Annals of Indian Academy of Otorhinolaryngology Head and Neck Surgery

ORIGINAL ARTICLE
Year
: 2020  |  Volume : 4  |  Issue : 2  |  Page : 39--44

Effect of poor auditory stimulation on neural activity reflected in auditory brainstem response: Comparative case study


Preeti Sahu1, Monalisa Jati1, Anu Nitin Nagarkar2, Nitin M Nagarkar1,  
1 Department of ENT and HNS, AIIMS, Raipur, Chhattisgarh, India
2 Department of Otolaryngology (ENT), PGIMER, Chandigarh, India

Correspondence Address:
Mrs. Preeti Sahu
AIIMS, Raipur, Chhattisgarh
India

Abstract

Background: Hearing loss is often referred as an invisible disability as there are no telltale markers. Late identification and late intervention not only affects a child's speech and language development, but also it can result in poor academic performance which can ultimately lead to limited career options. Communication outcomes in hearing impaired children are influenced by a number of factors including age at onset of hearing loss, age at and adequacy of intervention, degree of hearing loss, audiometric configuration, intervention program, and family and environmental influences. Methods: A detailed comparative case history was taken followed by complete Audiological evaluative for the present paper. Purpose of the Study: The primary purpose of the current study was to determine the effects of age on auditory intervention and degree of hearing loss on auditory-based outcomes including speech perception and speech production. The study hypothesized that language outcome is not necessarily an auditory skill. The present study also highlighted the importance of correlation between different audiological tests. Research Design: This was retrospective study. Results and Conclusion: Electrophysiological test like brainstem evoked response audiometry is a reliable indicator of hearing level in an individual. A number of tests are administered to identify the hearing status of a person. A correlation between the test findings provides evidence about the anatomical and physiological substrate of the auditory system. This study provides an insight that, not only the auditory stimulation but also the nonauditory stimulation of brain is required for the development of normal communication ability in human being.



How to cite this article:
Sahu P, Jati M, Nagarkar AN, Nagarkar NM. Effect of poor auditory stimulation on neural activity reflected in auditory brainstem response: Comparative case study.Ann Indian Acad Otorhinolaryngol Head Neck Surg 2020;4:39-44


How to cite this URL:
Sahu P, Jati M, Nagarkar AN, Nagarkar NM. Effect of poor auditory stimulation on neural activity reflected in auditory brainstem response: Comparative case study. Ann Indian Acad Otorhinolaryngol Head Neck Surg [serial online] 2020 [cited 2021 Apr 20 ];4:39-44
Available from: https://www.aiaohns.in/text.asp?2020/4/2/39/309780


Full Text

 Introduction



Hearing loss is the most prevalent sensory disability in the world.[1] Consequences of hearing loss include speech disorder, communication disorder and delay in language development, educational disadvantage, social separation, and stigmatization.[2],[3] Different tests have been developed to identify the degree and type of hearing loss. These tests are broadly classified as subjective versus objective, based on the participation of individuals. The basic subjective tests which are used for threshold estimation of an individual include pure tone audiometry (PTA), speech audiometry and the objective tests include admittance audiometry, otoacoustic emissions (OAEs), and brainstem evoked response audiometry (BERA).

Auditory brainstem response (ABR) is a reliable indicator of hearing level in a person. Rushaidinetal in 2009[4] estimated that instantaneous energy of peak V of ABR discriminated normal and abnormal hearing persons on the basis of their threshold values. At a high stimulus level, wave I-V can be observed in normal hearing individuals. If stimulus level is reduced, early ABR waves disappear. However, wave V is the most robust wave of ABR which can be detected for a level, close to behavioral threshold.[5] Various authors[6],[7],[8],[9],[10],[11],[12] tried to determine the hearing threshold level by identifying the ABR peaks and few others[13],[14],[16],[17] had analyzed the entire AEP signal. The areas responsible for ABR undergo distinct maturational transformations in early life. Although the precise physio-anatomic substrate of the ABR remains speculative, experimental manipulations, and selective response measures have been utilized to clarify the developmental process and to extract underlying detailed information about the auditory pathway.[18] Auditory steady state response (ASSR) is also used as a predictor of behavioral thresholds across all the age groups for frequency range of 250 Hz–4000 Hz[19] but the threshold prediction is confirmed from 500 Hz to 4000 Hz.[20]

The various tests used for the estimation of hearing status have a significant role in identification of hearing difficulty and communication ability of an individual. A correlation between the test findings provides an insight into the anatomical and physiological substrate of the hearing system. Research has shown one-to-one relationship between ABR threshold and pure-tone threshold in the region of 2–4 KHz. The major part of this is due to unknown factors that are involved in the physiological relationship between the two thresholds.[21]

Purpose of the study

The study attempts to find the possible reason/explanation for poor correlation between PTA and ABR findings using two similar reported casesThe study also tries to determine the effects of age on auditory intervention and also hypothesizes that language outcome is not necessarily an auditory skill.

 Methods



Case report

Case A

A female aged 16 years with bilateral hearing deficit and partially intelligible speech reported to the hospital. Parental interview revealed the case had subnormal hearing at birth as she responded to moderate-loud sounds. At 3 years of age, she had high fever followed by reduced auditory response. Audiological findings were suggestive of bilateral moderately severe hearing loss through ABR test. She was then fitted with a body level hearing aid with Y cord, at 4 years of age. Later on at 8 years of age, she was fitted with binaural digital behind the ear hearing aid [Table 1].{Table 1}

Case B

A 17-year-old male with congenital bilateral hearing deficit and partially intelligible speech reported to the hospital. Parental interview was suggestive of subnormal hearing at birth without any confirmatory tests. There was a definite history of rubella infection to mother during first trimester. The case then underwent audiological evaluation by his first birthday. Behavioral observation audiometry of the case was suggestive of moderate-to-severe hearing loss. Initially, the child was fitted with a body level hearing aid with Y cord at his first birthday. Later on, he was fitted with binaural digital behind the ear hearing aid at the age of 5 years.

Instrumentation

A single channeled audiometer was used for pure tone and speech threshold estimation from 250 Hz to 8 KHz. MAICO MI 44 admittance audiometer using 226 Hz probe tone was used for the evaluation of middle ear condition. Acoustic reflex thresholds were also measured for ipsilateral and contra lateral stimulation from 500 Hz to 4 KHz. The hermetic seal was ensured using proper sized tips before performing tympanometry testing. OAE was also performed using Neuro-Audio (version 2010) instrument. Both Transient Evoked Oto Acoustic Emission (TEOAE) and Distortion Product Oto Acoustic emission (DPOAE) were recorded to evaluate the status of outer hair cells (OHCs). DPOAE was done using two different frequencies (F1 = 500 Hz, F2 = 1000 Hz) with two different intensity levels (L1 = 65 dB, L2 = 55 dB) whereas TEOAE was done at 80 dB. In order to assess the integrity of auditory pathways BERA and ASSR tests were conducted. BERA was done using rarefaction click stimuli with a rate of 19.1 clicks/s. Intensities were varied from 60 dBnHL till the highest level where identifiable Wave peak V was observed. ASSR test was done for frequency specific responses, using frequency modulated and amplitude-modulated stimulus at various intensity level for frequencies starting from 500 Hz to 4 KHz.

 Results



Audiological findings

Pure tone audiometry

Both the cases had bilateral moderately severe sensorineural hearing loss. For both the cases, thresholds were better at low frequencies compared to mid and high frequencies. A sloping pattern audiogram was obtained in both the cases with pure tone average for Case A: Right ear (RE): 66.6 dB HL, Left ear (LE): 60 dB HL, and for Case B: RE: 60 dBHL LE: 60 dBHL. The details are shown in [Table 2] and [Figure 1].{Figure 1}{Table 2}

Speech audiometry

Speech audiometry was administered using closed set of stimuli which included picture cards and the mode of response was pointing. This was due to unintelligible speech in both the cases. For both the cases, speech recognition threshold was found to be 55 dB HL and speech discrimination score was 70% in both ears. The details are shown in [Table 3].{Table 3}

Immittance audiometry findings

Bilateral A-type Tympanogram was found with absence of both ipsilateral and contralateral reflexes. It was suggestive of bilateral normal middle ear conditions. The details are shown in [Table 4].{Table 4}

Otoacoustic emission findings

Both TEOAE and DPOAE screening was administered for both the cases. The result was “Refer” bilaterally suggestive of abnormal function of OHCs. The details are shown in [Table 5].{Table 5}

Brainstem evoked response audiometry findings

For case A, the wave peak-V was not observed even at highest intensity level, i.e., 100 dBnHL on repeated trials for both the ears was suggestive of bilateral severe to profound hearing loss. For Case B, a well-identifiable wave Peak V was observed at 70 dBnHL in both the ears indicative of bilateral moderately severe of hearing loss. Even though a well-identifiable wave peak-V was found in Case B, but the wave morphology was poor. The details are shown in [Figure 2] and [Table 6].{Figure 2}{Table 6}

Auditory steady state response findings

ASSR testing was done to obtain frequency specific thresholds at neural level. The thresholds obtained in ASSR reflected a similar pattern that of PTA in frequency range of 500 Hz–4 KHz. These values obtained were a bit higher for Case A. The details are shown in [Figure 3] and [Table 7].{Figure 3}{Table 7}

 Discussion



In the present study, the primary difference was observed for objective test findings (ABR and ASSR). The findings were correlated with subjective test outcome which was PTA. Case B was identified and appropriate intervention was started by the age of 1 year. On the contrary for case A, diagnosis was confirmed after third birthday and intervention was started at 4 years of age. This indicated a minimal amount of auditory stimuli was provided to the auditory brainstem in childhood during which it remained immature and virtually unchanged. The auditory pathways mature, with age and become adult-like once the cochlea is functional.

Electrophysiological tests such as ABR and ASSR assess the integrity of auditory brainstem in response to auditory stimuli. The signal travels from cochlear nuclear complex to inferior-colliculus proximally. Auditory evoked potentials change over time and become more evident in terms of amplitude and latency in normal hearing children.[22],[23],[24],[25],[26] Latency of ABR decreases over 1st year of life in normal hearing infants.[24],[27],[28],[29] These changes had been explained in terms of increased myelination and improved synaptic efficiency proposed by Hebb.[22],[23]

In case A, there was lack of auditory stimulation during critical age period. ABR finding in this case showed unidentifiable wave peak V till 100 dBnHL suggestive of severe to profound hearing loss whereas PTA was suggestive of bilateral moderately severe sensorineural hearing loss. In this case, lack of auditory input during the developmental age lead to insignificant changes of auditory pathway which was reflected as insignificant changes of latency or amplitude values with respect to time period.

Speech audiometry findings for both the cases were similar which suggested, the changes related to auditory deprivation occurred only at the brainstem level. This stipulated the importance of different sensitive periods during auditory development. Auditory deprivation in both the above-mentioned cases was resulted due to delayed identification and intervention of hearing loss. This probably compromised the thalamocortical development compromising speech and language acquisition. Hebbian view of neural development showed changes in the thalamocortical areas were dependent on the child's age/duration of deafness.[30]

A lot of studies correlated the speech perception performance with AEPs findings. These findings suggested, earlier the use of amplification devices better the AEP results. It also recommended early intervention is necessary for a better overall outcome. The correlation between duration of deafness and speech perception performance suggested intervention of the deaf patients should be provided at the earliest.[31],[32]

In the present study, the diagnosis of case A was delayed compared to Case B along with the time of intervention. As discussed above poor auditory stimulation in the early stage of life lead to dormant brain stem condition indicating unidentifiable wave peaks even at high intensity level of ABR and ASSR. In this study, less pronounced impact on speech perception ability was probably due to the stimulation of speech perception area through other nonauditory pathways of thalamocortical region[33] along with deprived auditory stimulation. It is a usual mode for the development of auditory based speech perception. This indicated the development of speech perception was not only depended on auditory-based stimulation, but also depended on nonauditory stimulations of brain.

In case B, even though the auditory stimulation was provided on time leading to more auditory based development of speech perception but stimulation to brain through nonauditory pathway was restricted. It might be due to inadequately stimulated auditory system. Hence, Case A had got speech perception ability developed through more of nonauditory stimulation and the reverse was true for the Case B. If the hypothesis is correct, this gives an insight that for normal speech perception both auditory as well as nonauditory stimulation of brain is required to achieve normal speech perception ability.

 Conclusion



The present study reflected the importance of administering complete audiological test battery to get the holistic idea regarding the individual's hearing ability. This not only involved the understanding of hearing status but also the speech perception ability which is very important for communication. The administration of part of test battery might lead to incomplete or ambiguous diagnosis leading to substandard intervention approach selection which will affect the quality of life of the individual. The present study also highlighted the importance of correlation between the different audiological test findings. The poor correlation between the test findings provided a new way to look into the individual conditions in a more practical and unique form. The present study gives an idea that further research is required to find the impact of other nonauditory stimulation to brain that might lead to normal development of speech perception along with good auditory skills in an individual.

Clinicians should administer a complete audiological test battery to get a holistic idea about the audiological status of the person. It can be correlated later with the anatomical substrate which can help to decide the specific intervention programs.

Acknowledgment

We would like to convey our thanks to the Department of ENT & HNS, AIIMS Raipur, for their co-operation throughout the study.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the legal guardian has given his consent for images and other clinical information to be reported in the journal. The guardian understands that names and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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