As we age, hair cells die. This is natural and unavoidable. For reasons we can’t explain, the hair cells corresponding to the high frequencies often die first. We might notice when the sibilant sounds in speech, such as ‘s’, ‘f’ and ‘sh’, become harder to distinguish and we might lose the sounds of waves lapping, leaves rustling and birds singing. By the age of 60, more than half the population will be aware of at least some loss of hearing. Many people assume that those with hearing loss experience a world with the volume turned down. In fact, hearing loss can be experienced very differently depending on its causes; sometimes with loss of frequencies; sometimes with distortion of sound; sometimes with less ability to separate, or attend to, specific sounds.

Noise-induced hearing loss is caused by a combination of loudness of sound and length of exposure. The louder the sound (measured in decibels), the less exposure is needed to suffer a hearing loss. Sounds loud enough to cause ringing in the ears afterwards are loud enough to cause hearing damage. Prolonged exposure to loud noise will kill hair cells. A single very loud sound (such as a gun shot or explosion) can cause instant hearing loss. Earplugs can be worn or loud noises avoided to prevent noise-induced hearing loss.

  Close

The treatment of hearing loss depends on the cause. Bacterial infections of the middle ear can be treated with antibiotics; blockages of the outer and middle ears can be cleared; surgery can repair damaged ear drums, and bones of the middle ear affected by otosclerosis (a hereditary condition where bone grows around one of the bones of the middle ear) can be replaced by artificial bones.

At present, age-related hearing loss cannot be cured, but a hearing aid may help. There are many different types of hearing aids and an audiologist will advise which one is most suitable. For the profoundly deaf, a cochlear implant may assist. This device transmits sound directly into the auditory nerve via electrodes surgically implanted into the cochlea. Recipients of a cochlear implant will need to learn how to marry the electronic sounds produced by the implant with lip reading skills.

  Close

We are exploring the potential of adult stem cells to replace damaged hair cells. We now know that adult stem cells from the brain can generate new nerve cells thus dispelling the long-held belief that nerve cells could not be regenerated.

A readily accessible and abundant source of adult stem cells is the lining of the nose. These stem cells constantly replace cells that enable us to smell. Olfactory stem cells, as they are known, have the potential to be used for a range of stem cell therapies. They can also be taken from one’s own body thus eliminating the problems of tissue rejection.

Garvan scientists have successfully converted adult olfactory stem cells are into hair cell-like cells and, using fine microsurgical techniques, have successfully injected the stem cells them into the cochlea of deaf mice . We will now test for the recovery of hearing with a non-invasive hearing test, called the auditory brainstem response (ABR), which is routinely used in humans. This will determine if the injected stem cells have converted into hair cells and can form functional connections to the brain to repair hearing loss.

  Close