Cross-modal interactions of auditory and somatic inputs in the brainstem and midbrain and their imbalance in tinnitus and deafness

Blast Overpressures as a Military and Occupational Health Concern

PURPOSE

This tutorial reviews effects of environmental stressors like blast overpressures and other well-known acoustic contaminants (continuous, intermittent, and impulsive noise) on hearing, tinnitus, vestibular, and balance-related functions. Based on the overall outcome of these effects, detailed consideration is given to the health and well-being of individuals.

METHOD

Because hearing loss and tinnitus are consequential in affecting quality of life, novel neuromodulation paradigms are reviewed for their positive abatement and treatment-related effects. Examples of clinical data, research strategies, and methodological approaches focus on repetitive transcranial magnetic stimulation (rTMS) and electrical stimulation of the vagus nerve paired with tones (VNSt) for their unique contributions to this area.

RESULTS

Acoustic toxicants transmitted through the atmosphere are noteworthy for their propensity to induce hearing loss and tinnitus. Mounting evidence also indicates that high-level rapid onset changes in atmospheric sound pressure can significantly impact vestibular and balance function. Indeed, the risk of falling secondary to loss of, or damage to, sensory receptor cells in otolith organs (utricle and saccule) is a primary reason for this concern. As part of the complexities involved in VNSt treatment strategies, vocal dysfunction may also manifest. In addition, evaluation of temporospatial gait parameters is worthy of consideration based on their ability to detect and monitor incipient neurological disease, cognitive decline, and mortality.

CONCLUSION

Highlighting these respective areas underscores the need to enhance information exchange among scientists, clinicians, and caregivers on the benefits and complications of these outcomes.

Effectiveness of Dry Needling in Bothersome Chronic Tinnitus in Patients with Myofascial Trigger Points

Introduction  Therapeutic dry needling (DN) is effective in reducing the discomfort of chronic somatosensory tinnitus in patients with myofascial trigger points (MTP)s.

Objective  To evaluate the efficacy of DN in chronic somatosensory tinnitus discomfort in patients with MTP.

Methods  Placebo-controlled paired trial that included 16 patients with a diagnosis of somatosensory chronic tinnitus and with the presence of at least one active or latent MTP. Treatment was performed in two phases: (1) four sessions (one session per week for four consecutive weeks) of placebo DN and (2) four sessions of therapeutic DN with a gap (washout) of 15 days between these phases.

Results  The Tinnitus Handicap Inventory (THI) variable and its emotional domain had a statistically significant reduction in therapeutic DN when compared with placebo DN ( p  = 0.024 and p = 0.011, respectively).

The tinnitus visual analogic scale (VAS) signaled a reduction in tinnitus discomfort when compared with moments before and after therapeutic DN ( p  < 0.05).

Conclusion  The therapeutic DN technique for MTP in patients with chronic tinnitus of somatosensory origin proved effective in reducing symptom discomfort, as measured by the THI (total score) and its emotional domain when compared with placebo DN.

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.

Electrophysiological assessment and pharmacological treatment of blast-induced tinnitus

Tinnitus, the phantom perception of sound, often occurs as a clinical sequela of auditory traumas. In an effort to develop an objective test and therapeutic approach for tinnitus, the present study was performed in blast-exposed rats and focused on measurements of auditory brainstem responses (ABRs), prepulse inhibition of the acoustic startle response, and presynaptic ribbon densities on cochlear inner hair cells (IHCs). Although the exact mechanism is unknown, the “central gain theory” posits that tinnitus is a perceptual indicator of abnormal increases in the gain (or neural amplification) of the central auditory system to compensate for peripheral loss of sensory input from the cochlea. Our data from vehicle-treated rats supports this rationale; namely, blast-induced cochlear synaptopathy correlated with imbalanced elevations in the ratio of centrally-derived ABR wave V amplitudes to peripherally-derived wave I amplitudes, resulting in behavioral evidence of tinnitus. Logistic regression modeling demonstrated that the ABR wave V/I amplitude ratio served as a reliable metric for objectively identifying tinnitus. Furthermore, histopathological examinations in blast-exposed rats revealed tinnitus-related changes in the expression patterns of key plasticity factors in the central auditory pathway, including chronic loss of Arc/Arg3.1 mobilization. Using a formulation of N-acetylcysteine (NAC) and disodium 2,4-disulfophenyl-N-tert-butylnitrone (HPN-07) as a therapeutic for addressing blast-induced neurodegeneration, we measured a significant treatment effect on preservation or restoration of IHC ribbon synapses, normalization of ABR wave V/I amplitude ratios, and reduced behavioral evidence of tinnitus in blast-exposed rats, all of which accorded with mitigated histopathological evidence of tinnitus-related neuropathy and maladaptive neuroplasticity.

Tinnitus and Brain Stimulation

The pathophysiological mechanisms that underlie the generation and maintenance of tinnitus are being unraveled progressively. Based on this knowledge, a large variety of different neuromodulatory interventions have been developed and are still being designed, adapting to the progressive mechanistic insights in the pathophysiology of tinnitus. rTMS targeting the temporal, temporoparietal, and the frontal cortex has been the mainstay of non-invasive neuromodulation. Yet, the evidence is still unclear, and therefore systematic meta-analyses are needed for drawing conclusions on the effectiveness of rTMS in chronic tinnitus. Different forms of transcranial electrical stimulation (tDCS, tACS, tRNS), applied over the frontal and temporal cortex, have been investigated in tinnitus patients, also without robust evidence for universal efficacy. Cortex and deep brain stimulation with implanted electrodes have shown benefit, yet there is insufficient data to support their routine clinical use. Recently, bimodal stimulation approaches have revealed promising results and it appears that targeting different sensory modalities in temporally combined manners may be more promising than single target approaches.While most neuromodulatory approaches seem promising, further research is required to help translating the scientific outcomes into routine clinical practice.

Tinnitus and auditory cortex; Using adapted functional near-infrared-spectroscopy to expand brain imaging in humans

Objectives

Phantom sound perception (tinnitus) may arise from altered brain activity within auditory cortex. Auditory cortex neurons in tinnitus animal models show increased spontaneous firing rates. This may be a core characteristic of tinnitus. Functional near‐infrared spectroscopy (fNIRS) has shown similar findings in human auditory cortex. Current fNIRS approaches with cap recordings are limited to ∼3 cm depth of signal penetration due to the skull thickness. To address this limitation, we present an innovative fNIRS approach via probes adapted to the external auditory canal. The adapted probes were placed deeper and closer to temporal lobe of the brain to bypass confining skull bone and improve neural recordings.

Methods

Twenty adults with tinnitus and 20 nontinnitus controls listened to periods of silence and broadband noise (BBN) during standard cap and adapted ear canal fNIRS neuroimaging. The evaluators were not blinded, but the protocol and postprocessing for the two groups were identical.

Results

Standard fNIRS measurements in participants with tinnitus revealed increased auditory cortex activity during silence that was suppressed during auditory stimulation with BBN. Conversely, controls displayed increased activation with noise but not during silence. Importantly, adapted ear canal fNIRs probes showed similar hemodynamic responses seen with cap probes in both tinnitus and controls.

Conclusions

In this proof of concept study, we have successfully fabricated, adapted, and utilized a novel fNIRS technology that replicates established findings from traditional cap fNIRS probes. This exciting new innovation, validated by replicating previous and current cap findings in auditory cortex, may have applications to future studies to investigate brain changes not only in tinnitus but in other pathologic states that may involve the temporal lobe and surrounding brain regions.

Level of Evidence

NA.

Switching Tinnitus-On: Maps and source localization of spontaneous EEG

OBJECTIVE

To identify the spectrotemporal changes and sources in patients that could "turn on" tinnitus with multichannel electroencephalography (EEG) system.

METHODS

Multichannel EEG was recorded from six patients during the Tinnitus-On and Tinnitus-Off states. The EEG power spectrum and eLORETA-based sources were measured.

RESULTS

There was a global increase in delta and theta during Tinnitus-On plus large changes in alpha 1 and alpha 2. During the Tinnitus-On state, many new sources in delta, theta, alpha 1 and gamma bands emerged in the opposite hemisphere in the inferior temporal gyrus (Brodmann area, BA 20), middle temporal gyrus (BA 21), lateral perirhinal cortex (BA 36), ventral entorhinal cortex (BA 28) and anterior pole of the temporal gyrus (BA 38).

CONCLUSIONS

The emergence of new delta, theta and gamma band sources in the inferior temporal gyrus (BA 20), middle temporal gyrus (BA 21) and lateral perirhinal cortex (BA 36) plus the appearance of new delta and theta sources in the ventral entorhinal cortex (BA28) and anterior pole of the temporal lobe (BA 38) may comprise a network capable of evoking the phantom sound of tinnitus by simultaneously engaging brain regions involved in memory, sound recognition, and distress which together contribute to tinnitus severity.

SIGNIFICANCE

The sudden appearance of new sources of activity in the opposite hemisphere within the inferior temporal gyrus, middle temporal gyrus and perirhinal cortex may initiate the perception of tinnitus perception.

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.

Lingual electrotactile discrimination ability is associated with the presence of specific connective tissue structures (papillae) on the tongue surface

Electrical stimulation of nerve endings in the tongue can be used to communicate information to users and has been shown to be highly effective in sensory substitution applications. The anterior tip of the tongue has very small somatosensory receptive fields, comparable to those of the finger tips, allowing for precise two-point discrimination and high tactile sensitivity. However, perception of electrotactile stimuli varies significantly between users, and across the tongue surface. Despite this, previous studies all used uniform electrode grids to stimulate a region of the dorsal-medial tongue surface. In an effort to customize electrode layouts for individual users, and thus improve efficacy for sensory substitution applications, we investigated whether specific neuroanatomical and physiological features of the tongue are associated with enhanced ability to perceive active electrodes. Specifically, the study described here was designed to test whether fungiform papillae density and/or propylthiouracil sensitivity are positively or negatively associated with perceived intensity and/or discrimination ability for lingual electrotactile stimuli. Fungiform papillae number and distribution were determined for 15 participants and they were exposed to patterns of electrotactile stimulation (ETS) and asked to report perceived intensity and perceived number of stimuli. Fungiform papillae number and distribution were then compared to ETS characteristics using comprehensive and rigorous statistical analyses. Our results indicate that fungiform papillae density is correlated with enhanced discrimination ability for electrical stimuli. In contrast, papillae density, on average, is not correlated with perceived intensity of active electrodes. However, results for at least one participant suggest that further research is warranted. Our data indicate that propylthiouracil taster status is not related to ETS perceived intensity or discrimination ability. These data indicate that individuals with higher fungiform papillae number and density in the anterior medial tongue region may be better able to use lingual ETS for sensory substitution.

A backward encoding approach to recover subcortical auditory activity

Several subcortical nuclei along the auditory pathway are involved in the processing of sounds. One of the most commonly used methods of measuring the activity of these nuclei is the auditory brainstem response (ABR). Due to its low signal-to-noise ratio, ABR's have to be derived by averaging over activity generated by thousands of artificial sounds such as clicks or tone bursts. This approach cannot be easily applied to natural listening situations (e.g. speech, music), which limits auditory cognitive neuroscientific studies to investigate mostly cortical processes. We propose that by individually training backward encoding models to reconstruct evoked ABRs from high-density electrophysiological data, spatial filters can be tuned to auditory brainstem activity. Since these individualized filters can be applied (i.e. generalized) to any other data set using the same spatial coverage, this could allow for the estimation of auditory brainstem activity from any continuous sensor level data. In this study, we established a proof-of-concept by using backward encoding models generated using a click stimulation rate of 30 ​Hz to predict ABR activity recorded using EEG from an independent measurement using a stimulation rate of 9 ​Hz. We show that individually predicted and measured ABR's are highly correlated (r ​~ ​0.7). Importantly these predictions are stable even when applying the trained backward encoding model to a low number of trials, mimicking a situation with an unfavorable signal-to-noise ratio. Overall, this work lays the necessary foundation to use this approach in more interesting listening situations.

Increased risk of tinnitus following a trigeminal neuralgia diagnosis: a one-year follow-up study

Background

Tinnitus due to hyperactivity across neuronal ensembles along the auditory pathway is reported. We hypothesized that trigeminal neuralgia patients may subsequently suffer from tinnitus. Using nationwide, population-based data and a retrospective cohort study design, we investigated the risk of tinnitus within 1 year following trigeminal neuralgia.

Methods

We used the Taiwan National Health Insurance Research Dataset, a claims database, to identify all patients diagnosed with trigeminal neuralgia from January 2001 to December 2014, 12,587 patients. From the remaining patients, we identified 12,587 comparison patients without trigeminal neuralgia by propensity score matching, using sex, age, monthly income, geographic region, residential urbanization level, and tinnitus-relevant comorbidities (hyperlipidemia, diabetes, coronary heart disease, hypertension, cervical spondylosis, temporomandibular joint disorders and injury to head and neck and index year). All study patients (n = 25,174) were tracked for a one-year period to identify those with a subsequent diagnosis of tinnitus over 1-year follow-up.

Results

Among total 25,174 sample patients, the incidence of tinnitus was 18.21 per 100 person-years (95% CI = 17.66 ~ 18.77), the rate being 23.57 (95% CI = 22.68 ~ 24.49) among patients with trigeminal neuralgia and 13.17 (95% CI = 12.53 ~ 13.84) among comparison patients. Furthermore, the adjusted Cox proportional hazard ratio for tinnitus in the trigeminal neuralgia group was 1.68 (95% CI = 1.58 ~ 1.80) relative to the comparison cohort.

Conclusions

We found a significantly increased risk of tinnitus within 1 year of trigeminal neuralgia diagnosis compared to those without the diagnosis. Further studies in other countries and ethnicities are needed to explore the relationship between trigeminal neuralgia and subsequent tinnitus.

Multi-sensory (auditory and somatosensory) pre-pulse inhibition in mice

We investigated the perception of two mechanoreceptive modalities alone and in combination: main effects and interaction between auditory and somatosensory stimulation in mice. Fifteen C57BL/6J mice between the ages of 1 and 6 months were tested three times each. Experimental design roughly followed published procedures using pre-pulse inhibition (PPI) of the acoustic startle response, except pre-pulses included vibration of the test chamber as well as soft sounds. Auditory pre-pulses were 80 dB broadband noises of 4, 9, 25, or 45 ms duration. Vibrations were of the same duration but of different frequencies (500, 460, 360, and 220 Hz). Pre-pulse inhibition increased with duration of the auditory pre-pulses, as expected. There was significant PPI to some but not all vibrotactile pre-pulses. Multimodal PPI was approximately additive (no significant auditory-by-somatosensory interaction). PPI increased more with age to somatosensory than to auditory pre-pulses. Future studies of multi-modal psychophysics in various mouse mutants could lend support to more mechanistic studies of neural specificity and possibly autism, tinnitus, and PTSD.

Current Validated Medical Treatments: Pharmacologic Interventions

The search for an effective medication that will eliminate tinnitus has a long history. Currently, no drugs exist that universally cure tinnitus. Pharmacologic interventions that have been investigated can be divided into those that attempt to eliminate the perception of tinnitus, and those that are designed to treat the negative comorbidities associated with tinnitus, thereby mitigating tinnitus' negative impact on quality of life. A third category of drugs can also be considered that addresses an identified pathologic condition that has tinnitus as an associated symptom (for example, Meniere's disease, otosclerosis, migraine-associated vertigo). This third category is not addressed.

Vagus nerve stimulation paired with tones for tinnitus suppression: Effects on voice and hearing

OBJECTIVE

In individuals with chronic tinnitus, our interest was to determine whether daily low-level electrical stimulation of the vagus nerve paired with tones (paired-VNSt) for tinnitus suppression had any adverse effects on motor-speech production and physiological acoustics of sustained vowels. Similarly, we were also interested in evaluating for changes in pure-tone thresholds, word-recognition performance, and minimum-masking levels. Both voice and hearing functions were measured repeatedly over a period of 1 year.

STUDY DESIGN

Longitudinal with repeated-measures.

METHODS

Digitized samples of sustained frontal, midline, and back vowels (/e/, /o/, /ah/) were analyzed with computer software to quantify the degree of jitter, shimmer, and harmonic-to-noise ratio contained in these waveforms. Pure-tone thresholds, monosyllabic word-recognition performance, and MMLs were also evaluated for VNS alterations. Linear-regression analysis was the benchmark statistic used to document change over time in voice and hearing status from a baseline condition.

RESULTS

Most of the regression functions for the vocal samples and audiometric variables had slope values that were not significantly different from zero. Four of the nine vocal functions showed a significant improvement over time, whereas three of the pure tone regression functions at 2-4 kHz showed some degree of decline; all changes observed were for the left ear, all were at adjacent frequencies, and all were ipsilateral to the side of VNS. However, mean pure-tone threshold changes did not exceed 4.29 dB from baseline and therefore, would not be considered clinically significant. In some individuals, larger threshold shifts were observed. No significant regression/slope effects were observed for word-recognition or MMLs.

CONCLUSION

Quantitative voice analysis and assessment of audiometric variables showed minimal if any evidence of adverse effects using paired-VNSt over a treatment period of 1 year. Therefore, we conclude that paired-VNSt is a safe tool for tinnitus abatement in humans without significant side effects.

LEVEL OF EVIDENCE

Level IV.

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.

An Integrative Model Accounting for the Symptom Cluster Triggered After an Acoustic Shock

Acoustic shocks and traumas sometimes result in a cluster of debilitating symptoms, including tinnitus, hyperacusis, ear fullness and tension, dizziness, and pain in and outside the ear. The mechanisms underlying this large variety of symptoms remain elusive. In this article, we elaborate on the hypothesis that the tensor tympani muscle (TTM), the trigeminal nerve (TGN), and the trigeminal cervical complex (TCC) play a central role in generating these symptoms. We argue that TTM overuse (due to the acoustic shock), TTM overload (due to muscle tension), and ultimately, TTM injury (due to hypoxia and "energy crisis") lead to inflammation, thereby activating the TGN, TCC, and cortex. The TCC is a crossroad structure integrating sensory inputs coming from the head-neck complex (including the middle ear) and projecting back to it. The multimodal integration of the TCC may then account for referred pain outside the ear when the middle ear is inflamed and activates the TGN. We believe that our model proposes a synthetic and explanatory framework to explain the phenomena occurring postacoustic shock and potentially also after other nonauditory causes. Indeed, due to the bidirectional properties of the TCC, musculoskeletal disorders in the region of the head-neck complex, including neck injury due to whiplash or temporomandibular disorders, may impact the middle ear, thereby leading to otic symptoms. This previously unavailable model type is experimentally testable and must be taken as a starting point for identifying the mechanisms responsible for this particular subtype of tinnitus and its associated symptoms.

Neuroplastic change of cytoskeleton in inferior colliculus after auditory deafferentation

Neural plasticity is a characteristic of the brain that helps it adapt to changes in sensory input. We hypothesize that auditory deafferentation may induce plastic changes in the cytoskeleton of the neurons in the inferior colliculus (IC). In this study, we evaluated the dynamic status of neurofilament (NF) phosphorylation in the IC after hearing loss. We induced auditory deafferentation via unilateral or bilateral cochlear ablation in rats, aged 4 weeks. To evaluate cytoskeletal changes in neurons, we evaluated mRNA fold changes in NF heavy chain expression, non-phosphorylated NF protein fold changes using SMI-32 antibody, and the ratio of SMI-32 immunoreactive (SMI-32-ir) neurons to the total neuronal population in the IC at 4 and 12 weeks after deafness. In the bilateral deafness (BD) group, the ratios of SMI-32-ir neurons significantly increased at 4 weeks after ablation in the right and left IC (6.1 ± 4.4%, 5.0 ± 3.4%, respectively), compared with age-matched controls (P < 0.01, P < 0.01). At 12 weeks after ablation, the ratio of SMI-32 positive neurons was higher (right, 3.4 ± 2.0%; left, 3.2 ± 2.3%) than that in the age-matched control group, albeit not significant in the right and left side (P = 0.38, P = 0.24, respectively). Consistent with the results of the ratio of SMI-32-ir neurons, SMI-32-ir protein expression was increased at 4 weeks after BD, and the changes at 12 weeks after bilateral ablation were not significant in the right or left IC. The age-matched control fold changes of NF mRNA expression after bilateral deafness were not significant at 4 and 12 weeks after deafness in right and left IC. Unilateral deafness did not induce significant change of NF mRNA expression, SMI-32-ir protein expression, and the ratio of SMI-32-ir neurons in the IC at 4 and 12 weeks after hearing loss. Bilateral auditory deafferentation induces structural changes in the neuronal cytoskeleton within the IC, which is prominent at 4 weeks after BD. The structural remodeling of neurons stabilized at 12 weeks after BD. Unlike BD, unilateral auditory deafferentation did not affect the dynamic status of NFs in the IC.

Somatosensory Cross-Modal Reorganization in Adults With Age-Related, Early-Stage Hearing Loss

Under conditions of profound sensory deprivation, the brain has the propensity to reorganize. For example, intact sensory modalities often recruit deficient modalities' cortices for neural processing. This process is known as cross-modal reorganization and has been shown in congenitally and profoundly deaf patients. However, much less is known about cross-modal cortical reorganization in persons with less severe cases of age-related hearing loss (ARHL), even though such cases are far more common. Thus, we investigated cross-modal reorganization between the auditory and somatosensory modalities in older adults with normal hearing (NH) and mild-moderate ARHL in response to vibrotactile stimulation using high density electroencephalography (EEG). Results showed activation of the somatosensory cortices in adults with NH as well as those with hearing loss (HL). However, adults with mild-moderate ARHL also showed robust activation of auditory cortical regions in response to somatosensory stimulation. Neurophysiologic data exhibited significant correlations with speech perception in noise outcomes suggesting that the degree of cross-modal reorganization may be associated with functional performance. Our study presents the first evidence of somatosensory cross-modal reorganization of the auditory cortex in adults with early-stage, mild-moderate ARHL. Our findings suggest that even mild levels of ARHL associated with communication difficulty result in fundamental cortical changes.

Excitation of the Auditory System as a Result of Non-invasive Extra-Cochlear Stimulation in Normal Subjects and Tinnitus Patients

One of possible approach that may suppress tinnitus is electrical stimulation of the ear. At first invasive techniques were used (promontory or round window stimulation), nowadays a non-invasive method, namely hydrotransmissive electric stimulation (ES) through external acoustic canal, has been developed. The aim of the study is to investigate the effect of applying ES with positive and negative current polarities on the ears of healthy subjects and on the tinnitus ears of patients with tinnitus. This comparison further clarifies the mechanisms of operation of non-invasive extra-cochlear ear ES. A second aim is to assess the effects of ES on tinnitus in tinnitus patients. The material was composed of two groups: tinnitus group—49 patients suffering from tinnitus, and healthy students group—34 healthy individuals. ES was performed with the use of a custom-made apparatus. The active, silver probe–was immersed inside saline filling external ear canal. The passive electrode was placed on the forehead. Positive and next negative DC stimulation was provided with the use following frequencies: 0.25, 1, 2, 3, 4, 5, 6, 7, 8 kHz. We checked for the presence of the auditory percept (AP) and, if AP was present, the minimum current amplitude necessary to produce AP was measured. In our research both positive and negative polarities were efficient to evoke AP in the participants. This effect, however, was more pronounced for positive polarity in no tinnitus and normal hearing individuals (healthy students group). In the tinnitus group, current intensity needed to evoke AP was higher than in the healthy students group. However, comparing normal hearing vs. hearing loss patients within the tinnitus group, we did not observe the relationship between hearing threshold and current intensity evoking AP. Afterwards, we analyzed the effect of multi-frequency ES on tinnitus. It appeared to be effective in 75% of tinnitus ears (with a high score of disappearance–22%). Our study proved that extracochlear ES with positive and negative current was efficient to stimulate the auditory system. Stimulating tinnitus ears with two polarities we obtained a higher ratio of improvement (75%) comparing to positive stimulations.

A Pilot Study of Peripheral Muscle Magnetic Stimulation as Add-on Treatment to Repetitive Transcranial Magnetic Stimulation in Chronic Tinnitus

While brain stimulation techniques have been examined as treatment options for chronic tinnitus for many years, they have recently been extended to multimodal treatment approaches. As chronic tinnitus is often accompanied by comorbid muscular tension in the neck and back, we performed a one-arm pilot study to explore the feasibility of a new multimodal treatment approach. In detail, repetitive peripheral magnetic stimulation (rPMS) of the back was performed before and after each session of repetitive transcranial magnetic stimulation (rTMS) of the brain. Data of 41 patients were analyzed, all of which were treated with ten sessions of rTMS of the left prefrontal and left temporoparietal cortex followed by rPMS of the neck and back muscles. Tinnitus severity was measured using the tinnitus questionnaire (TQ). Neck pain was assessed using the neck pain and disability scale (NPAD). The new treatment approach was feasible and well accepted by the majority of patients. However, the overall patient group did not improve significantly in either of the questionnaires. If patients were divided in different subgroups depending on whether they were suffering from neck pain or somatosensory tinnitus, explorative post-hoc tests suggested differential effects: patients with both neck pain and somatosensory tinnitus had better outcomes than patients without those conditions or with neck pain only. This was true for both the TQ and the NPAD. This effect was of transient nature though: the TQ score went back to its baseline level after a follow-up period of 12 weeks. Based on our results we recommend that in studies that investigate tinnitus treatments targeting somatosensory afferents patients should be stratified according to somatic co-morbidities and somatosensory influence on the tinnitus percept.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov, NCT02306447.

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.

Changes of metabolism and functional connectivity in late-onset deafness: Evidence from cerebral 18F-FDG-PET

Hearing loss is known to impact brain function. The aim of this study was to characterize cerebral metabolic Positron Emission Tomography (PET) changes in elderly patients fulfilling criteria for cochlear implant and investigate the impact of hearing loss on functional connectivity. Statistical Parametric Mapping-T-scores-maps comparisons of ¹⁸F-FDG-PET of 27 elderly patients fulfilling criteria for cochlear implant for hearing loss (best-aided speech intelligibility lower or equal to 50%) and 27 matched healthy subjects (p < 0.005, corrected for volume extent) were performed. Metabolic connectivity was evaluated through interregional correlation analysis. Patients were found to have decreased metabolism within the right associative auditory cortex, while increased metabolism was found in prefrontal areas, pre- and post-central areas, the cingulum and the left inferior parietal gyrus. The right associative auditory cortex was integrated into a network of increased metabolic connectivity that included pre- and post-central areas, the cingulum, the right inferior parietal gyrus, as well as the striatum on both sides. Metabolic values of the right associative auditory cortex and left inferior parietal gyrus were positively correlated with performance on neuropsychological test scores. These findings provide further insight into the reorganization of the connectome through sensory loss and compensatory mechanisms in elderly patients with severe hearing loss.

Synaptic distribution and plasticity in primary auditory cortex (A1) exhibits laminar and cell-specific changes in the deaf

The processing sequence through primary auditory cortex (A1) is impaired by deafness as evidenced by reduced neuronal activation in A1 of cochlear-implanted deaf cats. Such a loss of neuronal excitation should be manifest as changes in excitatory synaptic number and/or size, for which the post-synaptic correlate is the dendritic spine. Therefore, the present study sought evidence for this functional disruption using Golgi-Cox/light microscopic techniques that examined spine-bearing neurons and their dendritic spine features across all laminae in A1 of early-deaf (ototoxic lesion <1 month; raised into adulthood >16 months) and hearing cats. Surprisingly, in the early-deaf significant increases in spine density and size were observed in the supragranular layers, while significant reductions in spine density were observed for spiny non-pyramidal, but not pyramidal, neurons in the granular layer. No changes in dendritic spine density consistent with loss of excitatory inputs were seen for infragranular neurons. These results indicate that long-term early-deafness induces plastic changes in the excitatory circuitry of A1 that are laminar and cell-specific. An additional finding was that, unlike the expected abundance of stellate neurons that characterize the granular layer of other primary sensory cortices, pyramidal neurons predominate within layer 4 of A1. Collectively, these observations are important for understanding how neuronal connectional configurations contribute to region-specific processing capabilities in normal brains as well as those with altered sensory experiences.

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.

Is territorial expansion a mechanism for crossmodal plasticity?

Crossmodal plasticity is the phenomenon whereby, following sensory damage or deprivation, the lost sensory function of a brain region is replaced by one of the remaining senses. One of several proposed mechanisms for this phenomenon involves the expansion of a more active brain region at the expense of another whose sensory inputs have been damaged or lost. This territorial expansion hypothesis was examined in the present study. The cat ectosylvian visual area (AEV) borders the auditory field of the anterior ectosylvian sulcus (FAES), which becomes visually reorganized in the early deaf. If this crossmodal effect in the FAES is due to the expansion of the adjoining AEV into the territory of the FAES after hearing loss, then the reorganized FAES should exhibit connectional features characteristic of the AEV. However, tracer injections revealed significantly different patterns of cortical connectivity between the AEV and the early deaf FAES, and substantial cytoarchitectonic and behavioral distinctions occur as well. Therefore, the crossmodal reorganization of the FAES cannot be mechanistically attributed to the expansion of the adjoining cortical territory of the AEV and an overwhelming number of recent studies now support unmasking of existing connections as the operative mechanism underlying crossmodal plasticity.

Cross-modal plasticity in developmental and age-related hearing loss: Clinical implications

This review explores cross-modal cortical plasticity as a result of auditory deprivation in populations with hearing loss across the age spectrum, from development to adulthood. Cross-modal plasticity refers to the phenomenon when deprivation in one sensory modality (e.g. the auditory modality as in deafness or hearing loss) results in the recruitment of cortical resources of the deprived modality by intact sensory modalities (e.g. visual or somatosensory systems). We discuss recruitment of auditory cortical resources for visual and somatosensory processing in deafness and in lesser degrees of hearing loss. We describe developmental cross-modal re-organization in the context of congenital or pre-lingual deafness in childhood and in the context of adult-onset, age-related hearing loss, with a focus on how cross-modal plasticity relates to clinical outcomes. We provide both single-subject and group-level evidence of cross-modal re-organization by the visual and somatosensory systems in bilateral, congenital deafness, single-sided deafness, adults with early-stage, mild-moderate hearing loss, and individual adult and pediatric patients exhibit excellent and average speech perception with hearing aids and cochlear implants. We discuss a framework in which changes in cortical resource allocation secondary to hearing loss results in decreased intra-modal plasticity in auditory cortex, accompanied by increased cross-modal recruitment of auditory cortices by the other sensory systems, and simultaneous compensatory activation of frontal cortices. The frontal cortices, as we will discuss, play an important role in mediating cognitive compensation in hearing loss. Given the wide range of variability in behavioral performance following audiological intervention, changes in cortical plasticity may play a valuable role in the prediction of clinical outcomes following intervention. Further, the development of new technologies and rehabilitation strategies that incorporate brain-based biomarkers may help better serve hearing impaired populations across the lifespan.

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.

Electrical Stimulation of the Ear, Head, Cranial Nerve, or Cortex for the Treatment of Tinnitus: A Scoping Review

Tinnitus is defined as the perception of sound in the absence of an external source. It is often associated with hearing loss and is thought to result from abnormal neural activity at some point or points in the auditory pathway, which is incorrectly interpreted by the brain as an actual sound. Neurostimulation therapies therefore, which interfere on some level with that abnormal activity, are a logical approach to treatment. For tinnitus, where the pathological neuronal activity might be associated with auditory and other areas of the brain, interventions using electromagnetic, electrical, or acoustic stimuli separately, or paired electrical and acoustic stimuli, have been proposed as treatments. Neurostimulation therapies should modulate neural activity to deliver a permanent reduction in tinnitus percept by driving the neuroplastic changes necessary to interrupt abnormal levels of oscillatory cortical activity and restore typical levels of activity. This change in activity should alter or interrupt the tinnitus percept (reduction or extinction) making it less bothersome. Here we review developments in therapies involving electrical stimulation of the ear, head, cranial nerve, or cortex in the treatment of tinnitus which demonstrably, or are hypothesised to, interrupt pathological neuronal activity in the cortex associated with tinnitus.

Origins of thalamic and cortical projections to the posterior auditory field in congenitally deaf cats

Crossmodal plasticity takes place following sensory loss, such that areas that normally process the missing modality are reorganized to provide compensatory function in the remaining sensory systems. For example, congenitally deaf cats outperform normal hearing animals on localization of visual stimuli presented in the periphery, and this advantage has been shown to be mediated by the posterior auditory field (PAF). In order to determine the nature of the anatomical differences that underlie this phenomenon, we injected a retrograde tracer into PAF of congenitally deaf animals and quantified the thalamic and cortical projections to this field. The pattern of projections from areas throughout the brain was determined to be qualitatively similar to that previously demonstrated in normal hearing animals, but with twice as many projections arising from non-auditory cortical areas. In addition, small ectopic projections were observed from a number of fields in visual cortex, including areas 19, 20a, 20b, and 21b, and area 7 of parietal cortex. These areas did not show projections to PAF in cats deafened ototoxically near the onset of hearing, and provide a possible mechanism for crossmodal reorganization of PAF. These, along with the possible contributions of other mechanisms, are considered.

Human Auditory and Adjacent Nonauditory Cerebral Cortices Are Hypermetabolic in Tinnitus as Measured by Functional Near-Infrared Spectroscopy (fNIRS)

Tinnitus is the phantom perception of sound in the absence of an acoustic stimulus. To date, the purported neural correlates of tinnitus from animal models have not been adequately characterized with translational technology in the human brain. The aim of the present study was to measure changes in oxy-hemoglobin concentration from regions of interest (ROI; auditory cortex) and non-ROI (adjacent nonauditory cortices) during auditory stimulation and silence in participants with subjective tinnitus appreciated equally in both ears and in nontinnitus controls using functional near-infrared spectroscopy (fNIRS). Control and tinnitus participants with normal/near-normal hearing were tested during a passive auditory task. Hemodynamic activity was monitored over ROI and non-ROI under episodic periods of auditory stimulation with 750 or 8000 Hz tones, broadband noise, and silence. During periods of silence, tinnitus participants maintained increased hemodynamic responses in ROI, while a significant deactivation was seen in controls. Interestingly, non-ROI activity was also increased in the tinnitus group as compared to controls during silence. The present results demonstrate that both auditory and select nonauditory cortices have elevated hemodynamic activity in participants with tinnitus in the absence of an external auditory stimulus, a finding that may reflect basic science neural correlates of tinnitus that ultimately contribute to phantom sound perception.

Maladaptive plasticity in tinnitus--triggers, mechanisms and treatment

Tinnitus is a phantom auditory sensation that reduces quality of life for millions of people worldwide, and for which there is no medical cure. Most cases of tinnitus are associated with hearing loss caused by ageing or noise exposure. Exposure to loud recreational sound is common among the young, and this group are at increasing risk of developing tinnitus. Head or neck injuries can also trigger the development of tinnitus, as altered somatosensory input can affect auditory pathways and lead to tinnitus or modulate its intensity. Emotional and attentional state could be involved in the development and maintenance of tinnitus via top-down mechanisms. Thus, military personnel in combat are particularly at risk owing to combined risk factors (hearing loss, somatosensory system disturbances and emotional stress). Animal model studies have identified tinnitus-associated neural changes that commence at the cochlear nucleus and extend to the auditory cortex and other brain regions. Maladaptive neural plasticity seems to underlie these changes: it results in increased spontaneous firing rates and synchrony among neurons in central auditory structures, possibly generating the phantom percept. This Review highlights the links between animal and human studies, and discusses several therapeutic approaches that have been developed to target the neuroplastic changes underlying tinnitus.

Tinnitus: Is there a place for brain stimulation?

Tinnitus is the perception of a “phantom sound” and has a high prevalence. Although many therapies have been investigated within the last decades, there is still no effective standard therapy. Animal studies and human functional imaging studies revealed that tinnitus perception is associated with many complex changes in multiple brain structures. There is growing evidence that brain stimulation might be able to interrupt the local altered neuronal activity and hereby inhibit tinnitus perception. In this editorial review, an update is given on the most promising targets for brain stimulation. Promising structures for stimulation are the dorsal cochlear nucleus, the inferior colliculus and the medial geniculate body of the thalamus. For cortical stimulation, the auditory cortex is considered as a target. Nevertheless, the field is waiting for evidence from well-designed clinical trials, based on supporting evidence from experimental/mechanistic research, to support or discourage the application of brain stimulation in tinnitus.

Sensorineural Tinnitus: Its Pathology and Probable Therapies

Tinnitus is not a single disease but a group of different diseases with different pathologies and therefore different treatments. Regarding tinnitus as a single disease is hampering progress in understanding of the pathophysiology of tinnitus and perhaps, more importantly, it is a serious obstacle in development of effective treatments for tinnitus. Subjective tinnitus is a phantom sound that takes many different forms and has similarities with chronic neuropathic pain. The pathology may be in the cochlea, in the auditory nerve, or, most commonly, in the brain. Like chronic neuropathic pain tinnitus is not life threatening but influences many normal functions such as sleep and the ability to concentrate on work. Some forms of chronic tinnitus have two components, a (phantom) sound and a component that may best be described as suffering or distress. The pathology of these two components may be different and the treatment that is most effective may be different for these two components. The most common form of treatment of tinnitus is pharmacological agents and behavioral treatment combined with sound therapy. Less common treatments are hypnosis and acupuncture. Various forms of neuromodulation are becoming in use in an attempt to reverse maladaptive plastic changes in the brain.

The onset of visual experience gates auditory cortex critical periods

Sensory systems influence one another during development and deprivation can lead to cross-modal plasticity. As auditory function begins before vision, we investigate the effect of manipulating visual experience during auditory cortex critical periods (CPs) by assessing the influence of early, normal and delayed eyelid opening on hearing loss-induced changes to membrane and inhibitory synaptic properties. Early eyelid opening closes the auditory cortex CPs precociously and dark rearing prevents this effect. In contrast, delayed eyelid opening extends the auditory cortex CPs by several additional days. The CP for recovery from hearing loss is also closed prematurely by early eyelid opening and extended by delayed eyelid opening. Furthermore, when coupled with transient hearing loss that animals normally fully recover from, very early visual experience leads to inhibitory deficits that persist into adulthood. Finally, we demonstrate a functional projection from the visual to auditory cortex that could mediate these effects.

Visual and auditory systems influence each other during development. Here, the authors show that the onset of eyelid opening regulates critical points during which the auditory cortex is sensitive to hearing loss or the restoration of hearing

A new concept for noninvasive tinnitus treatment utilizing multimodal pathways

Current noninvasive treatments for tinnitus have shown mixed results. There have been encouraging developments in using invasive brain or vagal nerve stimulation to modulate neural populations driving the tinnitus percept. However, these invasive treatments can only be used in a small patient population with severe conditions. In this preliminary study, we present a new treatment option we call Multimodal Synchronization Therapy (MST), which attempts to achieve synchronized and localized brain activation without invasive neural stimulation. MST combines multiple sensory, motor, limbic, and cognitive inputs to elicit activation of multimodal neurons to potentially modulate specific neurons driving the tinnitus percept. We present preliminary data in a guinea pig model showing activation of somatosensory and auditory pathways to alter neural activity within the inferior colliculus, a multimodal integration region that has shown pathological changes in animals and patients with tinnitus. Electrical stimulation of different body locations induced excitatory responses in the inferior colliculus, eliciting responses in up to 41% of all recording sites for a given somatic site. Paired somatic and acoustic stimulation resulted in enhanced or suppressed acoustic-driven neural activity in the inferior colliculus that varied depending on stimulation and recording location. Similar modulation effects were observed in the auditory cortex, which may relate to changes in auditory perception. Further studies need to incorporate multiple multimodal pathways and must also confirm that MST can suppress the abnormal neural patterns that directly drive the tinnitus percept.

L, B. T, M. A. P, K. K, C. M. S, G. D. S. Multisensory attention training for treatment of tinnitus

Tinnitus is the conscious perception of sound with no physical sound source. Some models of tinnitus pathophysiology suggest that networks associated with attention, memory, distress and multisensory experience are involved in tinnitus perception. The aim of this study was to evaluate whether a multisensory attention training paradigm which used audio, visual, and somatosensory stimulation would reduce tinnitus. Eighteen participants with predominantly unilateral chronic tinnitus were randomized between two groups receiving 20 daily sessions of either integration (attempting to reduce salience to tinnitus by binding with multisensory stimuli) or attention diversion (multisensory stimuli opposite side to tinnitus) training. The training resulted in small but statistically significant reductions in Tinnitus Functional Index and Tinnitus Severity Numeric Scale scores and improved attentional abilities. No statistically significant improvements in tinnitus were found between the training groups. This study demonstrated that a short period of multisensory attention training reduced unilateral tinnitus, but directing attention toward or away from the tinnitus side did not differentiate this effect.

The effectiveness of neuro-music therapy according to the Heidelberg model compared to a single session of educational counseling as treatment for tinnitus: a controlled trial

OBJECTIVES

Tinnitus is a very common symptom, yet the quest for an effective treatment is challenging. Results from several clinical trials support the notion that neuro-music therapy is an effective means to reduce tinnitus distress with short duration and long lasting effect. However, until now, the effectiveness has not been tested in a controlled trial against an active comparator.

METHODS

The trial was designed as two-center, parallel intervention group controlled study with two intervention groups: Counseling (50minute individualized personal instruction) or neuro-music therapy (counseling plus eight 50-minute sessions of individualized music therapy). Data of n=290 patients suffering from chronic tinnitus were analyzed. Outcome measure was the change in Tinnitus Questionnaire Total Scores (TQ) from baseline (admission) to end of treatment.

RESULTS

Both treatment groups achieved a statistically relevant reduction in TQ scores, though 66% of patients in the music therapy group attained a clinically meaningful improvement compared to 33% in the counseling group. A binary logistic regression revealed two variables significantly influencing therapy outcome: initial tinnitus score and type of therapy with an OR for the music therapy compared to the counseling of 4.34 (CI 2.33-8.09).

CONCLUSIONS

Counseling is an appropriate treatment option with well above chance of improvement. The neuro-music therapy outperformed the counseling. This treatment targets the tinnitus sound itself, is short in duration, intrinsically motivating and easy to operate and thus presents a possible complement to the therapeutic spectrum in chronic tinnitus. The trial was registered at the ClinicalTrials.gov registry (ID: NCT01845155).

Tinnitus Holistic Simplified Classification (THoSC): A New Assessment for Subjective Tinnitus, With Diagnostic and Therapeutic Implications

OBJECTIVE

One of the most debated topics in tinnitus is its standard and practical classification. The most popular classification distinguishes subjective from objective tinnitus. Other classifications are based on different features. On the whole, they seem incomplete, and the diagnostic and therapeutic algorithms are often difficult for practical purposes. The aim of this work is to develop a new diagnostic and therapeutic algorithm.

METHODS

Our model is based on 10 years of experience. In particular, the starting point is the data retrieved from 212 consecutive patients in our Tinnitus Unit between May and December 2013: We found a clear auditory disorder in 74.5% of the population, muscolo-skeletal disorders and/or trigeminal disease in 57.1%, and psychiatric comorbidities in 43.8%. Different features coexisted in 59.9% of the population.

RESULTS

Following such data we propose the Tinnitus Holistic Simplified Classification, which takes into account the different tinnitogenic mechanisms and the interactions between them. It differentiates tinnitus that arises from: (1) auditory alterations (Auditory Tinnitus), (2) complex auditory-somatosensory interactions (Somatosensory Tinnitus), (3) psychopathological-auditory interactions (Psychopathology-related Tinnitus), and (4) 2 or all of the previous mechanisms (Combined Tinnitus).

CONCLUSIONS

In our opinion this classification provides an accurate and easy tailored path to manage tinnitus patients.

An audiometric study of the effects of paraspinal stimulation on hearing acuity in human subjects - understanding the Harvey Lillard phenomenon

Background

The founder of chiropractic, Daniel David Palmer, constructed a model of causation of disease based on his seminal experience with a patient, Harvey Lillard, who lost his hearing at the instant of injuring his upper back, but had his hearing restored suddenly 17 years later after receiving spinal manipulation. Palmer’s model of disease causation, that of displaced vertebrae impinging on spinal nerves and thereby disrupting the innervation of dependent organs, was in fact incongruent with what was known at the time about human neuroanatomy and neurophysiology. The current study proposes and tests an alternative hypothesis: that increased afferent input from paraspinal muscles attenuates the central transmission of auditory information.

Methods

Between September 13 and November 13, 2013, forty healthy young adults were recruited and randomly divided into two cohorts: one receiving successive trials of sham TENS, and the second receiving sham and then authentic TENS. During the administration of sham and authentic TENS to the upper thoracic spine, hearing acuity was measured to determine perception thresholds at the frequencies normally tested clinically.

Results

In the first cohort, there were no differences in perception thresholds in the first and second trials of sham TENS, speaking to the reliability of the testing process. In the second cohort, there were no significant differences in perception thresholds during sham and authentic TENS.

Conclusions

Within the constraints of the current study design, including demographic characteristics and TENS parameters, there was no evidence that innocuous afferent input to upper thoracic paraspinal muscles modulated thresholds of audibility.

Underlying mechanisms of tinnitus: review and clinical implications

BACKGROUND

The study of tinnitus mechanisms has increased tenfold in the last decade. The common denominator for all of these studies is the goal of elucidating the underlying neural mechanisms of tinnitus with the ultimate purpose of finding a cure. While these basic science findings may not be immediately applicable to the clinician who works directly with patients to assist them in managing their reactions to tinnitus, a clear understanding of these findings is needed to develop the most effective procedures for alleviating tinnitus.

PURPOSE

The goal of this review is to provide audiologists and other health-care professionals with a basic understanding of the neurophysiological changes in the auditory system likely to be responsible for tinnitus.

RESULTS

It is increasingly clear that tinnitus is a pathology involving neuroplastic changes in central auditory structures that take place when the brain is deprived of its normal input by pathology in the cochlea. Cochlear pathology is not always expressed in the audiogram but may be detected by more sensitive measures. Neural changes can occur at the level of synapses between inner hair cells and the auditory nerve and within multiple levels of the central auditory pathway. Long-term maintenance of tinnitus is likely a function of a complex network of structures involving central auditory and nonauditory systems.

CONCLUSIONS

Patients often have expectations that a treatment exists to cure their tinnitus. They should be made aware that research is increasing to discover such a cure and that their reactions to tinnitus can be mitigated through the use of evidence-based behavioral interventions.

Prevalence and factors associated with neck and jaw muscle modulation of tinnitus

Forceful contractions of neck and jaw muscles have consistently been shown to modulate tinnitus and can be used to screen patients who are responsive to somatic stimulation and, therefore, optimal candidates for somatosensory-based treatment. To identify the factors associated with somatic modulation of tinnitus, 163 patients underwent 19 neck and jaw maneuvers after an extensive physiological and audiological profile was compiled. Overall, tinnitus was modulated in 57.1% of ears tested. Unilateral tinnitus showed greater prevalence of modulation. Neck maneuvers generally decreased tinnitus loudness, whereas jaw maneuvers increased loudness. Female gender and buzzing tinnitus were associated with a high prevalence of modulation and a decrease in tinnitus loudness. Loud tinnitus and low-pitched tonal tinnitus were associated with exacerbation of the condition as a result of somatic testing. Use of these characteristics to select optimal candidates for somatosensory-based tinnitus therapies may be essential for the development of an effective approach for tinnitus treatment.

Up-regulation of GAP-43 in the chinchilla ventral cochlear nucleus after carboplatin-induced hearing loss: correlations with inner hair cell loss and outer hair cell loss

Inner ear damage leads to nerve fiber growth and synaptogenesis in the ventral cochlear nucleus (VCN). In this study, we documented the relationship between hair cell loss patterns and synaptic plasticity in the chinchilla VCN using immunolabeling of the growth associated protein-43 (GAP-43), a protein associated with axon outgrowth and modification of presynaptic endings. Unilateral round window application of carboplatin caused hair cell degeneration in which inner hair cells (IHC) were more vulnerable than outer hair cells (OHC). One month after carboplatin treatment (0.5-5 mg/ml), we observed varying patterns of cochlear hair cell loss and GAP-43 expression in VCN. Both IHC loss and OHC loss were strongly correlated with increased GAP-43 immunolabeling in the ipsilateral VCN. We speculate that two factors might promote the expression of GAP-43 in the VCN; one is the loss of afferent input through IHC or the associated type I auditory nerve fibers. The other occurs when the medial olivocochlear efferent neurons lose their cochlear targets, the OHC, and may as compensation increase their synapse numbers in the VCN.

Differential auditory-oculomotor interactions in patients with right vs. left sided subjective tinnitus: a saccade study

Subjective tinnitus (ST) is a frequent but poorly understood medical condition. Recent studies demonstrated abnormalities in several types of eye movements (smooth pursuit, optokinetic nystagmus, fixation, and vergence) in ST patients. The present study investigates horizontal and vertical saccades in patients with tinnitus lateralized predominantly to the left or to the right side. Compared to left sided ST, tinnitus perceived on the right side impaired almost all the parameters of saccades (latency, amplitude, velocity, etc.) and noticeably the upward saccades. Relative to controls, saccades from both groups were more dysmetric and were characterized by increased saccade disconjugacy (i.e., poor binocular coordination). Although the precise mechanisms linking ST and saccadic control remain unexplained, these data suggest that ST can lead to detrimental auditory, visuomotor, and perhaps vestibular interactions.

Cholinergic neurons in the mouse rostral ventrolateral medulla target sensory afferent areas

The rostral ventrolateral medulla (RVLM) primarily regulates respiration and the autonomic nervous system. Its medial portion (mRVLM) contains many choline acetyltransferase (ChAT)-immunoreactive (ir) neurons of unknown function. We sought to clarify the role of these cholinergic cells by tracing their axonal projections. We first established that these neurons are neither parasympathetic preganglionic neurons nor motor neurons because they did not accumulate intraperitoneally administered Fluorogold. We traced their axonal projections by injecting a Cre-dependent vector (floxed-AAV2) expressing either GFP or mCherrry into the mRVLM of ChAT-Cre mice. Transduced neurons expressing GFP or mCherry were confined to the injection site and were exclusively ChAT-ir. Their axonal projections included the dorsal column nuclei, medullary trigeminal complex, cochlear nuclei, superior olivary complex and spinal cord lamina III. For control experiments, the floxed-AAV2 (mCherry) was injected into the RVLM of dopamine beta-hydroxylase-Cre mice. In these mice, mCherry was exclusively expressed by RVLM catecholaminergic neurons. Consistent with data from rats, these catecholaminergic neurons targeted brain regions involved in autonomic and endocrine regulation. These regions were almost totally different from those innervated by the intermingled mRVLM-ChAT neurons. This study emphasizes the advantages of using Cre-driver mouse strains in combination with floxed-AAV2 to trace the axonal projections of chemically defined neuronal groups. Using this technique, we revealed previously unknown projections of mRVLM-ChAT neurons and showed that despite their close proximity to the cardiorespiratory region of the RVLM, these cholinergic neurons regulate sensory afferent information selectively and presumably have little to do with respiration or circulatory control.