question: Why does our hearing degrade over time and can it be restored?
comment: We hear by sensing when sound waves bending little hairs in our ears. The more they bend, the more we detect the loudness of a sound. Repeated bending of these hairs can wear them out, or even bend them so far they dont bend back. This especially happens when you are exposed to very loud noises or fairly loud noises for long periods of time. As we age, our ability to “bounce back” wears down, so those bendy hairs dont recover as much and are less able to respond to sound waves, even if you havent been exposed to a lot of loud noises - like everything else, bodies wear out over time. The only way to “restore” hearing once its damaged is by bypassing the hairs with an electric device “wired” right into the hearing system which mimics the signal of these sound-detecting “hairs”.
passages: Section::::Treatment.
  
  Treatment modalities fall into three categories: pharmacological, surgical, and management. As SNHL is a physiologic degradation and considered permanent, there are as of this time, no approved or recommended treatments.
  
  There have been significant advances in identification of human deafness genes and elucidation of their cellular mechanisms as well as their physiological function in mice. Nevertheless, pharmacological treatment options are very limited and clinically unproven. Such pharmaceutical treatments as are employed are palliative rather than curative, and addressed to the underlying cause if one can be identified, in order to avert progressive damage.
   The risk of having cognitive impairment increased 7 percent for every 10 dB of hearing loss at baseline. No effect of hearing aids was seen in the Lin Baltimore study. 
  
  Section::::Causes.
  
  The aging process has three distinct components: physiologic degeneration, extrinsic damage (nosocusis), and intrinsic damage (sociocusis). These factors are superimposed on a genetic substrate, and may be overshadowed by general age-related susceptibility to diseases and disorders.
   Section::::Factors.:Hearing impairment.
  
  People with mild and moderate hearing loss were tested for the effectiveness of phonemic restoration. Those with mild hearing loss performed at the same level of a normal listener. Those with moderate hearing loss had almost no perception and failed to identify the missing phonemes. This research is also dependent on the amount of words the observer is comfortable understanding because of the nature of top-down processing.
  
  Section::::Factors.:Cochlear implants.
   BULLET::::4. preservation of the ear canal wall. If poorly performed, it may result in a high rate of both residual and recurrent cholesteatoma.
  
  BULLET::::5. reconstruction of the chain of hearing bones.
  
  Clearly, preservation and restoration of ear function at the same time as total removal of cholesteatoma requires a high level of surgical expertise.
  
  Section::::Prognosis.
  
  It is important that the patient attend periodic follow-up checks, because even after careful microscopic surgical removal, cholesteatomas may recur. Such recurrence may arise many years, or even decades, after treatment.
   Section::::Hearing loss.:Management.
  
  The loss of hearing, when it is caused by neural loss, cannot presently be cured. Instead, its effects can be mitigated by the use of audioprosthetic devices, i.e. hearing assistive devices such as hearing aids and cochlear implants. In a clinical setting, this management is offered by otologists and audiologists.
  
  Section::::Hearing loss.:Relation to health.
  
  Hearing loss is associated with Alzheimer's disease and dementia with a greater degree of hearing loss tied to a higher risk. There is also an association between type 2 diabetes and hearing loss.
  
  Section::::Hearing underwater.
   In most cases, tympanosclerosis does not cause any recognisable hearing loss up to ten years after the initial disease onset. Sclerotic changes seem to stabilise, but not resolve or dissolve, after 3 years.
  
  Section::::Epidemiology.
   Section::::Causes.:Presbycusis.
   BULLET::::- Coenzyme Q10 – a substance similar to a vitamin, with antioxidant properties. It is made in the body, but levels fall with age.
  
  BULLET::::- ebselen, a synthetic drug molecule that mimics glutathione peroxidase (GPx), a critical enzyme in the inner ear that protects it from damage caused by loud sounds or noise
  
  Section::::Research.:Stem cell and gene therapy.
  
  Hair cell regeneration using stem cell and gene therapy is years or decades away from being clinically feasible. However, studies are currently underway on the subject, with the first FDA-approved trial beginning in February 2012.
  
  Section::::Sudden sensorineural hearing loss.
   Over time, the detection of high-pitched sounds becomes more difficult, and speech perception is affected, particularly of sibilants and fricatives. Patients typically express a decreased ability to understand speech. Once the loss has progressed to the 2–4 kHz range, there is increased difficulty understanding consonants. Both ears tend to be affected. The impact of presbycusis on communication depends on both the severity of the condition and the communication partner.
  
  Older adults with presbycusis often exhibit associated symptoms of social isolation, depression, anxiety, frailty and cognitive decline.
   The DRF funded research led, in 1987, to the discovery of spontaneous regeneration of hair cells in chickens, thus igniting the field of hair cell regeneration in humans. Research on the regrowth of cochlea cells may lead to medical treatments that restore hearing. Unlike birds and reptiles, humans and other mammals are normally unable to regrow the cells of the inner ear that convert sound into neural signals when those cells are damaged by age or disease.
  
  In 1989 the DRF funded Meniere's Disease Study Center for improved evaluation and better treatments of Ménière's disease.
   First reports on critical periods came from deaf children and animals that received a cochlear implant to restore hearing. Approximately at the same time, both an electroencephalographic study by Sharma, Dorman and Spahr and an in-vivo investigation of the cortical plasticity in deaf cats by Kral and colleagues demonstrated that the adaptation to the cochlear implant is subject to an early, developmental sensitive period. The closure of sensitive periods likely involves a multitude of processes that in their combination make it difficult to reopen these behaviorally. The understanding of the mechanisms behind critical periods has consequences for medical therapy of hearing loss. M. Merzenich and colleagues showed that during an early critical period, noise exposure can affect the frequency organization of the auditory cortex.
   Noise and ageing are the primary causes of presbycusis, or age-related hearing loss, the most common kind of hearing loss in industrial society.
   At the present time, no established clinical treatments exist to reverse the effects of permanent NIHL. However, current research for the possible use of drug and genetic therapies look hopeful. In addition, management options such as hearing aids and counseling exist.
   In cases where the causes are environmental, the treatment is to eliminate or reduce these causes first of all, and then to fit patients with a hearing aid, especially if they are elderly. When the loss is due to heredity, total deafness is often the end result. On the one hand, persons who experience gradual deterioration of their hearing are fortunate in that they have learned to speak. Ultimately the affected person may bridge communication problems by becoming skilled in sign language, speech-reading, using a hearing aid, or accepting elective surgery to use a prosthetic devices such as a cochlear implant.
   People with cochlear implants are at a higher risk for bacterial meningitis. Thus, meningitis vaccination is recommended. People who have hearing loss, especially those who develop a hearing problem in childhood or old age, may need support and technical adaptations as part of the rehabilitation process. Recent research shows variations in efficacy but some studies show that if implanted at a very young age, some profoundly impaired children can acquire effective hearing and speech, particularly if supported by appropriate rehabilitation.
  
  Section::::Education.
   Section::::Diagnosis.:Magnetic resonance imaging (MRI).
  
  As part of differential diagnosis, an MRI scan may be done to check for vascular anomalies, tumors, and structural problems like enlarged mastoids. MRI and other types of scan cannot directly detect or measure age-related hearing loss.
  
  Section::::Treatment.
  
  At present, presbycusis, being primarily sensorineural in nature, cannot be prevented, ameliorated or cured. Treatment options fall into three categories: pharmacological, surgical and management.
  
  BULLET::::- There are no approved or recommended pharmaceutical treatments for presbycusis.
  
  Section::::Treatment.:Cochlear implant.
   Many vertebrates such as fish, birds and amphibians do not suffer presbycusis in old age as they are able to regenerate their cochlear sensory cells, whereas mammals including humans have genetically lost this regenerative ability.
  
  Section::::Presentation.
  
  Primary symptoms:
  
  BULLET::::- sounds or speech becoming dull, muffled or attenuated
  
  BULLET::::- need for increased volume on television, radio, music and other audio sources
  
  BULLET::::- difficulty using the telephone
  
  BULLET::::- loss of directionality of sound
  
  BULLET::::- difficulty understanding speech, especially women and children
  
  BULLET::::- difficulty in speech discrimination against background noise (cocktail party effect)
  
  Secondary symptoms:
   Section::::Management.
  
  Management depend on the specific cause if known as well as the extent, type and configuration of the hearing loss. Most hearing loss, that resulting from age and noise, is progressive and irreversible, and there are currently no approved or recommended treatments. A few specific kinds of hearing loss are amenable to surgical treatment. In other cases, treatment is addressed to underlying pathologies, but any hearing loss incurred may be permanent.
  
  Some management options include hearing aids, cochlear implants, assistive technology, and closed captioning. This choice depends on level of hearing loss, type of hearing loss, and personal preference.
   The cause of presbycusis is a combination of genetics, cumulative environmental exposures and pathophysiological changes related to aging. At present there are no preventative measures known; treatment is by hearing aid or surgical implant.
  
  Presbycusis is the most common cause of hearing loss, afflicting one out of three persons by age 65, and one out of two by age 75. Presbycusis is the second most common illness next to arthritis in aged people.
   Section::::Causes.:Presbycusis.:Noise.
   Hearing loss is most commonly caused by long-term exposure to loud noises, from recreation or from work, that damage the hair cells, which do not grow back on their own.
  
  Older people may lose their hearing from long exposure to noise, changes in the inner ear, changes in the middle ear, or from changes along the nerves from the ear to the brain.
  
  Section::::Diagnosis.
   Auditory fatigue
  
  Auditory fatigue is defined as a temporary loss of hearing after exposure to sound. This results in a temporary shift of the auditory threshold known as a "temporary threshold shift" (TTS). The damage can become permanent ("permanent threshold shift", PTS) if sufficient recovery time is not allowed before continued sound exposure. When the hearing loss is rooted from a traumatic occurrence, it may be classified as noise-induced hearing loss, or NIHL.
  
  There are two main types of auditory fatigue, short-term and long-term. These are distinguished from each other by several characteristics listed individually below.
  
  Short-term fatigue
   Sensorineural hearing loss is one caused by dysfunction of the inner ear, the cochlea or the nerve that transmits the impulses from the cochlea to the hearing centre in the brain. The most common reason for sensorineural hearing loss is damage to the hair cells in the cochlea. Depending on the definition it could be estimated that more than 50% of the population over the age of 70 has impaired hearing.
  
  BULLET::::- Central deafness
   Researchers reported in 2015 that genetically deaf mice which were treated with TMC1 gene therapy recovered some of their hearing. In 2017, additional studies were performed to treat Usher syndrome and here, a recombinant adeno-associated virus seemed to outperform the older vectors.
  
  Section::::Research.:Audition.
   Hearing may deteriorate gradually from chronic and repeated noise exposure (such as to loud music or background noise) or suddenly from exposure to impulse noise, which is a short high intensity noise (such as a gunshot or airhorn). In both types, loud sound overstimulates delicate hearing cells, leading to the permanent injury or death of the cells. Once lost this way, hearing cannot be restored in humans.
  