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Low-frequency sounds are more penetrating, damaging. Hearing damage caused by blasts typically occurs at frequencies around 2 - 8 kHz, while age-related hearing loss starts at the high frequencies. The frequency range for noise-induced damage is biased upward, because the low-frequency conductive structures damage first.
Why does hearing loss occur at high frequency first? It should occur at low frequency, because that is the more damaging sound. The distribution of hearing loss is totally incompatible with the noise exposure explanation. It could be due to growth factors, i.e., the high frequency parts die first because more distal.
Noise-induced hearing loss affects primarily the mid-frequencies, because the inner ear is most sensitive to these frequencies.
Noise-induced hearing loss occurs typically in the mid-frequencies (Rabinowitz, 2000), typically around 4 kHz (3 - 6 kHz), see Fig. 1. This can be explained by the fact that the human ear is most sensitive in this frequency range (Fig. 2). In turn this relates with the frequency range where speech understanding is most important, namely between roughly 2 and 6 kHz (Killion & Mueller, 2000). Hence, noise exposure neither targets the base, nor the apical parts of the cochlea, as claimed by asker and answerer, respectively. High-frequency hair cells in the rat cochlea have been shown to be very susceptible to damaging noise, but the low-frequency hair cells may go unscathed (source: eMedicine).
The other answerer claims that
parts of our hearing apparatus responsible for perceiving these [low-frequency] sounds are more fragile…
Hence, the claim that low-frequency regions in the cochlea are more sensitive than the more basal parts is not a claim supported by the bulk of the literature. In fact, as a rule of thumb, cochlear damage (inner ear damage) occurs most frequently first in the base, where the high frequencies are resolved. This holds for age-induced HL where high frequencies are lost first (Ciorba et al., 2011), as well as chemically-induced HL (Campo et al, 2013, barred some specific organic solvents that apparently do not follow this rule (Cappaert et al., 2002.
Fig. 1. Typical audiogram of noise-induced hearing loss showing loss of functional hearing at the mid-frequencies (Rabinowitz, 2000)
Fig. 2. Relation between perceived loudness and intensity (equal-loudness curves) for a normal-hearing person. source: Lumen Phsyics
- Campo et al., Dis Mon (2013); 59(4): 119-38
- Cappaert et al., Neurotoxicol Teratol (2002); 24: 503-10
- Ciorba et al., J Laryngol Otol (2011); 125(8):776-80
- Killion & Mueller, The Hearing Journal (2010); 63(1): 10-7
- Rabinowitz, Am Fam Physician (2000); 61*(9):2749-56
One has to distinguish between the frequency of a sound, its intensity (i.e., energy that it carries), and its loudness.
- Frequency, known more conventionally as the pitch, is what distinguishes high and low sounds. E.g., male voices are on average lower than female voices, i.e., male voices have lower frequency. Frequency is what changes when we hit different keys of a piano or different strings of a guitar. Frequency is measured in Hertz (Hz).
- Intensity is the energy carried by a sound wave. Intuitively it is clear that the sounds of the same frequency can have different intensity, e.g., the same key of a piano can be hit stronger or weaker, producing a louder or quieter sound. It is the intensity rather than the frequency of a sound that causes hearing damage. Intensity is however not the same as loudness, as I explain below. Intensity of a sound is measured in bells/decibells (dB).
- Loudness is our perception of a sound. Two sounds that we perceive as equally loud, do not necessarily have the same intensity. In fact, the higher frequency sounds have much higher energy/intensity when perceived as equally loud with lower frequency sounds.
- Spectrum While musical instruments can produce continuous sounds of a specific frequency, this is not the case for many sounds that we encounter in a real life. Combination of frequencies in a sound is called its spectrum. Blasts are an extreme case of sounds that are very short and therefore combine large number of frequencies, ranging from very low to very high ones, all having approximately the same intensity.
Since lower frequency sounds generally carry lower energy, the parts of our hearing apparatus responsible for perceiving these sounds are more fragile, i.e., more easily damaged by high energy sounds. While blast is a complex physical phenomenon, it can be roughly viewed as a sound carrying many frequencies of the same high intensity, which will thus cause more damage to lower frequency hearing. On the other hand, the loss of hearing with age reflects the "normal wear" by hearing the sounds that our ear is adapted for. Throughout our life the high frequency hearing deals with sounds of high energy and wears out faster.
Disclaimer: I admit that my answer reflects my stronger background in physics than in biology, and I will readily accept help in improving the last paragraph, (making it more precise).
Evidence supports Covid hearing loss link, say scientists
Hearing loss and other auditory problems are strongly associated with Covid-19 according to a systematic review of research evidence led by University of Manchester and NIHR Manchester Biomedical Research Centre (BRC) scientists.
Professor Kevin Munro and PhD researcher Ibrahim Almufarrij found 56 studies that identified an association between COVID-19 and auditory and vestibular problems.
They pooled data from 24 of the studies to estimate that the prevalence of hearing loss was 7.6%, tinnitus was 14.8% and vertigo was 7.2%.
However, the team - who followed up their review carried out a year ago - described the quality of the studies as fair.
Their data primarily used self-reported questionnaires or medical records to obtain COVID- 7 19-related symptoms, rather than the more scientifically reliable hearing tests.
The study was funded by is NIHR Manchester Biomedical Research Centre (BRC)
Kevin Munro, Professor of Audiology at The University of Manchester and Manchester BRC Hearing Health Lead said: "There is an urgent need for a carefully conducted clinical and diagnostic study to understand the long-term effects of COVID-19 on the auditory system.
"It is also well-known that viruses such as measles, mumps and meningitis can cause hearing loss little is understood about the auditory effects of the SARS-CoV-2 virus."
"Though this review provides further evidence for an association, the studies we looked at were of varying quality so more work needs to be done."
Professor Munro, is currently leading a year-long UK study to investigate the possible long-term impact of COVID-19 on hearing among people who have been previously treated in hospital for the virus.
His team hope to accurately estimate the number and severity of COVID-19 related hearing disorders in the UK, and discover what parts of the auditory system might be affected
They will also explore the association between these and other factors such as lifestyle, the presence of one or more additional conditions and critical care interventions.
A recent study led by Professor Munro, suggested that more than 13 per cent of patients who were discharged from a hospital reported a change in their hearing.
Ibrahim Almufarrij said: "Though the evidence is of varying quality, more and more studies are being carried out so the evidence base is growing. What we really need are studies that compare COVID-19 cases with controls, such as patients admitted to hospital with other health conditions.
"Though caution needs to be taken, we hope this study will add to the weight of scientific evidence that there is a strong association between Covid-19 and hearing problems."
Professor Munro added: "Over the last few months I have received numerous emails from people who reported a change in their hearing, or tinnitus after having COVID-19.
"While this is alarming, caution is required as it is unclear if changes to hearing are directly attributed to COVID-19 or to other factors, such as treatments to deliver urgent care."
Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.
Hearing loss (HL) is a significant public health concern that costs the UK economy £25 billion a year in productivity and unemployment , an amount that equates to one-fifth of the total annual health spending in England in 2018/19 . HL affects over nine million people in England, and it is estimated that, by 2035, the number of people with HL will rise to around 13 million. The above estimates, along with the local hearing needs in England, are calculated by population projections based on the study of Davis , who collected and analysed audiological data in the 1980s. This study remains the primary source of local estimates of HL prevalence  recently, these estimates have also been visualised in the form of a hearing map, offering a rough guide to the prevalence of HL among adults across the UK .
Despite its importance to the history of hearing care in the UK, Davis’s study had some significant limitations. First, the English samples were solely derived from the cities of Nottingham and Southampton, which are very unlikely to be representative of the whole population of England . The role of place in health is well-established [6, 7], and research has shown that it affects health outcomes . Second, scientific thinking in HL research was formed in previous decades around the concepts of older age and the male sex being the main leading causes of HL in adults, with little or no consideration for modifiable risk factors for hearing acuity. However, recent findings have suggested that socio-economic factors and modifiable lifestyle behaviours are associated with the likelihood of HL as firmly as well-established demographic factors such as age and sex . Thus, the study of Davis did not consider in its estimations the effects of place and socio-economic factors such as high occupational noise exposure from manual occupations  and differences in regions with strong and weak manufacturing industries .
The Clinical Commissioning Groups (CCGs) are currently responsible for the NHS audiology services in England, including the provision of hearing aids . However, the lack of robust hearing data makes it difficult to plan efficient, effective and sustainable models of hearing care based on patient needs . Exploratory spatial data analysis of hearing data from a representative population sample in England would reveal regional patterns and trends of HL, shedding light on potential socio-economic inequalities in hearing health. This updated analysis of HL prevalence could inform the health policy strategies of the NHS England and Department of Health, particularly in respect of the new governmental programme, ‘Action Plan on Hearing Loss’ .
The aim of this study was, therefore, to explore regional patterns and trends of HL in a representative longitudinal prospective cohort study of the English population aged 50 and over.
Distribution of hearing loss - Biology
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Health Disparities Among Adults With Hearing Loss: United States, 2000-2006
In 2006, 37 million adults in the United States had trouble hearing (ranging from a little trouble to being deaf), representing a substantial increase since 2000 when 31.5 million U.S. adults reported trouble hearing (1,2). Self-reported trouble hearing is a measure of hearing loss that is defined as &ldquothe total or partial inability to hear sound in one or both ears&rdquo (3). The National Healthy People Objectives for 2010 include goals to reduce prevalence of hearing loss as well as goals to eliminate health disparities among persons with disabilities (4). Accommodations are needed for adults who do not hear well to ensure equal access to health services (5,6). Services mandated by the Americans with Disabilities Act have improved access for this group of Americans, but disparities in access to health care and health information remain (7&ndash9). The goal of this report is to highlight disparities in health status and health risk behaviors of interest to the health community working to meet the needs of adults with hearing loss. Based on a nationally representative sample of U.S. adults, this report describes selected sociodemographic characteristics, health status and conditions, and health risk behavior characteristics of adults who were deaf or had a lot of trouble hearing and adults who had a little trouble hearing compared with adults with good hearing.
Prevalence of trouble hearing
During the period 2000-2006, 3.3% of U.S. adults aged 18 years and over were deaf or had a lot of trouble hearing without the use of a hearing aid (Table 1). Men (4.3%) were more likely than women (2.4%) to be deaf or have a lot of trouble hearing. Deafness or a lot of trouble hearing increased dramatically with age, rising from 0.9% among adults under age 45 to 3.1% among adults aged 45-64 and 11.1% among adults aged 65 and over. These age-related increases in deafness or a lot of trouble hearing were similar for men and women (Figure 1). Rates of a lesser degree of hearing trouble (i.e., &ldquoa little trouble&rdquo) also rose with age, increasing more than fourfold between ages 18-44 (6.7%) and ages 65 and over (27.8%). Non-Hispanic white adults and non-Hispanic American Indian or Alaska Native (AIAN) adults had the highest rates of any hearing trouble of the race/ethnicity groups studied (Figure 2). Adults with the most education (a bachelor&rsquos degree or higher) and those with the highest incomes were somewhat less likely than other adults to have any trouble hearing, although the differences were not large.
Health status characteristics
Prevalence of fair or poor health status, difficulties with physical functioning, and serious psychological distress increased with degree of hearing loss (Table 2 and Figure 3). Adults who were deaf or had a lot of trouble hearing were about three times as likely as adults with good hearing to be in fair or poor health and to have difficulty with physical functioning (such as walking, bending, reaching, etc). These adults were more than four times as likely as adults with good hearing to have experienced serious psychological distress. Adults who had a little trouble hearing also had higher rates of these health problems compared with adults who considered their hearing to be good. Diabetes and high blood pressure were more prevalent among adults who were deaf or had a lot of trouble hearing, compared with adults with good hearing. Analysis of differences by age (not shown) indicated that these disparities were greatest among adults under age 65.
Health risk behaviors
Adults who were deaf or had a lot of trouble hearing and those who had a little trouble hearing were more likely than adults with good hearing to: (a) currently smoke cigarettes (b) have had five or more drinks in 1 day in the past year (a proxy for at-risk drinking) (c) have engaged in no leisure-time physical activity (a measure of sedentary behavior) (d) be obese and (e) usually sleep 6 hours or less (Table 3). Analysis of differences by age (not shown) revealed that disparities in health risk behavior prevalence between adults with and without hearing loss are largely concentrated among adults under age 65. Figure 4 illustrates a sharp age difference in the disparities for smoking prevalence. Among adults aged 18-44 years, more than 40% of those who were deaf or had a lot of trouble hearing currently smoked cigarettes compared with 24% of those with good hearing. Disparities in smoking prevalence persisted among middle aged adults but were not found for adults aged 65 years and over, an age group for which hearing loss is more prevalent and smoking rates are generally low. Age-specific estimates for other behaviors are available upon request.
In this report, disparities in selected health status characteristics and health risk behaviors were found by hearing status: adults with hearing loss had poorer health and increased risk of engaging in health risk behaviors than adults with good hearing. The reasons for higher rates of smoking, alcohol use, leisure-time physical inactivity, obesity, and inadequate sleep among adults with hearing loss compared with adults with good hearing cannot be determined from this analysis.
Barriers to optimal medical care for adults with hearing loss have been identified by the medical community and specific suggestions for effectively addressing the needs of these patients have been offered (5&ndash8). Increased attention to the unique health care and health information needs of adults with hearing loss may help reduce disparities identified in this report. Media and other public health campaigns that use auditory techniques to promote healthy behaviors among the U.S. adult population may require modifications to more effectively reach adults with hearing loss. Inclusion of communication modalities appropriate for adults with hearing loss may aid in reducing health risk behaviors in this population.
About the data
The National Health Interview Survey (NHIS), a survey of the noninstitutionalized civilian population of the United States, has been an important source of information about health and health care in the United States since it was first conducted in 1957. NHIS is a multistage probability sample survey that is conducted continuously throughout the year by interviewers of the U. S. Census Bureau for the Centers for Disease Control and Prevention&rsquos National Center for Health Statistics. For further information see the NHIS website. Questions about hearing status, developed in collaboration with researchers at Gallaudet University, were first asked in the NHIS in 1962-1963 (10). Subsequently, hearing questions were asked in supplement questionnaires in 1970, 1971, 1977, 1990, and 1991 (11&ndash15). Since 1997, questions about hearing status have been asked annually in the NHIS Sample Adult Core questionnaire. Adults are asked &ldquoWhich statement best describes your hearing without a hearing aid: good, a little trouble, a lot of trouble, deaf?&rdquo Annual estimates of the number and percentage of adults with any trouble hearing are available for major population subgroups (1,2,16&ndash20).
New research delivers hope for one of South America's 'lost' bird species
Unearthed photo of a captive female purple-winged ground dove. Credit: Carlos Keller
The discovery of new information relating to a critically endangered bird species has given scientists new hope for finding the last remaining individuals in the wild—and a roadmap to save the species from extinction.
The South American purple-winged ground dove (Paraclaravis geoffroyi) has been critically endangered since 1994, due to loss and fragmentation of its Atlantic Rainforest habitat.
The species has occasionally been reported, even as recently as 2017, but with no published photographs or sound recordings of the birds in the wild, scientists were increasingly pessimistic for the survival of the bird.
However, thanks to a new study, published in Frontiers in Ecology and Evolution and led by Manchester Metropolitan University, a group of researchers from the UK, Brazil and Argentina have found evidence that the species might still exist and have discovered files which could help them with their search.
After collating historical records relating to the bird and analyzing their distribution in space and in time, the team found the most recent reported sightings came from large remaining rainforest patches in Northern Argentina—which is where most hope now lies that the species may survive.
They also interviewed amateur bird keepers as records showed the species were once kept in captivity—and by doing so unearthed new videos and sound recordings of the birds, along with detailed notes about their biology and habits.
Researchers now plan to use the newly discovered sound recordings to search for existing bird species in the wild.
Dr. Alexander Lees, senior lecturer in conservation biology at Manchester Metropolitan University and lead author, said: "Finding this previously unknown sound recording could prove critical in helping us locate this species in the wild again, as now we know what they sound like, we are far more likely to be successful in our search.
"Our chances of hearing the species are of course low, but by deploying dozens of autonomous sound recorders near seeding bamboo, and automatically searching for the vocalizations along the recordings takes the searching effort to a whole new level.
"It is also promising that our analysis of the sighting records do offer a glimmer of hope that the species may still persist—especially in the rainforests of Northern Argentina."
The team came across the recordings after speaking to aviculturist Carlos Keller, who bred purple-winged ground doves more than 30 years ago—before captive breeding of the species was banned in an attempt to protect the birds from illegal trapping.
Researchers believe the loss of the captive population at this time was a bitter blow for conservation efforts, but hope that in the future, if they can find and capture wild birds, they could establish a successful conservation breeding program using Carlos' specialist knowledge in the area.
Carlos said: "In the 1980s, we knew this was a rare bird, but it still had a very wide distribution, so nobody realized just how close to extinction it was.
"It was a sophisticated bird, moving quietly through the darker, shadier parts of the rainforest. My hope is that although this is a species that is almost impossible to see, it is still out there and hopefully our research and the models we have created can help to guide searches to the most likely places that this species may still be clinging on."
Ototoxicant Chemicals and Workplace Hearing Loss
Image © OSHA
Since the 19 th century, many therapeutic drugs have been known to affect hearing. Known as ototoxic drugs, many are used today in clinical situations despite these negative side effects because they are effective in treating serious, sometimes life-threatening conditions. Research has shown that exposure to certain chemicals in the workplace may also negatively affect how the ear functions, potentially causing hearing loss or balance problems, regardless of noise exposure. Substances containing ototoxicants include certain pesticides, solvents, metals and pharmaceuticals. The risk of hearing loss they pose can be increased when workers are exposed to these chemicals while working around elevated noise levels. This combination often results in hearing loss that can be temporary or permanent, depending on the level of noise, the dose of the chemical, and the duration of the exposure. This hearing impairment affects many occupations and industries, from machinists to firefighters.
A new informational bulletin developed by OSHA and NIOSH raises awareness of this issue, provides examples of ototoxic chemicals, lists the industries and occupations at risk and provides prevention information. The hearing loss caused by chemicals can be very similar to a hearing loss caused by excessive noise. The fact that noise exposure is so common in modern societies might explain the delay in recognizing the risk to hearing that these chemicals can pose. Pure tone audiometry is a basic clinical test used to determine a person’s hearing sensitivity at specific frequencies, i.e., the softest sound that can be perceived in a quiet environment. It clearly identifies various hearing loss characteristics, but not its cause. Other hearing tests such as word recognition or otoacoustic emission tests examine other auditory functions. In some cases, these tests can help differentiate the effects of chemicals from the effects of noise, since chemicals might affect the more central portions of the auditory system (nerves or nuclei of the central nervous system, the pathways to the brain or in the brain itself). These hearing deficits may have a more pronounced impact on the worker’s life because not only are sounds be perceived as less loud, but also as distorted. Word recognition may be compromised, particularly in background noise, making it difficult, for instance, to hold a conversation in a busy restaurant or at a party.
The first step in preventing exposure to ototoxicants is to know if they are in the workplace. The publications cited in the bulletin identify known ototoxicants for example: toluene, styrene, carbon monoxide, acrylonitrile, and lead. When there is no information on a certain chemical’s ototoxicity, information on the chemical’s general toxicity, nephrotoxicity, and neurotoxicity may provide clues about the potential ototoxicity. Most chemicals that are known to affect the auditory system are also neurotoxic and/or nephrotoxic. One can review Safety Data Sheets (SDS) for ototoxic substances and/or chemicals, and ototoxic health hazards associated with ingredients in the product. For example, Figure 1 shows an SDS where ototoxicants may be in a product.
NIOSH continues its research on this subject, in collaboration with several partners, including France’s Research and Safety Institute (INRS) and other institutions in the U.S., Canada and China (Fuente et al., 2018). For more information, see the recent paper in the Journal of the Acoustical Society of America, “Use of the Kurtosis Statistic in an Evaluation of the Effects of Noise and Solvent Exposures on the Hearing Thresholds of Workers: An Exploratory Study”
For more information on risk factors for hearing loss please visit the NIOSH Noise and Hearing Loss Prevention topic page.
Update: Since this blog posted, a new study was published (Dement 2018) which examined work history, health behavior, and hearing test results from more than 19,000 former construction workers to identify factors contributing to hearing loss. The researchers found that exposure to exposure to organic solvents along with exposure to loud noise on the job, and smoking each increased a worker’s risk of hearing loss by 15-20%. The prevalence of hearing impairment and risk ratios varied across sites and trade groups, which was accounted by the difference in exposure and other risk factors. Those who do not have access to the journal article can contact the author at [email protected] Key findings were summarized by the CPWR – The Center for Construction Research and Training.
Thais C. Morata, PhD, is a research audiologist with the NIOSH Division of Applied Research and Technology and the Coordinator of the NORA Manufacturing Sector Council.
CAPT Chuck Kardous,MS, PE, is a senior research engineer with the NIOSH Division of Applied Research and Technology.
Fuente A, Qiu W, Zhang M, Xie H, Kardous CA, Campo P, Morata TC. Use of the kurtosis statistic in an evaluation of the effects of noise and solvent exposures on the hearing thresholds of workers: An exploratory study. J Acoust Soc Am. 2018 Mar 143(3):1704. https://doi.org/10.1121/1.5028368
Dement J, Welch L, Ringen K, Cranford K, Quinn P. Hearing loss among older construction workers: Updated analyses. AJIM. 2018 April:61(4): 326. https://doi.org/10.1002/ajim.22827
11 comments on &ldquoOtotoxicant Chemicals and Workplace Hearing Loss&rdquo
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My name Is Erica M. Bluff-Hopp,
I work as an Animal Control Officer for the city of Rialto,. I have been a ACO for 14 yrs.’ and I work with very loud barking dogs, screaming, meowing cats, metal truck doors slamming and chemicals to clean the animal control trucks from diseases. I have lost two decimals of hearing loss and I have a hard time hearing anyone talking over white noise. Is there anyway I can prove that all of this is due to my work? I understand this might not be the right forum, but Workman’s Comp does not believe my hearing lose is due to work and Animal Control is forgotten about as a whole when it comes to dangers, chemicals, noise at the job.
Hello Erica and thanks for sharing your concerns with us. NIOSH is a research organization and is not an enforcement agency. We also do not get involved in individual workers compensation cases. We do conduct research to prevent illnesses and injuries for workers. Part of our research program involves responding to requests from employers, unions, or groups of workers to conduct health hazard evaluations (HHE) upon request. The completed HHEs form the basis to recommend risk reduction strategies.
NIOSH researchers have evaluated noise exposure and hearing loss of employees of kennels, animal hospitals, and animal shelters. We have several HHEs that you can find on this page (scroll down to noise): https://www.cdc.gov/niosh/topics/veterinary/physical.html. In all of the HHE’s conducted at kennels and animal shelters, NIOSH reported cases of hearing loss among employees. In all of these cases NIOSH recommended: (1) enroll employees in a hearing loss prevention program (2) require the use of ear plugs or ear muffs in the kennel area and (3) maintain ear muffs by making sure they are clean and by replacing the cushions every 6 months or sooner if necessary.
Guessing your in CA, CA has an OSHA State Plan so public sector employees should be covered by the hearing conservation standard. It’s not guaranteed but Cal OSHA may determine that your employer should have enrolled you in a hearing conservation program and provided u an initial audiogram and subsequent annual audiograms. However workers comp is it’s own thing and does not always match up with OSHA hearing loss definitions and etc.
How hearing loss in old age affects the brain
If your hearing deteriorates in old age, the risk of dementia and cognitive decline increases. So far, it hasn't been clear why. A team of neuroscientists has examined what happens in the brain when hearing gradually deteriorates: key areas of the brain are reorganized, and this affects memory.
Daniela Beckmann, Mirko Feldmann, Olena Shchyglo and Professor Denise Manahan-Vaughan from the Department of Neurophysiology of the Medical Faculty worked together for the study.
When sensory perception fades
The researchers studied the brain of mice that exhibit hereditary hearing loss, similar to age related hearing loss in humans. The scientists analysed the density of neurotransmitter receptors in the brain that are crucial for memory formation. They also researched the extent to which information storage in the brain's most important memory organ, the hippocampus, was affected.
Adaptability of the brain suffers
Memory is enabled by a process called synaptic plasticity. In the hippocampus, synaptic plasticity was chronically impaired by progressive hearing loss. The distribution and density of neurotransmitter receptors in sensory and memory regions of the brain also changed constantly. The stronger the hearing impairment, the poorer were both synaptic plasticity and memory ability.
"Our results provide new insights into the putative cause of the relationship between cognitive decline and age-related hearing loss in humans," said Denise Manahan-Vaughan. "We believe that the constant changes in neurotransmitter receptor expression caused by progressive hearing loss create shifting sands at the level of sensory information processing that prevent the hippocampus from working effectively," she adds.
Genetics of Hearing Loss
Hearing loss has many causes. 50% to 60% of hearing loss in babies is due to genetic causes. There are also a number of things in the environment that can cause hearing loss. 25% or more of hearing loss in babies is due to &ldquoenvironmental&rdquo causes such as maternal infections during pregnancy and complications after birth. Sometimes both genes and environment work together to cause hearing loss. For example, there are some medicines that can cause hearing loss, but only in people who have certain mutations in their genes.
Genes contain the instructions that tell the cells of people&rsquos bodies how to grow and work. For example, the instructions in genes control what color a person&rsquos eyes will be. There are many genes that are involved in hearing. Sometimes, a gene does not form in the expected manner. This is called a mutation. Some mutations run in families and others do not. If more than one person in a family has hearing loss, it is said to be &ldquofamilial&rdquo. That is, it runs in the family.
About 70% of all mutations causing hearing loss are non-syndromic. This means that the person does not have any other symptoms. About 30% of the mutations causing hearing loss are syndromic. This means that the person has other symptoms besides hearing loss. For example, some people with hearing loss are also blind.
The cochlea (the part of the ear that changes sounds in the air into nerve signals to the brain) is a very complex and specialized part of the body that needs many instructions to guide its development and function. These instructions come from genes. Changes in any one of these genes can result in hearing loss. The GJB2 gene is one of the genes that contains the instructions for a protein called connexin 26 this protein plays an important role in the functioning of the cochlea. In some populations about 40% of newborns with a genetic hearing loss who do not have a syndrome, have a mutation in the GJB2 gene.
Molecular Genetics of Hearing Loss
▪ AbstractHereditary isolated hearing loss is genetically highly heterogeneous. Over 100 genes are predicted to cause this disorder in humans. Sixty loci have been reported and 24 genes underlying 28 deafness forms have been identified. The present epistemic stage in the realm consists in a preliminary characterization of the encoded proteins and the associated defective biological processes. Since for several of the deafness forms we still only have fuzzy notions of their pathogenesis, we here adopt a presentation of the various deafness forms based on the site of the primary defect: hair cell defects, nonsensory cell defects, and tectorial membrane anomalies. The various deafness forms so far studied appear as monogenic disorders. They are all rare with the exception of one, caused by mutations in the gene encoding the gap junction protein connexin26, which accounts for between one third to one half of the cases of prelingual inherited deafness in Caucasian populations.