Interactions between the vestibular nucleus and the dorsal cochlear nucleus: implications for tinnitus

Vestibular contribution to spatial encoding

Determining the spatial relation between objects and our location in the surroundings is essential for survival. Vestibular inputs provide key information about the position and movement of our head in the three-dimensional space, contributing to spatial navigation. Yet, their role in encoding spatial localisation of environmental targets remains to be fully understood. We probed the accuracy and precision of healthy participants' representations of environmental space by measuring their ability to encode the spatial location of visual targets (Experiment 1). Participants were asked to detect a visual light and then walk towards it. Vestibular signalling was artificially disrupted using stochastic galvanic vestibular stimulation (sGVS) applied selectively during encoding targets' location. sGVS impaired the accuracy and precision of locating the environmental visual targets. Importantly, this effect was specific to the visual modality. The location of acoustic targets was not influenced by vestibular alterations (Experiment 2). Our findings indicate that the vestibular system plays a role in localising visual targets in the surrounding environment, suggesting a crucial functional interaction between vestibular and visual signals for the encoding of the spatial relationship between our body position and the surrounding objects.

Association of Dual Sensory Impairment with Declining Physical Function in Community-Dwelling Older Adults

Few studies have investigated whether dual sensory impairment (DSI) adversely affects the deterioration of physical function in older adults compared to single sensory impairment (SSI, visual or auditory). We studied the association between DSI and declining physical function by analyzing the data of 2780 Korean community-dwelling adults aged 70-84 years. Sensory impairment was assessed through pure tone audiometry and visual acuity testing. Muscle strength (handgrip strength) and physical performance (timed up and go test and short physical performance battery (SPPB)) were evaluated. In the cross-sectional analysis, DSI was associated with higher odds of having low muscle strength (odds ratio (OR), 1.78; 95% confidence interval (CI), 1.27-2.48) and poor physical performance (SPPB: OR, 2.04; 95% CI, 1.38-3.00) than SSI. Among all sensory impairment groups in the longitudinal analysis, DSI at baseline increased the risk of deteriorating physical performance during the follow-up period (OR, 1.94; 95% CI, 1.31-2.88; p < 0.01) the most. DSI showed a more severe adverse effect on the decline in physical function among community-dwelling older adults than SSI. More comprehensive care is needed to prevent the deterioration of physical function in older adults due to DSI.

How much I moved: Robust biases in self-rotation perception

Vestibular cues are crucial to sense the linear and angular acceleration of our head in three-dimensional space. Previous literature showed that vestibular information precociously combines with other sensory modalities, such as proprioceptive and visual, to facilitate spatial navigation. Recent studies suggest that auditory cues may improve self-motion perception as well. The present study investigated the ability to estimate passive rotational displacements with and without virtual acoustic landmarks to determine how vestibular and auditory information interact in processing self-motion information. We performed two experiments. In both, healthy participants sat on a Rotational-Translational Chair. They experienced yaw rotations along the earth-vertical axis and performed a self-motion discrimination task. Their goal was to estimate both clockwise and counterclockwise rotations’ amplitude, with no visual information available, reporting whether they felt to be rotated more or less than 45°. According to the condition, vestibular-only or audio-vestibular information was present. Between the two experiments, we manipulated the procedure of presentation of the auditory cues (passive vs. active production of sounds). We computed the point of subjective equality (PSE) as a measure of accuracy and the just noticeable difference (JND) as the precision of the estimations for each condition and direction of rotations. Results in both experiments show a strong overestimation bias of the rotations, regardless of the condition, the direction, and the sound generation conditions. Similar to previously found heading biases, this bias in rotation estimation may facilitate the perception of substantial deviations from the most relevant directions in daily navigation activities.

Hearing loss versus vestibular loss as contributors to cognitive dysfunction

In the last 5 years, there has been a surge in evidence that hearing loss (HL) may be a risk factor for cognitive dysfunction, including dementia. At the same time, there has been an increase in the number of studies implicating vestibular loss in cognitive dysfunction. Due to the fact that vestibular disorders often present with HL and other auditory disorders such as tinnitus, it has been suggested that, in many cases, what appears to be vestibular-related cognitive dysfunction may be due to HL (e.g., Dobbels et al. Front Neurol 11:710, 2020). This review analyses the studies of vestibular-related cognitive dysfunction which have controlled HL. It is suggested that despite the fact that many studies in the area have not controlled HL, many other studies have (~ 19/44 studies or 43%). Therefore, although there is certainly a need for further studies controlling HL, there is evidence to suggest that vestibular loss is associated with cognitive dysfunction, especially related to spatial memory. This is consistent with the overwhelming evidence from animal studies that the vestibular system transmits specific types of information about self-motion to structures such as the hippocampus.

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

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

Weak Vestibular Response in Persistent Developmental Stuttering

Vibrational energy created at the larynx during speech will deflect vestibular mechanoreceptors in humans (Todd et al., 2008; Curthoys, 2017; Curthoys et al., 2019). Vestibular-evoked myogenic potential (VEMP), an indirect measure of vestibular function, was assessed in 15 participants who stutter, with a non-stutter control group of 15 participants paired on age and sex. VEMP amplitude was 8.5 dB smaller in the stutter group than the non-stutter group (p = 0.035, 95% CI [−0.9, −16.1], t = −2.1, d = −0.8, conditional R² = 0.88). The finding is subclinical as regards gravitoinertial function, and is interpreted with regard to speech-motor function in stuttering. There is overlap between brain areas receiving vestibular innervation, and brain areas identified as important in studies of persistent developmental stuttering. These include the auditory brainstem, cerebellar vermis, and the temporo-parietal junction. The finding supports the disruptive rhythm hypothesis (Howell et al., 1983; Howell, 2004) in which sensory inputs additional to own speech audition are fluency-enhancing when they coordinate with ongoing speech.

Metabolic changes in the brain and blood of rats following acoustic trauma, tinnitus and hyperacusis

It has been increasingly recognized that tinnitus is likely to be generated by complex network changes. Acoustic trauma that causes tinnitus induces significant changes in multiple metabolic pathways in the brain. However, it is not clear whether those metabolic changes in the brain could also be reflected in blood samples and whether metabolic changes could discriminate acoustic trauma, hyperacusis and tinnitus. We analyzed brain and serum metabolic changes in rats following acoustic trauma or a sham procedure using metabolomics. Hearing levels were recorded before and after acoustic trauma and behavioral measures to quantify tinnitus and hyperacusis were conducted at 4 weeks following acoustic trauma. Tissues from 11 different brain regions and serum samples were collected at about 3 months following acoustic trauma. Among the acoustic trauma animals, eight exhibited hyperacusis-like behavior and three exhibited tinnitus-like behavior. Using Gas chromatography-mass spectrometry and multivariate statistical analysis, significant metabolic changes were found in acoustic trauma animals in both the brain and serum samples with a number of metabolic pathways significantly perturbated. Furthermore, metabolic changes in the serum were able to differentiate sham from acoustic trauma animals, as well as sham from hyperacusis animals, with high accuracy. Our results suggest that serum metabolic profiling in combination with machine learning analysis may be a promising approach for identifying biomarkers for acoustic trauma, hyperacusis and potentially, tinnitus.

Is Asymmetric Hearing Loss a Risk Factor for Vestibular Dysfunction? Lesson From Big Data Analysis Based on the Korean National Health and Nutrition Survey

OBJECTIVE

The purpose of this study was to investigate whether asymmetric hearing loss affects vestibular function.

STUDY DESIGN

Retrospective cross-sectional study.

PATIENTS

Data from the 2010 Korean National Health and Nutrition Survey for adults aged 40 years or more were used.

INTERVENTIONS

The modified Romberg test and pure-tone audiometry were performed. Data were analyzed using a complex sample χ test of independence and complex sample logistic regression analysis.

MAIN OUTCOME MEASURES

Vestibular dysfunction and hearing thresholds.

RESULTS

The overall prevalence of vestibular dysfunction was 3.3% (95% confidence interval [CI], 2.5-4.3%). In adults more than 40 years of age, multivariate linear regression analyses showed that the odds ratio (OR) of vestibular dysfunction was 3.067 times higher than the reference for a 30-dB difference in hearing thresholds between both ears (CI, 1.481-6.351; p = 0.007) after adjusting for factors associated with vestibular dysfunction. Among these individuals, the risk of equilibrium disturbance was higher in the presence of low-frequency asymmetric hearing loss (OR, 2.148; CI, 1.216-3.793; p = 0.009); on the other hand, high-frequency asymmetry did not lead to a higher risk.

CONCLUSIONS

As low-frequency asymmetric hearing thresholds tend to coexist with vestibular dysfunction in adults, those with asymmetric hearing loss should be closely monitored.

Early multisensory integration of self and source motion in the auditory system

Discriminating external from self-produced sensory inputs is a major challenge for brains. In the auditory system, sound localization must account for movements of the head and ears, a computation likely to involve multimodal integration. Principal neurons (PNs) of the dorsal cochlear nucleus (DCN) are known to be spatially selective and to receive multimodal sensory information. We studied the responses of PNs to body rotation with or without sound stimulation, as well as to sound source rotation with stationary body. We demonstrated that PNs are sensitive to head direction, and, in the presence of sound, they differentiate between body and sound source movement. Thus, the output of the DCN provides the brain with enough information to disambiguate the movement of a sound source from an acoustically identical relative movement produced by motion of the animal.

What vestibular tests to choose in symptomatic patients after a cochlear implant? A systematic review and meta-analysis

Vestibular function after cochlear implantation is difficult to understand, as subjective vestibular symptoms seem uncorrelated with the results of objective tests. Consequently, clinicians may struggle to decide what assessments to perform for a symptomatic patient. We used a systematic review and meta-analysis approach to enlighten this point. After a study inclusion process, results were classified into four different groups for each test in each study: (1) 'true positive' if the test showed impairment from pre-operative to post-operative in symptomatic patients; (2) 'false positive' if the test showed impairment from pre-operative to post-operative in asymptomatic patients; (3) 'true negative' if the test showed no impairment in asymptomatic patients; and (4) 'false negative' if the test showed no impairment in symptomatic patients. From these groups, sensitivities and specificities of each test were calculated in a meta-analysis. After reviewing more than 3000 references, 16 studies were included, representing 957 patients. The meta-analysis revealed a sensitivity of 0.21 (CI 95 % 0.08-0.40) for the caloric tests, of 0.32 (CI 95 % 0.15-0.54) for the cervical vestibular evoked myogenic potentials (c-VEMP), and of 0.5 (CI 95 % 0.07-0.93) for the head impulse tests. The analysis of prevalence revealed that c-VEMPs were the most often impaired, and the HIT the most often conserved. Our review and meta-analysis revealed that no vestibular test is sensitive enough to be recommended as a single test. Ideally, all the five vestibular sensors should be tested. In clinical practice, we suggest a case-to-case strategy according to patient's symptoms and their suspected origin.