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Light-based implant restores hearing in rats

Image credit: Mykola Romanovskyy/Dreamstime

Scientists have created an implant based on LED lights that can safely and partially restore the sensation of hearing in deaf rodents – a feature that could be applied to hearing aids for humans.

The study on rodents, conducted by researchers at the University Medical Center Göttingen in Germany, shows that cochlear implants that restore hearing could be improved by genetically modifying the nerve cells in people’s ears so that they respond to light instead of electricity. 

According to the researchers, their design’s light-based approach delivers more accurate and pinpointed signals to auditory nerves compared with current implants based on electricity, which often suffer from poor sound quality. It also offers some improvements over previous experimental optical implants suggesting it could boost the clinical viability of cochlear implants to treat hearing impairment.

“This is so much better than what we currently have with electrical implants,” said Tobias Moser, a professor of Auditory Neuroscience at the university. 

Our hearing relies on hair cells inside the cochlea of our ears detecting sounds of different frequencies and then stimulating the right auditory nerve cells. Damage to these hair cells is a common cause of deafness, which affects approximately 5 per cent of people worldwide.

Cochlear implants can partly restore hearing by electrically stimulating nerve cells, bypassing the hair cells. However, the electrical signals stimulate lots of nerve cells at once, meaning the resulting sound is less detailed – the audio equivalent of a low-resolution image. 

The issue at hand is that salty fluid inside the cochlea conducts electricity, making it difficult to confine the signal. To overcome this, Moser’s team is developing optical cochlear implants that use light to stimulate the nerve cells.

Moser’s team has previously shown that the concept works by using a single optical fibre to stimulate the cochlea in deaf animals that have modified auditory nerve cells. Now the researchers have tested an implant with 10 LED chips in rats.

A silicone-molded optical cochlear implant undergoing a bending test

A silicone-molded optical cochlear implant undergoing a bending test.

Image credit: D. Keppeler et al., Science Translational Medicine (2020)

After the implant was inserted into deaf rats with modified auditory nerve cells the animals responded to a sound they had been trained to respond to before being deafened.

The scientists confirmed that the device generated more selective signals than prior designs when implanted into deafened rats and gerbils, and the animals successfully navigated sound-based behavioural tests over the course of several weeks. 

“This shows that what they [rodents] heard via the implant was sufficiently similar,” Moser explained. “I think this is a great achievement.”

The researchers noted that more work is needed to address the device’s large size and broad spread of light before it can be tested in human clinical studies. However, they said that for people, they will create implants with 64 light sources or channels, and hope to begin human trials around 2025.

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