders Among Adults of European Ancestry

Importance

Tinnitus affects at least 16 million US adults, but its pathophysiology is complicated, and treatment options remain limited. A heritable component has been identified in family and twin studies; however, no large-scale genome-wide association studies (GWAS) have been accomplished.

Objective

To identify genetic risk loci associated with tinnitus, determine genetic correlations, and infer possible relationships of tinnitus with hearing loss and neuropsychiatric disorders and traits.

Design, Setting, and Participants

A GWAS of self-reported tinnitus was performed in the UK Biobank (UKB) cohort using a linear mixed-model method implemented in BOLT-LMM (linear mixed model). Replication of significant findings was sought in the nonoverlapping US Million Veteran Program (MVP) cohort. A total of 172 995 UKB (discovery) and 260 832 MVP (replication) participants of European ancestry with self-report regarding tinnitus and hearing loss underwent genomic analysis. Linkage-disequilibrium score regression and mendelian randomization were performed between tinnitus and hearing loss and neuropsychiatric disorders. Data from the UKB were acquired and analyzed from September 24, 2018, to December 13, 2019. Data acquisition for the MVP cohort was completed July 22, 2019. Data analysis for both cohorts was completed on February 11, 2020.

Main Outcomes and Measures

Estimates of single nucleotide variation (SNV)-based heritability for tinnitus, identification of genetic risk loci and genes, functional mapping, and replication were performed. Genetic association and inferred causality of tinnitus compared with hearing loss and neuropsychiatric disorders and traits were analyzed.

Results

Of 172 995 UKB participants (53.7% female; mean [SD], 58.0 [8.2] years), 155 395 unrelated participants underwent SNV-based heritability analyses across a range of tinnitus phenotype definitions that explained approximately 6% of the heritability. The GWAS based on the most heritable model in the full UKB cohort identified 6 genome-wide significant loci and 27 genes in gene-based analyses, with replication of 3 of 6 loci and 8 of 27 genes in 260 832 MVP cohort participants (92.8% men; mean [SD] age, 63.8 [13.2] years). Mendelian randomization indicated that major depressive disorder had a permissive effect (β = 0.133; P = .003) and years of education had a protective effect (β = -0.322, P = <.001) on tinnitus, whereas tinnitus and hearing loss inferred a bidirectional association (β = 0.072, P = .001 and β = 1.546, P = <.001, respectively).

Conclusions and Relevance

This large GWAS characterizes the genetic architecture of tinnitus, demonstrating modest but significant heritability and a polygenic profile with multiple significant risk loci and genes. Genetic correlation and inferred causation between tinnitus and major depressive disorder, educational level, and hearing impairment were identified, consistent with clinical and neuroimaging evidence. These findings may guide gene-based diagnostic and therapeutic approaches to this pervasive disorder.

Bimodal neuromodulation combining sound and tongue stimulation reduces tinnitus symptoms in a large randomized clinical study

Tinnitus is a phantom auditory perception coded in the brain that can be bothersome or debilitating, affecting 10 to 15% of the population. Currently, there is no clinically recommended drug or device treatment for this major health condition. Animal research has revealed that sound paired with electrical somatosensory stimulation can drive extensive plasticity within the brain for tinnitus treatment. To investigate this bimodal neuromodulation approach in humans, we evaluated a noninvasive device that delivers sound to the ears and electrical stimulation to the tongue in a randomized, double-blinded, exploratory study that enrolled 326 adults with chronic subjective tinnitus. Participants were randomized into three parallel arms with different stimulation settings. Clinical outcomes were evaluated over a 12-week treatment period and a 12-month posttreatment phase. For the primary endpoints, participants achieved a statistically significant reduction in tinnitus symptom severity at the end of treatment based on two commonly used outcome measures, Tinnitus Handicap Inventory (Cohen’s d effect size: −0.87 to −0.92 across arms; P < 0.001) and Tinnitus Functional Index (−0.77 to −0.87; P < 0.001). Therapeutic improvements continued for 12 months after treatment for specific bimodal stimulation settings, which had not previously been demonstrated in a large cohort for a tinnitus intervention. The treatment also achieved high compliance and satisfaction rates with no treatment-related serious adverse events. These positive therapeutic and long-term results motivate further clinical trials toward establishing bimodal neuromodulation as a clinically recommended device treatment for tinnitus.

Prevalence of Tinnitus in an Aging Population and Its Relation to Age and Hearing Loss

Objectives

Tinnitus is a common hearing-related disorder, which may have a large impact on daily life. With aging populations worldwide, it is important to gain insight in the occurrence of tinnitus at older ages and to understand its relationship with age-related hearing loss. We investigated the prevalence of tinnitus among a general aging population, across age strata and hearing status.

Study Design

Cross-sectional.

Setting

The population-based Rotterdam Study.

Methods

A total of 6098 participants underwent tinnitus assessment, and 4805 had additional hearing assessment. We determined tinnitus prevalence per 5-year age groups. Hearing impairment was defined as ≥25–dB HL worse ear pure tone average (0.5, 1, 2, 4 kHz). We investigated with multivariable logistic regression the association between hearing impairment and tinnitus. Tinnitus handicap was assessed in 663 participants with daily tinnitus via the Tinnitus Handicap Inventory–screening version (THI-s).

Results

Tinnitus was prevalent in 21.4% (n = 1304). Prevalent tinnitus was evenly distributed over 5-year age groups. Participants with hearing impairment were more likely to have tinnitus (odds ratio, 2.27; 95% CI, 1.92-2.69) as compared with those without hearing impairment. The median THI-s score was 4 (interquartile range, 0-10), indicating a slight handicap, and 14.6% of the participants reported a moderate or severe handicap (THI-s ≥16).

Conclusions

In a general elderly population, 1 in 5 persons has tinnitus. Of those with tinnitus, for 1 per 10 persons, the presence of tinnitus interfered with daily life. Participants with hearing impairment were twice as likely to have tinnitus. Despite the age-dependent occurrence of hearing impairment, no such age dependency was found for tinnitus.

Hearing what you see: Distinct excitatory and disinhibitory mechanisms contribute to visually-evoked auditory sensations

Visual motion or flashing lights can evoke auditory sensations in some people. This large-scale internet study aimed to validate a combined subjective/objective test of the genuineness of this putative form of synaesthesia (visually-evoked auditory response, vEAR). Correlations were measured between each individual's ratings of the vividness of auditory sensations evoked by a series of looping videos, and measurement of the videos' physical low-level motion energy, calculated using Adelson and Bergen's (1985) computational model of low-level visual motion processing. The strength of this association for each individual provided a test of how strongly subjective vEAR was driven by objective motion energy ('ME-sensitivity'). A second aim was to infer whether vEAR depends on cortical excitation and/or disinhibition of early visual and/or auditory brain areas. To achieve this, correlations were measured between the above vEAR measures and visual contrast surround-suppression, which is thought to index lateral inhibition in the early visual system. As predicted by a disinhibition account of vEAR, video ratings were overall higher in individuals showing weaker surround-suppression. Interestingly, surround-suppression and ME-sensitivity did not correlate. Additionally, both surround-suppression and ME-sensitivity each independently predicted different clusters of trait measures selected for their possible association with cortical excitability and/or disinhibition: Surround-suppression was associated with vEAR self-ratings and auditory-evoked visual phosphenes, while ME-sensitivity was independently associated with ratings of other traits including susceptibility to migraine and pattern glare. Altogether, these results suggest there are two independent mechanisms underlying vEAR and its associated traits, based putatively on cortical disinhibition versus excitability.

Identifying non-otologic risk factors for tinnitus: A systematic review

BACKGROUND

The origin of tinnitus has been attributed to a peripheral auditory lesion, inducing bottom-up changes and resulting in the perception of a "phantom sound." However, non-auditory factors can co-exist as well, and can even lie at the origin of tinnitus development. An increasing body of literature focuses on psychological, (neuro)muscular, cardiovascular and many other influences and their respective associations with tinnitus prevalence.

OBJECTIVE OF REVIEW

The purpose of this study was to provide a comprehensive description of these non-otologic risk factors, and to summarise the evidence in literature about their link with tinnitus.

TYPE OF REVIEW

A narrative systematic review was conducted, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses statement.

SEARCH STRATEGY

The MEDLINE, Embase and Web of Science databases were systematically searched for eligible articles, supplemented with manual search methods and grey literature search. Epidemiological studies reporting on the relationship between various non-otologic risk factors and tinnitus were included.

EVALUATION METHOD

Quality assessment was performed using the Hoy & Brooks tool.

RESULTS

Fifty-five studies were included. Studies were of variable quality, with poor tinnitus definitions and evaluations or questionable sampling of the study population as main contributing factors for high risk of bias. Multiple associated factors have been identified, including cardiovascular, psychological, neurological, musculoskeletal and dietary factors.

CONCLUSIONS

The current literature review identified multiple risk factors that could be of significant importance for tinnitus development, maintenance or aggravation. While causality remains uncertain, this systematic elaboration of possible tinnitus comorbidities/risk factors can help provide direction for future research, and can direct clinicians to identify patients at risk and treat relevant symptoms accordingly.

Sound Therapy for Tinnitus: Options for Audiologists

Purpose

Sound therapy to reduce the emotional and functional effects of tinnitus has been used by audiologists since the 1970s when Jack Vernon introduced the masking method to provide a sense of relief from tinnitus distress. Our group renamed masking sound as “soothing” sound and distinguished it from “interesting” and “background” sound, each of which has a different purpose for tinnitus sound therapy. Other methods of sound therapy have the potential to reduce the “sensation” of tinnitus, including notched noise, matched noise, desynchronization, and residual inhibition. The purpose of this article is to provide an overview of the different sound therapy approaches to serve as a resource for audiologists who often provide sound therapy to their patients with tinnitus.

Conclusion

Although, according to systematic reviews, sound therapy does not have strong evidence for treatment of tinnitus, it is nonetheless well evidenced both through abundant research and clinical utilization mostly by audiologists. It is unknown if any one form of sound therapy is superior to any other.

Animal Models of Tinnitus: A Review

Animal models have significantly contributed to understanding the pathophysiology of chronic subjective tinnitus. They are useful because they control etiology, which in humans is heterogeneous; employ random group assignment; and often use methods not permissible in human studies. Animal models can be broadly categorized as either operant or reflexive, based on methodology. Operant methods use variants of established psychophysical procedures to reveal what an animal hears. Reflexive methods do the same using elicited behavior, for example, the acoustic startle reflex. All methods contrast the absence of sound and presence of sound, because tinnitus cannot by definition be perceived as silence.

Regulation of auditory plasticity during critical periods and following hearing loss

Sensory input has profound effects on neuronal organization and sensory maps in the brain. The mechanisms regulating plasticity of the auditory pathway have been revealed by examining the consequences of altered auditory input during both developmental critical periods—when plasticity facilitates the optimization of neural circuits in concert with the external environment—and in adulthood—when hearing loss is linked to the generation of tinnitus. In this review, we summarize research identifying the molecular, cellular, and circuit-level mechanisms regulating neuronal organization and tonotopic map plasticity during developmental critical periods and in adulthood. These mechanisms are shared in both the juvenile and adult brain and along the length of the auditory pathway, where they serve to regulate disinhibitory networks, synaptic structure and function, as well as structural barriers to plasticity. Regulation of plasticity also involves both neuromodulatory circuits, which link plasticity with learning and attention, as well as ascending and descending auditory circuits, which link the auditory cortex and lower structures. Further work identifying the interplay of molecular and cellular mechanisms associating hearing loss-induced plasticity with tinnitus will continue to advance our understanding of this disorder and lead to new approaches to its treatment.

•

During CPs, brain plasticity is enhanced and sensitive to acoustic experience.

•

Enhanced plasticity can be reinstated in the adult brain following hearing loss.

•

Molecular, cellular, and circuit-level mechanisms regulate CP and adult plasticity.

•

Plasticity resulting from hearing loss may contribute to the emergence of tinnitus.

•

Modifying plasticity in the adult brain may offer new treatments for tinnitus.

Objective Verification of Acute Tinnitus and Validation of Efficacy of Systemic Steroids in Rats

BACKGROUND

This study was performed to identify acute tinnitus and evaluate the efficacy of steroids for noise-induced acute tinnitus by measuring the gap-prepulse inhibition of the acoustic startle (GPIAS) value in an animal model.

METHODS

Nineteen rats (the noise group [n = 7] and the noise + dexamethasone [DEX] group [n = 12]) were exposed to narrow-band noise centered at 16 kHz from a sound generator for 4 hours. The noise + DEX group received intraperitoneal steroid administration daily for 5 days (1.5 mg/kg/day) after completing noise exposure. Auditory brainstem response and GPIAS value were measured just prior to, and 1 day after noise exposure and on days 1 and 10 days after completing steroid administration. The changes in cochlear structure were evaluated by histological analysis.

RESULTS

The threshold shift was checked 1 and 10 days after intraperitoneal steroid injection, and no differences in threshold shift were observed between the two groups in each frequency except for 32 kHz 1 day after steroid injection. The mean GPIAS value in the noise + DEX group (36.4% ± 14.1%) was significantly higher than that in the noise group (16.4% ± 18.8%) 10 days after intraperitoneal steroid administration (P = 0.017). There were no pathological changes associated with noise trauma in the two groups as determined on hematoxylin and eosin and immunohistochemical staining.

CONCLUSION

An acute tinnitus model with minimal structural changes by noise exposure was set up, and used to verify tinnitus objectively by measuring the GPIAS value. Steroid therapy for control of tinnitus was validated in this animal model.

A proof-of-principle study of the short-term effects of 3,4-methylenedioxymethamphetamine (MDMA) on tinnitus and neural connectivity

Background: This study was conducted to investigate the short-term behavioural and neurophysiological effects of 3,4-methylenedioxymethamphetamine (MDMA) on tinnitus perception.Methods: A double-blind randomized controlled cross-over design. Part 1. Behavioural measures of tinnitus following 30 mg MDMA or placebo administration (N = 5 participants) and Part 2. Behavioural measures of tinnitus and correlations between pairs of apriori regions of interest (ROI) using resting-state functional magnetic resonance imaging (rs-fMRI) before and after 70 mg of MDMA or placebo (N = 8 participants).Results: The results to MDMA were similar to placebo. For the 70 mg dose, there was a significant reduction after 4 h in annoyance and ignore ratings. RsMRI showed decreased connectivity compared with placebo administration between the left hippocampal, right hippocampal, left amygdala and right amygdala regions, and between the right posterior parahippocampal cortex and the left amygdala after two hours of 70 mg MDMA administration. Increased connectivity compared to placebo administration was found post MDMA between the right post-central gyrus and right posterior and superior temporal gyrus, and between the thalamus and frontoparietal network.Conclusions: Following 70 mg of MDMA two tinnitus rating scales significantly improved. There was, however, a placebo effect. Compared with placebo the rsMRI following the MDMA showed reductions in connectivity between the amygdala, hippocampus and parahippocampal gyrus. There is sufficient proof of concept to support future investigation of MDMA as a treatment for tinnitus.

Tinnitus and event related potentials: a systematic review

Introduction

Tinnitus is sound perception in the absence of a sound source. Changes in parameters of latency and amplitude on the auditory event related potentials or long latency potentials waves have been cited in tinnitus patients when compared to a control group.

Objective

To perform an assessment of scientific evidence that verifies the possibility of alterations in latency or amplitude of the waves of event related potentials in individuals with tinnitus.

Methods

By using SciELO, Lilacs, ISI Web and PubMed, scientific databases, a review was performed. Articles published in English, Portuguese, French and Spanish that correlated tinnitus with changes in event related potentials were included in this review.

Results

Twelve articles were located, however only eight fulfilled the criteria for inclusion.

Conclusion

The sample of selected studies demonstrate that the long latency auditory evoked potentials related to events between the control and tinnitus patients showed some changes in latency and or amplitude in tinnitus patients. There are changes in event-related potentials when comparing patients with tinnitus and the control group. These changes take place considering the severity of tinnitus, tinnitus site of lesion, and capacity for changes after interventions. The event related potentials can help to determine the neurotransmitter involved in tinnitus generation and evaluate tinnitus treatments.

Alleviation of Tinnitus With High-Frequency Stimulation of the Dorsal Cochlear Nucleus: A Rodent Study

Deep brain stimulation of the central auditory pathway is emerging as a promising treatment modality for tinnitus. Within this pathway, the dorsal cochlear nucleus (DCN) plays a key role in the pathophysiology of tinnitus and is believed to be a tinnitus generator. We hypothesized that high-frequency stimulation (HFS) of the DCN would influence tinnitus-related abnormal neuronal activity within the auditory pathway and hereby suppress tinnitus. To this end, we assessed the effect of HFS of the DCN in a noise-induced rat model of tinnitus. The presence of tinnitus was verified using the gap prepulse inhibition of the acoustic startle response paradigm. Hearing thresholds were determined before and after noise trauma by measuring the auditory brainstem responses. In addition, changes in neuronal activity induced by noise trauma and HFS were assessed using c-Fos immunohistochemistry in related structures. Results showed tinnitus development after noise trauma and hearing loss ipsilateral to the side exposed to noise trauma. During HFS of the DCN, tinnitus was suppressed. There was no change in c-Fos expression within the central auditory pathway after HFS. These findings suggest that DCN-HFS changes patterns of activity and results in information lesioning within the network and hereby blocking the relay of abnormal tinnitus-related neuronal activity.

Tinnitus Correlates with Downregulation of Cortical Glutamate Decarboxylase 65 Expression But Not Auditory Cortical Map Reorganization

Hearing loss is the biggest risk factor for tinnitus, and hearing-loss-related pathological changes in the auditory pathway have been hypothesized as the mechanism underlying tinnitus. However, due to the comorbidity of tinnitus and hearing loss, it has been difficult to differentiate between neural correlates of tinnitus and consequences of hearing loss. In this study, we dissociated tinnitus and hearing loss in FVB mice, which exhibit robust resistance to tinnitus following monaural noise-induced hearing loss. Furthermore, knock-down of glutamate decarboxylase 65 (GAD65) expression in auditory cortex (AI) by RNA interference gave rise to tinnitus in normal-hearing FVB mice. We found that tinnitus was significantly correlated with downregulation of GAD65 in the AI. By contrast, cortical map distortions, which have been hypothesized as a mechanism underlying tinnitus, were correlated with hearing loss but not tinnitus. Our findings suggest new strategies for the rehabilitation of tinnitus and other phantom sensation, such as phantom pain.SIGNIFICANCE STATEMENT Hearing loss is the biggest risk factor for tinnitus in humans. Most animal models of tinnitus also exhibit comorbid hearing loss, making it difficult to dissociate the mechanisms underlying tinnitus from mere consequences of hearing loss. Here we show that, although both C57BL/6 and FVB mice exhibited similar noise-induced hearing threshold increase, only C57BL/6, but not FVB, mice developed tinnitus following noise exposure. Although both strains showed frequency map reorganization following noise-induced hearing loss, only C57BL/6 mice had reduced glutamate decarboxylase 65 (GAD65) expression in the auditory cortex (AI). Knocking down GAD65 expression in the AI resulted in tinnitus in normal-hearing FVB mice. Our results suggest that reduced inhibitory neuronal function, but not sensory map reorganization, underlies noise-induced tinnitus.

Blast-induced tinnitus: Animal models

Blast-induced tinnitus is a prevalent problem among military personnel and veterans, as blast-related trauma damages the vulnerable microstructures within the cochlea, impacts auditory and non-auditory brain structures, and causes tinnitus and other disorders. Thus far, there is no effective treatment of blast-induced tinnitus due to an incomplete understanding of its underlying mechanisms, necessitating development of reliable animal models. This article focuses on recent animal studies using behavioral, electrophysiological, imaging, and pharmacological tools. The mechanisms underlying blast-induced tinnitus are largely similar to those underlying noise-induced tinnitus: increased spontaneous firing rates, bursting, and neurosynchrony, Mn++ accumulation, and elevated excitatory synaptic transmission. The differences mainly lie in the data variability and time course. Noise trauma-induced tinnitus mainly originates from direct peripheral deafferentation at the cochlea, and its etiology subsequently develops along the ascending auditory pathways. Blast trauma-induced tinnitus, on the other hand, results from simultaneous impact on both the peripheral and central auditory systems, and the resultant maladaptive neuroplasticity may also be related to the additional traumatic brain injury. Consequently, the neural correlates of blast-induced tinnitus have different time courses and less uniform manifestations of its neural correlates.

Untangling the genomics of noise-induced hearing loss and tinnitus: Contributions of Mus musculus and Homo sapiens

Acoustic trauma is a feature of the industrial age, in general, and mechanized warfare, in particular. Noise-induced hearing loss (NIHL) and tinnitus have been the number 1 and number 2 disabilities at U.S. Veterans hospitals since 2006. In a reversal of original protocols to identify candidate genes associated with monogenic deafness disorders, unbiased genome-wide association studies now direct animal experiments in order to explore genetic variants common in Homo sapiens. However, even these approaches must utilize animal studies for validation of function and understanding of mechanisms. Animal research currently focuses on genetic expression profiles since the majority of variants occur in non-coding regions, implying regulatory divergences. Moving forward, it will be important in both human and animal research to define the phenotypes of hearing loss and tinnitus, as well as exposure parameters, in order to extricate genes related to acoustic trauma versus those related to aging. It has become clear that common disorders like acoustic trauma are influenced by large numbers of genes, each with small effects, which cumulatively lead to susceptibility to a disorder. A polygenic risk score, which aggregates these small effect sizes of multiple genes, may offer a more accurate description of risk for NIHL and/or tinnitus.

Evidence of Hyperacusis in Adult Rats Following Non-traumatic Sound Exposure

Manipulations that enhance neuroplasticity may inadvertently create opportunities for maladaptation. We have previously used passive exposures to non-traumatic white noise to open windows of plasticity in the adult rat auditory cortex and induce frequency-specific functional reorganizations of the tonotopic map. However, similar reorganizations in the central auditory pathway are thought to contribute to the generation of hearing disorders such as tinnitus and hyperacusis. Here, we investigate whether noise-induced reorganizations are accompanied by electrophysiological or behavioral evidence of tinnitus or hyperacusis in adult Long-Evans rats. We used a 2-week passive exposure to moderate-intensity (70 dB SPL) broadband white noise to reopen a critical period for spectral tuning such that a second 1-week exposure to 7 kHz tone pips produced an expansion of the 7 kHz frequency region in the primary auditory cortex (A1). We demonstrate for the first time that this expansion also takes place in the ventral auditory field (VAF). Sound exposure also led to spontaneous and sound-evoked hyperactivity in the anterior auditory field (AAF). Rats were assessed for behavioral evidence of tinnitus or hyperacusis using gap and tone prepulse inhibition of the acoustic startle response. We found that sound exposure did not affect gap-prepulse inhibition. However, sound exposure led to an improvement in prepulse inhibition when the prepulse was a 7 kHz tone, showing that exposed rats had enhanced sensorimotor gating for the exposure frequency. Together, our electrophysiological and behavioral results provide evidence of hyperacusis but not tinnitus in sound-exposed animals. Our findings demonstrate that periods of prolonged noise exposure may open windows of plasticity that can also be understood as windows of vulnerability, potentially increasing the likelihood for maladaptive plasticity to take place.