Hearing and Balance Restoration Research Areas

With your support, DRF primary funds research in the following areas:

• Hearing and Balance Restoration
• Investigation of age-related atrophy vascularis (strial atrophy) with a long-term goal of remediation through biologic and other (as yet unknown) means.
• Genetic Hearing Loss
• Acoustic Trauma (Noise Induced Hearing Loss)
• Tinnitus (Ringing in the Ears) and Hyperacusis (Decreased Tolerance of Sound)
• Vestibular and Balance Disorders (Dizziness and Vertigo)
• Temporal Bone Research

Hearing and Balance Restoration
Replacement of damaged cells in the inner ear is known to occur by spontaneous regeneration in birds and other non-mammalian vertebrates, but not in mammals. However, recent research has shown great promise in regenerating damaged cells. Research advances to-date indicates that hearing restoration may be achieved through cellular therapy (genetics/stem cell), chemical stimulation or mechanical modification – or a combination of techniques. DRF empowers the search for the right combination of conditions and treatments that might restore function in the inner ear.

Scope of the Problem

• Over 26 million people in the United States suffer irreversible hearing loss.
• About 36 million people in the United States have some degree of reduced hearing - roughly the total population of Florida and Pennsylvania combined.
• Over 1 million children in the United States are challenged with a hearing loss.
• One in ten Americans has a hearing loss that affects their ability to understand speech.
• Nearly 1 million people are totally deaf.
• Worldwide statistics are more staggering.

Investigation of age-related atrophy vascularis
The sense of hearing depends on receiving and converting sound energy from the environment into nerve impulses that can transmitted to the brain. The inner ear converts (transduces) these sound waves into nerve impulses through a complex system of sensory and motor cells known as
the inner and outer hair cells. The high energy requirements for transduction are provided the band of cells on the lateral wall of the cochlea known as the stria vascularis. The stria has an exceedingly high metabolic rate fueled by enzymes that release energy from biochemical compounds to “pump” the flow of potassium ions that form the electrical current.

This high electrical potential is necessary to power the action of the motile outer hair cells that amplify soft sounds reaching the inner ear. The outer hair cells actually change their shape in this process, getting longer and shorter at the same frequency as the sound stimulus. This vibrational mechanism provides acoustic tuning as well as amplifying soft sounds. At high sound input levels, outer hair cell motility is turned off and all the electrical energy is available for powering the inner hair (sensory) cells.

As we age, the function of these energy producing enzymes declines. The result is a decrease in power of the cochlear amplifier. When the strial battery gets weaker or goes dead, hearing is not possible even though the sensory cells are intact. Research has shown a temporary improvement in hearing when inner ear of a laboratory animal is infused with electrical current. Building on these observations is the next step in the search for a practical source of replacement current to power inner ear transduction.

A unique aspect of strial hearing loss is the relatively good ability to understand speech. This is in sharp contrast to loss of hair cells where no amount of amplification can restore lost speech understanding. Of course, when strial dysfunction is severe, both speech detection and speech understanding are lost. This is analogous to trying to read in the dark. Once the power is turned back on the sensory cells would function normally or near normally. Whereas with sensory cells are absent their ability to respond sharply to specific stimuli is permanently lost. Loss of hair cells is the hallmark of noise or other toxicity to the ear. Loss of the stria is a very common finding in age-related hearing loss (presbycusis). In fact, the decline in the metabolism of the stria vascularis may well be the hallmark of inner ear aging.

The fact that hearing aids provide good results for people with mild to moderate strial loss suggests that the power provided by the hearing aid is sufficient to overcome the decline in physiologic power within the inner ear. However, once that power declines too much, hearing aids would be of little
benefit. Here is where research aimed at providing an external source of power is aimed. Cochlear implants are the procedure of choice when the sensory cells are missing. However, in strial loss the sensory cells are normal. Therefore, inserting an implant into the inner ear might damage these cells. Thus, the ideal treatment would be to correct the loss of energy systems within the inner ear. On-going research is actually using an electrical current to power the system. Whether or not this will result in a practical therapy remains to be seen. Other approaches would be to restore the depleted enzyme systems with replacement cells or energy generating compounds. Again, these approaches are in their infancy at present. Because these approaches are logical but unproven, private sources of research funding are more appropriate because governmental funding agencies tend to be risk-adverse.

Genetic Hearing Loss
Several hundred genes are known to cause hereditary hearing loss and deafness. The hearing loss may be conductive, sensorineural, or mixed; syndromic or nonsyndromic; and prelingual (before language develops) or postlingual (after language develops). About half of all cases of childhood deafness are due to genetic problems. This means that the deafness has been passed down through the family. Even if you don't know anyone in your family who has a hearing loss, there may be a genetic reason for your child’s hearing loss. A lot of what is known about the genetics of hearing loss has been learned only in the past 10 years. With further research, new research contributions are being made every day.

Scope of the Problem
Deafness is the most common sensory defect. About 2 to 3 out of every 1,000 children in the United States are born with profound deafness, and more than half of these cases are caused by genetic factors. In adults, the chance of developing hearing loss increases with age; hearing loss affects half of people older than 80 years.

Acoustic Trauma (Noise Induced Hearing Loss)
Acoustic Trauma is an injury to the hearing mechanisms within the inner ear caused by excessively loud noise. Acoustic trauma is a common cause of sensory hearing loss. Damage to the hearing mechanisms within the inner ear may result from explosion near the ear (such as gunshots), long exposure to loud noises (such as loud music or loud machinery). Acoustic trauma is a form of occupational hearing loss. A good indicator of acoustic trauma is a hearing loss that follows exposure to noise. This hearing loss (which may not be correctable) may be slowly progressive and accompanied by ringing in the ear (tinnitus). The goal of treatment is to heal the injury and protect the ear from further damage. However, research is revealing new understanding, treatment and prevention options.

Scope of the Problem
Nearly 10 million Americans suffer noise induced hearing loss – one third of all Americans with hearing loss – making it the most common preventable cause of permanent sensorineural hearing loss. It is estimated that over 9 million American laborers are exposed to potentially hazardous levels of noise throughout their employment. An additional 1 million Americans are affected by non-industrial noise exposure.

Tinnitus (Ringing in the Ears) and Hyperacusis (Decreased Tolerance of Sound)
Tinnitus (ringing, roaring, clicking, or hissing sound in your ears) is a common symptom associated with many forms of hearing loss and other health problems. People with severe cases of tinnitus may find it difficult to hear, work, or even sleep. Tinnitus is accompanied by hyperacusis in about 40% of the cases. Hyperacusis is a decreased tolerance of sound and can be a serious problem.

Currently, there is no treatment that will eliminate tinnitus. With research, the mechanisms of tinnitus may be unlocked leading to improved treatment and meaningful prevention methods.

Scope of the Problem
Tinnitus affects about 26 million Americans. Tinnitus is accompanied by hyperacusis in about 18 million people in the U.S.

Vestibular and Balance Disorders (Dizziness and Vertigo)
The inner ear is an important part of the vestibular system which controls the sense of movement and balance. This system is the sensory system considered to have the most important influence on the other sensory systems and on the ability to function in everyday life. Directly or indirectly, the vestibular system influences nearly everything we do. People with vestibular disorders most commonly suffer dizziness, unsteadiness or imbalance when walking, nausea and vertigo (a sense of imbalance with spinning). Causes of dizziness and vertigo include: Meniere's Disease, Acoustic Neuroma, Benign Paroxysmal Positional Vertigo (BPPV), and Labyrinthitis (damage to the inner ear due to infection, trauma, and ototoxicity).

Scope of the Problem
Vestibular disorders occur frequently and it is estimated that 90 million Americans will complain to their doctors of dizziness at least once in their lifetime. In many cases, the cause will lie in the inner ear. Balance disorders increase in frequency in the older age groups and by age 75 become one of the most common reasons for seeking help from physicians.

Temporal Bone Research
The collection and study of temporal bones is essential for continued progress in the hearing and balance sciences. In 1960, the National Temporal Bone Banks Program (NTBB) was established by the Deafness Research Foundation to encourage individuals with ear disorders to pledge their temporal bones at death for scientific research. The program has grown into the National Temporal Bone Hearing and Balance Pathology Resource Registry (The Registry) sponsored by NIH's National Institute on Deafness and Other Communication Disorders (NIDCD). In addition to financially supporting DRF's innovative research, you can help advance hearing and balance science by becoming a temporal bone donor.