Auditory brainstem responses in the aged

Neurophysiological aspects of brainstem processing of speech stimuli in audiometric-normal geriatric population

Objective:

Poor auditory speech perception in geriatrics is attributable to neural de-synchronisation due to structural and degenerative changes of ageing auditory pathways. The speech-evoked auditory brainstem response may be useful for detecting alterations that cause loss of speech discrimination. Therefore, this study aimed to compare the speech-evoked auditory brainstem response in adult and geriatric populations with normal hearing.

Methods:

The auditory brainstem responses to click sounds and to a 40 ms speech sound (the Hindi phoneme |da|) were compared in 25 young adults and 25 geriatric people with normal hearing. The latencies and amplitudes of transient peaks representing neural responses to the onset, offset and sustained portions of the speech stimulus in quiet and noisy conditions were recorded.

Results:

The older group had significantly smaller amplitudes and longer latencies for the onset and offset responses to |da| in noisy conditions. Stimulus-to-response times were longer and the spectral amplitude of the sustained portion of the stimulus was reduced. The overall stimulus level caused significant shifts in latency across the entire speech-evoked auditory brainstem response in the older group.

Conclusion:

The reduction in neural speech processing in older adults suggests diminished subcortical responsiveness to acoustically dynamic spectral cues. However, further investigations are needed to encode temporal cues at the brainstem level and determine their relationship to speech perception for developing a routine tool for clinical decision-making.

Auditory brainstem gap responses start to decline in mice in middle age: a novel physiological biomarker for age-related hearing loss

The auditory function of the CBA/CaJ mouse strain is normal during the early phases of life and gradually declines over its lifespan, much like human age-related hearing loss (ARHL) but within the "time frame" of a mouse life cycle. This pattern of ARHL is similar to that of most humans: difficult to diagnose clinically at its onset and currently not treatable medically. To address the challenge of early diagnosis, we use CBA mice to analyze the initial stages and functional onset biomarkers of ARHL. The results from Auditory Brainstem Response (ABR) audiogram and Gap-in-noise (GIN) ABR tests were compared for two groups of mice of different ages, namely young adult and middle age. ABR peak components from the middle age group displayed minor changes in audibility but had a significantly higher prolonged peak latency and decreased peak amplitude in response to temporal gaps in comparison with the young adult group. The results for the younger subjects revealed gap thresholds and recovery rates that were comparable with previous studies of auditory neural gap coding. Our findings suggest that age-linked degeneration of the peripheral and brainstem auditory system begins in middle age, allowing for the possibility of preventative biomedical or hearing protection measures to be implemented in order to attenuate further damage to the auditory system attributable to ARHL.

Age-related changes of auditory brainstem responses in nonhuman primates

Nonhuman primates, compared with humans and rodents, have historically been far less used for studies of age-related hearing loss, primarily because of their long life span and high cost of maintenance. Strong similarities in genetics, anatomy, and neurophysiology of the auditory nervous system between humans and monkeys, however, could provide fruitful opportunities to enhance our understanding of hearing loss. The present study used a common, noninvasive technique for testing hearing sensitivity in humans, the auditory brainstem response (ABR), to assess the hearing of 48 rhesus macaques from 6 to 35 yr of age to clicks and tone stimuli between 0.5 and 16.0 kHz. Old monkeys, particularly those above 21.5 yr of age, had missing ABR waveforms at high frequencies. Regression analyses revealed that ABR threshold increased as a function of age at peaks II and IV simultaneously. In the suprathreshold hearing condition (70 dB peak sound pressure level), ABR-based audiograms similarly varied as a function of age such that old monkeys had smaller peak amplitudes and delayed latencies at low, middle, and high frequencies. Peripheral hearing differences remained a major influence associated with age-related changes in audiometric functions of old monkeys at a comparable sensation level across animals. The present findings suggest that hearing loss occurs in old monkeys across a wide range of frequencies and that these deficits increase in severity with age. Parallel to prior studies in monkeys, we found weak effects of sex on hearing, and future investigations are necessary to clarify its role in age-related hearing loss.

Brainstem evoked response audiometry in normal hearing subjects

Brainstem Evoked Response Audiometry (BERA) is an objective and non-invasive method of hearing assessment which detects electrical activity from the inner ear to the inferior colliculus.

Aim

To assess the hearing pathway in normal hearing individuals and compare differences associated with gender, age and ear side (left and right). Study Design: A retrospective study.

Materials and Methods

Sixty normal hearing individuals, aged between 09 and 66 years old, were subjected to clinical ENT examination and audiologic tests.

Results

Wave latencies differed significantly between males and females, although there were no differences regarding right or left ear sides. Comparing latency averages regarding age and gender we noticed important differences. By the same token, significant differences were also seen comparing this study with the information present in the handbook of the BERA device used and results published by Fukuda, in another study.

Conclusion

Knowing the great importance of BERA, it is crucial that each service develops its own standards in order to enhance the accuracy of the electrophysiological diagnosis of the hearing pathway.

Presbyacusis and the auditory brainstem response

Age-related hearing loss (ARHL or presbyacusis) is an increasingly common form of sensorineural hearing loss (SNHL) as a result of changing demographics, and the auditory brainstem response (ABR) is a common experimental and clinical tool in audiology and neurology. Some of the changes that occur in the aging auditory system may significantly influence the interpretation of the ABR in comparison to the ABRs of younger adults. The approach of this review will be to integrate physiological and histopathological data from human and animal studies to provide a better understanding of the array of age-related changes in the ABR and to determine how age-related changes in the auditory system may influence how the ABR should be interpreted in presbyacusis. Data will be described in terms of thresholds, latencies, and amplitudes, as well as more complex auditory functions such as masking and temporal processing. Included in the review of data will be an attempt to differentiate between age-related effects that may strictly be due to threshold elevation from those that may be due to the aging process.

Objective detection of brainstem auditory evoked potentials with a priori information from higher presentation levels

This paper describes a brainstem auditory evoked potentials (BAEPs) detection method based on supervised pattern recognition. A previously used pattern recognition technique relying on cross-correlation with a template was modified in order to include a priori information allowing detection accuracy. Reference is made to the patient's audiogram and to the latency-intensity (LI) curve with respect to physiological mechanisms. Flexible and adaptive constraints are introduced in the optimization procedure by means of eight rules. Several data samples were used in this study. The determination of parameters was performed through 270 BAEPs from 20 subjects with normal and high audiometric thresholds and through additional BAEPs from 123 normal ears and 14 ears showing prominent wave VI BAEPs. The evaluation of the detection performance was performed in two steps: first, the sensitivity, specificity and accuracy were estimated using 283 BAEPs from 20 subjects showing normal and high audiometric thresholds and secondly, the sensitivity, specificity and accuracy of the detection and the accuracy of the response threshold were estimated using 213 BAEPs from 18 patients in clinic. Taking into account some a priori information, the accuracy in BAEPs detection was enhanced from 76 to 90%. The patient response thresholds were determined with a mean error of 5 dB and a standard deviation error of 8.3 dB. Results were obtained using experimental data; therefore, they are promising for routine use in clinic.

Age-related changes in the brainstem auditory evoked potentials of the marmoset

Changes in brain-stem auditory evoked potentials (BAEPs) with age were recorded in common marmosets (Callithrix jacchus) at the age of 1-2, 6-8 and 10-12 years. The auditory function was assessed by thresholds, latencies and amplitudes of BAEPs evoked by use of tone burst stimulations with audible frequencies ranging from 1 to 99 kHz. Prolongation of the latencies of later waves was observed in the animals at the age of 6-8 and 10-12 years at high frequencies, suggesting that aging in marmosets, as reported previously in humans and other animals, may cause earlier hearing loss at high frequency than at low frequency within the hearing range. At 10-12 years of age, the elevations of BAEP thresholds and the declines of BAEP amplitudes in older animals were also observed. As the differences in the parameters are small, it was suggested that only a moderate hearing loss occurred with onset late in life in common marmoset similar to that in CBA/Ca mice. Based on the results obtained in this study, BAEP latencies appear to be more sensitive indicators than BAEP thresholds and amplitudes for the early detection of hearing impairment.

The auditory brainstem response of aged guinea pigs

The auditory brainstem response (ABR) technique was used to investigate potential dysfunctions in the auditory brainstem of the pigmented guinea pig (Cavia porcellus) associated with biological ageing. Animals aged from 58 days to 4 years 3 months were tested. ABRs were recorded at stimulation intensities from 85 dB HL to -10 dB HL. The auditory thresholds were found to undergo marked elevations in old animals, by an average of 32 dB. From the traces obtained, four positive deflection waves were reliably recorded. The latency of each of the four waves was evaluated at different stimulation intensities in guinea pigs of different ages. Although there was a trend for the latencies to increase in old age, these differences were not statistically significant. Similarly, there were no significant age-related changes in the inter-peak intervals. The latency/intensity functions of the four waves produced parallel curves. However, the curve from the old age group was shifted to the right, by an average of 35 dB, indicative of conductive hearing loss. There was no evidence of retro-cochlear hearing loss. Therefore, it appears that the threshold elevations in the old animals can be accounted for by conductive hearing loss, presumably in the middle ear. In 24% of the old animals tested, no ABR could be elicited. It would appear that these animals had suffered severe sensorineural hearing loss.

The effects of cochlear hearing loss, age and sex on the auditory brainstem response

This study analyzed the effects of auditory impairment, age and sex on the auditory brainstem response (ABR) wave latencies. ABR wave I, wave V and I-V interval measures were extracted from the clinical records of 201 patients with cochlear hearing loss. Females had consistently earlier wave V latencies and shorter I-V intervals than males. No age effects were observed. Degree of impairment had a systematic effect on ABR wave latencies and I-V intervals. Wave I displayed latency extension with increasing levels of high-frequency hearing loss, whilst for wave V increases in latency were dependent upon both degree and slope of the hearing loss. Present results suggest that many of the previously reported sex differences and variable interactions seen for the ABR can be accounted for by differences in the underlying distribution of audiogram shapes within and between study populations. Different audiometric configurations were found to produce consistent differential effects on both wave I and wave V latency and thus influence the I-V interval. This study underlines the need to develop a more detailed model of impairment effects if correction factors are to be employed more effectively in ABR testing for retrocochlear pathology.

Auditory abnormalities, including 'precocious presbyacusis', in myotonic dystrophy

Auditory function tests were performed on 13 patients with myotonic dystrophy (MD). Seven patients had a sensorineural high-frequency hearing loss (HFL) of 30-85 dB at 8 kHz in their pure-tone audiogram, which was in excess of that expected for their age and could be attributed to MD. Their hearing loss resembled 'precocious presbyacusis', i.e. if the patients had been considerably older (or 'functionally' older) than they really were, their HFL could (to some extent) have been attributed to presbyacusis alone. The HFL showed the phenomenon of (genetic) anticipation. Tympanograms and acoustic reflexes were normal. Brainstem auditory evoked potentials (BAEPs) showed a significant increase in the I-V interpeak interval (by 0.35-0.7 ms) and in the III-V interpeak interval (by 0.21-0.67 ms). There was no correlation between the BAEP and the audiometric findings. It should be noted that precocious presbyacusis may be linked to specific gene defects.

Age-related changes in auditory evoked potentials of gerbils. II. Response latencies

Auditory brainstem responses (ABR) were recorded in young (6-10 month) and aged (36 month) Mongolian gerbils. Data from the young animals served as the baselines for comparison to aged animals which were categorized on the basis of ABR thresholds. Aged gerbils with normal thresholds (re young controls) had wave i and ii latencies of the ABR which were relatively normal at 1-4 kHz and slightly reduced at 8 and 16 kHz. Wave iv latencies in the aged gerbils with normal thresholds were reduced at all frequencies. Aged gerbils with 10-30 dB of hearing loss had wave i, ii, and iv latencies which were prolonged at low sound pressure levels and normal at high stimulus levels. Aged gerbils with 30 dB or greater losses had prolonged wave i, ii, and iv latencies at most levels. Slopes of latency-intensity (L/I) functions were steeper at 1-4 kHz than controls in aged subjects with hearing losses of 10 dB or greater. Slopes of L/I functions for wave iv were normal in aged subjects. The wave i-iv interval was shorter than normal in aged subjects with no hearing loss, normal in aged subjects with 10-30 dB of loss, and prolonged in subjects with greater than 30 dB of loss.