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Hearing and Balance Research
Why the NIDCD Supports Hearing and Balance Research
Loss of hearing or balance negatively impacts quality of life and imposes a significant social and economic burden upon individuals, their families, and the communities in which they live. Millions of Americans experience a hearing or balance disorder at some point in their life, especially as young children or older adults. Common examples include middle-ear infections (otitis media), noise-induced hearing loss, tinnitus, age-related hearing loss, dizziness, and vertigo. Hearing and balance disorders cross all ethnic and socioeconomic lines. Approximately 37.5 million American adults report some degree of hearing loss and 33.4 million adults report a problem during the past 12 months with dizziness or balance, such as vertigo, unsteadiness, or blurred vision after moving the head.1, 2 Among the younger age group, an additional 5.3 percent of American children (3.3 million) also experienced balance and dizziness problems in the last 12 months, as reported by their parents or other adult caregivers.3-6 About two to three of every 1,000 children in the U.S. are born with a detectable level of hearing loss in one or both ears that can affect speech, language, social, and cognitive development. 4, 5 In 2014, one in six U.S. adults aged 18 and older reports trouble hearing without a hearing aid.6
Noise-Induced Hearing Loss
Excess noise is a major contributor to hearing loss in the U.S. Based on nationally representative hearing exam surveys (1999-2004), an estimated 15 percent of Americans aged 20 to 69, or 26 million Americans, reported a history of loud noise exposure and also had high-frequency audiogram results suggesting exposure to excess noise.7 Recent animal studies suggest that noise exposure causing temporary measurable hearing loss may also cause permanent hearing loss that is not readily detectable using standard audiometric testing. Such damage may underlie the common complaint of having difficulty in understanding speech in noisy situations. The NIDCD encourages research to better understand noise-induced auditory damage to inform potential therapies.
Otitis media (OM), or middle ear infection, is a condition that affects most young children before three years of age. Repeated episodes of OM can contribute to hearing loss and possibly delay language and cognitive skills development. NIDCD-supported research is improving our understanding of susceptibility and pathogenesis of OM. In the future, this research might identify immune pathways to guide effective OM vaccine development.
Age-related Hearing Loss
Age-related hearing loss (presbycusis) is the loss of hearing that gradually occurs during aging. It is one of the most common conditions affecting older and elderly adults with approximately one in three people in the U.S. aged 65 to 74 exhibiting a hearing loss, and nearly half of those older than 75 have difficulty hearing.8 There are many causes of age-related hearing loss. Most commonly, it arises from changes in the inner ear, but it can also result from complex changes along the nerve pathways from the ear to the brain. Understanding the cause of age-related hearing loss and finding ways to prevent it are important research areas supported by the NIDCD.
Tinnitus, or ringing in the ears, is a disorder that affects approximately 25 million Americans, many of whom also have hearing loss. Severity can range from a mild condition, which requires no intervention, to a severe debilitating disease with significant emotional, social, and economic impact. NIDCD-supported research aims to determine the neural basis of tinnitus, and to develop effective interventions for affected people.
Technology Interventions for Hearing Loss
Individuals with mild-to-severe hearing loss can benefit from using a hearing aid, and many with severe to profound hearing loss benefit from having a cochlear implant. Advances in both hearing aid and cochlear implant technology are improving treatment options for many people with various degrees of hearing loss. For example, individuals may be fitted with hearing aids or cochlear implants on both ears instead of only one ear to improve sound localization and discrimination. In recent years, some people with residual hearing for low-frequency sounds have received both a cochlear implant, to aid them in hearing higher frequency sounds, and a hearing aid to allow them to take advantage of their residual low-frequency hearing. In many cases, this combination (‘hybrid’) strategy results in a significant improvement when listening to speech in background noise.
Animal models of hereditary hearing impairment continue to be instrumental in mapping and cloning many of the gene mutations that contribute to deafness. They help scientists focus on how gene mutations affect protein function and result in deafness, and are a model in which to test therapeutic approaches to treat or prevent hearing loss. These models help us understand the importance of genes in the development and maintenance of the human ear. In addition, mouse and zebrafish models have enabled scientists to examine auditory sensory cells and to characterize the inner ear’s response to sound. Recent research has identified some of the cellular processes that contribute to hair cell damage and death, heralding future studies that may determine the inner ear’s response to mechanical and chemical trauma.
The inner ear contains the vestibular system, which includes sensory parts of the inner ear called the vestibular organs. Tiny canals and pouches on both sides of the head are specialized to detect motion and gravity. Their nerve signals interact with other sensory, motor, autonomic and cognitive circuits in the brain for several functions. The vestibular system regulates balanced posture and locomotion, provides spatial and heading orientation for navigation, and stabilizes visual gaze during movement. Normal balance is maintained by integrating inputs from the vestibular, visual, proprioceptive (position sensation), and musculoskeletal systems. Vestibular disorders can lead to dizziness, vertigo, nausea, migraines, blurred vision, and various forms of postural instability. Dysfunctions of the vestibular system can occur independently or with a hearing loss. The NIDCD supports the development of more efficient vestibular testing for improved clinical diagnoses and safer, better tolerated, and more effective treatments for vertigo. NIDCD-supported scientists are also developing vestibular prosthetic devices and minimally invasive surgical techniques to control imbalance and vertigo while preserving hearing and other functions.
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