Plasticity of somatosensory inputs to the cochlear nucleus--implications for tinnitus

Tinnitus in patients with orofacial complaints

BACKGROUND

This study explored subjective tinnitus frequency in patients referred to an interdisciplinary orofacial pain clinic using the "web-based interdisciplinary symptom evaluation" (WISE) tool, which included a wide range of psychometric data. Our goal was to analyze the correlation between orofacial complaints and tinnitus, as well as their association with other psychometric data-an approach that, to our knowledge, has not been undertaken to this extent before.

METHODS

From 2017 to 2020, we analyzed 1369 anonymized patient records using completed WISE. This included diverse questionnaires and symptom-related screener questions. Positive screening responses triggered additional assessments, such as short Tinnitus Handicap Inventory (THI-12) and Patient Health Questionnaire 4 (PHQ-4). Ear symptoms, tinnitus severity and tinnitus frequency were evaluated. Furthermore, Spearman correlations were performed with other questionnaires addressing pain, anxiety, depression, health, stress and insomnia.

RESULTS

Among 1369 patients with orofacial complaints, 69% were female. Notably, 19.7% (269) completed THI-12 due to severe ear symptoms; of these, 62.1% were female. Female mean THI-12 score was significantly lower (p = 0.007) with 9.3 (SD = 7.0) compared to males 11.6 (SD = 6.8). Additionally, there was a significantly different gender distribution between all patients with tinnitus and those with severe tinnitus (p = 0.032), with an increased proportion of men in the latter group. THI-12 positively correlated with all WISE questionnaires, strongest with PHQ-4 (p < 0.01).

CONCLUSIONS

Our study unveils a common co-occurrence of orofacial and ear complaints, particularly tinnitus. The practical implication of the observed gender differences suggests that in male patients presenting with orofacial pain, tinnitus and its associated distress should be actively addressed to initiate a multidisciplinary treatment approach.

CLINICAL TRIAL NUMBER

Not applicable. Since this study was a retrospective analysis of anonymized data, trial registration was not necessary.

Reducing Tinnitus via Inhibitory Influence of the Sensorimotor System on Auditory Cortical Activity

Tinnitus is the subjective perception of a sound without corresponding external acoustic stimuli. Research highlights the influence of the sensorimotor system on tinnitus perception. Associated neuronal processes, however, are insufficiently understood, and it remains unclear how and at which hierarchical level the sensorimotor system interacts with the tinnitus-processing auditory system. We therefore asked 23 patients suffering from chronic tinnitus (11 males) to perform specific exercises, aimed at relaxing or tensing the jaw area, which temporarily modulated tinnitus perception. Associated neuronal processes were assessed using magnetencephalography. Results show that chronic tinnitus patients experienced their tinnitus as weaker and less annoying after completion of relaxing compared with tensing exercises. Furthermore, (1) sensorimotor alpha power and alpha-band connectivity directed from the somatosensory to the auditory cortex increased and (2) gamma power in the auditory cortex reduced, which (3) related to reduced tinnitus annoyance perception on a trial-by-trial basis in the relaxed state. No effects were revealed for 23 control participants without tinnitus (six males) performing the same experiment. We conclude that the increase in directed alpha-band connectivity from the somatosensory to the auditory cortex most likely reflects the transmission of inhibition from the somatosensory to the auditory cortex during relaxation, where concurrently tinnitus-related gamma power reduces. We suggest that revealed neuronal processes are transferable to other tinnitus-modulating systems beyond the sensorimotor one that is involved in attentional or emotional tinnitus modulation and provides deeper mechanistic insights into how and through which channels phantom sound perception might be modulated on a neuronal level.

Impact of the somatosensory influence on annoyance and quality of life of individuals with tinnitus: A cross-sectional study

OBJECTIVE

To assess the impact of the somatosensory influence on annoyance and quality of life of individuals with tinnitus.

METHODS

This cross-sectional study included individuals with tinnitus of both sexes, aged ≥18 years, recruited from a specialized otolaryngology outpatient, and evaluated by a multidisciplinary team (otorhinolaryngologists, physical therapists, and audiologists). An evaluation adapted from the Diagnostic Criteria of Somatosensory Tinnitus (ST) was performed to verify the influence of the somatosensory system on the cause of tinnitus. The intensity of discomfort from tinnitus was assessed by the Numerical Rating Scale, the impact on quality of life by the Tinnitus Handicap Inventory (THI), and factors of exacerbation of tinnitus were self-reported. Individuals were divided into ST and non-ST groups. Unpaired t-test and Chi-Square were used for group comparisons; Cohen's d and Phi measured effect sizes.

RESULTS

A total of 100 individuals were evaluated: 46 from the ST group and 54 from the non-ST group. The ST group demonstrated greater discomfort from tinnitus (p <  0.01); stress was identified as a factor of exacerbation 82.6 (p <  0.01), and sleep disturbance as a consequence of tinnitus 63% (p =  0.04). Additionally, the ST group presented a greater impact on quality of life in the functional domain (p = 0.03) and total THI score (p =  0.05) than the non-ST group.

CONCLUSION

Individuals with ST reported greater discomfort from tinnitus and a more significant impact on the quality of life.

Stochastic resonance in the sensory systems and its applications in neural prosthetics

Noise is generally considered to be detrimental. In the right conditions, however, noise can improve signal detection or information transmission. This counterintuitive phenomenon is called stochastic resonance (SR). SR has generated significant interdisciplinary interest, particularly in physics, engineering, and medical and environmental sciences. In this review, we discuss a growing empirical literature that suggests that noise at the right intensity may improve the detection and processing of auditory, sensorimotor, and visual stimuli. We focus particularly on applications of SR in sensory biology and investigate whether SR-based technologies present a pathway to improve outcomes for individuals living with sensory impairments. We conclude that there is considerable evidence supporting the application of SR in developing sensory prosthetics. However, the progression of SR-based technologies is variable across the sensory modalities. We suggest opportunities for further advancements in each modality, considering the best approaches to maximise benefits and capitalise on progress already made. Overall, SR can offer opportunities to improve existing technologies or to motivate innovations.

Candidate Key Proteins in Tinnitus-A Bioinformatic Study of Synaptic Transmission in the Cochlear Nucleus

The aim of this study was to identify key proteins of synaptic transmission in the cochlear nucleus (CN) that are involved in normal hearing, acoustic stimulation, and tinnitus. A gene list was compiled from the GeneCards database using the keywords "synaptic transmission" AND "tinnitus" AND "cochlear nucleus" (Tin). For comparison, two gene lists with the keywords "auditory perception" (AP) AND "acoustic stimulation" (AcouStim) were built. The STRING protein-protein interaction (PPI) network and the Cytoscape data analyzer were used to identify the top two high-degree proteins (HDPs) and their high-score interaction proteins (HSIPs), together referred to as key proteins. The top1 key proteins of the Tin-process were BDNF, NTRK1, NTRK3, and NTF3; the top2 key proteins are FOS, JUN, CREB1, EGR1, MAPK1, and MAPK3. Highly significant GO terms in CN in tinnitus were "RNA polymerase II transcription factor complex", "late endosome", cellular response to cadmium ion", "cellular response to reactive oxygen species", and "nerve growth factor signaling pathway", indicating changes in vesicle and cell homeostasis. In contrast to the spiral ganglion, where important changes in tinnitus are characterized by processes at the level of cells, important biological changes in the CN take place at the level of synapses and transcription.

Hydralazine alleviates noise-induced hearing loss by scavenging acrolein

Noise-induced hearing loss (NIHL) is the most common cause of hearing loss. This study investigates the therapeutic efficacy of the acrolein scavenger hydralazine for NIHL in rats. NIHL was induced by exposure to a continuous pure tone of 10 kHz. Auditory function was evaluated by auditory brainstem response (ABR) testing and scanning electron microscopy. The expression of acrolein and glial cell markers GFAP and OX42 was assessed by immunofluorescence staining. The protein and mRNA expression of GFAP, OX42, interleukin-18 (IL-18), IL-1β, and fractalkine (FTK) was measured by qRT-PCR and western blotting. A rat model of NIHL was successfully developed, as evidenced by increased ABR thresholds. The results showed that noise exposure increased the expression of acrolein, GFAP, OX42, FTK, IL-1β, and IL-18 in the rat cochlear nucleus. Furthermore, hydralazine alleviates NIHL by reversing the effects of acrolein. These results demonstrate that acrolein is involved in glial cell activation and NIHL, it's also a therapeutic potential target for NIHL.

Suffering from chronic tinnitus, chronic neck pain, or both: Does it impact the presence of signs and symptoms of central sensitization?

Chronic subjective tinnitus is a prevalent symptom, which has many similarities with chronic pain. Central sensitization is considered as a possible underlying mechanism of both symptoms. Central sensitization has already been investigated in chronic pain populations but not in patients with chronic subjective tinnitus. Therefore, the main objective of this cross-sectional study was to compare signs and symptoms, indicative for central sensitization, in tinnitus patients with and without chronic idiopathic neck pain, patients with chronic idiopathic neck pain only, and healthy controls. Also, differences in psychological and lifestyle factors, possibly influencing the association between central sensitization and tinnitus, were examined as well as correlations between signs and symptoms of central sensitization, and tinnitus, pain, psychological and lifestyle factors. Differences in signs and symptoms of central sensitization were examined using the self-report Central Sensitization Inventory and QST protocol (local and distant mechanical and heat hyperalgesia, conditioned pain modulation). Tinnitus, pain, psychological and lifestyle factors were evaluated using self-report questionnaires. Symptoms of central sensitization and local mechanical hyperalgesia were significantly more present in both tinnitus groups, compared to healthy controls, but were most extensive in the group with chronic tinnitus+chronic idiopathic neck pain. Distant mechanical hyperalgesia, indicative for central sensitization, was only observed in the group with both chronic tinnitus+chronic idiopathic neck pain. This group also displayed a significantly higher psychological burden and poorer sleep than patients with chronic tinnitus only and healthy controls. Signs and symptoms of central sensitization were also shown to be associated with tinnitus impact, pain-related disability, psychological burden and sleep disturbances. This study shows preliminary evidence for the presence of central sensitization in patients with chronic tinnitus+chronic idiopathic neck pain. This could be explained by the higher perceived tinnitus impact, psychological burden and sleep problems in this group. Trial registration: This study is registered as NCT05186259 (www.clinicaltrials.gov).

Pilot study on the role of somatic modulation in hyperacusis

BACKGROUND

Hyperacusis is a reduced tolerance to sounds that often co-occurs with tinnitus. Both symptoms have convergent as well as divergent characteristics. Somatic modulation, changes in pitch or loudness during certain movements, is common in patients with a primary complaint of tinnitus. However, thus far, this is not documented in patients with hyperacusis.

OBJECTIVES

This study aimed to examine the influence of somatic manoeuvres on the perception of external sounds in patients with a primary complaint of hyperacusis.

METHODOLOGY

In this prospective cross-sectional pilot study, 18 patients with a primary complaint of hyperacusis were recruited at the Tinnitus Treatment and Research Center Antwerp (TINTRA). While patients listened to a 1 kHz broadband noise of 30 dB sensation level, six neck manoeuvres (flexion, extension, lateroflexion left/right, traction and compression), three jaw manoeuvres (protrusion, laterotrusion left/right) and one placebo manoeuvre (hand on head) were performed. The primary outcome measure was the change in the perception of the presented sound in terms of loudness and intrusiveness between baseline and each modulation measured by a visual analogue scale (VAS).

RESULTS

No overall significant changes were found; however, individual results indicated that five patients presented a clinically relevant change of more than three points out of ten on VAS in terms of hyperacusis after at least one of the executed somatic manoeuvres.

CONCLUSIONS

This pilot study did not demonstrate an overall significant change in hyperacusis after somatic manoeuvres but does not rule out the possibility of somatic modulation in some hyperacusis patients.

TRIAL REGISTRATION

The protocol of this prospective cross-sectional pilot study was registered on clinicaltrials.gov with registration number NCT04693819.

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.

Effects of Physical Interventions on Subjective Tinnitus, a Systematic Review and Meta-Analysis

Increasingly, patients suffering from subjective tinnitus seek help from physical therapists. Numerous randomised controlled trials (RCTs) have investigated the effect of physical interventions commonly used in physical therapy practice on subjective tinnitus. This systematic review and meta-analysis aimed to analyse the effects of physical interventions on tinnitus loudness, tinnitus annoyance, and scores on the Tinnitus Handicap Index (THI). Four databases were searched from inception up to March 2022. A total of 39 RCTs were included in the systematic review, and 23 studies were appropriate for meta-analyses. Risk of bias assessments were also performed. Interventions analysed in at least five studies were summarised, including transcutaneous electrical nerve stimulation (TENS), laser therapy, and acupuncture. Random-effects meta-analysis models were used, and effect sizes were expressed as Hedge's standardised mean differences (SMD) with 95%CI's. The quality of three-quarters of the studies was limited due to insufficient allocation concealment, lack of adequate blinding, and small sample sizes. Large, pooled effects sizes were found for acupuncture (SMD: 1.34; 95%CI: 0.79, 1.88) and TENS (SMD: 1.17; 95%CI: 0.48, 1.87) on THI as well as for acupuncture on tinnitus loudness (VAS Loudness (SMD: 0.84; 95%CI: 0.33, 1.36) and tinnitus annoyance (SMD: 1.18; 95%CI: 0.00, 2.35). There is some evidence that physical interventions (TENS and acupuncture, but not laser therapy) may be effective for tinnitus. However, the lack of high-quality studies and the risk of bias in many studies prohibits stronger conclusions.

Intrinsic Noise Improves Speech Recognition in a Computational Model of the Auditory Pathway

Noise is generally considered to harm information processing performance. However, in the context of stochastic resonance, noise has been shown to improve signal detection of weak sub- threshold signals, and it has been proposed that the brain might actively exploit this phenomenon. Especially within the auditory system, recent studies suggest that intrinsic noise plays a key role in signal processing and might even correspond to increased spontaneous neuronal firing rates observed in early processing stages of the auditory brain stem and cortex after hearing loss. Here we present a computational model of the auditory pathway based on a deep neural network, trained on speech recognition. We simulate different levels of hearing loss and investigate the effect of intrinsic noise. Remarkably, speech recognition after hearing loss actually improves with additional intrinsic noise. This surprising result indicates that intrinsic noise might not only play a crucial role in human auditory processing, but might even be beneficial for contemporary machine learning approaches.

Reduction of Somatic Tinnitus Severity is Mediated by Improvement of Temporomandibular Disorders

BACKGROUND

Successful orofacial treatment can reduce tinnitus severity in patients with somatic tinnitus (ST). However, it is still unclear to what extent the degree of reduction in temporomandibular disorders (TMD) actually contributes to the decrease in tinnitus severity after orofacial treatment. Therefore, the aim of this study was to analyze the mediating effect of reduction in TMD pain on the improvement of tinnitus severity after multidisciplinary orofacial treatment.

METHODS

A total of 80 patients with moderate to severe ST attributed to the temporomandibular region, were recruited from a tertiary tinnitus clinic. At baseline, patients were randomly assigned to the orofacial treatment group or to the control group. Both groups received a minimum of information and advice regarding their tinnitus complaints. The orofacial treatment group received orofacial physical therapy complemented with occlusal splints when needed, while the control group received no other treatment. A mediation analysis was performed according to the steps described by Baron and Kenny and the proportion of the mediating effect was calculated for the potential mediator: "change in TMD pain," measured by a one-point decrease in TMD pain screener score.

RESULTS

Our analysis showed that 35% of the observed decrease in tinnitus severity can be attributed to a reduction in TMD pain. A significant total effect of orofacial treatment compared with control on the change in tinnitus functional index (TFI) score was found (B = 0.253 p = 0.025 Cl for B = 1.265-18.576). Orofacial treatment was also significantly related to the change in TMD pain (Exp (B) = 2.800, p = 0.034 Cl for Exp B 1.081-7.251). Additionally, the change in TMD pain screener score was significantly related to the change in TFI score (B = -0.273 p = 0.016 Cl for B = -19.875 to -2.119).

CONCLUSION

Reduction of TMD pain is a mediating factor in the decrease of tinnitus severity after multidisciplinary orofacial treatment.

PRACTICAL IMPLICATIONS

Orofacial treatment can be used to decrease tinnitus severity in patients with TMD related somatic tinnitus.

Evaluation and Treatment of Trigeminal Symptoms of Cervical Origin After a Motor-Vehicle Crash: A Case Report With 9-Month Follow-up

Objective

The purpose of this case report is to describe the management of a patient with trigeminal symptoms of cervical origin after a motor-vehicle crash (MVC).

Clinical Features

After a head-on MVC, a 65-year-old woman presented with complaints of dizziness, headaches, facial tingling, visual disturbance, tinnitus, loss of cervical motion, and pain in the cervical spine.

Intervention and Outcome

The intervention applied was manipulation of the left C1-C2 and right C2-C3, with targeted exercise to strengthen the cervical musculature. After 4 weeks of treatment, the patient reported improvement in functional tasks and reduction in overall pain, headaches, facial tingling, tinnitus, and dizziness. At a 9-month follow-up, the patient had no report of facial tingling, tinnitus, loss of motion, or eye pain.

Conclusion

This patient with trigeminal symptoms of cervical origin after an MVC responded well to manual therapy to the cervical spine as part of a combination of services.

Tinnitus-like "hallucinations" elicited by sensory deprivation in an entropy maximization recurrent neural network

Sensory deprivation has long been known to cause hallucinations or "phantom" sensations, the most common of which is tinnitus induced by hearing loss, affecting 10-20% of the population. An observable hearing loss, causing auditory sensory deprivation over a band of frequencies, is present in over 90% of people with tinnitus. Existing plasticity-based computational models for tinnitus are usually driven by homeostatic mechanisms, modeled to fit phenomenological findings. Here, we use an objective-driven learning algorithm to model an early auditory processing neuronal network, e.g., in the dorsal cochlear nucleus. The learning algorithm maximizes the network's output entropy by learning the feed-forward and recurrent interactions in the model. We show that the connectivity patterns and responses learned by the model display several hallmarks of early auditory neuronal networks. We further demonstrate that attenuation of peripheral inputs drives the recurrent network towards its critical point and transition into a tinnitus-like state. In this state, the network activity resembles responses to genuine inputs even in the absence of external stimulation, namely, it "hallucinates" auditory responses. These findings demonstrate how objective-driven plasticity mechanisms that normally act to optimize the network's input representation can also elicit pathologies such as tinnitus as a result of sensory deprivation.

Sparsely Distributed, Pre-synaptic Kv3 K+ Channels Control Spontaneous Firing and Cross-Unit Synchrony via the Regulation of Synaptic Noise in an Auditory Brainstem Circuit

Spontaneous subthreshold activity in the central nervous system is fundamental to information processing and transmission, as it amplifies and optimizes sub-threshold signals, thereby improving action potential initiation and maintaining reliable firing. This form of spontaneous activity, which is frequently considered noise, is particularly important at auditory synapses where acoustic information is encoded by rapid and temporally precise firing rates. In contrast, when present in excess, this form of noise becomes detrimental to acoustic information as it contributes to the generation and maintenance of auditory disorders such as tinnitus. The most prominent contribution to subthreshold noise is spontaneous synaptic transmission (synaptic noise). Although numerous studies have examined the role of synaptic noise on single cell excitability, little is known about its pre-synaptic modulation owing in part to the difficulties of combining noise modulation with monitoring synaptic release. Here we study synaptic noise in the auditory brainstem dorsal cochlear nucleus (DCN) of mice and show that pharmacological potentiation of Kv3 K⁺ currents reduces the level of synaptic bombardment onto DCN principal fusiform cells. Using a transgenic mouse line (SyG37) expressing SyGCaMP2-mCherry, a calcium sensor that targets pre-synaptic terminals, we show that positive Kv3 K⁺ current modulation decreases calcium influx in a fifth of pre-synaptic boutons. Furthermore, while maintaining rapid and precise spike timing, positive Kv3 K⁺ current modulation increases the synchronization of local circuit neurons by reducing spontaneous activity. In conclusion, our study identifies a unique pre-synaptic mechanism which reduces synaptic noise at auditory synapses and contributes to the coherent activation of neurons in a local auditory brainstem circuit. This form of modulation highlights a new therapeutic target, namely the pre-synaptic bouton, for ameliorating the effects of hearing disorders which are dependent on aberrant spontaneous activity within the central auditory system.

[Tinnitus: clinical and pathogenetic aspects]

The article discusses the pathogenetic and clinical features of tinnitus. It is emphasized that various causes contribute to the appearance of tinnitus, including somatic diseases, excess body weight, iatrogenies, otological diseases with an outcome in hearing loss. The anatomical and physiological features of the structure of the central part of the auditory system are considered. It is suggested that the occurrence of tinnitus is associated with the processes of maladaptive neuroplasticity caused by pathological changes in the neuronal activity of cortical structures of the CNS, and not with changes in the peripheral part of the auditory analyzer - the structures of the cochlea. The results of recent studies, including those using functional neuroimaging methods, indicate the significance of cortical connection disorders (human connectome) in patients with tinnitus. In patients with tinnitus, there are changes in regional neuronal activity and connections not only in the auditory cortex, but also in areas not directly related to the analysis of auditory afferentation. Thus, tinnitus can be considered as one of the variants of dysfunction of the human connectome, triggered primarily from the «auditory input».

Somatosensory Tinnitus Diagnosis: Diagnostic Value of Existing Criteria

BACKGROUND

Tinnitus can be influenced by changes in somatosensory afference from the cervical spine or temporomandibular area, then called somatosensory or somatic tinnitus (ST). In 2018, a new set of diagnostic criteria for ST was agreed upon by a large group of ST experts. Currently, however, it still requires extensive and specific expertise to diagnose ST correctly. The next step in the development of easily applicable diagnostic criteria is to assess the diagnostic value of each individual criterion.

OBJECTIVES

The aim of this study was, therefore, to further investigate the diagnostic value of these criteria, validate them empirically, and identify their sensitivity and specificity.

METHODS

An online survey, questioning the presence of 12 diagnostic criteria for ST in a convenience sample of participants with tinnitus, was launched on the online forum Tinnitus Talk, managed by Tinnitus Hub. Participants were divided into three groups: a group with no somatic influence, a group with some somatic influence and a group with large somatic influence on their tinnitus. Chi-square tests were used to calculate differences between these groups. Afterward, sensitivity, specificity, positive and negative likelihood ratios (LR), and pre- and posttest probabilities were calculated for each ST diagnostic criterion. For this analysis, all patients with some and large somatic influence were compared as one group to the group with no somatic influence.

RESULTS

In total, 8221 participants filled out the online survey. As expected, the diagnostic criteria for ST are more prevalent in the groups with somatic influence, but the criterium of tinnitus modulation also often occurs in the group with no somatic influence. The simultaneous onset or increase and decrease of both tinnitus and pain complaints have the highest positive LR (6.29 and 10.72, respectively), next to the influence of certain postures on the tinnitus (+LR: 6.04). To rule out ST, the absence of neck pain or tension in the neck extensor muscles are most suited, as they decrease the posttest probability to 18% and 19%, respectively.

CONCLUSION

The simultaneous onset or increase and decrease of tinnitus and neck or jaw pain and the influence of certain postures are most suited to use as a single criterion for identifying patients with a somatic influence on their tinnitus. On the other hand, the absence of neck pain or tension in the neck extensor muscles is valid criterion to rule out a somatic influence. Additional analysis is needed to identify clusters of symptoms and criteria to further aid ST diagnosis.

The stochastic resonance model of auditory perception: A unified explanation of tinnitus development, Zwicker tone illusion, and residual inhibition

Stochastic resonance (SR) has been proposed to play a major role in auditory perception, and to maintain optimal information transmission from the cochlea to the auditory system. By this, the auditory system could adapt to changes of the auditory input at second or even sub-second timescales. In case of reduced auditory input, somatosensory projections to the dorsal cochlear nucleus would be disinhibited in order to improve hearing thresholds by means of SR. As a side effect, the increased somatosensory input corresponding to the observed tinnitus-associated neuronal hyperactivity is then perceived as tinnitus. In addition, the model can also explain transient phantom tone perceptions occurring after ear plugging, or the Zwicker tone illusion. Vice versa, the model predicts that via stimulation with acoustic noise, SR would not be needed to optimize information transmission, and hence somatosensory noise would be tuned down, resulting in a transient vanishing of tinnitus, an effect referred to as residual inhibition.

Prognostic Indicators for Positive Treatment Outcome After Multidisciplinary Orofacial Treatment in Patients With Somatosensory Tinnitus

Introduction

Subjective tinnitus that is influenced by the somatosensory system is called somatosensory tinnitus (ST). When ST is related to the temporomandibular area, multidisciplinary orofacial treatment can reduce tinnitus severity. It is, however, unknown if we can predict this positive outcome. The aim of this study is to look for prognostic indicators that can predict a positive outcome after multidisciplinary orofacial treatment in patients with ST.

Methods

Patients were included when they were diagnosed with temporomandibular-related ST and received a maximum of 18 sessions of orofacial treatment during a 9-week program. Predictors for positive treatment outcome were identified using univariate and multiple logistic regression analyses with the Tinnitus Questionnaire (TQ) and the Tinnitus Functional Index (TFI) as dependent variables.

Results

The results of 101 patients were included in the analysis. Immediately after multidisciplinary orofacial treatment, a clinically relevant decrease in TQ score was significantly associated with “shorter duration of tinnitus” [odds ratio (OR) 0.99], “higher initial score on the TQ somatic subscale” (OR 1.52), and “painful palpation of the temporomandibular joint (TMJ)” (OR 2.46). After 9 weeks of follow-up, the “higher initial score on the TQ somatic subscale” remained as the sole predictor (OR 1.44). A clinically relevant decrease on TFI after 9 weeks of follow-up was predicted by “female gender” (OR 2.70), “younger age” (OR 0.96), “shorter duration of the tinnitus” (OR 0.99), “lower pressure pain thresholds (PPT) on TMJ” (OR 0.99), “lower PPT on sternocleidomastoid origin” (OR 0.99), and “better speech in noise perception” (OR 0.88). A multivariate model comprising “shorter duration of tinnitus” and “higher initial score on the somatic subscale of the TQ” correctly predicts the clinically relevant decrease in TQ score after treatment in 68.5%. A second multivariate model comprising “female gender,” “younger age,” and “shorter duration of the tinnitus” correctly predicts a clinically significant decrease on TFI after follow-up in 68.1%.

Conclusion

We were able to identify various prognostic indicators. “Younger female patients” with a “shorter duration of tinnitus” and a “higher initial score on the TQ somatic subscale” appear to have the best prognosis after multimodal orofacial therapy.

Lidocaine injections to the otic ganglion for the treatment of tinnitus-A pilot study

Tinnitus is defined as the perception of noise without an external acoustic stimulus. Due to the heterogeneity of tinnitus, no treatment has proven equally beneficial to every single of these patients. Previous studies have shown that trigeminal input can interfere with the perception of tinnitus. Therefore, we aimed to explore the therapeutic potential of lidocaine injections in trigeminal structures. We conducted a pilot study with 19 participants to explore feasibility and tolerability of this approach. The intervention consisted of three injections of lidocaine in the anatomical area of the trigeminal ganglion and the ganglion oticum via an oral approach corresponding to the affected side of tinnitus. We performed an assessment that included the Mini-TQ, CGII, and numeric rating scales of tinnitus loudness and severity at different time points over a follow-up period of 12 weeks. In addition to changes of subjective tinnitus complaints, potential adverse events were documented. Patients were treated at the Centre of Otorhinolaryngology in Traunstein, Germany, and data were analyzed at the University of Regensburg, Germany. We did not observe any relevant side effects. There was a significant reduction of tinnitus distress (Mini-TQ, Tinnitus severity) and loudness (measured subjectively) over time. Our pilot data suggests that lidocaine injections targeting trigeminal structures may be able to reduce tinnitus complaints. Future studies should investigate the effects of lidocaine injections in placebo-controlled trials in an extended sample size to further explore the potential benefits of this therapeutic approach on tinnitus.

Temporomandibular disorders, neck disability, and oral parafunctions in tinnitus patients: A cross-sectional epidemiological study from Southern Italy

OBJECTIVE

To assess the prevalence of temporomandibular disorders (TMD) in a sample of tinnitus patients and to determine the association between tinnitus, TMD, neck disability, and oral parafunctions.

METHODS

Seventy-nine tinnitus patients were enrolled and underwent standardized clinical examination for TMD. The tinnitus severity was measured with the Tinnitus Handicap Inventory (THI). The oral parafunctions were self-reported with the Oral Behavior Checklist (OBC). The neck disability was recorded with the Neck Disability Index (NDI).

RESULTS

More than half of the sample presented TMD, and the most frequent diagnosis was TMD pain. Higher THI was observed in TMD-pain individuals, compared to TMD-free (β 18.4; 95%CI 6.7, 30.1; p = 0.002). The OBC showed a significant low-to-moderate positive correlation with the THI (rho= 0.368, p = 0.001), while the NDI did not.

DISCUSSION

Standardized assessment of TMD and oral behaviors should be integrated into the routine diagnostic evaluations of tinnitus patients.

Larger tumor size and female gender suggest better tinnitus prognosis after surgical treatment in vestibular schwannoma patients with tinnitus

Background: Tinnitus is a subjective auditory phantom phenomenon which can be highly distressing. About 63%-75% vestibular schwannoma (VS) had a symptom of tinnitus.Objectives: To investigate the tinnitus maintenance mechanism from the view of tinnitus change after surgical treatment in VS patients.Material and methods: We conducted a retrospective study of VS patients with tinnitus from August 2008 to February 2019 and did follow-ups on their changes of tinnitus after surgery.Results: Among 298 VS cases, 201 of them had tinnitus symptom (67.4%). No statistical difference in the surgical approach was found between the tinnitus poor outcome and good outcome groups (p = .14), and statistical difference was found in gender (p = .04) and tumor size (p = .01) between the two groups. Binary logistic regression analysis revealed that gender (odds ratio [OR], 2.12; 95% CI, 1.10-4.08 [p = .03]) and tumor size (OR, 2.22; 95% CI, 1.16-4.24 [p = .02]) emerged as a significant and independent factor associated with the good outcome of tinnitus.Conclusions and significance: The results of this study confirmed that the cochlear nucleus of the brainstem and above part of the brainstem may play an important role in the maintenance of tinnitus.

Noise: Acoustic Trauma and Tinnitus, the US Military Experience

Tinnitus is commonly experienced by military Service Members and Veterans, especially by the newest generation who served in Iraq and Afghanistan. When patients seek health care for tinnitus, it is important to determine its type, check for comorbid conditions that might be triggering or exacerbating the condition, and to address its functional and psychosocial effects. Otolaryngologists are usually the first health care professional to evaluate a patient with tinnitus, and it is essential to provide appropriate referrals for this high-burden condition. Noise-induced tinnitus is multifaceted; by performing a thorough assessment, appropriate action can be taken to best meet the needs of patients.

Tinnitus, hearing loss and inflammatory processes in an older Portuguese population

Objective: Tinnitus is associated with various conditions such as presbycusis, infectious, autoimmune and many other diseases. Our study aims to identify an association between inflammatory markers and the presence of tinnitus or hearing loss (HL).Design: Exploratory study including a structured interview, complete ENT observation, audiological and inflammatory markers evaluation.Study Sample: Sixty women and 54 men (55 to 75 years) from the Portuguese population, with or without sensory presbycusis and/or tinnitus.Results: IL10 levels were significantly lower in participants with tinnitus than in those without tinnitus. Moreover, TGF-β was lower in older participants (p = 0.034), IL1α was higher in participants with tonal tinnitus (p = 0.033), and IL2 was lower in participants who reported partial or complete residual inhibition (p = 0.019). Additionally, we observed a negative correlation between tinnitus duration and IL10 levels (r= -.281), and between HSP70 levels and tinnitus loudness (r= -.377). TNF-α and HSP70 levels appears to be sensitive to the time when samples were collected (morning or afternoon).Conclusions: The results of our study showing fluctuations in inflammatory markers along the hearing loss process, reinforce the idea that inflammatory mechanisms are involved in hearing loss pathogenesis but also in tinnitus. IL10 levels appear significantly altered in tinnitus but not in hearing loss.

Amino acid and acetylcholine chemistry in mountain beaver cochlear nucleus and comparisons to pocket gopher, other rodents, and cat

The mountain beaver and pocket gopher are two rodents that live mostly underground in tunnel systems. Previous studies have suggested that their cochlear nucleus structure, particularly that of the dorsal cochlear nucleus (DCN), differs significantly from that of other mammals, that the hearing ability of the pocket gopher is deficient compared to that of other rodents, and that the DCN of the mountain beaver is more responsive to slow oscillations of air pressure than to sounds. We conducted some electrophysiological recordings from mountain beaver DCN and then used microchemical methods to map in mountain beaver cochlear nuclei the distributions of amino acids, including the major neurotransmitters of the brain, and enzyme activities related to the metabolism of the neurotransmitter acetylcholine, which functions in centrifugal pathways to the cochlear nucleus. Similar measurements were made for a pocket gopher cochlear nucleus. Responses to tonal stimuli were found in mountain beaver DCN. Distributions and magnitudes of neurotransmitter and related amino acids within mountain beaver and pocket gopher cochlear nuclei were not very different from those of other rodents and cat. However, the enzyme of synthesis for acetylcholine, choline acetyltransferase, had only low activities in the DCN of both mountain beaver and pocket gopher. The chemical distributions in the mountain beaver DCN support a conclusion that it corresponds to just the superficial DCN portion of other mammals. High correlations between the concentrations of γ-aminobutyrate (GABA) and glycine were found for both mountain beaver and pocket gopher cochlear nuclei, suggesting that their co-localization in cochlear nucleus synapses may be especially prominent in these animals. Previous evidence suggests convergence of somatosensory and auditory information in the DCN, and this may be especially true in animals spending most of their time underground. Our results suggest that the enlarged DCN of the mountain beaver and that of the pocket gopher are not very different from those of other rodents with respect to involvement of amino acid neurotransmitters, but they appear to have reduced cholinergic innervation.

The Role of the Brainstem in Generating and Modulating Tinnitus

Purpose The purpose of this work is to present a perspective article summarizing ideas pertaining to the brainstem's role in generating and modulating tinnitus. It is organized in 4 sections: Part 1, the role of the brainstem as a tinnitus generator; Part 2, the role of the brainstem in modulating tinnitus; Part 3, the role of the brainstem in nonauditory comorbid conditions associated with tinnitus; and Part 4, clinical implications. In Part 1, well-established neurophysiological models are discussed providing the framework of evidence that auditory brainstem nuclei play a role in generating tinnitus. In Part 2, ideas are presented explaining modulatory effects on tinnitus related to underlying pathways originating from or projecting to brainstem auditory and nonauditory nuclei. This section addresses multiple phenomena including somatic-related, attention-mediated, and emotion-mediated changes in the tinnitus percept. In Part 3, the role of the brainstem in common nonauditory comorbidities that occur in patients with tinnitus is discussed. Part 4 presents clinical implications of these new ideas related to the brainstem's involvement in generating and modulating tinnitus. Impact Knowledge of the brainstem's involvement in generating and modulating tinnitus provides a context for health care professionals to understand the temporal relationship between tinnitus and common nonauditory comorbid conditions.

Prolonged Exposure of CBA/Ca Mice to Moderately Loud Noise Can Cause Cochlear Synaptopathy but Not Tinnitus or Hyperacusis as Assessed With the Acoustic Startle Reflex

Hearing loss changes the auditory brain, sometimes maladaptively. When deprived of cochlear input, central auditory neurons become more active spontaneously and begin to respond more strongly and synchronously to better preserved sound frequencies. This spontaneous and sound-evoked central hyperactivity has been postulated to trigger tinnitus and hyperacusis, respectively. Localized hyperactivity has also been observed after long-term exposure to noise levels that do not damage the cochlea. Adult animals exposed to bands of nondamaging noise exhibited suppressed spontaneous and sound-evoked activity in the area of primary auditory cortex (A1) stimulated by the exposure band but had increased spontaneous and evoked activity in neighboring A1 areas. We hypothesized that the cortically suppressed frequencies should for some time after exposure be perceived as less loud than before (hypoacusis), whereas the hyperactivity outside of the exposure band might lead to frequency-specific hyperacusis or tinnitus. To investigate this, adult CBA/Ca mice were exposed for >2 months to 8 to 16 kHz noise at 70 or 75 dB sound pressure level and tested for hypo-/hyperacusis and tinnitus using tone and gap prepulse inhibition of the acoustic startle reflex. Auditory brainstem responses and distortion product otoacoustic emissions showed evidence of cochlear synaptopathy after exposure at 75 but not 70 dB, putting a lower bound on damaging noise levels for CBA/Ca mice. Contrary to hypothesis, neither exposure significantly shifted startle results from baseline. These negative findings nevertheless have implications for startle test methodology and for the putative role of central hyperactivity in hyperacusis and tinnitus.

Association Between Subjective Tinnitus and Cervical Spine or Temporomandibular Disorders: A Systematic Review

Movements of the neck and jaw may modulate the loudness and pitch of tinnitus. The aim of the present study was to systematically analyze the strength of associations between subjective tinnitus, cervical spine disorders (CSD), and temporomandibular disorders (TMD). A systematic literature search of the Medline, Embase, and Pedro databases was carried out on articles published up to September 2017. This covered studies in which tinnitus and CSD or TMD were studied as a primary or a secondary outcome and in which outcomes were compared with a control group. Included articles were evaluated on nine methodological quality criteria. Associations between tinnitus and CSD or TMD were expressed as odds ratios. In total, 2,139 articles were identified, of which 24 studies met the inclusion criteria. Twice, two studies were based on the same data set; consequently, 22 studies were included in the meta-analysis. Methodological quality was generally limited by a lack of blinding, comparability of groups, and nonvalidated instruments for assessing CSD. Results indicated that patients with tinnitus more frequently reported CSD than subjects without tinnitus. The odds ratio was 2.6 (95% CI [1.1, 6.4]). For TMD, a bidirectional association with tinnitus was found; odds ratios ranged from 2.3 (95%CI [1.5, 3.6]) for arthrogenous TMD to 6.7 (95%CI [2.4, 18.8]) for unspecified TMD. Funnel plots suggested a publication bias. After adjusting for this, the odds ratios decreased, but associations persisted. There is weak evidence for an association between subjective tinnitus and CSD and a bidirectional association between tinnitus and TMD.

Diagnostic Criteria for Somatosensory Tinnitus: A Delphi Process and Face-to-Face Meeting to Establish Consensus

Since somatic or somatosensory tinnitus (ST) was first described as a subtype of subjective tinnitus, where altered somatosensory afference from the cervical spine or temporomandibular area causes or changes a patient’s tinnitus perception, several studies in humans and animals have provided a neurophysiological explanation for this type of tinnitus. Due to a lack of unambiguous clinical tests, many authors and clinicians use their own criteria for diagnosing ST. This resulted in large differences in prevalence figures in different studies and limits the comparison of clinical trials on ST treatment. This study aimed to reach an international consensus on diagnostic criteria for ST among experts, scientists and clinicians using a Delphi survey and face-to-face consensus meeting strategy. Following recommended procedures to gain expert consensus, a two-round Delphi survey was delivered online, followed by an in-person consensus meeting. Experts agreed upon a set of criteria that strongly suggest ST. These criteria comprise items on somatosensory modulation, specific tinnitus characteristics, and symptoms that can accompany the tinnitus. None of these criteria have to be present in every single patient with ST, but in case they are present, they strongly suggest the presence of ST. Because of the international nature of the survey, we expect these criteria to gain wide acceptance in the research field and to serve as a guideline for clinicians across all disciplines. Criteria developed in this consensus paper should now allow further investigation of the extent of somatosensory influence in individual tinnitus patients and tinnitus populations.

Subtyping patients with somatic tinnitus: Modulation of tinnitus and history for somatic dysfunction help identify tinnitus patients with temporomandibular joint disorders

OBJECTIVE

Determine in a cohort of patients with normal hearing and chronic tinnitus if self-reported history for temporomandibular joint (TMJ) dysfunction and a positive modulation of tinnitus in the TMJ region could be suggestive of an underlying TMJ disorder.

PATIENTS AND METHODS

The study included 226 patients presenting to the Head and Neck Service of our University Hospital. Following audiological and somatic tinnitus evaluation, patients were divided into two groups. The study group (n = 134) included subjects that met both the following criteria: A) a self-reported history for TMJ dysfunction and B) a positive modulation of tinnitus following somatic maneuvers in the TMJ region. The control group (n = 92) included patients with similar demographic and tinnitus characteristics that did not meet the proposed criteria for somatic tinnitus. Afterwards, patients underwent clinical TMJ evaluation in the Service of Clinical Gnathology of our University.

RESULTS

One hundred thirty-one patients (57.9%) received a clinical diagnosis of TMJ disorder according to DC/TMD Axis I; 79.1% in the study group and 27.2% in the control group. Ninety-five (42.1%) patients were negative for TMJ disorders; 20.9% in the study group and 72.8% in the control group. A significantly higher number of TMJ disorders was found in patients in the study group compared to the control group (p<0.0001). Most patients had joint disorders (67.2%), followed by other (29.8%) and pain disorders (29%). Logistic regression analysis in the study group showed that female gender was more prevalent in patients with TMJ disorders.

CONCLUSION

Our findings in patients with chronic tinnitus and normal hearing suggest that self-reported history for somatic dysfunction and modulation of tinnitus, when occurring simultaneously in the TMJ region, can be useful to preliminarily identify patients with TMJ disorders.

Characteristics of somatic tinnitus patients with and without hyperacusis

Objective

Determine if somatic tinnitus patients with hyperacusis have different characteristics from those without hyperacusis.

Patients and methods

172 somatic tinnitus patients with (n = 82) and without (n = 90) hyperacusis referred to the Tinnitus Unit of Sapienza University of Rome between June 2012 and June 2016 were compared for demographic characteristics, tinnitus features, self-administered questionnaire scores, nature of somatic modulation and history.

Results

Compared to those without hyperacusis, patients with somatic tinnitus and hyperacusis: (a) were older (43.38 vs 39.12 years, p = 0.05), (b) were more likely to have bilateral tinnitus (67.08% vs 55.56%, p = 0.04), (c) had a higher prevalence of somatic modulation of tinnitus (53.65% vs 36.66%, p = 0.02) and (d) scored significantly worse on tinnitus annoyance (39.34 vs 22.81, p<0.001) and subjective hearing level (8.04 vs 1.83, p<0.001).

Conclusion

Our study shows significantly higher tinnitus modulation and worse self-rating of tinnitus and hearing ability in somatic tinnitus patients with hyperacusis versus somatic tinnitus patients without hyperacusis. These differences could prove useful in developing a better understanding of the pathophysiology and establishing a course of treatment for these two groups of patients.

Somatosensory tinnitus: Current evidence and future perspectives

In some individuals, tinnitus can be modulated by specific maneuvers of the temporomandibular joint, head and neck, eyes, and limbs. Neuroplasticity seems to play a central role in this capacity for modulation, suggesting that abnormal interactions between the sensory modalities, sensorimotor systems, and neurocognitive and neuroemotional networks may contribute to the development of somatosensory tinnitus. Current evidence supports a link between somatic disorders and higher modulation of tinnitus, especially in patients with a normal hearing threshold. Patients with tinnitus who have somatic disorders seems to have a higher chance of modulating their tinnitus with somatic maneuvers; consistent improvements in tinnitus symptoms have been observed in patients with temporomandibular joint disease following targeted therapy for temporomandibular disorders. Somatosensory tinnitus is often overlooked by otolaryngologists and not fully investigated during the diagnostic process. Somatic disorders, when identified and treated, can be a valid therapeutic target for tinnitus; however, somatic screening of subjects for somatosensory tinnitus is imperative for correct selection of patients who would benefit from a multidisciplinary somatic approach.

Electro-Tactile Stimulation Enhances Cochlear Implant Speech Recognition in Noise

For cochlear implant users, combined electro-acoustic stimulation (EAS) significantly improves the performance. However, there are many more users who do not have any functional residual acoustic hearing at low frequencies. Because tactile sensation also operates in the same low frequencies (<500 Hz) as the acoustic hearing in EAS, we propose electro-tactile stimulation (ETS) to improve cochlear implant performance. In ten cochlear implant users, a tactile aid was applied to the index finger that converted voice fundamental frequency into tactile vibrations. Speech recognition in noise was compared for cochlear implants alone and for the bimodal ETS condition. On average, ETS improved speech reception thresholds by 2.2 dB over cochlear implants alone. Nine of the ten subjects showed a positive ETS effect ranging from 0.3 to 7.0 dB, which was similar to the amount of the previously-reported EAS benefit. The comparable results indicate similar neural mechanisms that underlie both the ETS and EAS effects. The positive results suggest that the complementary auditory and tactile modes also be used to enhance performance for normal hearing listeners and automatic speech recognition for machines.

Pathophysiology, Diagnosis and Treatment of Somatosensory Tinnitus: A Scoping Review

Somatosensory tinnitus is a generally agreed subtype of tinnitus that is associated with activation of the somatosensory, somatomotor, and visual-motor systems. A key characteristic of somatosensory tinnitus is that is modulated by physical contact or movement. Although it seems common, its pathophysiology, assessment and treatment are not well defined. We present a scoping review on the pathophysiology, diagnosis, and treatment of somatosensory tinnitus, and identify priority directions for further research. Methods: Literature searches were conducted in Google Scholar, PubMed, and EMBASE databases. Additional broad hand searches were conducted with the additional terms etiology, diagnose, treatment. Results: Most evidence on the pathophysiology of somatosensory tinnitus suggests that somatic modulations are the result of altered or cross-modal synaptic activity within the dorsal cochlear nucleus or between the auditory nervous system and other sensory subsystems of central nervous system (e.g., visual or tactile). Presentations of somatosensory tinnitus are varied and evidence for the various approaches to treatment promising but limited. Discussion and Conclusions: Despite the apparent prevalence of somatosensory tinnitus its underlying neural processes are still not well understood. Necessary involvement of multidisciplinary teams in its diagnosis and treatment has led to a large heterogeneity of approaches whereby tinnitus improvement is often only a secondary effect. Hence there are no evidence-based clinical guidelines, and patient care is empirical rather than research-evidence-based. Somatic testing should receive further attention considering the breath of evidence on the ability of patients to modulate their tinnitus through manouvers. Specific questions for further research and review are indicated.

Long-Lasting forward Suppression of Spontaneous Firing in Auditory Neurons: Implication to the Residual Inhibition of Tinnitus

Tinnitus is the perception of a sound that has no external source. Sound stimuli can suppress spontaneous firing in auditory neurons long after stimulus offset. It is unknown how changes in sound stimulus parameters affect this forward suppression. Using in vivo extracellular recording in awake mice, we found that about 40 % of spontaneously active inferior colliculus (IC) neurons exhibited forward suppression of spontaneous activity after sound offset. The duration of this suppression increased with sound duration and lasted about 40 s following a 30-s stimulus offset. Pure tones presented at the neuron's characteristic frequency (CF) were more effective in triggering suppression compared to non-CF or wideband noise stimuli. In contrast, non-CF stimuli often induced forward facilitation. About one third of IC neurons exhibited shorter suppression durations with each subsequent sound presentation. These characteristics of forward suppression are similar to the psychoacoustic properties of residual inhibition of tinnitus: a phenomenon of brief (about 30 s) suppression of tinnitus observed in tinnitus patients after sound presentations. Because elevated spontaneous firing in central auditory neurons has been linked to tinnitus, forward suppression of this firing with sound might be an underlying mechanism of residual inhibition.

Optimization of Transcutaneous Vagus Nerve Stimulation Using Functional MRI

OBJECTIVE/HYPOTHESIS

Vagus nerve stimulation (VNS) is an established therapy for drug-resistant epilepsy, depression, and a number of other disorders. Transcutaneous stimulation of the auricular branch of the vagus nerve (tVNS) has been considered as a non-invasive alternative. Several functional magnetic resonance imaging (fMRI) studies on the effects of tVNS used different stimulation parameters and locations in the ear, which makes it difficult to determine the optimal tVNS methodology. The present study used fMRI to determine the most effective location for tVNS.

MATERIALS AND METHODS

Four stimulation locations in the ear were compared: the inner tragus, inferoposterior wall of the ear canal, cymba conchae, and earlobe (sham). Thirty-seven healthy subjects underwent two 6-min tVNS stimulation runs per electrode location (monophasic rectangular 500 μs pulses, 25 Hz). General linear model was performed using SPM; region-of-interest analyses were performed for the brainstem areas.

RESULTS

Stimulation at the ear canal resulted in the weakest activation of the nucleus of solitary tract (NTS), the recipient of most afferent vagal projections, and of the locus coeruleus (LC), a brainstem nucleus that receives direct input from the NTS. Stimulation of the inner tragus and cymba conchae activated these two nuclei as compared to sham. However, ROI analysis showed that only stimulation of the cymba conchae produced a significantly stronger activation in both the NTS and LC than did the sham stimulation.

CONCLUSIONS

These findings suggest that tVNS at the cymba conchae properly activates the vagal pathway and results in its strongest activation, and thus may be the optimal location for tVNS therapies applied to the auricle.

Volumes of cochlear nucleus regions in rodents

The cochlear nucleus receives all the coded information about sound from the cochlea and is the source of auditory information for the rest of the central auditory system. As such, it is a critical auditory nucleus. The sizes of the cochlear nucleus as a whole and its three major subdivisions - anteroventral cochlear nucleus (AVCN), posteroventral cochlear nucleus (PVCN), and dorsal cochlear nucleus (DCN) - have been measured in a large number of mammals, but measurements of its subregions at a more detailed level for a variety of species have not previously been made. Size measurements are reported here for the summed granular regions, DCN layers, AVCN, PVCN, and interstitial nucleus in 15 different rodent species, as well as a lagomorph, carnivore, and small primate. This further refinement of measurements is important because the granular regions and superficial layers of the DCN appear to have some different functions than the other cochlear nucleus regions. Except for DCN layers in the mountain beaver, all regions were clearly identifiable in all the animals studied. Relative regional size differences among most of the rodents, and even the 3 non-rodents, were not large and did not show a consistent relation to their wide range of lifestyles and hearing parameters. However, the mountain beaver, and to a lesser extent the pocket gopher, two rodents that live in tunnel systems, had relative sizes of summed granular regions and DCN molecular layer distinctly larger than those of the other mammals. Among all the mammals studied, there was a high correlation between the size per body weight of summed granular regions and that of the DCN molecular layer, consistent with other evidence for a close relationship between granule cells and superficial DCN neurons.

Volumes of cochlear nucleus regions in rodents

The cochlear nucleus receives all the coded information about sound from the cochlea and is the source of auditory information for the rest of the central auditory system. As such, it is a critical auditory nucleus. The sizes of the cochlear nucleus as a whole and its three major subdivisions - anteroventral cochlear nucleus (AVCN), posteroventral cochlear nucleus (PVCN), and dorsal cochlear nucleus (DCN) - have been measured in a large number of mammals, but measurements of its subregions at a more detailed level for a variety of species have not previously been made. Size measurements are reported here for the summed granular regions, DCN layers, AVCN, PVCN, and interstitial nucleus in 15 different rodent species, as well as a lagomorph, carnivore, and small primate. This further refinement of measurements is important because the granular regions and superficial layers of the DCN appear to have some different functions than the other cochlear nucleus regions. Except for DCN layers in the mountain beaver, all regions were clearly identifiable in all the animals studied. Relative regional size differences among most of the rodents, and even the 3 non-rodents, were not large and did not show a consistent relation to their wide range of lifestyles and hearing parameters. However, the mountain beaver, and to a lesser extent the pocket gopher, two rodents that live in tunnel systems, had relative sizes of summed granular regions and DCN molecular layer distinctly larger than those of the other mammals. Among all the mammals studied, there was a high correlation between the size per body weight of summed granular regions and that of the DCN molecular layer, consistent with other evidence for a close relationship between granule cells and superficial DCN neurons.

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

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

The occlusal imaging and analysis system by T-scan III in tinnitus patients

Background

Several studies have demonstrated that the prevalence of temporomandibular disorders (TMDs) in tinnitus patients ranges from 7% to 95%, and it is reported in literature that idiopathic tinnitus patients should be referred to a dentist to define whether or not the tinnitus is associated with TMD. However, the possible pathophysiological relation between TMDs and tinnitus is not generally investigated in clinical practice.

Methods

The patterns and forces of occlusal contacts have been studied by means of T-scan III in 47 tinnitus patients (23 suffering from idiopathic tinnitus and 24 affected by Ménière disease [MD]) and 13 healthy subjects.

Results

The center of force target was offset in the opposite direction in 15/23 idiopathic tinnitus and in 7/24 MD patients (p = 0.026). No significant variation was found in the occlusal force.

Conclusions

Our data suggest that a diagnostic screening method for occlusal stability in the intercuspidal position might be clinically useful in idiopathic tinnitus patients.