Animesh Barman

Involvement of peripheral vestibular nerve in individuals with auditory neuropathy

The vestibulocochlear nerve is a sensory nerve that serves the organs of hearing and equilibrium. Neuropathies of the nerve, particularly auditory neuropathy may be caused by primary demyelination or by axonal diseases. In disorders affecting the cochlear nerve, it is probable that the vestibular nerve is involved as well. There are isolated reports of the involvement of the inferior vestibular nerve (using vestibular-evoked myogenic potentials) in individuals with AN. However, there is a dearth of information on the involvement of the superior vestibular nerve and other functions such as optokinetic, saccade and vestibulo-occular reflex. A total of three subjects diagnosed as having auditory neuropathy, underwent an extensive vestibular assessment consisting of clinical tests of stability (Romberg, Fukuda stepping test), administration of dizziness questionnaire developed by Maryland hearing and balance centre, cervical vestibular-evoked myogenic potentials and a standard electronystagmography test battery. In the present study, the entire subject population assessed showed hypofunctional caloric responses and absent VEMPs. Two out of the three subjects were asymptomatic of vestibular dysfunction. On the clinical tests of stability, two subjects showed deviations to the right, while one subject performed normally. Thus, the present study indicates a possible involvement of peripheral vestibular nerve involvement in individuals with auditory neuropathy.

Characterizing the frequency tuning properties of air-conduction ocular vestibular evoked myogenic potentials in healthy individuals

Abstract Objective: Inconsistencies regarding frequency tuning of ocular vestibular evoked myogenic potentials (oVEMP) prompted the present study to aim at characterizing frequency tuning of oVEMP in healthy individuals. Design: Normative study. Study sample: The study was conducted to obtain oVEMP responses from 54 healthy individuals in age range of 18–30 years. The responses were acquired for tone-bursts at octave and mid-octave frequencies from 250 to 2000 Hz from the inferior oblique muscle using contralateral electrode placement. The frequencies were compared for amplitude and threshold. Results: oVEMPs were present in 100% of individuals at or below the frequency of 1000 Hz. The responses had maximum amplitude and lowest thresholds at 500 Hz. There were at least two replicable peak-complexes namely n1-p1 and p1-n2. Both these complexes revealed tuning at 500 Hz. Comparison between the two peak-complexes revealed higher amplitudes and lower thresholds for p1-n2 complex. Conclusions: oVEMPs are tuned to 500 Hz for both peak-complexes, with p1-n2 being more robust. Future studies using the threshold of oVEMP may be better suited to use p1-n2 complex for this purpose, provided vestibular origin of the second complex is proved. Additionally, careful use of tuning property is recommended when evaluating pathological conditions.

Comparison of vestibular evoked myogenic potentials elicited by click and short duration tone burst stimuli

INTRODUCTION Vestibular evoked myogenic potentials are short latency electrical impulses that are produced in response to higher level acoustic stimuli. They are used clinically to diagnose sacculocollic pathway dysfunction. AIM This study aimed to compare the vestibular evoked myogenic potential responses elicited by click stimuli and short duration tone burst stimuli, in normal hearing individuals. METHOD Seventeen subjects participated. In all subjects, we assessed vestibular evoked myogenic potentials elicited by click and short duration tone burst stimuli. RESULTS AND CONCLUSION The latency of the vestibular evoked myogenic potential responses (i.e. the p13 and n23 peaks) was longer for tone burst stimuli compared with click stimuli. The amplitude of the p13-n23 waveform was greater for tone burst stimuli than click stimuli. Thus, the click stimulus may be preferable for clinical assessment and identification of abnormalities as this stimulus has less variability, while a low frequency tone burst stimulus may be preferable when assessing the presence or absence of vestibular evoked myogenic potential responses.

Vestibular Evoked Myogenic Potential as a Tool to Identify Vestibular Involvement in Auditory Neuropathy

Abstract Auditory neuropathy is characterized by a unique pattern of hearing loss, absent or severely distorted ABR, preserved OAE, and measurable cochlear microphonics. As the vestibular and cochlear branches are parts of the same fiber bundle system called the vestibulocochlear nerve, it is likely that neuropathy in one (cochlear branch) might also form a feature in the other (vestibular branch). But none of these tests are able to explain the involvement of the vestibular system in these cases. Thus, the present study was undertaken to explore this aspect to determine: (1) the involvement of the vestibular pathway in cases with auditory neuropathy; (2) if there is any relationship between vestibular abnormalities and the symptoms they mimic; and (3) the incidence of vestibular abnormality in patients with auditory neuropathy. Ten subjects (7 male and 3 female) in the age range of 15 to 35 years participated in this study. The test battery administered included pure-tone audiometry, ABR, OAE, Immittance, and VEMP. The results showed: (1) nine out of the 10 subjects showed abnormal or absent VEMP; (2) there is no one-to-one correlation between the abnormal or absent VEMP and the vestibular symptoms that these subjects present; and (3) 80% of the ears with auditory neuropathy showed abnormal VEMP results giving an indication of high incidence of vestibular involvement in the auditory neuropathy population. The present study provides evidence for involvement of the vestibular branch of the VIIIth cranial nerve in a high percentage of the auditory neuropathy population; hence, it is suggested that there is need for vestibular assessment in cases of auditory neuropathy that would help to better understand the disorder. It is also suggested that the term “acoustic neuropathy” be used to indicate those patients in whom only the acoustic nerve is affected and “vestibuloacoustic neuropathy” to label those patients who also show involvement of the vestibular system.

Efficacy of ocular vestibular-evoked myogenic potential in identifying posterior semicircular canal benign paroxysmal positional vertigo.

Objectives: Benign paroxysmal positional vertigo (BPPV) is a unilateral peripheral vestibular pathology, mostly involving the semicircular canals and the otolith organs. Although equivocal findings exist on the utility of cervical vestibular-evoked myogenic potential in identifying BPPV-associated changes in saccule, ocular vestibular-evoked myogenic potential (oVEMP), which is primarily a utricular response, has sparingly been explored in this population. Hence, the present study aimed at examining oVEMP in individuals with BPPV and comparing them with healthy individuals to illustrate its efficacy in identifying BPPV-associated changes in the utricle. Design: Using a case-control design, oVEMPs were elicited by 500 Hz tone bursts at 125 dB peak sound pressure level and recorded bilaterally from 30 individuals with unilateral posterior canal BPPV and 30 age- and gender-matched healthy controls. Results: There were no inter- or intragroup differences in latency aspects (p > 0.05); however, amplitudes were significantly smaller in BPPV ears compared with the non-BPPV ears of individuals with BPPV as well as ears of healthy controls (p < 0.05). Exceptions to this were five participants with BPPV in whom the affected ears demonstrated larger response amplitude (augmentation) than the unaffected ears. Furthermore, there was significantly larger interaural amplitude ratio in individuals with BPPV compared with the healthy controls (p < 0.05). Interaural amplitude ratio produced the largest effect size among the oVEMP parameters for differentiating BPPV from healthy controls. Conclusions: Large asymmetry ratio of oVEMP, usually exceeding 26.8%, is the most potent characteristic of oVEMP in BPPV. Abnormal oVEMP results confirm utricular pathology in ears with BPPV, and therefore, oVEMP can be used as an objective tool with asymmetry ratio as the parameter of choice for the evaluation of utricular function in persons with posterior canal BPPV.

Characterizing the Effects of Frequency on Parameters of Short Tone‑bursts Induced Ocular Vestibular Evoked Myogenic Potentials

Stimulus is the essence of any audiovestibular investigation and ocular vestibular-evoked myogenic potential (oVEMP) would be no different. Several investigations have examined the effect of frequency of stimulus on oVEMP parameters with prime reports concentrated around amplitude and to a lesser extent threshold. Effects of stimulus frequency on latency-related parameters have been sparingly explored with equivocal results. Thus, the aim of this study was to investigate the effects of air-conducted frequency-specific short tone-bursts on latency, amplitude, and threshold-related parameters of various peaks of oVEMP. A normative study was conducted to obtain oVEMP responses from 50 healthy individuals in the age range of 18 - 30 years. Tone-bursts at octave and midoctave frequencies from 250 to 2000 Hz were used to acquire responses from the inferior oblique muscle using contralateral electrode placement. oVEMPs were present in 100% of the individuals at or below the frequency of 1000 Hz. The largest amplitudes and the lowest threshold corresponded to 500 Hz tone-burst, whereas 250 Hz produced largest absolute latencies as well as interpeak latency intervals (P < 0.05). Frequency had no effect on interaural latency difference as well as interaural amplitude ratio. Owing to largest amplitudes and best thresholds, 500 Hz appears better stimuli for clinical recording of oVEMPs. This is true irrespective of the peak complex being assessed is n1p1 or p1n2.

Rise/fall and plateau time optimization for cervical vestibular-evoked myogenic potential elicited by short tone bursts of 500 Hz

Abstract Objective: Literature on clinical utility of cervical vestibular-evoked myogenic potential (cVEMP) has been increasing rapidly, though not without inconsistencies in spite of involving similar populations. Close examination of methods across studies exposed the use of variable stimulus parameters, especially rise/fall time (R/FT) and plateau time (PT) as the possible reason. However the effect of variation in R/FT and PT on cVEMP response parameters has been largely uncharted. Design: The study aimed at evaluating the impact of R/FT and PT on cVEMPs elicited by 500-Hz short tone-bursts (STBs) at 95 dB nHL using R/FT from 1 to 4 ms and PT from 0 to 3 ms. Study sample: 30 healthy individuals with normal audio-vestibular system. Results: Significant prolongation of latencies with increasing R/FT and PT (p < 0.05) was noticed. The amplitude however varied significantly only for some R/FTs and PTs. R/FT of 2 ms, in combination with 1-ms PT, produced large amplitudes with lowest variability in amplitude and latency parameters. Conclusions: R/FT of 2 ms along with PT of 1 ms formed a good amalgamation and could be considered optimum for clinical recording of cVEMPs elicited by 500-Hz STBs, although slight deviances in these parameters might not impact the outcome significantly.

Vestibular test findings in individuals with auditory neuropathy: review

BACKGROUND The vestibulocochlear nerve is a sensory nerve that serves the organs of hearing and equilibrium. Neuropathies of the nerve, particularly auditory neuropathy, may be caused by primary demyelination or axonal disease. Cochlear amplification function is normal in cases of auditory neuropathy, but afferent neural conduction in the auditory pathway is disordered. It is highly probable that the vestibular nerve has some involvement in disorders affecting the cochlear nerve. OBJECTIVE To provide an overview of vestibular test findings in individuals with auditory neuropathy. METHOD A structured literature search was carried out, with no restrictions to the dates searched. CONCLUSION Auditory neuropathy implicated the vestibular branch of the VIIIth cranial nerve as well as the cochlear nerve. However, there was variability in terms of vestibular test findings.

Speech perception abilities for spectrally modified signals in individuals with auditory dys-synchrony

Abstract Objective. The objective of the study was to determine the speech perception abilities for spectrally modified speech signals in individuals with auditory dys-synchrony. Study Sample. The speech identification scores of 30 normal hearing and 12 individuals diagnosed as having auditory dys-synchrony were studied. Design. Phonemically balanced words in Kannada developed by 21 were presented unfiltered and filtered at 1700 Hz low-pass and 1700 Hz high-pass cut-off frequencies, and speech identification performance was assessed. Results. Results revealed that there is a highly significant difference in speech identification scores for unfiltered and low-pass filtered words. This difference could be attributed to the physiological coding deficits of low frequency information which are usually coded by phase locked responses in auditory nerve fibers (15). Conclusions. Thus, low-pass filtered words can be used as an effective tool to identify individuals with auditory dys-synchrony, especially those who have good speech identification scores in quiet. Sumario Objetivo. El objetivo de este estudio fue determinar las habilidades de percepción del lenguaje con señales de lenguaje espectralmente modificadas en sujetos con disincronía auditiva. Muestra de Estudio. Se estudiaron las puntuaciones de identificación de lenguaje de 30 normo-oyentes y de 12 individuos con diagnóstico de disincronía auditiva. Diseño. Se presentaron palabras fonéticamente balanceadas en Kannada, desarrolladas por 21 sin filtro y con filtro pasa/bajo de 1700 Hz y filtro pasa/alto de corte de frecuencias de 1700 Hz, y se evaluó el rendimiento en la identificación del lenguaje. Resultados. Los resultados revelan que existe una diferencia significativa muy alta en las puntuaciones de identificación de lenguaje para palabras no filtradas y con filtro pasa bajo. Esta diferencia puede ser atribuida al déficit fisiológico de codificación de la información e bajas frecuencias, que usualmente se codifican como respuestas con bloqueo de fase en las fibras del nervio auditivo (15). Conclusiones. Por lo tanto, las palabras filtradas pasa bajo pueden usarse como una herramienta útil para identificar personas con disincronía auditiva, especialmente aquellas que tienen buenas puntuaciones para la identificación de lenguaje en silencio.

Amplification strategy to enhance speech perception in individuals with auditory neuropathy spectrum disorder

Objective: The present study was conducted to determine if low-cut modified amplification improved aided speech perception compared to standard NAL-NL1 prescriptive amplification in individuals with ANSD. The study further aimed to check the influence of the number of channels in a hearing aid on speech perception with low-cut modification of amplification. Study design: A total of 22 individuals with ANSD in the age range 15–42 years were recruited for the study. The unaided and aided speech identification scores were obtained with standard amplification and low-cut amplification settings in both a four- and a 16-channel digital hearing aid. Results: The results showed that low-cut amplification was slightly better than standard amplification for aided speech perception. Such an improvement could be attributed to the elimination of upward spread of masking during low-cut modification of amplification. In addition, improvement was greater with a four-channel hearing aid compared to a 16-channel hearing aid. Conclusions: The use of low-cut amplification with a low number of channels in the hearing aid for individuals with ANSD is recommended. However, further studies are essential to determine whether the slight improvement in aided scores with a low-cut fitting strategy leads to actual improvement in quality of life.