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

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.

Depression, anxiety and brain volume after hearing loss and tinnitus: cohort study in the UK Biobank

BACKGROUND

Hearing loss and tinnitus have been proposed as potential indicators of impaired mental health and brain morphological changes.

AIMS

To assess the associations of hearing loss and tinnitus with the risk of depression and anxiety and with brain volume.

METHOD

We conducted a community-based cohort study including 129 610 participants aged 40-69 years at recruitment to the UK Biobank with a follow-up period during 2006-2021 to estimate the risk of depression and anxiety after detection of hearing loss and reported tinnitus. We also assessed the associations of hearing loss and tinnitus with brain volume in a subsample with available brain magnetic resonance imaging data (N = 5222).

RESULTS

We observed an increased risk of depression among individuals with hearing loss (hazard ratio [HR] 1.14, 95% CI 1.03-1.26), tinnitus (HR 1.30, 95% CI 1.21-1.41) or both (HR 1.32, 95% CI 1.15-1.52), compared with individuals with neither hearing loss nor tinnitus. Similar results were noted for anxiety (HR 1.18, 95% CI 1.07-1.30 for hearing loss; HR 1.32, 95% CI 1.22-1.43 for tinnitus; and HR 1.48, 95% CI 1.30-1.68 for both). Hearing loss was associated with decreased overall brain volume as well as decreased volume of different brain regions. The latter associations disappeared after adjustment for whole intracranial volume. Tinnitus was associated with greater left accumbens and right occipital pole volume after adjustment for the whole intracranial volume.

CONCLUSIONS

Individuals with tinnitus are at increased risk of depression and anxiety. Hearing loss, on the other hand, is associated with both mood disorders and altered brain morphology.

Increased fiber density of the fornix in patients with chronic tinnitus revealed by diffusion-weighted MRI

Up to 45% of the elderly population suffer from chronic tinnitus - the phantom perception of sound that is often perceived as ringing, whistling, or hissing "in the ear" without external stimulation. Previous research investigated white matter changes in tinnitus patients using diffusion-weighted magnetic resonance imaging (DWI) to assess measures such as fractional anisotropy (a measure of microstructural integrity of fiber tracts) or mean diffusivity (a measure for general water diffusion). However, findings overlap only minimally and are sometimes even contradictory. We here present the first study encompassing higher diffusion data that allow to focus on changes in tissue microstructure, such as number of axons (fiber density) and macroscopic alterations, including axon diameter, and a combination of both. In order to deal with the crossing-fibers problem, we applied a fixel-based analysis using a constrained spherical deconvolution signal modeling approach. We investigated differences between tinnitus patients and control participants as well as how cognitive abilities and tinnitus distress are related to changes in white matter morphology in chronic tinnitus. For that aim, 20 tinnitus patients and 20 control participants, matched in age, sex and whether they had hearing loss or not, underwent DWI, audiometric and cognitive assessments, and filled in questionnaires targeting anxiety and depression. Our results showed increased fiber density in the fornix in tinnitus patients compared to control participants. The observed changes might, reflect compensatory structural alterations related to the processing of negative emotions or maladaptive changes related to the reinforced learning of the chronic tinnitus sensation. Due to the low sample size, the study should be seen as a pilot study that motivates further research to investigate underlying white matter morphology alterations in tinnitus.

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

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

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.

Targeting the Limbic System: Insights into Its Involvement in Tinnitus

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

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

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

Tinnitus and Multimodal Cortical Interaction

The term of subjective tinnitus is used to describe a perceived noise without an external sound source. Therefore, it seems to be obvious that tinnitus can be understood as purely auditory, sensory problem. From a clinical point of view, however, this is a very inadequate description, as there are significant comorbidities associated with chronic tinnitus. Neurophysiological investigations with different imaging techniques give a very similar picture, because not only the auditory system is affected in chronic tinnitus patients, but also a widely ramified subcortical and cortical network. In addition to auditory processing systems, networks consisting of frontal and parietal regions are particularly disturbed. For this reason, some authors conceptualize tinnitus as a network disorder rather than a disorder of a circumscribed system. These findings and this concept suggest that tinnitus must be diagnosed and treated in a multidisciplinary and multimodal manner.

Tinnitus and Influencing Comorbidities

Numerous studies show that impairments in chronic tinnitus are closely connected with psychosomatic and other concomitant symptoms. This overview summarizes some of these studies. Beyond hearing loss, individual interactions of medical and psychosocial stress factors as well as resources are of central importance. Tinnitus related distress reflects a large number of intercorrelated, psychosomatic influences - such as personality traits, stress reactivity and depression or anxiety - which can be accompanied by cognitive difficulties and should be conceptualized and assessed within a vulnerability-stress-reaction model. Superordinate factors such as age, gender or education level can increase vulnerability to stress. Therefore, diagnosis and therapy of chronic tinnitus be individualised, multidimensional and interdisciplinary. Multimodal psychosomatic therapy approaches aim to address individually constellated medical, audiological and psychological influences in order to sustainably increase the quality of life of those affected. Counselling in the first contact is also indispensable for diagnosis and therapy.

The Comorbidity of Depression and Anxiety Symptoms in Tinnitus Sufferers: A Network Analysis

OBJECTIVE

Sufferers of tinnitus, especially of the prolonged type, frequently suffer from comorbid depression and anxiety. From the perspective of the network model, this comorbidity is thought to be an interacting system of these two symptoms. In our study, we conducted a network analysis of depression and anxiety comorbidity in tinnitus sufferers, aiming to identify the central and bridge symptoms and make informed suggestions for clinical interventions and psychotherapy.

METHOD

A total of 566 tinnitus sufferers were enrolled in our study. The Patient Health Questionnaire-9 (PHQ-9) and the Generalized Anxiety Disorder 7-Item Questionnaire (GAD-7) were selected to evaluate depression and anxiety symptoms, respectively, followed by network analysis to construct the interacting networks.

RESULTS

The findings identified six edges of strongest regularized partial correlations in this network. Of these, three were depression symptoms and three were anxiety symptoms. The anxiety symptoms "Unable to control worry" and "Relaxation difficulty" and the depression symptom "Feeling depressed or hopeless" had the highest expected influence centrality. The analysis results also revealed three bridge symptoms: "Afraid something awful might happen", "Feeling of worthlessness", and "Trouble concentrating". As for "Suicidal ideation", the direct relations between this symptom and "Afraid something awful might happen" and "Feeling depressed or hopeless" were the strongest.

CONCLUSIONS

The central and bridge symptoms of the interacting network of depression and anxiety symptoms in tinnitus sufferers can be considered a significant transdiagnostic intervention target for the management of this comorbidity. In particular, clinical prevention and psychotherapy should be implemented, targeting the symptoms that have the strongest associations with suicidal ideation.

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.

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

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

A genome-wide association study of tinnitus reveals shared genetic links to neuropsychiatric disorders

Tinnitus, a phantom perception of sound in the absence of any external sound source, is a prevalent health condition often accompanied by psychiatric comorbidities. Recent genome-wide association studies (GWAS) highlighted a polygenic nature of tinnitus susceptibility. A shared genetic component between tinnitus and psychiatric conditions remains elusive. Here we present a GWAS using the UK Biobank to investigate the genetic processes linked to tinnitus and tinnitus-related distress, followed by gene-set enrichment analyses. The UK Biobank sample comprised 132,438 individuals with tinnitus and genotype data. Among the study sample, 38,525 individuals reported tinnitus, and 26,889 participants mentioned they experienced tinnitus-related distress in daily living. The genome-wide association analyses were conducted on tinnitus and tinnitus-related distress. We conducted enrichment analyses using FUMA to further understand the genetic processes linked to tinnitus and tinnitus-related distress. A genome-wide significant locus (lead SNP: rs71595470) for tinnitus was obtained in the vicinity of GPM6A. Nineteen independent loci reached suggestive association with tinnitus. Fifteen independent loci reached suggestive association with tinnitus-related distress. The enrichment analysis revealed a shared genetic component between tinnitus and psychiatric traits, such as bipolar disorder, feeling worried, cognitive ability, fast beta electroencephalogram, and sensation seeking. Metabolic, cardiovascular, hematological, and pharmacological gene sets revealed a significant association with tinnitus. Anxiety and stress-related gene sets revealed a significant association with tinnitus-related distress. The GWAS signals for tinnitus were enriched in the hippocampus and cortex, and for tinnitus-related distress were enriched in the brain and spinal cord. This study provides novel insights into genetic processes associated with tinnitus and tinnitus-related distress and demonstrates a shared genetic component underlying tinnitus and psychiatric conditions. Further collaborative attempts are necessary to identify genetic components underlying the phenotypic heterogeneity in tinnitus and provide biological insight into the etiology.

Correlation Between Tinnitus Handicap and Depression and Anxiety Scores

OBJECTIVES

This study aimed to analyse the correlation between depression, anxiety, and tinnitus handicap in patients with primary tinnitus.

METHODS

A total of 102 patients (41 men, 61 women; mean age ± SD: 56.8 ± 11.6 years) were examined. They completed the Tinnitus Handicap Inventory (THI), Beck Depression Inventory (BDI), and Symptom-Checklist-90-Revised (SCL-90-R). Correlations were analysed using Pearson's and Spearman's tests. Logistic regression analysis was performed.

RESULTS

The demographic data suggested a slight female predominance. The THI questionnaires indicated a worsening handicap in 73.5% of the patients, of which the 'mild' category was the most frequent, followed by severe handicaps. According to BDI, 69.6% of individuals fell in the normal category, with mild cases being the most frequent. Of the two psychiatric symptoms, depression (BDI) and tinnitus were strongly correlated (rho= 0.579, P < .0001*). The correlation was also significant according to the SCL-90-R depression questions (rho= 0.523, P < .0001*). Upon comparing the depressive scores and the THI subscores (i.e., functional, emotional, and catastrophic), each showed a significant correlation, with the strongest correlation with functional and emotional scores. The correlation with anxiety was slightly weaker (rho= 0.480, P < .0001*) but also significant. According to the Kaplan-Meier curves and logistic regression, the appearance of depressive symptoms did not significantly influence the appearance of a worsening handicap [P = .428; OR: 1.124 (95% CI: 0.842-1.501)]. However, a worsening handicap significantly influenced the appearance of depressive symptoms [P < .0001*; OR: 1.35 (95% CI: 1.34-4.86)], indicating that tinnitus has a more expressed effect on the appearance of depressive symptoms than reversed.

CONCLUSIONS

The correlation between tinnitus handicap and psychiatric comorbidities indicates the importance of psychological factors in tinnitus management. Tinnitus handicap has a more profound effect on depression scores. To avoid the occurrence of comorbidities, tinnitus handicaps must be reduced.

Systems Medicine Approach for Tinnitus with Comorbid Disorders

Despite the fact that chronic diseases usually occur together with a spectrum of possible comorbidities that may differ strongly between patients, they are classically still viewed as distinct disease entities and, consequently, are often treated with uniform therapies. Unfortunately, such an approach does not take into account that different combinations of symptoms and comorbidities may result from different pathological (e.g., environmental, genetic, dietary, etc.) factors, which require specific and individualised therapeutic strategies. In this opinion paper, we aim to put forward a more differentiated, systems medicine approach to disease and patient treatment. To elaborate on this concept, we focus on the interplay of tinnitus, depression, and chronic pain. In our view, these conditions can be characterised by a variety of phenotypes composed of variable sets of symptoms and biomarkers, rather than distinct disease entities. The knowledge of the interplay of such symptoms and biomarkers will provide the key to a deeper, mechanistic understanding of disease pathologies. This paves the way for prediction and prevention of disease pathways, including more personalised and effective treatment strategies.

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.

Brain mapping of auditory hallucinations and illusions induced by direct intracortical electrical stimulation

BACKGROUND

The exact architecture of the human auditory cortex remains a subject of debate, with discrepancies between functional and microstructural studies. In a hierarchical framework for sensory perception, simple sound perception is expected to take place in the primary auditory cortex, while the processing of complex, or more integrated perceptions is proposed to rely on associative and higher-order cortices.

OBJECTIVES

We hypothesize that auditory symptoms induced by direct electrical stimulation (DES) offer a window into the architecture of the brain networks involved in auditory hallucinations and illusions. The intracranial recordings of these evoked perceptions of varying levels of integration provide the evidence to discuss the theoretical model.

METHODS

We analyzed SEEG recordings from 50 epileptic patients presenting auditory symptoms induced by DES. First, using the Juelich cytoarchitectonic parcellation, we quantified which regions induced auditory symptoms when stimulated (ROI approach). Then, for each evoked auditory symptom type (illusion or hallucination), we mapped the cortical networks showing concurrent high-frequency activity modulation (HFA approach).

RESULTS

Although on average, illusions were found more laterally and hallucinations more posteromedially in the temporal lobe, both perceptions were elicited in all levels of the sensory hierarchy, with mixed responses found in the overlap. The spatial range was larger for illusions, both in the ROI and HFA approaches. The limbic system was specific to the hallucinations network, and the inferior parietal lobule was specific to the illusions network.

DISCUSSION

Our results confirm a network-based organization underlying conscious sound perception, for both simple and complex components. While symptom localization is interesting from an epilepsy semiology perspective, the hallucination-specific modulation of the limbic system is particularly relevant to tinnitus and schizophrenia.

Increased Risk of Major Depressive Disorder Following Tinnitus: A Population-Based Study

Background and Purpose

In this study, we aimed to evaluate the relationship between tinnitus and a subsequent diagnosis of major depressive disorder (MDD) by studying the incidence of both entities.

Design

A retrospective cohort study.

Methods

Data for this observational follow-up study were retrieved from the Taiwan's National Health Insurance Dataset. A total of 375,272 patients with newly diagnosed tinnitus (study group) were retrieved. The date of first diagnosis of tinnitus was assigned as their index date. Comparison patients were selected by propensity score matching (one per case, n = 375,272 controls) from the same dataset, with their index date being the date of their first health service claim in the year of diagnosis of their matched index case. We tracked each patient's claims records for 1 year from the index date to identify those who received a diagnosis of MDD. Cox proportional hazards regression was performed to calculate the MDD hazard ratio for cases vs. controls.

Results

We found that the overall incidence rate for MDD was 0.78 (95% CI = 0.76~0.80) per 100 person-years, being 1.17 (95% CI = 1.14~1.21) among the study cohorts and 0.38 (95% CI = 0.36~0.40) among the comparison cohorts. The log-rank test revealed that the patients in the study cohort had significantly lower one-year MDD-free survival when compared to the comparison cohort (p < 0.001). Cox proportional hazards analysis showed that the patients in the study cohort had a higher hazard of developing MDD than the patients in the comparison cohort (adjusted HR = 3.08, 95% CI = 2.90~3.27).

Conclusions

In this study, we demonstrate that tinnitus is associated with an increased hazard of subsequent MDD in Taiwan.

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.

Cerebral Blood Flow Difference Between Acute and Chronic Tinnitus Perception: A Perfusion Functional Magnetic Resonance Imaging Study

Purpose: The central nervous mechanism of acute tinnitus is different from that of chronic tinnitus, which may be related to the difference of cerebral blood flow (CBF) perfusion in certain regions. To verify this conjecture, we used arterial spin labeling (ASL) perfusion magnetic resonance imaging (MRI) in this study to compare the CBF alterations of patients with acute and chronic tinnitus. Methods: The current study included patients with chronic tinnitus (n = 35), acute tinnitus (n = 30), and healthy controls (n = 40) who were age-, sex-, and education-matched. All participants underwent MRI scanning and then ASL images were obtained to measure CBF of the entire brain and analyze the differences between groups as well as the correlations with tinnitus characteristics. Results: The chronic tinnitus group showed increased z-CBF in the right superior temporal gyrus (STG) and superior frontal gyrus (SFG) when compared with the acute tinnitus patients. Further connectivity analysis found enhanced CBF connectivity between the right STG and fusiform gyrus (FG), the right SFG and left middle occipital gyrus (MOG), as well as the right parahippocampal gyrus (PHG). Moreover, in the chronic tinnitus group, the tinnitus handicap questionnaire (THQ) score was positively correlated with the normalized z-CBF of right STG (r = 0.440, p = 0.013). Conclusion: Our results confirmed that the CBF changes in some brain regions were different between acute and chronic tinnitus patients, which was correlated with certain tinnitus characteristics. This is of great value to further research on chronicity of tinnitus, and ASL has a promising application in the measurement of CBF.

Altered regional activity and connectivity of functional brain networks in congenital unilateral conductive hearing loss

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Focal brain function and seed-based functional connectivity were first analyzed in congenital unilateral CHL.

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Auditory and visual networks showed altered regional activity and functional connectivity.

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Abnormally high activity in the left ITG was positively correlated with duration of disease.

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Higher-order networks including frontoparietal regions and DMN demonstrated abnormal functional connectivity.

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GSR may produce spurious signals in SBFC analyses.

Neuroimaging studies have shown marked alterations in brain function after auditory deprivation, with these alterations mainly caused by sensorineural hearing loss. To date, however, little is known about the patterns of functional brain reorganization in conductive hearing loss (CHL). The effects of congenital unilateral CHL on human brain were assessed by resting-state functional magnetic resonance imaging in 24 patients with unilateral microtia (UM) and 25 healthy controls. Focal brain function and seed-based functional connectivity were analyzed to characterize spontaneous activity and network changes in UM. Patients with UM showed common alterations in focal brain activities in the left inferior temporal gyrus across different measurements, with these alterations significantly associated with the duration of hearing loss. Additionally, focal brain activities were decreased in the auditory system and increased in the visual system, with a disassociated pattern shown in the default-mode system. Using the left inferior temporal gyrus as the seed region, patients with UM showed lower connectivity with the default-mode system and right visual regions but higher connectivity with the left frontoparietal regions when compared with controls. These results indicate that congenital partial hearing deprivation, despite normal bone conduction hearing, can induce widespread reorganizations that continue into adolescence and adulthood.

The Pathological Mechanisms and Treatments of Tinnitus

Tinnitus is defined as the ringing, hissing, clicking or roaring sounds an individual consciously perceives in the absence of an external auditory stimulus. Currently, the literature on the mechanism of tinnitus pathology is multifaceted, ranging from tinnitus generation at the cellular level to its perception at the system level. Cellular level mechanisms include increased neuronal synchrony, neurotransmission changes and maladaptive plasticity. At the system level, the role of auditory structures, non-auditory structures, changes in the functional connectivities in higher regions and tinnitus networks have been investigated. The exploration of all these mechanisms creates a holistic view on understanding the changes the pathophysiology of tinnitus undertakes. Although tinnitus percept may start at the level of cochlear nerve deafferentation, the neuronal changes in the central auditory system to the neuronal and connectivity changes in non-auditory regions, such as the limbic system, become cardinal in chronic tinnitus generation. At the present moment, some tinnitus generation mechanisms are well established (e.g., increased neuronal synchrony) whereas other mechanisms have gained more traction recently (e.g., tinnitus networks, tinnitus-distress networks) and therefore, require additional investigation to solidify their role in tinnitus pathology. The treatments and therapeutics designed for tinnitus are numerous, with varied levels of success. They are generally two-fold: some treatments focus on tinnitus cessation (including cochlear implants, deep brain stimulation, transcranial direct current stimulation and transcranial magnetic stimulation) whereas the other set focuses on tinnitus reduction or masking (including hearing aids, sound therapy, cognitive behavioral therapy, tinnitus retraining therapy, and tailor made notched musical training).  Tinnitus management has focused on implementing tinnitus masking/reducing therapies more than tinnitus cessation, since cessation treatments are still lacking in streamlined treatment protocols and long-term sustainability and efficacy of the treatment. This review will focus on concisely exploring the current and most relevant tinnitus pathophysiology mechanisms, treatments and therapeutics.

Multidisciplinary Tinnitus Research: Challenges and Future Directions From the Perspective of Early Stage Researchers

Tinnitus can be a burdensome condition on both individual and societal levels. Many aspects of this condition remain elusive, including its underlying mechanisms, ultimately hindering the development of a cure. Interdisciplinary approaches are required to overcome long-established research challenges. This review summarizes current knowledge in various tinnitus-relevant research fields including tinnitus generating mechanisms, heterogeneity, epidemiology, assessment, and treatment development, in an effort to highlight the main challenges and provide suggestions for future research to overcome them. Four common themes across different areas were identified as future research direction: (1) Further establishment of multicenter and multidisciplinary collaborations; (2) Systematic reviews and syntheses of existing knowledge; (3) Standardization of research methods including tinnitus assessment, data acquisition, and data analysis protocols; (4) The design of studies with large sample sizes and the creation of large tinnitus-specific databases that would allow in-depth exploration of tinnitus heterogeneity.

Cortical and Subcortical Grey Matter Abnormalities in White Matter Hyperintensities and Subsequent Cognitive Impairment

Grey matter (GM) alterations may contribute to cognitive decline in individuals with white matter hyperintensities (WMH) but no consensus has yet emerged. Here, we investigated cortical thickness and grey matter volume in 23 WMH patients with mild cognitive impairment (WMH-MCI), 43 WMH patients without cognitive impairment, and 55 healthy controls. Both WMH groups showed GM atrophy in the bilateral thalamus, fronto-insular cortices, and several parietal-temporal regions, and the WMH-MCI group showed more extensive and severe GM atrophy. The GM atrophy in the thalamus and fronto-insular cortices was associated with cognitive decline in the WMH-MCI patients and may mediate the relationship between WMH and cognition in WMH patients. Furthermore, the main results were well replicated in an independent dataset from the Alzheimer's Disease Neuroimaging Initiative database and in other control analyses. These comprehensive results provide robust evidence of specific GM alterations underlying WMH and subsequent cognitive impairment.

Improving the assessment of functional impairment in tinnitus sufferers: validation of the German version of the Tinnitus Functional Index using a confirmatory factor analysis

OBJECTIVES

Chronic tinnitus negatively impacts daily functioning. To specifically assess this impairment, the Tinnitus Functional Index (TFI) was developed. The current study investigated the hierarchical, eight-factorial structure for the German TFI and examined its psychometric properties.

DESIGN

In an online assessment, the TFI and other validated health-related measurements were completed. Confirmatory factor analysis (CFA) was conducted to investigate the factorial structure by testing two competing models: (1) a general factor model, and (2) a hierarchical second-order factor model.

STUDY SAMPLE

316 research volunteers (59.8% female) with low to moderate tinnitus distress were included.

RESULTS

CFA revealed an insufficient fit of the data to the general factor model. For the hierarchical second-order factor model, an acceptable model fit was shown (χ²/df ratio = 2.74, RMSEA = 0.07, SRMR = 0.05, CFI = 0.95, TLI = 0.95). Correlational analyses between the TFI and measures assessing tinnitus distress, depression, sleeping difficulties, subjective well-being, and personality dimensions indicated high convergent and moderate discriminant validity. Internal consistency reliability was excellent.

CONCLUSIONS

The results confirm the hierarchical, eight-factorial structure of the German TFI. The TFI is a promising inventory that should be used on a regular basis.HighlightsThe results of our study confirm the hierarchical eight-factorial structure of the German TFI.Confirmatory factor analysis revealed an acceptable model fit of the data.Convergent validity of the German TFI was high.Discriminant validity of the German TFI was moderate.The German TFI is a reliable questionnaire to assess tinnitus functional impairment.

Brain Structural and Functional Reorganization in Tinnitus Patients Without Hearing Loss After Sound Therapy: A Preliminary Longitudinal Study

Sound therapy is one of the most common first-line treatments for idiopathic tinnitus. We aimed to investigate the brain structural and functional alterations between patients with idiopathic tinnitus without hearing loss (HL) and healthy controls (HCs) and between patients before and after sound therapy (narrow band noise). Structural and resting-state functional images were acquired from 13 tinnitus patients without HL and 18 HCs before and after 6 months of narrow band sound therapy (only patients received the treatment). Voxel-based morphometry (VBM) and independent component analysis (ICA) were conducted to separately investigate the brain structural and functional changes. Associations between brain changes and clinical variables were also performed. After the treatment, the % improvement of THI score was −1.30% (± 63.40%). Compared with HCs, tinnitus patients showed gray matter and white matter atrophy in the left middle temporal gyrus at baseline, and the gray matter volume was further reduced after the treatment. The patients also showed increased white matter volume in the cingulum (cingulate), right calcarine, left rolandic operculum, and left parietal and frontal lobes. Additionally, compared with HCs, tinnitus patients exhibited positive [medial visual network (mVN) and sensorimotor network (SMN), mVN and auditory network (AN)] and negative [mVN and lateral visual network (lVN)] internetwork functional connectivity (FC) at baseline and negative [left frontoparietal network (LFPN) and dorsal attention network (DAN), AN and posterior default mode network (pDMN)] internetwork FC after the narrow band sound therapy. The patients also showed negative [LFPN and right frontoparietal network (RFPN), LFPN and RFPN, anterior default mode network (aDMN) and AN, aDMN and DAN] internetwork FC after the treatment when compared with baseline. Our findings suggest that although the outcomes of idiopathic tinnitus patients without HL were not very good when the improvement of THI scores was used as an evaluation indicator, the patients experienced significant differences in auditory-related and non-auditory-related brain reorganization before and after the narrow band sound therapy, that is, sound therapy may have a significant effect on brain reorganization in patients with idiopathic tinnitus. This study may provide some new useful information for the understanding of mechanisms underlying idiopathic tinnitus.

Altered brain responses to emotional facial expressions in tinnitus patients

Tinnitus, the phantom perception of sound, is a frequent disorder that can lead to severe distress and stress-related comorbidity. The pathophysiological mechanisms involved in the etiology of tinnitus are still under exploration. Electrophysiological and functional neuroimaging studies provide increasing evidence for abnormal functioning in auditory but also in non-auditory, e.g., emotional, brain areas. In order to elucidate alterations of affective processing in patients with chronic tinnitus, we used functional magnetic resonance imaging (fMRI) to measure neural responses to emotionally expressive and neutral faces. Twelve patients with chronic tinnitus and a group of 11 healthy controls, matched for age, sex, hearing loss and depressive symptoms were investigated. While viewing emotionally expressive faces compared to neutral faces brain activations in the tinnitus patients differed from those of the controls in a cluster that encompasses the amygdala, the hippocampus and the parahippocampal gyrus bilaterally. Whereas in controls affective faces induced higher brain activation in these regions than neutral faces, these regions in tinnitus patients were deactivated. Our results (1) provide evidence for alterations of affective processing of facial expressions in tinnitus patients indicating general domain-unspecific dysfunctions in emotion processing and (2) indicate the involvement of medial temporal areas in the pathophysiology of tinnitus.

Cortical Thickness Alterations in Patients With Tinnitus Before and After Sound Therapy: A Surface-Based Morphometry Study

This study aimed to explore brain surface-based morphometry cortical thickness changes in patients with idiopathic tinnitus before and after 24 weeks of sound therapy. In this prospective observational study, we recruited 33 tinnitus patients who had undergone 24 weeks of sound therapy and 26 matched healthy controls. For the two groups of subjects, a 3D-BRAVO pulse sequence was acquired both at baseline and at the 24th week. Structural image data preprocessing was performed using the DPABISurf toolbox. The Tinnitus Handicap Inventory (THI) score was assessed to determine the severity of tinnitus before and after treatment. Two-way mixed-model analysis of variance (ANOVA) and Pearson’s correlation analysis were used in the statistical analysis. Student–Newman–Keuls (SNK) tests were used in the post hoc analysis. Significantly lower cortical thickness was found in the left somatosensory and motor cortex (SMC), left posterior cingulate cortex (PCC), and right orbital and polar frontal cortex (OPFC) of the participants in the tinnitus group at baseline than in the participants in the HC group at baseline and after 24 weeks; in the tinnitus group, significantly higher cortical thickness was found after the 24 weeks sound therapy in comparison to the baseline in the left SMC, bilateral superior parietal cortex (SPC), left inferior parietal cortex (IPC), left PCC, and right OPFC. In the HC group, no statistically significant difference in cortical thickness was found after the 24 weeks treatment in comparison to the baseline in the bilateral SMC, bilateral SPC, left IPC, left PCC, or right OPFC. The changes in cortical thickness before and after sound therapy can provide certain reference values for clinical tinnitus treatment. These brain regions could serve as potential targets for neuroimaging.

[Efficacy of percutaneous vagal stimulation in the treatment of chronic tinnitus]

Objective:The aim of this study is to investigate the efficacy of transcutaneous vagus nerve stimulation（taVNS） in the treatment of chronic tinnitus. Methods:taVNS was used to treat chronic decompensated tinnitus, 10 days as a course of treatment. Record and analyze the improvement of the patient's subjective symptoms during treatment. The THI, PSQI and DASS-21 scores were performed at 10 days, 3 months and 6 months after treatment. The improvement of tinnitus in taVNS group and control group at the above recorded time points was compared, and the THI score of taVNS group was compared before and after treatment. Results:① During the taVNS treatment, 93.65% of the patients achieved improvement in subjective symptoms, and 28.6% of the patients voluntarily accepted the second course of taVNS treatment; ② The sleep improvement was optimal when the treatment was 10 days, and some patients had poor sleep status after 3 or 6 months; ③ The anxiety of taVNS group was improved during and after treatment, and the best effect time was 3 months and 6 months after treatment; ④ There was no significant difference in THI score between the two groups, but there was significant improvement in taVNS group at 3 months and 6 months after treatment. Conclusion:taVNS treatment can significantly improve the sleep disorder, anxiety disorder and tinnitus disturbance of tinnitus patients, and the curative effect is good after 3 months and 6 months of prevention.

Phonetic perception but not perception of speaker gender is impaired in chronic tinnitus

While tinnitus is known to compromise the perception of speech, it is unclear if the same holds for extralinguistic speaker information. Furthermore, research with simple tone stimuli showed that unilateral tinnitus binds spatial attention, thereby impeding the detection of auditory changes in the non-affected ear. Using dichotic listening tasks, we tested left-ear tinnitus patients and control patients for their ability to ignore speech and speaker information in the task-irrelevant ear. To this end they heard vowel-consonant-vowel (VCV) syllables simultaneously spoken by gender-ambiguous voices in one ear and male or female voices in the contralateral ear. They selectively attended to speech (Exp. 1) or speaker (Exp. 2) information in a designated target ear, by classifying either the consonant (/b/ or /g/) in VCV syllables or voice gender (male or female) while ignoring distractor voices in the other ear. While performance was comparable across groups in the gender task, tinnitus patients responded slower than controls in the consonant task, with no effect of target ear. This suggests that tinnitus hampers phonetic perception in speech, while preserving the processing of extralinguistic speaker information. These findings support the growing evidence for speech perception impairments in tinnitus.

Neuroanatomical Alterations in Patients With Tinnitus Before and After Sound Therapy: A Combined VBM and SCN Study

Many neuroanatomical alterations have been detected in patients with tinnitus in previous studies. However, little is known about the morphological and structural covariance network (SCN) changes before and after long-term sound therapy. This study aimed to explore alterations in brain anatomical and SCN changes in patients with idiopathic tinnitus using voxel-based morphometry (VBM) analysis 24 weeks before and after sound therapy. Thirty-three tinnitus patients underwent magnetic resonance imaging scans at baseline and after 24 weeks of sound therapy. Twenty-six age- and sex-matched healthy control (HC) individuals also underwent two scans over a 24-week interval; 3.0T MRI and high-resolution 3D structural images were acquired with a 3D-BRAVO pulse sequence. Structural image data preprocessing was performed using the VBM8 toolbox. The Tinnitus Handicap Inventory (THI) score was assessed for the severity of tinnitus before and after treatment. Two-way mixed model analysis of variance (ANOVA) and post hoc analyses were performed to determine differences between the two groups (patients and HCs) and between the two scans (at baseline and on the 24th week). Student-Newman-Keuls (SNK) tests were used in the post hoc analysis. Interaction effects between the two groups and the two scans demonstrated significantly different gray matter (GM) volume in the right parahippocampus gyrus, right caudate, left superior temporal gyrus, left cuneus gyrus, and right calcarine gyrus; we found significantly decreased GM volume in the above five brain regions among the tinnitus patients before sound therapy (baseline) compared to that in the HC group. The 24-week sound therapy group demonstrated significantly greater brain volume compared with the baseline group among these brain regions. We did not find significant differences in brain regions between the 24-week sound therapy and HC groups. The SCN results showed that the left superior temporal gyrus and left rolandic operculum were significantly different in nodal efficiency, nodal degree centrality, and nodal betweenness centrality after FDR correction. This study characterized the effect of sound therapy on brain GM volume, especially in the left superior temporal lobe. Notably, sound therapy had a normalizing effect on tinnitus patients.

Neurobiology of Stress-Induced Tinnitus

Emotional stress has accompanied humans since the dawn of time and has played an essential role not only in positive selection and adaptation to an ever-changing environment, but also in the acceleration or even initiation of many illnesses. The three main somatic mechanisms induced by stress are the hypothalamus-pituitary-adrenal axis (HPA axis), the sympathetic-adreno-medullar (SAM) axis, and the immune axis. In this chapter, the stress-induced mechanisms that can affect cochlear physiology are presented and discussed in the context of tinnitus generation and auditory neurobiology. It is concluded that all of the presented mechanisms need to be further investigated. It is advised that clinical practitioners ask patients about stressful events or chronic stress preceding the tinnitus onset and measure the vital signs. Finally, taking into account that tinnitus itself acts as a stressor, the implementation of anti-stress therapies for tinnitus treatment is recommended.

Tinnitus Update

This article provides an update on tinnitus for audiologists and other clinicians who provide tinnitus-specific services. Tinnitus can be attributable to hearing loss, somatosensory system dysfunction, or auditory cortex dysfunction, with hearing loss being the most common cause and serious underlying pathologies being rare. Hearing loss does not always lead to tinnitus, and patients with tinnitus do not always suffer from hearing loss. The first scenario is explained by a so-called inhibitory gating mechanism, whereas the second assumes that all tinnitus sufferers have some degree of hearing impairment, which might not be detected in standard audiological examinations. The treatments should aim at symptomatic relief and management of associated distress. Current treatment options include pharmacotherapy, education, counseling, cognitive behavioral therapy, and sound therapy.

Alterations of brain activity and functional connectivity in transition from acute to chronic tinnitus

The objective of this study was to investigate alterations to brain activity and functional connectivity in patients with tinnitus, exploring neural features in the transition from acute to chronic phantom perception. Twenty‐four patients with acute tinnitus, 23 patients with chronic tinnitus, and 32 healthy controls were recruited. High‐density electroencephalography (EEG) was used to explore changes in brain areas and functional connectivity in different groups. When compared with healthy subjects, acute tinnitus patients had a significant reduction in superior frontal cortex activity across all frequency bands, whereas chronic tinnitus patients had a significant reduction in the superior frontal cortex at beta 3 and gamma frequency bands as well as a significant increase in the inferior frontal cortex at delta‐band and superior temporal cortex at alpha 1 frequency band. When compared to the chronic tinnitus group, the acute tinnitus group activity was significantly increased in the middle frontal and parietal gyrus at the gamma‐band. Functional connectivity analysis showed that the chronic tinnitus group had increased connections between the parahippocampus gyrus, posterior cingulate cortex, and precuneus when compared with the healthy group. Alterations of local brain activity and connections between the parahippocampus gyrus and other nonauditory areas appeared in the transition from acute to chronic tinnitus. This indicates that the appearance and development of tinnitus is a dynamic process involving aberrant local neural activity and abnormal connectivity in multifunctional brain networks.

Altered Topological Patterns of Gray Matter Networks in Tinnitus: A Graph-Theoretical-Based Study

Objective

Tinnitus is a prevalent hearing disorder, which could have a devastating impact on a patient’s life. Functional studies have revealed connectivity pattern changes in the tinnitus brains that suggested a change of network dynamics as well as topological organization. However, no studies have yet provided evidence for the topological network changes in the gray matter. In this research, we aim to use the graph-theoretical approach to investigate the changes of topology in the tinnitus brain using structural MRI data, which could provide insights into the underlying anatomical basis for the neural mechanism in generating phantom sounds.

Methods

We collected 3D MRI images on 46 bilateral tinnitus patients and 46 age and gender-matched healthy controls. Brain networks were constructed with correlation matrices of the cortical thickness and subcortical volumes of 80 cortical/subcortical regions of interests. Global network properties were analyzed using local and global efficiency, clustering coefficient, and small-world coefficient, and regional network properties were evaluated using the betweenness coefficient for hub connectivity, and interregional correlations for edge properties. Between-group differences in cortical thickness and subcortical volumes were assessed using independent sample t-tests, and local efficiency, global efficiency, clustering coefficient, sigma, and interregional correlation were compared using non-parametric permutation tests.

Results

Tinnitus was found to have increased global efficiency, local efficiency, and cluster coefficient, indicating generally heightened connectivity of the network. The small-world coefficient remained normal for tinnitus, indicating intact small-worldness. Betweenness centrality analysis showed that hubs in the amygdala and parahippocampus were only found for tinnitus but not controls. In contrast, hubs in the auditory cortex, insula, and thalamus were only found for controls but not tinnitus. Interregional correlation analysis further found in tinnitus enhanced connectivity between the auditory cortex and prefrontal lobe, and decreased connectivity of the insula with anterior cingulate gyrus and parahippocampus.

Conclusion

These findings provided the first morphological evidence of altered topological organization of the brain networks in tinnitus. These alterations suggest that heightened efficiency of the brain network and altered auditory-limbic connection for tinnitus, which could be developed in compensation for the auditory deafferentation, leading to overcompensation and, ultimately, an emotional and cognitive burden.

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.