At present, more than 1.4 billion people live with hearing loss globally. Hearing disorders are often caused by aging, frequent exposure to loud noises and even hereditary factors. In this article, we will look at some of the latest advancements in hearing disorders research which could broaden the scope for treatments and other measures to curb auditory loss.
Hearing loss research was first documented in 1550 BC in an Ancient Egyptian medical text Ebers Papyrus, which contained a remedy for ‘Ear that Hears Badly’; an outlandish concoction of liquids like olive oil, red lead, goat urine and ant eggs, to be injected into the ear.
Then, in the 16th century, the first school to teach sign language to pupils who were deaf, was established in Spain. And, in a major breakthrough in scientific research, the first-ever pair of hearing aids, ‘ear trumpets’ were developed in the 1610s, which resembled a horn.
In 1898, the first portable hearing aid which used a carbon transmitter to convert weak signals to strong ones, was developed by American electrical engineer Miller Rees Hutchinson.
However, the mass production of hearing aids only began in the early 1900s, with the devices getting more compact and convenient to use as technology progressed. Soon enough, the invention of the cochlear implant (CI) transformed therapeutic research when the first one was successfully implanted by two doctors in California, in the U.S..
Currently, there are various studies being conducted to determine how the factors contributing to hearing loss could be altered to potentially cure hearing disorders. Here are five of the latest studies on hearing disorders, which could possibly influence therapeutic research in the field.
New research indicates link between hearing loss and dementia
A new research has revealed a link between hearing loss and dementia in older adults.
The research, which was published by Johns Hopkins Bloomberg School of Public Health in Maryland, U.S.A in January 2023, showed that people, specifically older adults who have been diagnosed with hearing disorders, are more likely to have dementia – a condition that is associated with the decline in brain functioning where symptoms affect memory, attention and other mental abilities.
However, the greater discovery is that the likelihood of dementia was lower among those who wore hearing aids.
“This study refines what we’ve observed about the link between hearing loss and dementia, and builds support for public health action to improve hearing care access,” said Alison Huang, who is the lead author of the research paper and a senior research associate in the Bloomberg School’s Department of Epidemiology and at the Cochlear Center for Hearing and Public Health.
The medical trials studied 2,413 individuals, nearly 50% of them being over the age of 80, where the prevalence of dementia was 61% higher among those participants with moderate to severe hearing loss when compared to participants who had normal hearing. Moreover, the use of hearing aids exhibited a decrease in the prevalence of dementia by 32% in 853 participants who had moderate and severe hearing loss, indicating that treating hearing disorders could lower the risk of dementia.
The research is part of a larger investigative analysis – National Health and Aging Trends Study (NHATS) – which began in 2011, and is funded by the National Institute on Aging in the U.S..
Although the reason why people with hearing loss have a greater possibility of being diagnosed with dementia is yet to be determined through further clinical studies – which will take place this year – this breakthrough drives the need for more hearing loss therapies.
Could hearing loss be reversed? New study finds out
A step forward in hearing disorders research, studies have shown that there could be a potential for the reversal of hearing loss.
The research, which was conducted by Del Monte Institute for Neuroscience at the University of Rochester in New York, in the U.S., has found that although cochlear hair cells (sensory cells for hearing) cannot be repaired in human beings with hearing loss, the cells can be regenerated in birds and fish, influencing research in cell regeneration in mammals.
Previously, it was discovered that the expression of ERBB2 – an active growth gene – was able to activate the development of new hair cells in mammals, but the mechanism behind it was not fully understood initially, according to Patricia White, a professor of Neuroscience and Otolaryngology at the University of Rochester Medical Center. Eventually, it was found that the activation of ERBB2 triggered a cascade of cellular events where the cells began to multiply to become new sensory hair cells.
The study, published in January 2023, examined the process of regeneration of hair cells in mice using single-cell RNA sequencing, where the overactive ERBB2 was observed. It was determined that this signaling promoted stem cell-like development with the expression of proteins through the CD44 receptor – which are present in the hair cells.
“This discovery has made it clear that regeneration is not only restricted to the early stages of development. We believe we can use these findings to drive regeneration in adults,” said Dorota Piekna-Przybylska, scientist and an author of the study.
Risk of tinnitus increases with noise levels, study finds
Data from 3.5 million Danes were gathered to determine a link between traffic noise and the risk of tinnitus – a condition which causes a ringing in the ears.
The study was conducted by the University of Southern Denmark (SDU) and published in Environmental Health Perspectives in February 2023, to recognize whether varying degrees of noise can result in being diagnosed with tinnitus. The research established that with an increase in every ten decibels, the risk of developing tinnitus increases by six percent, according to Manuella Lech Cantuaria, researcher and assistant professor at the Maersk Mc-Kinney-Moller Institute at SDU.
This followed a study in 2021 that found a correlation between traffic noise and dementia, particularly Alzheimer’s disease.
These findings contribute to the growing evidence of sounds of traffic being a detrimental pollutant affecting health, particularly of city-dwellers in congested areas.
“We want to increase the focus on the health risks associated with being exposed to noise, which is not only an annoyance but also harmful to your health. Hopefully, our results can help influence urban development,” said Cantuaria, who believes that noise regulation programs such as highway shielding and noise-reducing asphalt should be considered.
Stimulating regions in the brain could bolster effect of cochlear implants
The efficacy of cochlear implants could be improved, according to a new study that targets the locus coeruleus – a region in the brainstem that produces the hormone noradrenaline which is a neurotransmitter.
The study used rat models that were fitted with cochlear implants to determine the performance of the devices. It was observed that the stimulation of the locus coeruleus through its production of noradrenaline led to improved effectiveness of the implants.
Researchers monitored two groups of rats – one set with a stimulated locus coeruleus and the other without, after training them to respond to auditory stimuli. The ones which had an activated brainstem learned faster and responded to the tasks quicker. These rats completed the auditory task within three days while those that did not receive the boost took up to 16 days, indicating the role of the locus coeruleus in reviving hearing.
Researchers of the study have pointed out the relevance of the locus coeruleus in mirroring the rat models’ ability and have stated the need for noninvasive mechanisms to trigger regions of the brain for further studies for hearing disorders.
Drug-induced hearing loss could be treated, study determines
Aminoglycosides, a class of antibiotics which are used as prophylactics – treatments to prevent diseases – and to treat infections in the urinary tract and abdomen, have been found to cause the dysfunction of autophagy – the recycling of old cells – in hair cells, leading to permanent hearing loss.
These findings have given rise to the research potential for therapeutic autophagy components to target aminoglycosides ototoxicity (drug-induced hearing loss), according to the research which was conducted by Indiana University School of Medicine in the U.S..
According to Bo Zhao, researcher and assistant professor at the Indiana University School of Medicine, the translocation of RIPOR2 – a protein required for auditory perception – caused by the binding of the aminoglycosides to the protein, affects autophagy activation, resulting in hair cell death.
The scientists found that reducing the expression of RIPOR2 prevented the death of hair cells in mice.
The proteins which were identified in the research could be significant drug targets for hearing loss which is caused by medicines like antibiotics.
