Effects Of Age-related Hearing Loss Research Articles

Prestin-Dependence of Outer Hair Cell Survival and Partial Rescue of Outer Hair Cell Loss in PrestinV499G/Y501H Knockin Mice.

A knockin (KI) mouse expressing mutated prestin V499G/Y501H (499 prestin) was created to study cochlear amplification. Recordings from isolated outer hair cells (OHC) in this mutant showed vastly reduced electromotility and, as a consequence, reduced hearing sensitivity. Although 499 prestin OHCs were normal in stiffness and longer than OHCs lacking prestin, accelerated OHC death was unexpectedly observed relative to that documented in prestin knockout (KO) mice. These observations imply an additional role of prestin in OHC maintenance besides its known requirement for mammalian cochlear amplification. In order to gain mechanistic insights into prestin-associated OHC loss, we implemented several interventions to improve survival. First, 499 prestin KI’s were backcrossed to Bak KO mice, which lack the mitochondrial pro-apoptotic gene Bak. Because oxidative stress is implicated in OHC death, another group of 499 prestin KI mice was fed the antioxidant diet, Protandim. 499 KI mice were also backcrossed onto the FVB murine strain, which retains excellent high-frequency hearing well into adulthood, to reduce the compounding effect of age-related hearing loss associated with the original 499 prestin KIs. Finally, a compound heterozygous (chet) mouse expressing one copy of 499 prestin and one copy of KO prestin was also created to reduce quantities of 499 prestin protein. Results show reduction in OHC death in chets, and in 499 prestin KIs on the FVB background, but only a slight improvement in OHC survival for mice receiving Protandim. We also report that improved OHC survival in 499 prestin KIs had little effect on hearing phenotype, reaffirming the original contention about the essential role of prestin’s motor function in cochlear amplification.

Effects of age-related hearing loss on verbal processing and short-term memory

Adult aging is frequently accompanied by hearing loss, as well as by cognitive decline. Both play a role in listeners' understanding of noisy, foreign-accented speech and fast conversational speech. Hearing loss leads to increased perceptual effort during listening, which affects memory encoding of the spoken message. Furthermore, some studies have suggested that acquired hearing loss also has long-term effects by degrading the quality or accessibility of phonological representations in long-term memory. This was investigated further by looking into non-word reading, thus bypassing immediate effects of hearing loss. A sample of 29 older adults, varying in degree of high-frequency hearing loss and visual digit span performance, saw 72 multisyllabic nonwords varying in phonotactic frequency (i.e., the phoneme-co-occurrence statistics of the language). They saw the nonwords for 5 seconds and were prompted to produce them from memory after another 3 seconds. As expected, response accuracy was influenced by phonotactic frequency of the nonword and digit span performance. Crucially, response accuracy was also higher if the participant had better hearing, supporting the claim that hearing loss degrades phonological representations in long-term memory. These results emphasize the broad consequences hearing loss has on language processing beyond its immediate effect on speech audibility.

Frequency of the Audiometric Notch Following Excessive Noise Exposure

Abstract The aim of the study was to determine the configuration of pathologic audiograms in patients with excessive noise exposure, and to calculate the frequency of notches in the audiogram in patients with and without excessive noise exposure by avoiding the effect of age-related hearing loss. We have analyzed 514 audiograms of 257 patients aged between 20 to 50 years: 240 patients (mean age of 38.7 years) with excessive noise exposure and 17 patients (mean age of 41.2 years) with notches in the audiogram, but without a history of excessive noise exposure. For statistical data analysis we have used the Chi-square test and Fisher exact test with the level of significance p < 0.05. Pathologic audiograms were classified into five different types: Slope at 4000 Hz (0.8%), Slope at 2000 Hz (15.1%), Notch at 4000 Hz (67.4%), Notch at 2000 Hz (0.8%), Flat (8.9%), and 7% were out of this classification. A total of 190 (79.2%) patients with excessive noise exposure had a notch in the audiogram. Left ear notches were the most common. Among the patients with notched audiograms, 91.8% had a history of excessive noise exposure, either occupational or nonoccupational, and 8.2% did not report any excessive noise exposure.

Cortical alpha oscillations as a tool for auditory selective inhibition.

Listening to speech is often demanding because of signal degradations and the presence of distracting sounds (i.e., “noise”). The question how the brain achieves the task of extracting only relevant information from the mixture of sounds reaching the ear (i.e., “cocktail party problem”) is still open. In analogy to recent findings in vision, we propose cortical alpha (~10 Hz) oscillations measurable using M/EEG as a pivotal mechanism to selectively inhibit the processing of noise to improve auditory selective attention to task-relevant signals. We review initial evidence of enhanced alpha activity in selective listening tasks, suggesting a significant role of alpha-modulated noise suppression in speech. We discuss the importance of dissociating between noise interference in the auditory periphery (i.e., energetic masking) and noise interference with more central cognitive aspects of speech processing (i.e., informational masking). Finally, we point out the adverse effects of age-related hearing loss and/or cognitive decline on auditory selective inhibition. With this perspective article, we set the stage for future studies on the inhibitory role of alpha oscillations for speech processing in challenging listening situations.

Effects of age-related hearing loss and background noise on neuromagnetic activity from auditory cortex

Aging is often accompanied by hearing loss, which impacts how sounds are processed and represented along the ascending auditory pathways and within the auditory cortices. Here, we assess the impact of mild binaural hearing loss on the older adults’ ability to both process complex sounds embedded in noise and to segregate a mistuned harmonic in an otherwise periodic stimulus. We measured auditory evoked fields (AEFs) using magnetoencephalography while participants were presented with complex tones that had either all harmonics in tune or had the third harmonic mistuned by 4 or 16% of its original value. The tones (75 dB sound pressure level, SPL) were presented without, with low (45 dBA SPL), or with moderate (65 dBA SPL) Gaussian noise. For each participant, we modeled the AEFs with a pair of dipoles in the superior temporal plane. We then examined the effects of hearing loss and noise on the amplitude and latency of the resulting source waveforms. In the present study, results revealed that similar noise-induced increases in N1m were present in older adults with and without hearing loss. Our results also showed that the P1m amplitude was larger in the hearing impaired than in the normal-hearing adults. In addition, the object-related negativity (ORN) elicited by the mistuned harmonic was larger in hearing impaired listeners. The enhanced P1m and ORN amplitude in the hearing impaired older adults suggests that hearing loss increased neural excitability in auditory cortices, which could be related to deficits in inhibitory control.

Age-related Hearing Loss and Ear Morphology Affect Vertical but not Horizontal Sound-Localization Performance

Several studies have attributed deterioration of sound localization in the horizontal (azimuth) and vertical (elevation) planes to an age-related decline in binaural processing and high-frequency hearing loss (HFHL). The latter might underlie decreased elevation performance of older adults. However, as the pinnae keep growing throughout life, we hypothesized that larger ears might enable older adults to localize sounds in elevation on the basis of lower frequencies, thus (partially) compensating their HFHL. In addition, it is not clear whether sound localization has already matured at a very young age, when the body is still growing, and the binaural and monaural sound-localization cues change accordingly. The present study investigated sound-localization performance of children (7-11 years), young adults (20-34 years), and older adults (63-80 years) under open-loop conditions in the two-dimensional frontal hemifield. We studied the effect of age-related hearing loss and ear size on localization responses to brief broadband sound bursts with different bandwidths. We found similar localization abilities in azimuth for all listeners, including the older adults with HFHL. Sound localization in elevation for the children and young adult listeners with smaller ears improved when stimuli contained frequencies above 7 kHz. Subjects with larger ears could also judge the elevation of sound sources restricted to lower frequency content. Despite increasing ear size, sound localization in elevation deteriorated in older adults with HFHL. We conclude that the binaural localization cues are successfully used well into later stages of life, but that pinna growth cannot compensate the more profound HFHL with age.

Hearing Loss in Older Adults

Hearing Loss in Older Adults

Age-Related Physical and Emotional Characteristics to Safety Warning Sounds: Design Guidelines for Intelligent Vehicles

Recent technological advances have made motor vehicles more intelligent to increase safety and comfort. An intelligent vehicle provides drivers with safety warning information through audible sounds, visual displays, and tactile feedback. However, elderly drivers often have decreased cognitive and psychomotor abilities in the areas such as hearing, eyesight, short-term memory, and spatial perception. Therefore, possible age-related deficits should be considered when designing effective warning systems. This paper evaluates the impact of advancing age on drivers' physical responses and emotional preferences with regard to audible safety warnings that are widely used to warn about driving hazards. Three sound characteristics (frequency, tempo, and intensity) and three age groups (younger, middle, and older) were considered in investigating the effect of age-related hearing loss and reduced speed of movement. Data were collected from 38 drivers who drove on a simulated rural road in a driving simulator. Experimental results showed that age influenced drivers' responses and emotional preference. An appropriate range of warning sounds is suggested.

Effects of hearing loss and spectral shaping on identification and neural response patterns of stop-consonant stimuli

In order to determine the effects of hearing loss and spectral shaping on a dynamic spectral speech cue, behavioral identification and neural response patterns of stop-consonant stimuli varying along the /b-d-g/ place-of-articulation continuum were measured from 11 young adults (mean age = 27 years) and 10 older adults (mean age = 55.2 years) with normal hearing, and compared to those from 10 older adults (mean age = 61.3 years) with mild-to-moderate hearing impairment. Psychometric functions and N1-P2 cortical evoked responses were obtained using consonant-vowel (CV) stimuli with frequency-independent (unshaped) amplification as well as with frequency-dependent (shaped) amplification that enhanced F2 relative to the rest of the stimulus. Results indicated that behavioral identification and neural response patterns of stop-consonant CVs were affected primarily by aging and secondarily by age-related hearing loss. Further, enhancing the audibility of the F2 transition cue with spectrally shaped amplification partially reduced the effects of age-related hearing loss on categorization ability but not neural response patterns of stop-consonant CVs. These findings suggest that aging affects excitatory and inhibitory processes and may contribute to the perceptual differences of dynamic spectral cues seen in older versus young adults. Additionally, age and age-related hearing loss may have separate influences on neural function.

Effects of age-related hearing loss on startle reflex and prepulse inhibition in mice on pure and mixed C57BL and 129 genetic background

The present study examined the developmental course of the age-related hearing loss and its consequences on the expression of acoustic startle reflex (ASR) and prepulse inhibition (PPI) generated by white-noise bursts in 129S2/SvPas (129) and C57BL/6J (C57) mouse strains and their F 1 hybrids. Auditory brainstem responses (ABR), ASR and PPI were assessed at various time points: 6, 28, 41 and 94 weeks. Both parental strains showed marked ABR threshold shifts with age, with C57 mice having the most pronounced deficits. By contrast, the hybrids displayed only minor hearing loss with age. The time courses of ASR and PPI varied considerably between the mouse strains. From 6 to 41 weeks of age, ASR and PPI elicited by weak stimuli (70–90 dB) increased in C57 mice, whereas the startle responses to intense stimuli (95–120 dB) declined progressively. In 129 and hybrid mice, PPI levels remained relatively stable during the first year, but a progressive increase of ASR was observed in the hybrids for intense stimuli (95–120 dB). When animals reached 94 weeks of age, marked deterioration of ASR was observed in all strains, while deficits in PPI were only seen in 129 and C57 mice. These findings show that the time course and the severity of the hearing loss vary considerably between 129, C57 strains and their hybrids, thus suggesting a marked heterogeneity in the genetic mechanisms underlying deafness in mice. They also demonstrate that the age-related hearing loss may have complex consequences on auditory behavioral performances depending of the severity of the deficits, the genetic background as well as the stimuli parameters.

The aging auditory system: anatomic and physiologic changes and implications for rehabilitation

Over the last century, research in the area of age-related hearing loss has provided a vast amount of knowledge regarding age-related effects on the anatomy and physiology of the auditory system. As we enter the new millennium, researchers are beginning to shift their attention towards developing methods of modulating the effects of age-related hearing loss and the development of efficacious intervention strategies to meet all of an individual's hearing-related rehabilitative needs. The purpose of this review is to provide a framework for considering how the biological aspects of the aging auditory system interact with the most common current therapeutic intervention for age-related hearing loss—the use of amplification—and also how the biological aspects point to other potential intervention strategies.

Central physiological correlates of ageing and presbycusis in mice

Responses of neurons in the central auditory system of ageing mice suggest several sources of age-related problems in hearing. The central representation of frequency (tonotopic organization) is disrupted in mice with presbycusis, implying a cause of problems with frequency coding. In very old mice with only minimal hearing loss, normal-responding neurons co-exist with "sluggish" neurons, which suggests there is a process of attrition that affects some neurons more than others. Spontaneous activity increases in neurons of older mice, implying a decrease in the physiological signal-to-noise ratio. The effects of age-related hearing loss are more severe in the ventral cochlear nucleus than in the dorsal cochlear nucleus, suggesting that various functional circuits may be more or less vulnerable to presbycusis.