An Insight into Role of Auditory Brainstem in Tinnitus: A Systematic Review of Diagnostic Assessments

Advances in Optogenetic-based Auditory Implants

The auditory brainstem response (ABR) is an electrophysiological test that examines the functionality of the auditory nerve and brainstem. Traumatic brain injury (TBI) can be detected if prolonged peak latency is observed in ABR measurements, since latency measures the neural conduction time in the brainstem, and an increase in latency can be a sign of pathological lesion at the auditory brainstem level. The ABR is elicited by brief sounds that can be used to measure hearing sensitivity as well as temporal processing. Reduction in peak amplitudes and increases in latency are indicative of dysfunction in the auditory nerve and/or central auditory pathways. In this study we used sixteen young adult mice that were divided into two groups: sham and mild traumatic brain injury (mTBI), with ABR measurements obtained prior to, and at 2, 6, and 14 weeks after injury. Abnormal ABRs were observed for the nine TBI cases as early as two weeks after injury and the deficits lasted for fourteen weeks after injury. Results indicated a significant reduction in the Peak 1 (P1) and Peak 4 (P4) amplitudes to the first noise burst, as well as an increase in latency response for P1 and P4 following mTBI. These results are the first to demonstrate auditory sound processing deficits in a rodent model of mild TBI.

Contemporary Audiologic Assessment for Auditory Dys-Synchrony

Hearing screening.

Year 2000 Position Statement: Principles and Guidelines for Early Hearing Detection and Intervention Programs.

1. Jordan K. Yoeli, MD*,† 2. Daniel Nicklas, MD*,† 1. *Children’s Hospital Colorado, Aurora, CO 2. †University of Colorado, Aurora, CO Screening for congenital and acquired deafness and hearing loss (HL) represents a significant responsibility for clinicians in all newborn units and medical homes. Approximately 1 to 3 infants of 1,000 born in a well infant nursery setting and 2 to 4 of 100 born in a NICU have significant bilateral HL. Outcomes in various developmental domains depend on the early recognition and subsequent intervention for HL. Developmental delay is present in 30% to 40% of children with HL; the goal of hearing screening (HS) and prompt intervention is to optimize a child’s language acquisition, cognitive development, literacy, social-emotional maturity and academic success. This article reviews the most up-to-date standards and practices to aid medical providers in the early detection and intervention for pediatric HL. In the United States, universal screening begins in the neonatal period. According to the American Academy of Pediatrics (AAP) Joint Commission on Infant Hearing (JCIH), all infants should be screened for congenital HL before 1 month of age. Most infants are screened in nursery or NICU settings, except for those born outside of a medical facility. For the latter population or for infants with no documented HS, screening should be completed by the medical home before 1 month of age. In a well nursery setting, most HSs are performed by otoacoustic emission (OAE) testing. During an OAE screen, a sensitive microphone in the ear canal records the cochlear responses (“acoustic emissions”) to acoustic stimuli, thereby testing the peripheral auditory system from the outer/middle ear (conduction zones) to the cochlear outer hair cells (sensory organ). A “pass” indicates that hearing is functional to the level of …

The auditory brainstem response (ABR) is a critical tool for assessing auditory brainstem function in biomedical mouse models. Remarkably, despite its importance, the origins of ABR waves specific to mice remain poorly identified. Here, we used EEG source reconstruction to reevaluate the mouse-specific ABR origins. We recorded the topography of ABRs using high-density EEG from the skull of adult mice of either sex combined with parallel multielectrode recordings in the auditory cortex. Individual ABR waves showed a series of distinct spatial topographies across the skull. Wave I' was strongly lateralized, supporting its auditory nerve origin. Waves II/III were also lateralized but had a more frontal distribution, supporting an origin in the cochlear nucleus and olivary complex. A distinct shift in wave IV topography showed focused activity directly above the inferior colliculus (IC). Source localization with beamforming supported the origin of wave IV and V in the IC. In addition, the slow IC wave, P0, temporally overlapped with responses in the auditory cortex. We identify ABR wave IV as a marker of IC activity, separating earlier brainstem contributions (cochlear nucleus, olivary complex) from later thalamic and cortical components. This finding improves the anatomical specificity of the mouse ABR as a noninvasive marker in biomedical mouse models.

Commercially available auditory steady state response (ASSR) systems are widely used to obtain hearing thresholds in the pediatric population objectively. Children are often examined during natural or induced sleep so that the recorded ASSRs are of subcortical origin, the inferior colliculus being often designated as the main ASSR contributor in these conditions. This report presents data from a battery of auditory neurophysiological objective tests obtained in 3 cases of severe brainstem dysfunction in sleeping children. In addition to ASSRs, envelope-following response (EFR) recordings designed to distinguish peripheral (cochlear nerve) from central (brainstem) were recorded to document the effect of brainstem dysfunction on the two types of phase-locked responses. Results obtained in the 3 children with severe brainstem dysfunctions were compared with those of age-matched controls. The cases were identified as posterior fossa tumor, undiagnosed (UD), and Pelizaeus-Merzbacher-Like Disease. The standard audiological objective tests comprised tympanograms, distortion product otoacoustic emissions, click-evoked auditory brainstem responses (ABRs), and ASSRs. EFRs were recorded using horizontal (EFR-H) and vertical (EFR-V) channels and a stimulus phase rotation technique allowing isolation of the EFR waveforms in the time domain to obtain direct latency measurements. The brainstem dysfunctions of the 3 children were revealed as abnormal (weak, absent, or delayed) ABRs central waves with a normal wave I. In addition, they all presented a summating and cochlear microphonic potential in their ABRs, coupled with a normal wave I, which implies normal cochlear and cochlear nerve function. EFR-H and EFR-V waveforms were identified in the two cases in whom they were recorded. The EFR-Hs onset latencies, response durations, and phase-locking values did not differ from their respective age-matched control values, indicating normal cochlear nerve EFRs. In contrast, the EFR-V phase-locking value and onset latency varied from their control values. Both patients had abnormal but identifiable and significantly phase-locked brainstem EFRs, even in a case with severely distorted ABR central waves. ASSR objective audiograms were recorded in two cases. They showed normal or slightly elevated (explained by a slight transmission loss) thresholds that do not yield any clue about their brainstem dysfunction, revealing the method's lack of sensitivity to severe brainstem dysfunction. The present study, performed on 3 sleeping children with severe brainstem dysfunction but normal cochlear responses (cochlear microphonic potential, summating potential, and ABR wave I), revealed the differential sensitivity of three auditory electrophysiological techniques. Estimated thresholds obtained by standard ASSR recordings (cases UD and Pelizaeus-Merzbacher-Like Disease) provided no clue to the brainstem dysfunction clearly revealed by the click-evoked ABR. EFR recordings (cases posterior fossa tumor and UD) showed preserved central responses with abnormal latencies and low phase-locking values, whereas the peripheral EFR attributed to the cochlear nerve was normal. The one case (UD) for which the three techniques could be performed confirms this sensitivity gradient, emphasizing the need for applying the Cross-Check Principle by avoiding resorting to ASSR recording alone. The entirely normal EFR-H recordings observed in two cases further strengthen the hypothesis of its cochlear nerve origin in sleeping children.

Background: Recreational noise exposure from personal listening devices (PLDs) may lead to hidden hearing loss (HHL), affecting auditory nerve function despite normal pure-tone audiometry (PTA) and otoacoustic emissions (OAE). Subclinical auditory damage at the synaptic level often goes undetected by conventional assessments, emphasizing the need for more sensitive measures. Recorded click ABR in the presence of various levels of ipsilateral maskers for the better identification of auditory damage at the synaptic level. These results could help to develop a better objective diagnostic tool that can detect hidden hearing loss. Objective: To examine the effects of PLD usage on extended high-frequency audiometric thresholds and on click-evoked auditory brainstem responses (ABR) with and without ipsilateral masking in individuals with normal hearing. Materials and Methods: Thirty-five young adults aged 18–35 years (18 PLD users, 17 controls) with clinically normal hearing were recruited. Extended high-frequency audiometry (EHFA) was conducted from 9 to 16 kHz. Click-evoked ABRs were recorded at 80 dB nHL under unmasked and ipsilateral broadband noise-masked conditions at 50, 60, and 70 dB SPL. ABR analyses included absolute and relative amplitude (V/I) and latencies of waves I, III, and V. Results: PLD users demonstrated significantly elevated extended high-frequency thresholds compared to controls. ABR analyses revealed reduced Wave I amplitudes across stimulus conditions in PLD users, while Wave V amplitudes were largely preserved, resulting in consistently higher V/I amplitude ratios under masked conditions. No group differences were observed for Wave III amplitudes or absolute/interpeak latencies, except for a modest prolongation of I–III latency at one masker level in PLD users. Conclusions: Conventional audiological tests may not detect early auditory damage; however, extended high-frequency audiometry and ABR with ipsilateral masking demonstrate greater sensitivity in identifying noise-induced functional changes within the auditory brainstem pathways.

Background: Multiple Sclerosis (MS) is a demyelinating neurodegenerative autoimmune disease. Auditory brainstem response (ABR) testing can detect subtle disturbances in auditory signal transmission, localize retrocochlear pathway lesions, and evaluate treatment effectiveness in MS patients. Objective: Evaluate the function of central and peripheral auditory pathways in MS patients using ABR and OAE. Methods: A case-control study was conducted involving 42 MS patients and 42 matched healthy controls. All participants underwent full clinical and audiological evaluation, including pure tone audiometry (PTA), tympanometry, ABR, and OAE. Results: Symmetrically prolonged absolute latencies of Wave III, Wave V, and interpeak latencies (IPLs) were observed in MS patients compared to controls, with no significant effects of sex or disease duration. ABR abnormalities were more frequent in MS than in controls, while no significant differences were found between study groups regarding transient evoked and distortion product otoacoustic emissions (DPOAE). Conclusions: The central auditory pathway appears to be mainly affected in MS, evidenced by the prolonged absolute latencies and ILPs on ABR testing. Peripheral auditory pathway involvement is generally less common, though significant dysfunction at 8 kHz can indicate early cochlear involvement. These findings reflect the importance of comprehensive audiological evaluation in the diagnosis and monitoring of MS patients.

Noise-induced tinnitus: auditory evoked potential in symptomatic and asymptomatic patients

This study aimed to evaluate audiological findings among patients with glutaric aciduria type 1 (GA-1). We used a large test battery for the audiological evaluation of 17 individuals with GA-1 (the study group) and 20 healthy individuals (the control group). Conventional audiometry (0.125-8kHz), distortion product otoacoustic emissions (DPOAEs) (1, 1.5, 2, 3, 4, 6, and 8kHz), contralateral suppression of otoacoustic emissions, and auditory brainstem response (ABR) ( 30, 50, 70 and 90 dB nHL) were measured for all participants (n = 37). Mild sensorineural hearing loss was found in 77.47% (n = 13) of the patients with GA-1, and normal hearing thresholds were seen in 23.53% (n = 4). There were three asymptomatic patients at the time of diagnosis [two developed mild mental motor retardation (MMR) and one developed severe MMR during the follow-up], one with a normal hearing threshold and two with mild hearing loss), and 14 symptomatic patients (three with normal hearing thresholds and 11 with mild hearing loss). Seven of the symptomatic patients diagnosed following an encephalopathic crisis required intensive care and showed significantly worse hearing thresholds than those without symptoms [20.86 ± 4.47 vs. 15.44 ± 3.96 decibel hearing level (dB HL), p = 0.039*], while five had mild-to-moderate hearing loss. Acute encephalopathic crisis had a negative effect on hearing function in the symptomatic patients. The emission and contralateral suppression amplitude values of the study group were significantly lower compared to the control group (p < 0.05). The I-V interpeak latency and absolute latencies of ABR waves I, III, and V of the study group were observed to be significantly prolonged and morphologically distorted compared to those of the control group (p < 0.05). Five patients had MMR, and three had moderate MMR; all eight had mild-to-moderate hearing loss. In addition, of the eight patients with mild MMR, four had mild hearing loss. In particular, the morphological findings of ABR waves were significantly worse in the patients with severe and moderate MMR (p < 0.05). There was a significant correlation between a macrocephaly history (12 patients) and hearing loss (p = 0.041*). Magnetic resonance imaging findings were evaluated in all the 17 patients with GA-1, and typical fronto-temporal atrophy and sylvian fissure enlargement were observed. Our findings support that GA-1 is associated with auditory impairment, primarily in symptomatic patients. Adequate audiological test battery evaluation is essential in this context, particularly for symptomatic patients with a history of encephalopathic crises.

To define both auditory nerve and cochlear receptor functions in subjects with auditory neuropathy (AN). We tested 33 AN subjects (66 ears) and compared them with 21 healthy subjects (28 ears). In AN subjects, the average pure-tone (1, 2, and 4 kHz) threshold loss was 57 dB HL. Click stimuli were used to elicit transient evoked otoacoustic emissions (TEOAEs), cochlear microphonics (CMs), and auditory brain stem responses (ABRs). Both cochlear and ABR potentials were recorded from surface electrodes (vertex-ipsilateral mastoid) using averaging procedures. The amplitudes and latencies of CMs and ABRs and the amplitude of the TEOAEs were analyzed. CM amplitudes recorded from normal ears decreased as a function of subject age. CMs recorded from AN subjects fell within the normal age-adjusted range in 60% of the subjects and were >2 SEEs (standard error of estimate) above the age-adjusted normal regression in 40% of the subjects. TEOAEs were absent in 19 (30%) AN ears (bilaterally in eight, and unilaterally in three subjects) and were present in 44 ears. In AN subjects, correlations among CM amplitude, TEOAE amplitude, and pure-tone average thresholds were not significantly related. CM amplitudes were not significantly different whether TEOAEs or ABRs were present or absent. The ABR was present in 21% of AN subjects and consisted of a low-amplitude Wave V without a preceding Wave I. Measures of CM amplitude and PTA hearing loss were not significantly different in those AN ears with a preserved ABR compared with ears with absent ABRs. Summating potentials to transient click stimuli were of small amplitude (<0.1 microV) and detectable in approximately 50% of the AN and healthy control subjects limiting formal analysis of summating potentials. In a significant proportion of AN subjects, we found abnormalities of cochlear receptor function, including elevated CM amplitudes and absence of TEOAEs. These two abnormalities occurred independently of each other. A low amplitude Wave V of the ABR was found in approximately one-fifth of AN subjects, evidence that neural synchrony can be partially preserved in some subjects with this disorder.

Objective: To compare otoacoustic emissions and auditory brain stem responses in hearing-impaired diabetic patients and matched controls in order to determine the lesion site for hearing loss in diabetic patients.Subjects and Methods: This matched case-control study compared 88 hearing-impaired type 2 diabetic patients with 63 age- and gender-matched controls. Cochlear function was evaluated on the basis of otoacoustic emissions. The presence and amplitude of spontaneous otoacoustic emissions, distortion product amplitudes and latencies were recorded. Retrocochlear function was evaluated on the basis of auditory brainstem response. Absolute latencies of waves I, III, and V and inter-peak latencies of I–III, III–V, and I–V of the auditory brainstem were compared.Results: In the case of diabetic patients, no spontaneous otoacoustic emissions were produced, suggesting cochlear damage. Distortion product otoacoustic emission amplitudes at 1, 2, 4, and 6 kHz, but not the latencies, were significantly different between diabetic and control patients. Wave V latency was also significantly different between the 2 groups while the values of all other auditory brainstem parameters were similar.Conclusion: Cochlear damage may be one of the causes of hearing loss in diabetic patients. Distortion product otoacoustic emission amplitude may be used for assessment of hearing loss in diabetic patients.

The advent of electrophysiological techniques for audiologic and neurologic assessment in the late 60s has generated at least 11 auditory brainstem response (ABR) studies in autism designed to test the integrity of the auditory brainstem pathways. The results reported are contradictory, involving prolongation, shortening, and no abnormalities in central transmission latencies. When sample and methodological factors influencing the ABR are taken into consideration in the interpretation of results, the ABR data available at present can be seen as only suggestive, rather than supportive, of brainstem involvement in autism. Paradoxically, these studies revealed the presence of peripheral hearing impairment in a non-negligible number of autistic individuals. Additional evidence of auditory abnormalities as well as the implications for the clinician are considered.