Neuroanatomical Alterations in Tinnitus Assessed with Magnetic Resonance Imaging

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

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

Causal Associations of Genetically Determined Tinnitus With Neuroimaging Traits: Evidence From a Mendelian Randomization Study

OBJECTIVES

Potential reverse causality and unmeasured confounding factors are common biases in most neuroimaging studies on tinnitus and central correlates. The causal association of tinnitus with neuroimaging features also remains unclear. This study aimed to investigate the causal relationship of tinnitus with neuroplastic alterations using Mendelian randomization.

DESIGN

Summary-level data from a genome-wide association study of tinnitus were derived from UK Biobank (n = 117,882). The genome-wide association study summary statistics for 4 global-brain tissue and 14 sub-brain gray matter volumetric traits were also obtained (n = up to 33,224). A bidirectional Mendelian randomization analysis was conducted to explore the causal relationship between tinnitus and neuroanatomical features at global-brain and sub-brain levels.

RESULTS

Genetic susceptibility to tinnitus was causally associated with increased white matter volume (odds ratio [OR] = 2.361, 95% confidence interval [CI], 1.033 to 5.393) and total brain volume (OR = 2.391, 95% CI, 1.047 to 5.463) but inversely associated with cerebrospinal fluid volume (OR = 0.362, 95% CI, 0.158 to 0.826). A smaller gray matter volume in the left Heschl's gyrus and right insular cortex and larger gray matter volume in the posterior division of the left parahippocampal gyrus may lead to an increased risk for tinnitus (OR = 0.978, 95% CI, 0.961 to 0.996; OR = 0.987, 95% CI, 0.976 to 0.998; and OR = 1.015, 95% CI, 1.001 to 1.028, respectively).

CONCLUSIONS

Genetic susceptibility to tinnitus was causally associated with increased white matter volume and total brain volume. Volume alteration in several cortical regions may indicate a higher tinnitus risk, and further research is recommended for causality inference at the level of sub-brain regions. Our findings provide genetic evidence for elucidating the underlying pathophysiological mechanisms of tinnitus-related neuroanatomical abnormalities.

What is the role of the hippocampus and parahippocampal gyrus in the persistence of tinnitus?

The hippocampus and parahippocampal gyrus have been implicated as part of a tinnitus network by a number of studies. These structures are usually considered in the context of a "limbic system," a concept typically invoked to explain the emotional response to tinnitus. Despite this common framing, it is not apparent from current literature that this is necessarily the main functional role of these structures in persistent tinnitus. Here, we highlight a different role that encompasses their most commonly implicated functional position within the brain-that is, as a memory system. We consider tinnitus as an auditory object that is held in memory, which may be made persistent by associated activity from the hippocampus and parahippocampal gyrus. Evidence from animal and human studies implicating these structures in tinnitus is reviewed and used as an anchor for this hypothesis. We highlight the potential for the hippocampus/parahippocampal gyrus to facilitate maintenance of the memory of the tinnitus percept via communication with auditory cortex, rather than (or in addition to) mediating emotional responses to this percept.

The neuroanatomical hallmarks of chronic tinnitus in comorbidity with pure-tone hearing loss

Tinnitus is one of the main hearing impairments often associated with pure-tone hearing loss, and typically manifested in the perception of phantom sounds. Nevertheless, tinnitus has traditionally been studied in isolation without necessarily considering auditory ghosting and hearing loss as part of the same syndrome. Hence, in the present neuroanatomical study, we attempted to pave the way toward a better understanding of the tinnitus syndrome, and compared two groups of almost perfectly matched individuals with (TIHL) and without (NTHL) pure-tone tinnitus, but both characterized by pure-tone hearing loss. The two groups were homogenized in terms of sample size, age, gender, handedness, education, and hearing loss. Furthermore, since the assessment of pure-tone hearing thresholds alone is not sufficient to describe the full spectrum of hearing abilities, the two groups were also harmonized for supra-threshold hearing estimates which were collected using temporal compression, frequency selectivity und speech-in-noise tasks. Regions-of-interest (ROI) analyses based on key brain structures identified in previous neuroimaging studies showed that the TIHL group exhibited increased cortical volume (CV) and surface area (CSA) of the right supramarginal gyrus and posterior planum temporale (PT) as well as CSA of the left middle-anterior part of the superior temporal sulcus (STS). The TIHL group also demonstrated larger volumes of the left amygdala and of the left head and body of the hippocampus. Notably, vertex-wise multiple linear regression analyses additionally brought to light that CSA of a specific cluster, which was located in the left middle-anterior part of the STS and overlapped with the one found to be significant in the between-group analyses, was positively associated with tinnitus distress level. Furthermore, distress also positively correlated with CSA of gray matter vertices in the right dorsal prefrontal cortex and the right posterior STS, whereas tinnitus duration was positively associated with CSA and CV of the right angular gyrus (AG) and posterior part of the STS. These results provide new insights into the critical gray matter architecture of the tinnitus syndrome matrix responsible for the emergence, maintenance and distress of auditory phantom sensations.

An Inverse Relationship Between Gray Matter Volume and Speech-in-Noise Performance in Tinnitus Patients with Normal Hearing Sensitivity

Speech-in-noise (SiN) recognition difficulties are often reported in patients with tinnitus. Although brain structural changes such as reduced gray matter (GM) volume in auditory and cognitive processing regions have been reported in the tinnitus population, it remains unclear how such changes influence speech understanding, such as SiN performance. In this study, pure-tone audiometry and Quick Speech-in-Noise test were conducted on individuals with tinnitus and normal hearing and hearing-matched controls. T1-weighted structural MRI images were obtained from all participants. After preprocessing, GM volumes were compared between tinnitus and control groups using whole-brain and region-of-interest analyses. Further, regression analyses were performed to examine the correlation between regional GM volume and SiN scores in each group. The results showed decreased GM volume in the right inferior frontal gyrus in the tinnitus group relative to the control group. In the tinnitus group, SiN performance showed a negative correlation with GM volume in the left cerebellum (Crus I/II) and the left superior temporal gyrus; no significant correlation between SiN performance and regional GM volume was found in the control group. Even with clinically defined normal hearing and comparable SiN performance relative to controls, tinnitus appears to change the association between SiN recognition and regional GM volume. This change may reflect compensatory mechanisms utilized by individuals with tinnitus who maintain behavioral performance.

Multi-tasking deep network for tinnitus classification and severity prediction from multimodal structural MR images

Objective:Subjective tinnitus is an auditory phantom perceptual disorder without an objective biomarker. Fast and efficient diagnostic tools will advance clinical practice by detecting or confirming the condition, tracking change in severity, and monitoring treatment response. Motivated by evidence of subtle anatomical, morphological, or functional information in magnetic resonance images of the brain, we examine data-driven machine learning methods for joint tinnitus classification (tinnitus or no tinnitus) and tinnitus severity prediction.Approach:We propose a deep multi-task multimodal framework for tinnitus classification and severity prediction using structural MRI (sMRI) data. To leverage complementary information multimodal neuroimaging data, we integrate two modalities of three-dimensional sMRI-T1 weighted (T1w) and T2 weighted (T2w) images. To explore the key components in the MR images that drove task performance, we segment both T1w and T2w images into three different components-cerebrospinal fluid, grey matter and white matter, and evaluate performance of each segmented image.Main results:Results demonstrate that our multimodal framework capitalizes on the information across both modalities (T1w and T2w) for the joint task of tinnitus classification and severity prediction.Significance:Our model outperforms existing learning-based and conventional methods in terms of accuracy, sensitivity, specificity, and negative predictive value.

Application of auditory mismatch negativity in tinnitus patients based on high-resolution electroencephalogram signals

Objective

The purpose of this study was to investigate the significance of mismatch negativity (MMN) by comparing high-resolution electroencephalogram signals from tinnitus patients and healthy controls.

Methods

The study included eight subjects with chronic subjective idiopathic tinnitus and seven healthy controls. Participants with clinical speech (512-2,000 Hz) hearing thresholds less than 25 dB HL and with negative Hospital Anxiety and Depression Scale scores were included in the study. The E-Prime 2.0 software and a 256-electrode EGI Net Station system were used to evoke and record the MMN signal, and the amplitude and latency parameters of the MMN responses were compared between the two groups.

Results

From 150 ms, there was a significant difference between the amplitude of standard stimulation and deviation stimulation, and the event-related potential amplitude under deviation stimulation in the tinnitus patient group was significantly different from that in the healthy group. The MMN amplitude of the FCz electrode was statistically significantly lower in the tinnitus patients compared to healthy controls.

Conclusion

MMN has application value in the evaluation of abnormal electrical activity in the auditory pathway, and electroencephalograms are feasible for follow-up monitoring after acoustic therapy.

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

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

A Combined Image- and Coordinate-Based Meta-Analysis of Whole-Brain Voxel-Based Morphometry Studies Investigating Subjective Tinnitus

Previous voxel-based morphometry (VBM) studies investigating tinnitus have reported structural differences in a variety of spatially distinct gray matter regions. However, the results have been highly inconsistent and sometimes contradictory. In the current study, we conducted a combined image- and coordinate-based meta-analysis of VBM studies investigating tinnitus to identify robust gray matter differences associated with tinnitus, as well as examine the possible effects of hearing loss on the outcome of the meta-analysis. The PubMed and Web of Science databases were searched for studies published up to August 2021. Additional manual searches were conducted for studies published up to December 2021. A whole-brain meta-analysis was performed using Seed-Based d Mapping with Permutation of Subject Images (SDM-PSI). Fifteen studies comprising 423 individuals with tinnitus and either normal hearing or hearing loss (mean age 50.94 years; 173 females) and 508 individuals without tinnitus and either normal hearing or hearing loss (mean age 51.59 years; 234 females) met the inclusion criteria. We found a small but significant reduction in gray matter in the left inferior temporal gyrus for groups of normal hearing individuals with tinnitus compared to groups of hearing-matched individuals without tinnitus. In sharp contrast, in groups with hearing loss, tinnitus was associated with increased gray matter levels in the bilateral lingual gyrus and the bilateral precuneus. Those results were dependent upon matching the hearing levels between the groups with or without tinnitus. The current investigation suggests that hearing loss is the driving force of changes in cortical gray matter across individuals with and without tinnitus. Future studies should carefully account for confounders, including hearing loss, hyperacusis, anxiety, and depression, to identify gray matter changes specifically related to tinnitus. Ultimately, the aggregation of standardized individual datasets with both anatomical and useful phenotypical information will permit a better understanding of tinnitus-related gray matter differences, the effects of potential comorbidities, and their interactions with tinnitus.

Advantages of Using Both Voxel- and Surface-based Morphometry in Cortical Morphology Analysis: A Review of Various Applications

Surface-based morphometry (SBM) is extremely useful for estimating the indices of cortical morphology, such as volume, thickness, area, and gyrification, whereas voxel-based morphometry (VBM) is a typical method of gray matter (GM) volumetry that includes cortex measurement. In cases where SBM is used to estimate cortical morphology, it remains controversial as to whether VBM should be used in addition to estimate GM volume. Therefore, this review has two main goals. First, we summarize the differences between the two methods regarding preprocessing, statistical analysis, and reliability. Second, we review studies that estimate cortical morphological changes using VBM and/or SBM and discuss whether using VBM in conjunction with SBM produces additional values. We found cases in which detection of morphological change in either VBM or SBM was superior, and others that showed equivalent performance between the two methods. Therefore, we concluded that using VBM and SBM together can help researchers and clinicians obtain a better understanding of normal neurobiological processes of the brain. Moreover, the use of both methods may improve the accuracy of the detection of morphological changes when comparing the data of patients and controls.

In addition, we introduce two other recent methods as future directions for estimating cortical morphological changes: a multi-modal parcellation method using structural and functional images, and a synthetic segmentation method using multi-contrast images (such as T1- and proton density-weighted images).

Surface-Based Amplitude of Low-Frequency Fluctuation Alterations in Patients With Tinnitus Before and After Sound Therapy: A Resting-State Functional Magnetic Resonance Imaging Study

This study aimed to investigate abnormal tinnitus activity by evaluating brain surface-based amplitude of low-frequency fluctuation (ALFF) changes detected by resting-state functional magnetic resonance imaging (RS-fMRI) in patients with idiopathic tinnitus before and after 24 weeks of sound therapy. We hypothesized that sound therapy could gradually return cortical local brain function to a relatively normal range. In this prospective observational study, we recruited thirty-three tinnitus patients who had undergone 24 weeks of sound therapy and 26 matched healthy controls (HCs). For the two groups of subjects, we analyzed the spontaneous neural activity of tinnitus patients by cortical ALFF and detected its correlation with clinical indicators of tinnitus. Patients’ Tinnitus Handicap Inventory (THI) scores were assessed to determine the severity of their tinnitus before and after treatment. Two-way mixed model analysis of variance and Pearson’s correlation analysis were used in the statistical analysis. Student–Newman–Keuls tests were used in the post hoc analysis. Interaction effects between the two groups and between the two scans revealing local neural activity as assessed by ALFF were observed in the bilateral dorsal stream visual cortex (DSVC), bilateral posterior cingulate cortex (PCC), bilateral anterior cingulate and medial prefrontal cortex (ACC and MPC), left temporo-parieto-occipital junction (TPOJ), left orbital and polar frontal cortex (OPFC), left paracentral lobular and mid cingulate cortex (PCL and MCC), right insular and frontal opercular cortex (IFOC), and left early visual cortex (EVC). Importantly, local functional activity in the left TPOJ and right PCC in the patient group was significantly lower than that in the HCs at baseline and was increased to relatively normal levels after treatment. The 24-week sound therapy tinnitus group demonstrated significantly higher ALFF in the left TPOJ and right PCC than in the tinnitus baseline group. Also, compared with the HC baseline group and the 24-week HC group, the 24-week sound therapy tinnitus group demonstrated slightly lower or higher ALFF in the left TPOJ and right PCC, and there were no differences between the 24-week sound therapy tinnitus and HC groups. Decreased THI scores and ALFF changes in the abovementioned brain regions were not correlated. Taken together, surface-based RS-fMRI can provide more subtle local functional activity to explain the mechanism of tinnitus treatment, and long-term sound therapy had a normalizing effect on tinnitus patients.

Analysis of cerebellum with magnetic resonance 3D T1 sequence in individuals with chronic subjective tinnitus

Tinnitus is a symptom in which the patient can hear ringing, buzzing and similar sounds in the ear for 3 months longer. In our study, we aimed to analyse the cerebellum volume and cerebellum connections in patients with chronic tinnitus using VolBrain program. A total number of 10 patients and 10 otherwise healthy peoples records were then enrolled. Volumetric analysis was performed with automated segmentation of the cerebellum and its lobules, using magnetic resonance imaging (MRI). The mean volumes of 10 cerebellar volume were compared between the tinnitus and control groups. Quadrangular lobular portion of the cerebellum, the flocculonodular part and the volume of the central cerebellar lobule were decreased in the tinnitus group. White and grey matter decreased and the amygdala size was increased. We found statistically important volumetric changes in our study. VolBrain can be used in the future for analysing, diagnosis and treatment tinnitus patients. We recommend to use this practical, free of charge and easy programme to analyse for tinnitus patients. This may provide us with practical and useful information about the disease. In patients with tinnitus, the volume loss was 17.48% in the quadrangular lobe, 21% in the central lobule, and 9.33% in the total cerebellum volume.

Auditory thalamus dysfunction and pathophysiology in tinnitus: a predictive network hypothesis

Tinnitus is the perception of a 'ringing' sound without an acoustic source. It is generally accepted that tinnitus develops after peripheral hearing loss and is associated with altered auditory processing. The thalamus is a crucial relay in the underlying pathways that actively shapes processing of auditory signals before the respective information reaches the cerebral cortex. Here, we review animal and human evidence to define thalamic function in tinnitus. Overall increased spontaneous firing patterns and altered coherence between the thalamic medial geniculate body (MGB) and auditory cortices is observed in animal models of tinnitus. It is likely that the functional connectivity between the MGB and primary and secondary auditory cortices is reduced in humans. Conversely, there are indications for increased connectivity between the MGB and several areas in the cingulate cortex and posterior cerebellar regions, as well as variability in connectivity between the MGB and frontal areas regarding laterality and orientation in the inferior, medial and superior frontal gyrus. We suggest that these changes affect adaptive sensory gating of temporal and spectral sound features along the auditory pathway, reflecting dysfunction in an extensive thalamo-cortical network implicated in predictive temporal adaptation to the auditory environment. Modulation of temporal characteristics of input signals might hence factor into a thalamo-cortical dysrhythmia profile of tinnitus, but could ultimately also establish new directions for treatment options for persons with tinnitus.

Cortical and subcortical gray matter changes in patients with chronic tinnitus sustaining after vestibular schwannoma surgery

Tinnitus is attributed to partial sensory deafferentation resulting in a central maladaptive neuroplasticity. Unfortunately, the agent of deafferentation is usually unknown or irreversible. In patients with unilateral vestibular schwannoma (VS), however, the auditory nerve is affected by a benign tumor. Hence, removal of the tumor can cease the tinnitus. In turn, sustaining complaints after surgery indicate cortical neuroplasticity. The present study is a cross sectional study which aims to track cortical structural changes by surface-based morphometry in 46 VS patients with sustained (i.e. centralized) or ceased (i.e. peripheral) tinnitus after surgery. A volumetric analysis of cortical and subcortical gray matter (GM) anatomy was performed on preoperative high-resolution MRI and related to the presence of hearing impairment, pre- and/or postoperative tinnitus. Patients with sustained (i.e. chronic) tinnitus showed an increased GM volume of the bilateral caudate nucleus, the contralateral superior colliculus, the middle frontal and middle temporal gyrus, the fusiform gyrus as well as the ipsilateral pars orbitalis when compared to those patients in whom tinnitus ceased postoperatively. Chronic tinnitus in VS patients is associated with characteristic structural changes in frontal, temporal and subcortical areas. Notably, a significant GM change of the caudate nucleus was detected providing further support for the striatal gaiting model of tinnitus.

Neuroanatomic Volume Differences in Tinnitus and Hearing Loss

OBJECTIVES

To investigate neuroanatomic volume differences in tinnitus and hearing loss.

STUDY DESIGN

Cross-sectional.

METHODS

Sixteen regions of interest (ROIs) in adults (43 male, 29 female) were examined using 3Tesla structural magnetic resonance imaging in four cohorts: 1) tinnitus with moderate hearing loss (N = 31), 2) moderate hearing loss only (N = 15), 3) tinnitus with normal hearing (N = 17), and 4) normal hearing only (N = 13). ROI volumes were corrected for brain size, age, and sex variations. Analysis of covariance (ANCOVA) and post hoc Tukey's test were used to isolate the effects of tinnitus and hearing loss on volume differences. Effect sizes were calculated as the fraction of total variance (η² ) in ANCOVA models and percent of mean volume difference relative to mean total volume.

RESULTS

The four cohort ANCOVA revealed tinnitus and hearing loss cohorts to have increased volume in the corona radiata (η²  = 0.192; P = .0018) and decreased volume in the nucleus accumbens (η²  = 0.252; P < .0001), caudate nucleus (η²  = 0.188; P = .002), and inferior fronto-occipital fasciculus (η²  = 0.250; P = .0001). Tinnitus with normal hearing showed decreased volume in the nucleus accumbens (22.0%; P = .001) and inferior fronto-occipital fasciculus (18.1%; P = .002), and hearing loss only showed increased volume in the corona radiata (10.7%; P = .01) and decreased volume in the nucleus accumbens (22.1%; P = .001), caudate nucleus (16.1%; P = .004), and inferior fronto-occipital fasciculus (18.3%; P = .003).

CONCLUSION

Tinnitus and hearing loss have overlapping effects on neurovolumetric alterations, especially impacting the nucleus accumbens and inferior fronto-occipital fasciculus. Neurovolumetric studies on tinnitus or hearing loss can be more complete by accounting for those two clinical dimensions separately and jointly.

LEVEL OF EVIDENCE

3 Laryngoscope, 131:1863-1868, 2021.

Tinnitus and Its Central Correlates: A Neuroimaging Study in a Large Aging Population

OBJECTIVES

To elucidate the association between tinnitus and brain tissue volumes and white matter microstructural integrity.

DESIGN

Two thousand six hundred sixteen participants (mean age, 65.7 years [SD: 7.5 years]; 53.9% female) of the population-based Rotterdam Study underwent tinnitus assessment (2011 to 2014) and magnetic resonance imaging of the brain (2011 to 2014). Associations between tinnitus (present versus absent) and total, gray, and white matter volume and global white matter microstructure were assessed using multivariable linear regression models adjusting for demographic factors, cardiovascular risk factors, depressive symptoms, Mini-Mental State Examination score, and hearing loss. Finally, potential regional gray matter density and white matter microstructural volume differences were assessed on a voxel-based level again using multivariable linear regression.

RESULTS

Participants with tinnitus (21.8%) had significantly larger brain tissue volumes (difference in SD, 0.09; 95% confidence interval, 0.06 to 0.13), driven by larger white matter volumes (difference, 0.12; 95% confidence interval, 0.04 to 0.21) independent of hearing loss. There was no association between tinnitus and gray matter volumes nor with global white matter microstructure. On a lobar level, tinnitus was associated with larger white matter volumes in each lobe, not with gray matter volume. Voxel-based results did not show regional specificity.

CONCLUSIONS

We found that tinnitus in older adults was associated with larger brain tissue volumes, driven by larger white matter volumes, independent of age, and hearing loss. Based on these results, it may be hypothesized that tinnitus potentially has a neurodevelopmental origin in earlier life independent of aging processes.

Gray matter declines with age and hearing loss, but is partially maintained in tinnitus

The impact of age-related hearing loss extends beyond the auditory pathway and impacts brain areas related to cognitive impairment and even dementia. The presence of tinnitus, a sensation of sound that frequently co-occurs with hearing loss, is additionally linked to cognitive decline. Interestingly, structural neuroimaging studies have reported that hearing loss may precede or modulate the onset of cognitive impairment. In this study, we aimed to disentangle the effects of age, hearing loss, and tinnitus on gray matter structure. In total, 39 participants with hearing loss and tinnitus, 21 with hearing loss but without tinnitus, and 39 controls were included in this voxel- and surface-based morphometry MRI study. Whole brain volume and surface thickness measures were compared between the groups. Age-related gray matter volume decline was observed in all groups. Several brain areas showed smaller gray matter volume and cortical surface thickness in hearing loss without tinnitus, relative to controls. This reduction was observed both within and outside of the auditory pathway. Interestingly, these reductions were not observed in participants with tinnitus, who had similar hearing loss and were of similar age. Since we have tools to improve hearing loss, hearing screening may aid in the battle against cognitive decline.

The Influence of Aging, Hearing, and Tinnitus on the Morphology of Cortical Gray Matter, Amygdala, and Hippocampus

Age related hearing loss (presbycusis) is a natural process represented by elevated auditory thresholds and decreased speech intelligibility, especially in noisy conditions. Tinnitus is a phantom sound that also potentially leads to cortical changes, with its highest occurrence coinciding with the clinical onset of presbycusis. The aim of our project was to identify age, hearing loss and tinnitus related structural changes, within the auditory system and associated structures. Groups of subjects with presbycusis and tinnitus (22 subjects), with only presbycusis (24 subjects), young tinnitus patients with normal hearing (10 subjects) and young controls (17 subjects), underwent an audiological examination to characterize hearing loss and tinnitus. In addition, MRI (3T MR system, analysis in Freesurfer software) scans were used to identify changes in the cortical and subcortical structures. The following areas of the brain were analyzed: Heschl gyrus (HG), planum temporale (PT), primary visual cortex (V1), gyrus parahippocampus (PH), anterior insula (Ins), amygdala (Amg), and hippocampus (HP). A statistical analysis was performed in R framework using linear mixed-effects models with explanatory variables: age, tinnitus, laterality and hearing. In all of the cortical structures, the gray matter thickness decreased significantly with aging without having an effect on laterality (differences between the left and right hemispheres). The decrease in the gray matter thickness was faster in the HG, PT and Ins in comparison with the PH and V1. Aging did not influence the surface of the cortical areas, however there were differences between the surface size of the reported regions in the left and right hemispheres. Hearing loss caused only a borderline decrease of the cortical surface in the HG. Tinnitus was accompanied by a borderline decrease of the Ins surface and led to an increase in the volume of Amy and HP. In summary, aging is accompanied by a decrease in the cortical gray matter thickness; hearing loss only has a limited effect on the structure of the investigated cortical areas and tinnitus causes structural changes which are predominantly within the limbic system and insula, with the structure of the auditory system only being minimally affected.

Outcomes at 6 months are related to brain structural and white matter microstructural reorganization in idiopathic tinnitus patients treated with sound therapy

This study aimed to explore brain structural and white matter microstructural reorganization in the early stage of tinnitus and identify brain alterations that contribute to its relief after 6 months of sound therapy. We studied 64 patients with idiopathic tinnitus, including 29 patients who were categorized into an effective group (EG) and 35 who were categorized into an ineffective group (IG) according to the 6-month follow-up improvement of the Tinnitus Handicap Inventory score, along with 63 healthy controls (HCs). All participants underwent structural and diffusion tensor imaging scanning on a 3-T magnetic resonance system. Differences in brain gray/white matter volume and white matter microstructure were evaluated using voxel-based morphometry analysis and tract-based spatial statistics among the three groups. Associations between brain reorganization and the improvement of tinnitus symptoms were also investigated. Compared with EG patients, IG patients experienced a significant gray matter volume decrease in the right middle frontal gyrus (MFG)/right precentral gyrus (PreCG). Meanwhile, both EG and IG patients showed significant changes (decrease or increase) in brain white matter integrity in the auditory-related or nonauditory-related white matter fiber tracts compared with HCs, while EG patients showed decreased axial diffusivity in the bilateral middle cerebellar peduncle (MCP) compared with IG patients. We combined the gray matter change of the MFG/PreCG and the white matter integrity of the bilateral MCP as an imaging indicator to evaluate the patient's prognosis and screen patients before treatment; this approach reached a sensitivity of 77.1% and a specificity of 82.8%. Our study suggests that there was a close relationship between brain reorganization and tinnitus improvement. The right MFG/PreCG and bilateral MCP may be indicators that can be used to predict prognoses in patients with idiopathic tinnitus and may be used to screen patients before sound therapy. These findings may provide new useful information that can lead to a better understanding of the tinnitus mechanism.

Neuroglial activation in the auditory cortex and medial geniculate body of salicylate-induced tinnitus rats

Neuroglial activation has been recognized as a pathological hallmark of a variety of neurological diseases, yet the role of neuroglia in tinnitus hasn't been well established so far. To explore the potential roles of two types of glia cells (astrocyte and microglia) in the development of tinnitus, we examined markers associated with them in the primary auditory (A1) cortex and medial geniculate body (MGB) of rats with salicylate-induced tinnitus. The results demonstrated that acute and chronic administrations of salicylate could cause reversible tinnitus-like behavior in rats. The expression level of GFAP markedly increased in the A1 cortex of rats following acute and chronic treatments of salicylate, accompanied by increased endpoint and process length of astrocyte. The expression level of GFAP and the morphology of astrocyte in the rat MGB remained almost constant following salicylate treatment. On the other hand, the expression level of Iba1 markedly increased in the rat A1 cortex and MGB following acute and chronic treatments of salicylate, together with increased endpoint and process length of microglia in the MGB. Additionally, interleukin 1β (IL-1β), a pro-inflammatory cytokine released by activated glia was significantly up-regulated in the A1 cortex and MGB of rats after salicylate treatments. These findings highlight astrocyte activation and microglia proliferation in the central auditory system of rats experiencing tinnitus, which potently implicate an indispensable glial regulation in tinnitus development.

Tinnitus Neuroimaging

This article reviews the use of human neuroimaging for chronic subjective tinnitus. Evidence-based guidance on the clinical use of imaging to identify relevant auditory lesions when evaluating tinnitus patients is given. After introducing the anatomy and imaging modalities most pertinent to the neuroscience of tinnitus, the article reviews tinnitus-associated alterations in key auditory and nonauditory networks in the central nervous system. Emphasis is placed on how these findings support proposed models of tinnitus and how this line of investigation is relevant to practicing clinicians.

A Multimodal Meta-Analysis of Structural and Functional Changes in the Brain of Tinnitus

Brain imaging studies of tinnitus patients have revealed marked changes in brain structure and function, but there are inconsistencies in those findings. In this meta-analysis, we investigated concurrence across studies to clarify those abnormalities in brain structure and function in tinnitus. Neuroimaging studies published up to December 6, 2019 were searched in the PubMed, Web of Science, EMBASE, and Cochrane Library databases, Chinese Nation Knowledge Infrastructure, Chinese Biomedical Literature Database, the Chongqing VIP, and Wanfang Database. Study selection, quality assessment, and data extraction were performed by two independent researchers. Anisotropic effect size signed differential mapping (AES-SDM) was used to perform a multimodal analysis of available studies reporting whole-brain structural or functional data in tinnitus patients. There were 14 studies that met the inclusion criteria. The structural dataset comprised 242 tinnitus patients and 217 matched healthy subjects (HS), while the functional dataset included 130 tinnitus patients and 140 matched HS. Our analysis revealed structural alterations in the superior temporal gyrus, middle temporal gyrus (MTG), angular gyrus, caudate nucleus, superior frontal gyrus, and supplementary motor area, as well as functional differences in the MTG, middle occipital gyrus, precuneus, and right inferior parietal (excluding supramarginal and angular) gyri. The multimodal analysis revealed significant differences in the right MTG of tinnitus patients relative to HS. These findings suggest the involvement of the cortico-striatal circuits in the neuropathology of tinnitus.

The Role of Magnetic Resonance Imaging of the Temporomandibular Joint to Investigate Tinnitus in Adults with Temporomandibular Joint Disorder: A Comparative Study

Introduction  The prevalence of tinnitus is higher in individuals with temporomandibular joint disorder (TMD) than in the general population. Magnetic resonance imaging (MRI) of the temporomandibular joint (TMJ) is the method of choice for investigation, and it has been hypothesized that specific MRI findings might be observed in TMD with comorbid tinnitus.

Objective  To comparatively describe MRI findings in patients with TMD with and without tinnitus, identifying the most common TMJ alterations and determining whether a correlation exists between severity of TMD and tinnitus.

Methods  A cross-sectional study of 53 adult patients with bilateral or unilateral TMD (30 with and 23 without tinnitus). The association between tinnitus and morphological aspects of TMD (changes in condylar morphology, articular eminence morphology, and disc morphology), disc displacement (with/without reduction), condylar translation, and intra-articular effusion was analyzed on MRI images.

Results  The mean patient age was 46.12 ± 16.1 years. Disc displacement was the most common finding in both groups (24 patients with tinnitus versus 15 without; p  = 0.043). Only the frequency of disc displacement with reduction was significantly different between groups.

Conclusion  Additional imaging techniques should be explored to detect specific aspects of the relationship between tinnitus and TMD.

Morphological Neuroimaging Biomarkers for Tinnitus: Evidence Obtained by Applying Machine Learning

According to previous studies, many neuroanatomical alterations have been detected in patients with tinnitus. However, the results of these studies have been inconsistent. The objective of this study was to explore the cortical/subcortical morphological neuroimaging biomarkers that may characterize idiopathic tinnitus using machine learning methods. Forty-six patients with idiopathic tinnitus and fifty-six healthy subjects were included in this study. For each subject, the gray matter volume of 61 brain regions was extracted as an original feature pool. From this feature pool, a hybrid feature selection algorithm combining the F-score and sequential forward floating selection (SFFS) methods was performed to select features. Then, the selected features were used to train a support vector machine (SVM) model. The area under the curve (AUC) and accuracy were used to assess the performance of the classification model. As a result, a combination of 13 cortical/subcortical brain regions was found to have the highest classification accuracy for effectively differentiating patients with tinnitus from healthy subjects. These brain regions include the bilateral hypothalamus, right insula, bilateral superior temporal gyrus, left rostral middle frontal gyrus, bilateral inferior temporal gyrus, right inferior parietal lobule, right transverse temporal gyrus, right middle temporal gyrus, right cingulate gyrus, and left superior frontal gyrus. The accuracy in the training and test datasets was 80.49% and 80.00%, respectively, and the AUC was 0.8586. To the best of our knowledge, this is the first study to elucidate brain morphological changes in patients with tinnitus by applying an SVM classifier. This study provides validated cortical/subcortical morphological neuroimaging biomarkers to differentiate patients with tinnitus from healthy subjects and contributes to the understanding of neuroanatomical alterations in patients with tinnitus.

Chronic tinnitus and the limbic system: Reappraising brain structural effects of distress and affective symptoms

Chronic tinnitus has been associated with brain structural changes in both the auditory system as well as limbic system. While there is considerable inconsistency across brain structural findings, growing evidence suggests that distress and other non-auditory symptoms modulate effects. In this study we addressed this issue, testing the hypothesis that limbic changes in tinnitus relate to both disease-related distress as well as co-morbid psychopathology. We obtained high-resolution structural magnetic resonance imaging (MRI) scans from a total of 125 subjects: 59 patients with bilateral chronic tinnitus (29 with a co-morbid psychiatric condition, 30 without), 40 healthy controls and 26 psychiatric controls with depression/anxiety disorders (without tinnitus). Voxel-based morphometry with the CAT12 software package was used to analyse data. First, we analysed data based on a 2 × 2 factorial design (tinnitus; psychiatric co-morbidity), showing trend-level effects for tinnitus in ROI analyses of the anterior cingulate cortex and superior/transverse temporal gyri, and for voxel-based analysis in the left parahippocampal cortex. Multiple regression analyses showed that the parahippocampal finding was mostly predicted by tinnitus rather than (dimensional) psychopathology ratings. Comparing only low-distress tinnitus patients (independent of co-morbid conditions) with healthy controls also showed reduced left parahippocampal grey matter. Our findings demonstrate that depression and anxiety (not only subjective distress) are major modulators of brain structural effects in tinnitus, calling for a stronger consideration of psychopathology in future neurobiological and clinical studies of tinnitus.

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Chronic tinnitus is associated with high psychiatric co-morbidity and distress.

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Parahippocamal grey matter is associated with tinnitus rather than distress.

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Psychiatric co-morbidity modulates tinnitus-related structural patterns.

Pathophysiology of Subjective Tinnitus: Triggers and Maintenance

Tinnitus is the conscious perception of a sound without a corresponding external acoustic stimulus, usually described as a phantom perception. One of the major challenges for tinnitus research is to understand the pathophysiological mechanisms triggering and maintaining the symptoms, especially for subjective chronic tinnitus. Our objective was to synthesize the published literature in order to provide a comprehensive update on theoretical and experimental advances and to identify further research and clinical directions. We performed literature searches in three electronic databases, complemented by scanning reference lists from relevant reviews in our included records, citation searching of the included articles using Web of Science, and manual searching of the last 6 months of principal otology journals. One-hundred and thirty-two records were included in the review and the information related to peripheral and central mechanisms of tinnitus pathophysiology was collected in order to update on theories and models. A narrative synthesis examined the main themes arising from this information. Tinnitus pathophysiology is complex and multifactorial, involving the auditory and non-auditory systems. Recent theories assume the necessary involvement of extra-auditory brain regions for tinnitus to reach consciousness. Tinnitus engages multiple active dynamic and overlapping networks. We conclude that advancing knowledge concerning the origin and maintenance of specific tinnitus subtypes origin and maintenance mechanisms is of paramount importance for identifying adequate treatment.

Dissociating tinnitus patients from healthy controls using resting-state cyclicity analysis and clustering

Chronic tinnitus is a common and sometimes debilitating condition that lacks scientific consensus on physiological models of how the condition arises as well as any known cure. In this study, we applied a novel cyclicity analysis, which studies patterns of leader-follower relationships between two signals, to resting-state functional magnetic resonance imaging (rs-fMRI) data of brain regions acquired from subjects with and without tinnitus. Using the output from the cyclicity analysis, we were able to differentiate between these two groups with 58–67% accuracy by using a partial least squares discriminant analysis. Stability testing yielded a 70% classification accuracy for identifying individual subjects’ data across sessions 1 week apart. Additional analysis revealed that the pairs of brain regions that contributed most to the dissociation between tinnitus and controls were those connected to the amygdala. In the controls, there were consistent temporal patterns across frontal, parietal, and limbic regions and amygdalar activity, whereas in tinnitus subjects, this pattern was much more variable. Our findings demonstrate a proof-of-principle for the use of cyclicity analysis of rs-fMRI data to better understand functional brain connectivity and to use it as a tool for the differentiation of patients and controls who may differ on specific traits.

Chronic tinnitus is a common, yet poorly understood, condition without a known cure. Understanding differences in the functioning of brains of tinnitus patients and controls may lead to better knowledge regarding the physiology of the condition and to subsequent treatments. There are many ways to characterize relationships between neural activity in different parts of the brain. Here, we apply a novel method, called cyclicity analysis, to functional MRI data obtained from tinnitus patients and controls over a period of wakeful rest. Cyclicity analysis lends itself to interpretation as analysis of temporal orderings between elements of time-series data; it is distinct from methods like periodicity analysis or time correlation analysis in that its theoretical underpinnings are invariant to changes in time scales of the generative process. In this proof-of-concept study, we use the feature generated from the cyclicity analysis of the fMRI data to investigate group level differences between tinnitus patients and controls. Our findings indicate that temporal ordering of regional brain activation is much more consistent in the control population than in tinnitus population. We also apply methods of classification from machine learning to differentiate between the two populations with moderate amount of success.

Tinnitus distress is associated with enhanced resting-state functional connectivity within the default mode network

PURPOSE

The default mode network (DMN) has been confirmed to be involved in chronic tinnitus perception. Tinnitus distress may be associated with abnormal functional connectivity (FC) within the DMN regions. The goal of this study was to determine whether tinnitus disrupted the FC patterns within the DMN as measured by using resting-state functional magnetic resonance imaging approach.

PATIENTS AND METHODS

Resting-state functional magnetic resonance imaging scans were acquired from 40 chronic bilateral tinnitus patients and 41 healthy controls. Both were age, sex, and education well-matched with normal hearing. Two important DMN regions, the anterior cingulate cortex and posterior cingulate cortex, were chosen as seed regions to detect the FC patterns within the DMN and then determine whether these changes were linked to clinical measures of tinnitus such as tinnitus duration and tinnitus severity.

RESULTS

Compared with healthy controls, chronic tinnitus patients manifested significantly enhanced FC between the anterior cingulate cortex and left precuneus, which was correlated with the tinnitus duration (r=0.451, p=0.007). Moreover, enhanced FC between the posterior cingulate cortex and right medial prefrontal cortex in tinnitus patients was positively correlated with the tinnitus distress (r=0.411, p=0.014).

CONCLUSION

Chronic tinnitus patients showed disrupted FC patterns within the DMN regions which are correlated with tinnitus distress. Increased resting-state connectivity pattern of the DMN may play a pivotal role in neuropathological features underlying chronic tinnitus.

A methodological assessment of studies that use voxel-based morphometry to study neural changes in tinnitus patients

BACKGROUND

The scientific understanding of tinnitus and its etiology has transitioned from thinking of tinnitus as solely a peripheral auditory problem to an increasing awareness that cortical networks may play a critical role in tinnitus percept or bother. With this change, studies that seek to use structural brain imaging techniques to better characterize tinnitus patients have become more common. These studies include using voxel-based morphometry (VBM) to determine if there are differences in regional gray matter volume in individuals who suffer from tinnitus and those who do not. However, studies using VBM in patients with tinnitus have produced inconsistent and sometimes contradictory results.

OBJECTIVE

This paper is a systematic review of all of the studies to date that have used VBM to study regional gray matter volume in people with tinnitus, and explores ways in which methodological differences in these studies may account for their heterogeneous results. We also aim to provide guidance on how to conduct future studies using VBM to produce more reproducible results to further our understanding of disease processes such as tinnitus.

METHODS

Studies about tinnitus and VBM were searched for using PubMed and Embase. These returned 15 and 25 results respectively. Of these, nine met the study criteria and were included for review. An additional 5 studies were identified in the literature as pertinent to the topic at hand and were added to the review, for a total of 13 studies.

RESULTS

There was significant heterogeneity among the studies in several areas, including inclusion and exclusion criteria, software programs, and statistical analysis. We were not able to find publicly shared data or code for any study.

DISCUSSION

The differences in study design, software analysis, and statistical methodology make direct comparisons between the different studies difficult. Especially problematic are the differences in the inclusion and exclusion criteria of the study, and the statistical design of the studies, both of which could radically alter findings. Thus, heterogeneity has complicated efforts to explore the etiology of tinnitus using structural MRI.

CONCLUSION

There is a pressing need to standardize the use of VBM when evaluating tinnitus patients. While some heterogeneity is expected given the rapid advances in the field, more can be done to ensure that there is internal validity between studies.

Diverse application of MRI for mouse phenotyping

Small animal models, particularly mouse models, of human diseases are becoming an indispensable tool for biomedical research. Studies in animal models have provided important insights into the etiology of diseases and accelerated the development of therapeutic strategies. Detailed phenotypic characterization is essential, both for the development of such animal models and mechanistic studies into disease pathogenesis and testing the efficacy of experimental therapeutics. MRI is a versatile and noninvasive imaging modality with excellent penetration depth, tissue coverage, and soft tissue contrast. MRI, being a multi-modal imaging modality, together with proven imaging protocols and availability of good contrast agents, is ideally suited for phenotyping mutant mouse models. Here we describe the applications of MRI for phenotyping structural birth defects involving the brain, heart, and kidney in mice. The versatility of MRI and its ease of use are well suited to meet the rapidly increasing demands for mouse phenotyping in the coming age of functional genomics. Birth Defects Research 109:758-770, 2017. © 2017 Wiley Periodicals, Inc.