Cochlear implants help hearing-impaired patients, but current technology is still far from perfect. A research team led by scientists at City University of Hong Kong (CityU) has shown that newborn hearing-impaired rats can be trained with cochlear implant stimulation to restore their ability to direct the source of sound. This finding suggests that the shortcomings of current cochlear implant techniques, rather than the lack of hearing experience in early childhood, may be the reason for the usually poor spatial hearing performance of cochlear implant patients.
The study is co-led by Professor Jan Schnupp of the City U Department of Neuroscience and Dr. Nicole Rosskothen-Kuhl of the University of Freiburg.Their findings were published in a scientific journal eLife, “Microsecond interaural time difference discrimination was restored by Cochlear implant After newborn deafness. “
Deficiencies in current cochlear implant technology
Common people Hearing Not only can the ability easily recognize different objects in the environment from the sounds they make, but they can also localize the sounds by knowing the direction in which they are coming. This ability is called spatial hearing.
Thanks to cochlear implants, many patients with such severe hearing loss can restore their hearing and talk to others. Implanted in the patient’s head, these bioengineering devices can bypass damaged inner ear hair cells and directly stimulate the nerves that connect the ear to the brain with electrical pulses. “But modern cochlea Implant “Technology is still far from perfect,” said Professor Schnup. “Especially, cochlear implant users have very poor spatial hearing.”
He explained that the human ear uses two mechanisms to collect sound information.Nerve impulses with “location codes” and accurate time patterns that have different sensitivities to specific sound frequencies in different parts of the inner ear Acoustic nerve It reflects the temporal characteristics of the incoming sound. Sensitivity to measure the arrival time difference of sound between two ears with an accuracy of 50 microseconds enables human spatial hearing. However, this ability is often completely lacking for users with cochlear implants, especially those born as hearing-impaired and who have no normal hearing experience.
Why cochlear implants cannot detect spatial hearing
Previously, many scientists assumed that this deficiency could be due to a lack of input during early childhood development. However, Professor Schnapp and his team believed that it was likely due to technical limitations or improper trade-offs in the design of current cochlear implant processors.
“Current cochlear implants strive to deliver a lot of” location information “by delivering patterns of electrical pulses along the length of the inner ear, but the amazing time that the human ear can. I haven’t taken advantage of the precision, “he explained.
To test this hypothesis, Professor Schnup, who has decades of experience in conducting physiological and behavioral studies of animal hearing, worked with Dr. Roscotencourt of the University of Freiburg to act on the ability of rats to discriminate hearing. We have developed a setup for measuring the target. Under very precisely controlled electrical stimulation.
They raised newborn deaf rats to adulthood, then fitted binaural cochlear implants and trained to determine the perceived sound direction of electrical pulses to each ear at very precise timing. Surprisingly, these hearing-impaired rats were able to learn to distinguish between 50 microsecond interaural time differences. Their ability to discriminate was no worse than that of normal hearing mice and humans.
Cochlear implant design
Professor Schnupp points out that this is the first study to show that, at least in rats, a significant reduction in early developmental hearing experience does not necessarily lead to impaired time processing in both ears in adulthood. bottom. These results mean that by paying due attention to the coordination of the stimuli presented through the two implants, those who use the implants should be able to learn to accurately localize the sound. To do.
Professor Schnupp has long underestimated how sensitive human ears are to temporal patterns because of the lack of technological advances in improving cochlear implants to fully enrich natural hearing. I thought it was because of it. Their research has proved that there is real potential for substantial benefits in new design directions, at least in animal models.
He added that the study was only the first step in a long series of studies they planned, and the team eventually found the findings. Cochlea It embeds a processor and provides “Bionic Year” users with a much richer hearing experience to overcome hearing loss.
Nicole Rosskothen-Kuhl et al, Interaural Time Difference Discrimination of Microseconds Recovered by Cochlear Implants After Newborn Hearing Loss, eLife (2021). DOI: 10.7554 / eLife.59300
City University of Hong Kong
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