A new model to analyze auditory-vestibular nerve damages
José Pichel Andrés/DICYT According to recent research, some hearing disorders caused by auditory-vestibular nerve damages are currently clinically undetectable, but they have important functional consequences, mainly because they lead to hearing impairment in noisy environments. The Instituto de Neurociencias de Castilla y León at the Universidad de Salamanca (Incyl), a neuroscience center in Spain, has formulated a theory to explain the impact those damages have on hearing and have come up with a method to simulate the problem in order to analyze it.
“There is recently published evidence that proves that both aging and noise exposure lead to the auditory-vestibular nerve fibers decrease.”, DiCYT was told by Enrique López Poveda, a researcher responsible for the study. A normal nerve has 30,000 nerve fibers, that is, “30,000 wires transmitting information to the brain”, but, with increasing age and noise exposure, they gradually and irretrievably decrease in number.
Denervation could seriously affect auditory perception. Nevertheless, at the present time, there is not any study proving the existence of this problem. “It is the classic case of the elderly people saying that they do not hear as before but the doctor said their hearing is perfect, because current tests do not detect that disorder.”, the expert explains.
Because of the auditory-vestibular nerve mechanism, the impact of this problem would be greater in noisy places; for instance, when several people are talking at the same time or when TV is on. The patient cannot make the difference between the information sources, even when audiometry results are normal.
In order to tackle this issue, Incyl has set up a new research area. “We have conducted a study to describe the possible neural mechanisms producing these damages and the impact they have on auditory perception”, López Poveda says.
Researchers have managed to simulate the effects of auditory damages in younger people with no hearing impairment. The system detracts the quality of sounds to make them similar to perceptions by patients with this type of hearing loss, so they can analyze the problem using healthy individuals. “We have proved that diminished sounds to normal people amount to elderly people hearing, that, even when test results are normal, are actually impaired.
The mechanism is based on the idea that the auditory-vestibular nerve tracks acoustic signals at random using thousands of fibers. By adding all records, it manages to reproduce the original signal, but as tracking is at random, when fibers are lost, they way the brain receives it is not very reliable. “The effect is greater in noisy places because, apart from random tracking, the noise around is random natured as well.”, he states.
“With this hearing damage model, we can analyze the daily conditions producing this pathology. As it is clinically undetectable, its impact on hearing remains unknown to us, but, this model provides us the neural mechanisms affecting hearing and allows us to simulate the way patients with this condition really hear.”, the experts says.
The first findings of the study are to be presented in June in a scientific conference in Montreal (Canada). The study has been conducted without any specific funding so far, but it has led to a new project with The University of Manchester (United Kingdom). “For two years, they have been researching on the impact of this hearing denervation on the brain and on perception. Simulating it with healthy individuals is an step forward.”, López Poveda states.
Incyl researcher assures that this work has good prospects and “will set people talking”. “It will compel us to establish a new point of view regarding hearing loss, because these auditory-vestibular nerve damages cannot be easily mended with current technologies; the solution does not lie on amplifying or restoring signals.”, he adds.
Moreover, these studies go beyond health issues; for example, “control of noise regulations are based on clinically measurable damages, but we are proving that some damages are clinically undetectable. Probably, this research area will lead us to a profound and systematic revision of preventive and protective measures regarding noise”, he states.