Modulation of presbycusis: current status and future directions

Evaluating the Effectiveness of a New Auditory Training Program on the Speech Recognition Skills and Auditory Event-Related Potentials in Elderly Hearing Aid Users

<b><i>Introduction:</i></b> The objective of this study was to evaluate the effectiveness of a new auditory training (AT) program on the speech recognition in the noise and on the auditory event-related potentials in elderly hearing aid users. <b><i>Methods:</i></b> Thirty-three elderly individuals using hearing aids aged from 60 to 80 years participated. A new AT program was developed for the study. AT program lasts for 8 weeks and includes sound discrimination exercises and cognitive exercises. Seventeen individuals (mean age 72.17 ± 6.94) received AT and 16 individuals (mean age 71.75 ± 6.81) did not receive AT. The mismatch negativity (MMN) test and matrix test were used to evaluate the effectiveness of AT. Tests were conducted for the study group before and after the AT. The tests were carried out for the control group at the same times with the study group and the results were compared. <b><i>Results:</i></b> In comparison with the first evaluation, the last evaluation of the study group demonstrated a significant difference regarding the decrease of mean latency in the MMN wave (<i>p</i> = 0.038), and regarding the improving score of matrix test (<i>p</i> = 0.004), there was no difference in the control group. <b><i>Conclusion:</i></b> The AT program prepared for the study was effective in improving speech recognition in noise in the elderly, and the efficiency of AT could be demonstrated with MMN and matrix test.

Differences in Auditory Perception Between Young and Older Adults When Controlling for Differences in Hearing Loss and Cognition

This study was designed to examine age effects on various auditory perceptual skills using a large group of listeners (155 adults, 121 aged 60-88 years and 34 aged 18-30 years), while controlling for the factors of hearing loss and working memory (WM). All subjects completed 3 measures of WM, 7 psychoacoustic tasks (24 conditions) and a hearing assessment. Psychophysical measures were selected to tap phenomena thought to be mediated by higher-level auditory function and included modulation detection, modulation detection interference, informational masking (IM), masking level difference (MLD), anisochrony detection, harmonic mistuning, and stream segregation. Principal-components analysis (PCA) was applied to each psychoacoustic test. For 6 of the 7 tasks, a single component represented performance across the multiple stimulus conditions well, whereas the modulation-detection interference (MDI) task required two components to do so. The effect of age was analyzed using a general linear model applied to each psychoacoustic component. Once hearing loss and WM were accounted for as covariates in the analyses, estimated marginal mean thresholds were lower for older adults on tasks based on temporal processing. When evaluated separately, hearing loss led to poorer performance on roughly 1/2 the tasks and declines in WM accounted for poorer performance on 6 of the 8 psychoacoustic components. These results make clear the need to interpret age-group differences in performance on psychoacoustic tasks in light of cognitive declines commonly associated with aging, and point to hearing loss and cognitive declines as negatively influencing auditory perceptual skills.

Analyzing protein-protein interactions in rare cells using microbead-based single-molecule pulldown assay

For studying protein-protein interactions (PPIs) in general, a powerful and commonly used technique is conventional coimmunoprecipitation (co-IP/pulldown) followed by western blotting. However, the technique does not provide precise information regarding the kinetics and stoichiometry of PPIs. Another drawback is that the sensitivity of conventional co-IP is not suitable for examining PPIs in rare cells such as sensory hair cells, circulating tumor cells, embryonic stem cells, and subsets of immune cells. The current single-molecule pulldown (SiMPull) assay can potentially be used for studying PPIs in rare cells but its wide application is hindered by the high technical barrier and time consumption. We report an innovative, agarose microbead-based approach for SiMPull. We used commercially available, pre-surface-functionalized agarose microbeads to capture the protein of interest together with its binding partners specifically from cell extracts and observed these interactions under a microscope at the single-molecule level. Relative to the original method, microbead-based SiMPull is considerably faster, easier to use, and more reproducible and yet provides similar sensitivity and signal-to-background ratio; specifically, with the new method, sample-preparation time is substantially decreased (from ∼10 to ∼3 h). These crucial features should facilitate wide application of the powerful and versatile SiMPull method in common biological and clinical laboratories. Notably, by exploiting the simplicity and ultrahigh sensitivity of microbead-based SiMPull, we used the method in the study of rare auditory hair cells and γδ T cells for the first time.

Perceived Stress Predicts Subsequent Self-Reported Problems With Vision and Hearing: Longitudinal Findings From the German Ageing Survey

Although stress is a risk factor for various diseases in later life, its role for sensory abilities in the second half of life has rarely been empirically addressed. We examined if perceived stress at baseline predicts self-reported difficulties with vision and hearing 3 years later. We also explored whether chronological age is a moderator of associations between stress and sensory difficulties. Our sample was derived from the German Ageing Survey and consisted of n = 5,085 individuals aged 40-95 years (M = 64.01 years, SD = 10.84 years). Controlling for baseline self-reported sensory functioning, socio-demographic indicators, self-rated health and chronic diseases, greater perceived stress at baseline predicted greater self-reported difficulties with vision and hearing 3 years later. The effect of stress did not vary by age. Our findings suggest that, from middle adulthood to advanced old age, stress is a risk factor for increases in self-perceived problems with vision and hearing.

Sensorial frailty: age-related hearing loss and the risk of cognitive impairment and dementia in later life

The peripheral hearing alterations and central auditory processing disorder (CAPD) associated with age-related hearing loss (ARHL), may impact cognitive disorders in older age. In older age, ARHL is also a significant marker for frailty, another age-related multidimensional clinical condition with a nonspecific state of vulnerability, reduced multisystem physiological reserve, and decreased resistance to different stressors (i.e. sensorial impairments, psychosocial stress, diseases, injuries). The multidimensional nature of frailty required an approach based on different pathogeneses because this clinical condition may include sensorial, physical, social, nutritional, cognitive, and psychological phenotypes. In the present narrative review, the cumulative epidemiological evidence coming from several longitudinal population-based studies, suggested convincing links between peripheral ARHL and incident cognitive decline and dementia. Moreover, a few longitudinal case-control and population-based studies also suggested that age-related CAPD in ARHL, may be central in determining an increased risk of incident cognitive decline, dementia, and Alzheimer's disease (AD). Cumulative meta-analytic evidence confirmed cross-sectional and longitudinal association of both peripheral ARHL and age-related CAPD with different domains of cognitive functions, mild cognitive impairment, and dementia, while the association with dementia subtypes such as AD and vascular dementia remained unclear. However, ARHL may represent a modifiable condition and a possible target for secondary prevention of cognitive impairment in older age, social isolation, late-life depression, and frailty. Further research is required to determine whether broader hearing rehabilitative interventions including coordinated counseling and environmental accommodations could delay or halt cognitive and global decline in the oldest old with both ARHL and dementia.

Effects of aging on the response of single neurons to amplitude-modulated noise in primary auditory cortex of rhesus macaque

Temporal envelope processing is critical for speech comprehension, which is known to be affected by normal aging. Whereas the macaque is an excellent animal model for human cerebral cortical function, few studies have investigated neural processing in the auditory cortex of aged, nonhuman primates. Therefore, we investigated age-related changes in the spiking activity of neurons in primary auditory cortex (A1) of two aged macaque monkeys using amplitude-modulated (AM) noise and compared these responses with data from a similar study in young monkeys (Yin P, Johnson JS, O'Connor KN, Sutter ML. J Neurophysiol 105: 582-600, 2011). For each neuron, we calculated firing rate (rate code) and phase-locking using phase-projected vector strength (temporal code). We made several key findings where neurons in old monkeys differed from those in young monkeys. Old monkeys had higher spontaneous and driven firing rates, fewer neurons that synchronized with the AM stimulus, and fewer neurons that had differential responses to AM stimuli with both a rate and temporal code. Finally, whereas rate and temporal tuning functions were positively correlated in young monkeys, this relationship was lost in older monkeys at both the population and single neuron levels. These results are consistent with considerable evidence from rodents and primates of an age-related decrease in inhibition throughout the auditory pathway. Furthermore, this dual coding in A1 is thought to underlie the capacity to encode multiple features of an acoustic stimulus. The apparent loss of ability to encode AM with both rate and temporal codes may have consequences for stream segregation and effective speech comprehension in complex listening environments.

The Ear-Brain Connection: Older Ears and Older Brains

PURPOSE

The purpose of this article is to review recent research from our laboratory on the topic of aging, and the ear-brain system, as it relates to hearing aid use and auditory rehabilitation. The material described here was presented as part of the forum on the brain and hearing aids, at the 2014 HEaling Across the Lifespan (HEAL) conference.

METHOD

The method involves a narrative review of previously reported electroencephalography (EEG) and magnetoencephalography (MEG) data from our laboratory as they relate to the (a) neural detection of amplified sound and (b) ability to learn new sound contrasts.

CONCLUSIONS

Results from our studies add to the mounting evidence that there are central effects of biological aging as well as peripheral pathology that affect a person's neural detection and use of sound. What is more, these biological effects can be seen as early as middle age. The accruing evidence has implications for hearing aid use because effective communication relies not only on sufficient detection of sound but also on the individual's ability to learn to make use of these sounds in ever-changing listening environments.

Functional changes in the human auditory cortex in ageing

Hearing loss, presbycusis, is one of the most common sensory declines in the ageing population. Presbycusis is characterised by a deterioration in the processing of temporal sound features as well as a decline in speech perception, thus indicating a possible central component. With the aim to explore the central component of presbycusis, we studied the function of the auditory cortex by functional MRI in two groups of elderly subjects (>65 years) and compared the results with young subjects (<lt;30 years). The elderly group with expressed presbycusis (EP) differed from the elderly group with mild presbycusis (MP) in hearing thresholds measured by pure tone audiometry, presence and amplitudes of transient otoacoustic emissions (TEOAE) and distortion-product oto-acoustic emissions (DPOAE), as well as in speech-understanding under noisy conditions. Acoustically evoked activity (pink noise centered around 350 Hz, 700 Hz, 1.5 kHz, 3 kHz, 8 kHz), recorded by BOLD fMRI from an area centered on Heschl’s gyrus, was used to determine age-related changes at the level of the auditory cortex. The fMRI showed only minimal activation in response to the 8 kHz stimulation, despite the fact that all subjects heard the stimulus. Both elderly groups showed greater activation in response to acoustical stimuli in the temporal lobes in comparison with young subjects. In addition, activation in the right temporal lobe was more expressed than in the left temporal lobe in both elderly groups, whereas in the young control subjects (YC) leftward lateralization was present. No statistically significant differences in activation of the auditory cortex were found between the MP and EP groups. The greater extent of cortical activation in elderly subjects in comparison with young subjects, with an asymmetry towards the right side, may serve as a compensatory mechanism for the impaired processing of auditory information appearing as a consequence of ageing.

Acoustic experience alters the aged auditory system

OBJECTIVES

Presbyacusis, one of the most common ailments of the elderly, is often treated with hearing aids, which serve to reintroduce some or all of those sounds lost to peripheral hearing loss. However, little is known about the underlying changes to the ear and brain as a result of such experience with sound late in life. The present study attempts to model this process by rearing aged CBA mice in an augmented acoustic environment (AAE).

DESIGN

Aged (22-23 months) male (n = 12) and female (n = 9) CBA/CaJ mice were reared in either 6 weeks of low-level (70 dB SPL) broadband noise stimulation (AAE) or normal vivarium conditions. Changes as a function of the treatment were measured for behavior, auditory brainstem response thresholds, hair cell cochleograms, and gamma aminobutyric acid neurochemistry in the key central auditory structures of the inferior colliculus and primary auditory cortex.

RESULTS

The AAE-exposed group was associated with sex-specific changes in cochlear pathology, auditory brainstem response thresholds, and gamma aminobutyric acid neurochemistry. Males exhibited significantly better thresholds and reduced hair cell loss (relative to controls) whereas females exhibited the opposite effect. AAE was associated with increased glutamic acid decarboxylase (GAD67) levels in the inferior colliculus of both male and female mice. However, in primary auditory cortex AAE exposure was associated with increased GAD67 labeling in females and decreased GAD67 in males.

CONCLUSIONS

These findings suggest that exposing aged mice to a low-level AAE alters both peripheral and central properties of the auditory system and these changes partially interact with sex or the degree of hearing loss before AAE. Although direct application of these findings to hearing aid use or auditory training in aged humans would be premature, the results do begin to provide direct evidence for the underlying changes that might be occurring as a result of hearing aid use late in life. These results suggest the aged brain retains significantly anatomical, electrophysiological, and neurochemical plasticity.

Auditory analysis of xeroderma pigmentosum 1971-2012: hearing function, sun sensitivity and DNA repair predict neurological degeneration

To assess the role of DNA repair in maintenance of hearing function and neurological integrity, we examined hearing status, neurological function, DNA repair complementation group and history of acute burning on minimal sun exposure in all patients with xeroderma pigmentosum, who had at least one complete audiogram, examined at the National Institutes of Health from 1971 to 2012. Seventy-nine patients, aged 1-61 years, were diagnosed with xeroderma pigmentosum (n = 77) or xeroderma pigmentosum/Cockayne syndrome (n = 2). A total of 178 audiograms were included. Clinically significant hearing loss (>20 dB) was present in 23 (29%) of 79 patients. Of the 17 patients with xeroderma pigmentosum-type neurological degeneration, 13 (76%) developed hearing loss, and all 17 were in complementation groups xeroderma pigmentosum type A or type D and reported acute burning on minimal sun exposure. Acute burning on minimal sun exposure without xeroderma pigmentosum-type neurological degeneration was present in 18% of the patients (10/55). Temporal bone histology in a patient with severe xeroderma pigmentosum-type neurological degeneration revealed marked atrophy of the cochlear sensory epithelium and neurons. The 19-year mean age of detection of clinically significant hearing loss in the patients with xeroderma pigmentosum with xeroderma pigmentosum-type neurological degeneration was 54 years younger than that predicted by international norms. The four frequency (0.5/1/2/4 kHz) pure-tone average correlated with degree of neurodegeneration (P < 0.001). In patients with xeroderma pigmentosum, aged 4-30 years, a four-frequency pure-tone average ≥10 dB hearing loss was associated with a 39-fold increased risk (P = 0.002) of having xeroderma pigmentosum-type neurological degeneration. Severity of hearing loss parallels neurological decline in patients with xeroderma pigmentosum-type neurological degeneration. Audiometric findings, complementation group, acute burning on minimal sun exposure and age were important predictors of xeroderma pigmentosum-type neurological degeneration. These results provide evidence that DNA repair is critical in maintaining neurological integrity of the auditory system.

[The diversity of aging models]

Most of the signalling pathways involved in aging regulation have been recently found well conserved at various levels throughout the evolution. Taking this into account, a diversity of model organisms, including worms, rodents, and lemurs as well, allows to address different questions: how to understand the interactions between genetic and environmental factors while challenging theories of aging, to preserve hearing integrity, to fight against senescence of neural stem cells, or to explore brain fitness from gene expression to cognitive and social behavior? Here are the main issues that can be considered, stressing the complementarities of the models. The differentiation of aging physiological aspects from those induced by age-related pathologies will also be specified. By emphasizing recent ability of technologies to promote new aging insights, we discuss towards a better understanding of mechanisms governing aging.

Correlation between plasma levels of radical scavengers and hearing threshold among elderly subjects with age-related hearing loss

CONCLUSION

Low plasma melatonin is significant in the development of high frequency hearing loss (HL) among the elderly.

OBJECTIVE

To determine the correlation between hearing threshold and the plasma melatonin and ascorbic acid (vitamin C).

METHODS

This was a cross-sectional study involving 126 apparently healthy elderly subjects, 59 males and 67 females, aged >60 years. Subjects underwent pure tone audiometry and plasma melatonin and vitamin C were assayed using high-performance liquid chromatography.

RESULTS

The mean ± SD of plasma melatonin among the subjects with normal hearing (NH) (0-30 dB) and those with HL in the speech frequencies was 18.3 ± 3.6 μg/L and 16.4 ± 4.7 μg/L, respectively. In the high frequencies the values were 17.7 ± 6.2 μg/L and 13.1 ± 6.4 μg/L for NH and HL, respectively. For vitamin C, the mean ± SD among subjects with NH and those with HL in the speech frequencies were 1.2 ± 0.2 μg/L and 1.0 ± 0.1 μg/L, respectively. In the high frequencies, the values were 1.0 ± 0.2 μg/L and 0.9 ± 0.3 μg/L for NH and HL, respectively. Among subjects with high frequency HL, Spearman's correlation revealed significant correlation between increasing hearing threshold and melatonin (correlation coefficient = -0.30, p = 0.01), but not for vitamin C (correlation coefficient = -0.12, p = 0.22). Linear regression, adjusting for age, still revealed significant correlation between the melatonin (correlation coefficient = -0.03, p = 0.00) and hearing threshold in the high frequencies.

Divergent aging characteristics in CBA/J and CBA/CaJ mouse cochleae

Two inbred mouse strains, CBA/J and CBA/CaJ, have been used nearly interchangeably as 'good hearing' standards for research in hearing and deafness. We recently reported, however, that these two strains diverge after 1 year of age, such that CBA/CaJ mice show more rapid elevation of compound action potential (CAP) thresholds at high frequencies (Ohlemiller, Brain Res. 1277: 70-83, 2009). One contributor is progressive decline in endocochlear potential (EP) that appears only in CBA/CaJ. Here, we explore the cellular bases of threshold and EP disparities in old CBA/J and CBA/CaJ mice. Among the major findings, both strains exhibit a characteristic age (∼18 months in CBA/J and 24 months in CBA/CaJ) when females overtake males in sensitivity decline. Strain differences in progression of hearing loss are not due to greater hair cell loss in CBA/CaJ, but instead appear to reflect greater neuronal loss, plus more pronounced changes in the lateral wall, leading to EP decline. While both male and female CBA/CaJ show these pathologies, they are more pronounced in females. A novel feature that differed sharply by strain was moderate loss of outer sulcus cells (or 'root' cells) in spiral ligament of the upper basal turn in old CBA/CaJ mice, giving rise to deep indentations and void spaces in the ligament. We conclude that CBA/CaJ mice differ both quantitatively and qualitatively from CBA/J in age-related cochlear pathology, and model different types of presbycusis.

Auditory sensitivity and the outer hair cell system in the CBA mouse model of age-related hearing loss

Age-related hearing loss is a highly prevalent sensory disorder, from both the clinical and animal model perspectives. Understanding of the neurophysiologic, structural, and molecular biologic bases of age-related hearing loss will facilitate development of biomedical therapeutic interventions to prevent, slow, or reverse its progression. Thus, increased understanding of relationships between aging of the cochlear (auditory portion of the inner ear) hair cell system and decline in overall hearing ability is necessary. The goal of the present investigation was to test the hypothesis that there would be correlations between physiologic measures of outer hair cell function (otoacoustic emission levels) and hearing sensitivity (auditory brainstem response thresholds), starting in middle age. For the CBA mouse, a useful animal model of age-related hearing loss, it was found that correlations between these two hearing measures occurred only for high sound frequencies in middle age. However, in old age, a correlation was observed across the entire mouse range of hearing. These findings have implications for improved early detection of progression of age-related hearing loss in middle-aged mammals, including mice and humans, and distinguishing peripheral etiologies from central auditory system decline.

Effects of aging on inner ear morphology in dogs in relation to brainstem responses to toneburst auditory stimuli

BACKGROUND

Age-related hearing loss (ARHL) is the most common form of hearing loss in humans and is increasingly recognized in dogs.

HYPOTHESIS

Cochlear lesions in dogs with ARHL are similar to those in humans and the severity of the histological changes is reflected in tone audiograms.

ANIMALS

Ten geriatric dogs (mean age: 12.7 years) and three 9-month-old dogs serving as controls for histological analysis.

METHODS

Observational study. Auditory thresholds were determined by recording brainstem responses (BERA) to toneburst auditory stimuli (1, 2, 4, 8, 12, 16, 24, and 32 kHz). After euthanasia and perfusion fixation, the temporal bones were harvested and processed for histological examination of the cochleas. The numbers of outer hair cells (OHCs) and inner hair cells (IHCs) were counted and the spiral ganglion cell (SGC) packing density and stria vascularis cross-sectional area (SVCA) were determined.

RESULTS

A combination of cochlear lesions was found in all geriatric dogs. There were significant reductions (P .001) in OHC (42%, 95% confidence interval [CI]; 24-64%) and IHC counts (21%, 95% CI; 62-90%) and SGC packing densities (323, 95% CI; 216-290) in the basal turn, SVCA was smaller in all turns. The greatest reduction in auditory sensitivity was at 8-32 kHz.

CONCLUSIONS AND CLINICAL IMPORTANCE

ARHL in this specific population of geriatric dogs was comparable histologically to the mixed type of ARHL in humans. The predominance of histological changes in the basal cochlear turn was consistent with the large threshold shifts observed in the middle- to high-frequency region.

Age-related changes in antioxidant enzymes related to hydrogen peroxide metabolism in rat inner ear

Oxidative stress is a pervasive factor in aging and has been implicated in noise-induced cochlear pathology. In this study, we measured the activities of two enzymes that catalyze the removal of hydrogen peroxide (H(2)O(2)), catalase and glutathione peroxidase (Gpx), in 3- and 24-month-old Fisher-344 rats, and reduced and oxidized glutathione in 3-, 12-, and 24-month-old rats. There was an increase in Gpx activity in vascular tissue (spiral ligament and stria vascularis), but no change in modiolar, sensory or vestibular tissue of the cochlea. The elevation in vascular tissue was age-related. We observed a significant elevation of catalase activity in vestibular tissue, a tendency for age-related elevation in the modiolus, but no change in vascular or sensory cochlear tissue. These findings suggest that increased Gpx activity in vascular cochlear tissue may be an age-related compensation for a decrease in glutathione and a decline in the redox state measured by the ratio of reduced to oxidized glutathione.

Prevalence of hearing loss in Black and White elders: results of the Cardiovascular Health Study

PURPOSE

The goal of this study was to determine the impact of age, gender, and race on the prevalence and severity of hearing loss in elder adults, aged 72-96 years, after accounting for income, education, smoking, and clinical and subclinical cardiovascular disease. Methods Air-conduction thresholds for standard and extended high-frequency pure-tones were obtained from a cohort of 548 (out of 717) elderly adults (ages 72-96 years) who were recruited during the Year 11 clinical visit (1999-2000) of the Cardiovascular Health Study (CHS) at the Pittsburgh, Pennsylvania site. Participant smoking, income, education, and cardiovascular disease histories were obtained from the CHS database and were included as factors.

RESULTS

Hearing loss was more common and more severe for the participants in their 80s than for those in their 70s-the men more than the women and the White participants more than the Black participants. The inclusion of education, income, smoking, and cardiovascular disease (clinical and subclinical) histories as factors did not substantively impact the overall results.

CONCLUSION

Although the data reported in this article were cross-sectional and a cohort phenomenon might have been operational, they suggested that hearing loss is more substantive in the 8th than the 7th decade of life and that race and gender influence this decline in audition. Given the high prevalence in the aging population and the differences across groups, there is a clear need to understand the nature and causes of hearing loss across various groups in order to improve prevention and develop appropriate interventions.

Interactions of hearing loss and diabetes mellitus in the middle age CBA/CaJ mouse model of presbycusis

Recently, we characterized the more severe nature of hearing loss in aged Type 2 diabetic human subjects [Frisina, S.T., Mapes, F., Kim, S., Frisina, D.R., Frisina, R.D., 2006. Characterization of hearing loss in aged type II diabetics. Hear. Res. 211, 103-113]. The current study prospectively assessed hearing abilities in middle age CBA/CaJ mice with Type 1 diabetes mellitus (T1DM) (STZ injection) or Type 2 diabetes mellitus (T2DM) (high fat diet), for a period of 6 months. Blood glucose, body weight and auditory tests (Auditory Brainstem Response-ABR, Distortion Product Otoacoustic Emissions-DPOAE) were evaluated at baseline and every 2 months. Tone and broad-band noise-burst responses in the inferior colliculus were obtained at 6 months. Body weights of controls did not change over 6 months (approximately 32 g), but there was a significant (approximately 5 g) decline in the T1DM, while T2DM exhibited approximately 10 g weight gain. Blood glucose levels significantly increased: 3-fold for T1DM, 1.3-fold for T2DM; with no significant changes in controls. ABR threshold elevations were found for both types of diabetes, but were most pronounced in the T2DM, starting as early as 2 months after induction of diabetes. A decline of mean DPOAE amplitudes was observed in both diabetic groups at high frequencies, and for the T2DM at low frequencies. In contrast to ABR thresholds, tone and noise thresholds in the inferior colliculus were lower for both diabetic groups. Induction of diabetes in middle-aged CBA/CaJ mice promotes amplification of age-related peripheral hearing loss which makes it a suitable model for studying the interaction of age-related hearing loss and diabetes. On the other hand, initial results of effects from very high blood glucose level (T1DM) on the auditory midbrain showed disruption of central inhibition, increased response synchrony or enhanced excitation in the inferior colliculus.

Radical scavengers for elderly patients with age-related hearing loss

CONCLUSION

The results of this study suggest that treatment with radical scavengers has the potential to become an effective new therapy for age-related hearing loss.

OBJECTIVE

To assess the efficacy of treatment with radical scavengers for age-related hearing loss.

SUBJECTS AND METHODS

Rebamipide (300 mg/day), alpha-lipoic acid (60 mg/day), and vitamin C (600 mg/day) were given orally for at least 8 weeks to 46 elderly patients with age-related hearing loss.

RESULTS

Hearing levels after treatment were significantly improved at all frequencies.

Effects of aging on brainstem responses to toneburst auditory stimuli: a cross-sectional and longitudinal study in dogs

BACKGROUND

It is assumed that the hearing of dogs becomes impaired with advancing age, but little is known about the prevalence and electrophysiologic characteristics of presbycusis in this species.

HYPOTHESIS

As in humans, hearing in dogs becomes impaired with aging across the entire frequency range, but primarily in the high-frequency area. This change can be assessed quantitatively by brainstem-evoked response audiometry (BERA).

ANIMALS

Three groups of 10 mixed-breed dogs with similar body weights but different mean ages were used. At the start of the study, the mean age was 1.9 years (range, 0.9-3.4) in group I, 5.7 years (3.5-7) in group II, and 12.7 years (11-14) in group III.

METHODS

In a cross-sectional study, the BERA audiograms obtained with toneburst stimuli were compared among the 3 groups. In a longitudinal study, changes in auditory thresholds of group II dogs were followed for 7 years.

RESULTS

Thresholds were significantly higher in group III than in groups I and II at all frequencies tested, and higher in group II than in group I at 4 kHz. The audiograms in group II indicated a progressive increase in thresholds associated with aging starting around 8-10 years of age and most pronounced in the middle- to high-frequency region (8-32 kHz).

CONCLUSIONS AND CLINICAL IMPORTANCE

Age-related hearing loss in these dogs started around 8-10 years of age and encompassed the entire frequency range, but started and progressed most rapidly in the middle- to high-frequency area. Its progression can be followed by BERA with frequency-specific stimulation.

The role of mitochondrial DNA large deletion for the development of presbycusis in Fischer 344 rats

Age-related hearing loss, or presbycusis, has been associated with large-scale mitochondrial DNA (mtDNA) deletion in previous studies. However, the role of this mtDNA damage in presbycusis is still not clear because the deletion in inner ears has not been measured quantitatively and analyzed in parallel with the time course of presbycusis. In the present study, the deletion was quantified using quantitative real-time PCR (qRT-PCR) in male Fischer 344 rats of different ages. It was found that the deletion increased quickly during young adulthood and reached over 60% at 6 months of age. However, a significant hearing loss was not seen until after 12 months of age. The results suggest that the existence of the deletion per se does not necessarily imply cochlear damage, but rather a critical level of the accumulated deletion seems to precede the hearing loss. The long delay may indicate the involvement of mechanisms other than mtDNA deletion in the development of presbycusis.

Audiometria de alta freqüência em adultos jovens e mais velhos quando a audiometria convencional é normal

A audiometria de alta freqüência é capaz de detectar precocemente alterações em sensibilidade advindas de processos como o envelhecimento. Seu uso é limitado, o que recomenda estudos para esclarecer seu desempenho, especialmente entre adultos de mais idade. OBJETIVO: Comparar os limiares para as freqüências de 250Hz a 16kHz, entre adultos jovens e mais velhos normoacúsicos, com e sem queixa audiológica. CASUÍSTICA E MÉTODO: A sensibilidade a tons puros de 250Hz a 16kHz foi avaliada com audiômetro AC-40, em 64 adultos, igualmente distribuídos: jovens (25 a 35 anos) e mais velhos (45 a 55 anos) de ambos os gêneros, com forma de estudo de coorte transversal. RESULTADOS: Os adultos mais velhos apresentaram limiares mais elevados em todas as freqüências, mais significativamente nas mais altas (8 a 16kHz), quando comparados com os adultos jovens. Homens apresentaram limiares mais elevados do que mulheres entre 3 e 10kHz. CONCLUSÃO: O processo de envelhecimento auditivo, envolvendo perda de sensibilidade auditiva para altas freqüências, pode ser detectado em idades anteriores às tipicamente pesquisadas, uma vez que a audiometria de alta freqüência demonstrou ser instrumento importante para distinguir a sensibilidade auditiva entre adultos jovens e mais velhos, quando audiologicamente normais.

High-frequency audiometry in young and older adults when conventional audiometry is normal

High-frequency audiometry can detect early changes in auditory sensitivity resulting from processes such as aging. Nonetheless its use is still limited, and additional studies are required to establish its use, particularly among older adults.

Aim

To compare pure tone thresholds for frequencies from 250 Hz to 16 kHz in young and older adults, with or without audiologic complaints.

Method

Pure tone sensitivity to 250 Hz to 16 kHz was assessed with an AC-40 audiometer in 64 adults, evenly distributed in young (25 to 35 years-old) and older (45 to 55 years-old) adults of both sexes. This is a cross-sectional study.

Results

Although all participants presented normal audiometry in frequencies from 250 Hz to 8 kHz, according to clinical parameters, older adults had significantly higher thresholds compared to young adults, according to statistical parameters, with greater significance in higher frequencies (8 to 16 kHz). Presence or absence of clinical complaints did not distinguish thresholds.

Conclusions

The process of auditory aging, including loss of sensitivity to higher frequencies, can be detected at earlier ages than those usually investigated. High frequency audiometry is an important instrument to distinguish auditory sensitivity in young and older adults, even for those considered as audiologically normal.

The neural representation of consonant-vowel transitions in adults who wear hearing AIDS

Hearing aids help compensate for disorders of the ear by amplifying sound; however, their effectiveness also depends on the central auditory system's ability to represent and integrate spectral and temporal information delivered by the hearing aid. The authors report that the neural detection of time-varying acoustic cues contained in speech can be recorded in adult hearing aid users using the acoustic change complex (ACC). Seven adults (50-76 years) with mild to severe sensorineural hearing participated in the study. When presented with 2 identifiable consonant-vowel (CV) syllables ("shee" and "see"), the neural detection of CV transitions (as indicated by the presence of a P1-N1-P2 response) was different for each speech sound. More specifically, the latency of the evoked neural response coincided in time with the onset of the vowel, similar to the latency patterns the authors previously reported in normal-hearing listeners.

Audiologic management of older adults with hearing loss and compromised cognitive/psychoacoustic auditory processing capabilities

The number and proportion of older adults in the United States population is increasing, and more clinical audiologists will be called upon to deliver hearing care to the approximately 35% to 50% of them who experience hearing difficulties. In recent years, the characteristics and sources of receptive communication difficulties in older individuals have been investigated by hearing scientists, cognitive psychologists, and audiologists. It is becoming increasingly apparent that cognitive compromises and psychoacoustic auditory processing disorders associated with aging may contribute to communication difficulties in this population. This paper presents an overview of best practices, based on our current knowledge base, for clinical management of older individuals with limitations in cognitive or psychoacoustic auditory processing capabilities, or both, that accompany aging.

Hearing Decline Predicted by Elders' Stereotypes

Although age-related hearing loss is one of the most prevalent conditions affecting older individuals, little research has been conducted on the social-psychological factors that might contribute to it. The present study examines whether older individuals' age stereotypes predict screened hearing over time. The sample consisted of 546 community-dwelling persons, aged 70 to 96 years old. Participants with more negative and more external (i.e., related to physical appearance) age stereotypes demonstrated worse screened hearing at 36 months, after adjusting for baseline-screened hearing, age, and other relevant variables. These findings suggest that age stereotypes influence older individuals' sensory perception.

Presbiacusia: degeneración neuronal y envejecimiento en el receptor auditivo del ratón C57/BL6J

Presbycusis is a progressive hearing impairment associated with aging, characterized by hearing loss and a degeneration of cochlear structures. In this paper we analyze the effects of aging on the auditory system of C57/BL6J mice, with electrophysiological and morphological studies. With this aim the auditory potentials of mice aging 1, 3, 6, 9, 12, 15, 18, 21 and 24 months were recorded, and then the morphology of the cochleal were analyzed. Auditory potentials revealed an increase in wave latencies, as well as a decrease in their amplitudes during aging. Morphological results showed a total Corti's organ degeneration, being replaced by a flat epithelial layer, and a total absence of hair cells.

Radical scavengers: a remedy for presbyacusis. A pilot study

CONCLUSION

The results of this study suggest that treatment with radical scavengers has the potential to become an effective new therapy for presbyacusis.

OBJECTIVE

To assess the efficacy of treatment with the radical scavengers rebamipide and vitamin C for presbyacusis.

MATERIAL AND METHODS

Rebamipide (300 mg/day) and vitamin C (600 mg/day) were taken orally for at least 8 weeks by 23 patients with presbyacusis.

RESULTS

Hearing levels after treatment were significantly improved at 125, 250, 500 and 8000 Hz but unchanged at 1000, 2000 and 4000 Hz.

Pivotal role of Harakiri in the induction and prevention of gentamicin-induced hearing loss

Gentamicin is a widely used ototoxic agent. In this study, we shed light on the mechanisms underlying gentamicin-induced hearing loss. More importantly, we demonstrate in vivo and in vitro the effectiveness of a strategy for preventing drug-induced hearing loss using l-carnitine (LCAR), a safe micronutrient that plays a key role in energy metabolism and detoxification [Rebouche, C. J. & Seim, H. (1998) Annu. Rev. Nutr. 18, 39-61]. We show that LCAR prevents changes in hearing threshold and cochlear damage in newborn guinea pigs exposed to gentamicin in utero. Mechanistically, gentamicin-induced apoptosis of auditory cells is mediated by the extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase (MAPK) pathway through up-regulation of the proapoptotic factor Harakiri (Hrk). Most important, small interfering RNA (siRNA) experiments demonstrate that Hrk up-regulation is crucial for gentamicin-induced apoptosis. LCAR, in contrast, prevents both gentamicin-induced Hrk up-regulation and apoptosis acting by means of c-Jun N-terminal kinase (JNK). Together, these results outline pathways for gentamicin-induced hearing loss and its prevention and assign a key role to Hrk in these processes. Thus, our data offer a conceptual framework for designing clinical trials using a safe micronutrient, LCAR, as a simple preventive strategy for iatrogenically induced ototoxicity.

Influence of environmental factors on the evolution of industrial noise-induced hearing loss

The aim of the study is to investigate how environmental factors, associated with exposure to industrial noise, affect the development of chronic noise-induced hearing loss. The study was conducted on 186 male subjects working in two bottling plants, situated respectively in a small farming community, and in a medium-sized city with significant levels of noise pollution. Levels of occupational exposure were the same for the two groups. The subjects were selected by means of a preliminary medical examination, and exposed to tonal hearing tests and acoustic impedance tests. Statistical analysis was performed on hearing threshold values obtained at the frequencies of 500, 1000, 2000 and 4000 Hz. The comparison between the thresholds obtained in the two groups showed a statistically significant difference, especially at the frequency of 4000 Hz and for occupational exposure exceeding 17 yr. The results led us to conclude that environmental factors, and urban noise in particular, influence the onset and development of occupational acoustic trauma, and that those working in the country are significantly less affected than those in the city. Since occupational exposure was the same for both groups, their different responses must therefore be interpreted as due to differences in non-occupational exposure, in turn dependent on different opportunities for rest from noise and different levels of exposure to noise pollution.

Older adult performance on an altered version of the SSI test

The Synthetic Sentence Identification (SSI) test has been used extensively in investigations of reduced speech understanding skills in older adults. In this study the SSI test was altered by adding noise to the competing message and by administering practice lists and equivalent test lists, as well as versions of the test that have 4- and 12-s interstimulus intervals (ISIs), along with the standard 8-s ISI. The purpose was to determine the effect of these alterations on performance in a group of older adults with average pure-tone average 2 values less than 33 dB HL. Performance changed as a function of the ISI, with less rollover occurring for the 4-s ISI condition than the other 2 ISIs.

Early postnatal sound exposure induces lasting neuronal changes in the inferior colliculus of senescence accelerated mice (SAMP8): a morphometric study on GABAergic neurons and NMDA expression

Senescence-acceleration-prone mice (SAMP8) provide a model to study the influence of early postnatal sound exposure upon the aging auditory midbrain. SAMP8 were exposed to a 9-kHz monotone of either 53- or 65-dB sound pressure level during the first 30 postnatal days, the neurons in the auditory midbrain responding selectively to 9 kHz were localized by c-fos immunohistochemistry and the following parameters were compared to control SAMP8 not exposed to sound: mortality after sound exposure, dendritic spine density, and quantitative neurochemical alterations in this 9-kHz isofrequency lamina. For morphometric analysis, animals were examined at 1, 4, and 8 months of age. Serial sections of the inferior colliculus were Golgi impregnated or stained immunohistochemically for the expression of epsilon1 subunit of NMDA receptor or GABA. Mortality after exposure to 53 dB was the same as in controls, but was markedly increased from 7 months of age onward after postnatal exposure to 65 dB. No gross morphological alterations were observed in the auditory midbrain after sound exposure. However, sound exposure to 53 or 65 dB significantly reduced dendritic spine density by 11% at 4 months or by 11-17% both at 1 and 4 months of age, respectively. The effect of sound exposure upon neurons expressing the NMDAepsilon1 subunit was dose-dependent. Increasing with age until 4 months in control mice and remaining essentially stable thereafter, the percentage of NMDAepsilon1-immunoreactive neurons was significantly elevated by 40-66% in 1- and 8-month-old SAMP8 exposed to 53 dB, whereas no significant effect of 65 dB was apparent. The proportion of GABAergic cells declined with age in controls. It was significantly decreased at 1 month after 53 and 65 dB sound exposure. In contrast, it was elevated at later stages, being significantly increased at 4 months after exposure to 53 dB and at 8 months after exposure to 65 dB. The total cell number in the 9-kHz isofrequency lamina of SAMP8 decreased with age, but was not affected by exposure to either 53 or 65 dB. The present results indicate that early postnatal exposure to a monotone of mild intensity has long-term effects upon the aging auditory brain stem. Some of the changes induced by sound exposure, e.g., decline in spine density, are interpreted as accelerations of the normal aging process, whereas other effects, e.g., increased NMDAepsilon1 expression after 53 dB and elevated GABA expression after both 53 and 65 dB, are not merely explicable by accelerated aging.

Expression of Klotho protein in the inner ear

The Klotho mouse is a recently developed model that exhibits phenotypes resembling human aging. We used this model to investigate sensorineural hearing loss from the point of view that it may be considered an issue of aging. Using reverse transcription-polymerase chain reaction, Western blotting and immunohistochemical staining, we were able to confirm klotho gene transcription and protein synthesis in the kidney and inner ear. Klotho protein was mainly expressed in the stria vascularis and spiral ligament of the inner ear and in the distal convoluted tubule of the kidney, likely serving a common function in the two organs, i.e., modulating ion transport. The threshold for the auditory brainstem response was significantly higher in Klotho mice than in wild-type mice, and wave I latencies were prolonged. On the other hand, Klotho mice exhibited a normal distribution of I-IV interpeak intervals. No obvious morphological abnormalities were detected in Klotho mice, although no expression of Klotho protein was detected, and there was an apparent hearing disorder. Taken together, these findings suggest that by contributing to the maintenance ion homeostasis in the endolymph, Klotho protein serves as a key mediator of auditory function.