Hearing - Use it or Lose it!

Thu, 06/25/2009 - 10:44am
By: The Citizen

By Dr. Andrew Waits
Special to The Citizen

We’ve all heard the saying “use it or lose it.” It applies to hearing as well as your mind and other parts of your body.

Twenty years ago it was thought one hearing aid would be enough to help someone with hearing loss. In a study, one hundred people with hearing loss were divided into two groups. Fifty wore two aids and the rest wore only one. A year later, they were all tested again without their hearing aids. The fifty who only wore one aid had poorer speech understanding in the un-aided ear than the year before. Every ear which utilized an aid had the same speech perception as before. The hearing levels themselves do not drop as a result of not wearing an aid but the ability to understand words does.

If not stimulated, as in the case of hearing loss, the part of the brain that processes sounds into words becomes dormant. This is an observable event I’ve seen in my own practice for over 20 years. If this goes on long enough, it results in what is called cochlear dead zones or regions of neglect.

The definition of cochlear dead regions is: the regions in the cochlea where the inner hair cells and/or the neurons are effectively not functioning at all and consequently no speech contained in those regions is transmitted to the brain. If the inner hair cells are badly damaged or non-functioning the neurons, which carry the signals to the brain, degenerate. Wide or narrow dead regions can occur and, most often, a dead region occurs in the higher frequencies along the basilar membrane. A high frequency dead region can be the consequence of age. Indeed those high frequencies that can be heard begin to diminish from the late teens but they don’t become dead high frequency regions.

They can also occur as a result of exposure to intense sounds, especially impact sounds such as gunshots or explosions. A low frequency dead region can occur in the late stages of Meniere’s disease. Other causes of dead regions which can affect any frequencies including the mid frequencies can arise as a result of genetic factor, infections, auto immune disease, or exposure to toxic agents. (i.e. some anticancer drugs)

Frank Musiek, Ph.D., the editor of Pathways and Director of Auditory Research at the University of Connecticut, states one odd characteristic of cochlear dead zones ; “Cases where patients report locating a sound source as originating directly in front of them regardless of the actual source of the sound. Brian Moore, Ph.D. of the University of Cambridge and the Royal Academy of Medical Society for Research in Otolaryngology is the leading authority on cochlear dead regions. He states that if a person has less than a moderate hearing loss, a dead region is rare but becomes increasingly common when the loss is severe or worse.

Dr. Moore has also found that a hearing loss that increases rapidly with rising frequency is sometimes indicative of a high frequency dead region. If a frequency of a tone falls well inside a dead region, the tone is consistently described as sounding distorted or noise-like.

It would seem dead regions would affect speech understanding in context but since speech information is distributed over a wide range of frequencies, a large effect on speech understanding may not be noticed quickly. There are specific tests which can help identify the dead regions that do not include a regular hearing test or speech testing.

Dr. Moore reports that knowing if a dead region is present has implications regarding the fitting of hearing aids. If there is only a deficit, which is usually the case, in the higher frequencies, hearing devices help the person begin to hear the soft consonant sounds again and as a result, words become more clear and understandable. For a person with a high frequency hearing loss without dead regions, amplifications should be applied up to the highest frequency possible. So, it’s important to establish which frequency can be improved upon and program the hearing device to target them.

Dr. Moore says more findings include that a person with a low frequency dead region, amplification can have a detrimental effect on the ability to understand speech in quiet or when background noise is present.

So the inactivity of the hair cells can fall under the phrase “use it or lose it.” We can help almost anyone with nerve damage and, in fact, ninety five percent of the patients we help have nerve damage. This term is somewhat of a misnomer as all of the cases called nerve damage is actually not the auditory nerve but the cochlea, the end organ of hearing. It is unfortunate but many hard of hearing persons have been told by some health care professionals that nerve damage can’t be helped. Typically, that is the main type of loss we do help.

The conclusion to make is for you to get help for your hearing before the cochlear regions die and can’t be helped. If they have only a deficit, even severe but not dead, hearing devices can help tremendously. Hearing devices keep these frequency regions alive because of the accurate and ongoing stimulation of the regions in questions.

Persons with hearing loss dead region should end up acquiring hearing aids anyway because some speech frequencies can be helped. So, why not get the help you need now and, in the process, keep brain regions from dying?

Hearing aids are absolutely essential for a healthy brain and for continued cognitive functioning

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