Neurophysiological changes occur as early as 20dB with the loss of GABA receptors. This results in greater degree of spontaneous activity of auditory neurons, more difficulty with temporal processing, a spread of the response of a nerve to a wider response instead of sharp frequency tuning. There are also studies that link mild hearing loss with cognitive decline and verbal memory difficulties. Let's not forget that the entire brain (exception of unimodal regions) responds to sound. There are auditory responsive neurons in the memory system, emotional system, attentional network. In fact, I made a list of the structures involved in auditory processing and the number comes to 19 that I could quickly spit out from the hippocampus to the amygdala to the prefrontal cortex, etc. etc.
We know that deprivation of any sense weakens the integrity of the neural system through reductions in synaptic density, reductions in cell size, etc. until eventually leading to atrophy.
The earlier the hearing loss is fit, the greater chance of preserving and recovering a higher degree of physiological capability than waiting until the hearing loss hits moderate levels. In addition, when hearing losses are fit earlier, they usually involve younger patients who are less likely to be on anticholinergic drugs that would impair neural plasticity. Their success with hearing aids is more likely than those patients who come in when their losses exceed 40 dB and their discrimination scores are reduced due to deprivation effects.
If one were to crunch the numbers( which I have), approximately 25% of the patients we see over the age of 65 will go on to some form of dementia. Hearing loss contributes to cognitive decline. In an article in Age and Aging 2003, they found after 24 weeks of wearing a hearing aid (should have been binaural, but that's another response), 30% of dementia patients showed no further cognitive decline and 40% showed improvement on cognitive measures. If through the use of appropriately fit hearing aids, we can slow down cognitive decline and keep people in their homes and functional, then that would be well worth any effort we can use to prevent degenerative effects. This would be accomplished by making the general public aware that not doing something about their hearing losses has consequences in other areas of their life instead of just the social issue. Telling someone that they will hear their spouse better has not been successful. It'! s only penetrated 25% of the hearing impaired population. Telling them they can help to preserve the integrity of multiple areas of the brain that respond to sound and they are much more likely to seek help and wear their hearing aids appropriately. But we must learn to fit hearing aids to the psychological comfort first and worry about prescription formulas, REMs, and audiograms later. Reducing volume to below a prescription formula is absolutely correct if the so called "prescription" is initially too loud.
I see people at 3 weeks post fit, 7 weeks, 4 months and 6 months post fit. It is a positive sign that if the aids are comfortable at the initial fitting and they then need to be turned up at the 7 week check, that the auditory system has regained some function and is more efficient at handling sound. Why do we continue to insist on telling patients "You'll get use to it". Some things they will, but wearing hearing aids beyond their neurophysiology is not one of them. 1/3 of patients stop wearing their hearing aids within the first year. In my 15.5 years of experience, the main reason is usually that the hearing aids are set too loud. Reduce the gain and reduce the compression and these people have a chance to rehabilitate their system and gradually increase responsiveness to sound. Telling someone to bench press 200 lbs when all they can do that day is 150 is unreasonable. Give them training at 150, gradually increasing the ! weight and over 6 months, they'll likely be closer to the 200, done in a manner that is far less discouraging and frustrating.
I apologize for any excessive tirade, but I care about my patients and once you have read the amount of material I have and continue to read, fitting hearing aids by prescription formulas or by the audiogram doesn't make sense. I fit them to the patients individual history, (psychological, medical, pharmacological) and then I worrry about what some machine tells me about the performance of the hearing aid at level of the eardrum. Last time I checked, the brain does the work. Let's give it the credit and consideration it deserves.