NIH Research Shows Light Can Activate Ear Cells

Scientists at the University of Utah, Salt Lake City, have used invisible infrared light to make toadfish inner-ear cells send signals to the brain. The discovery may lead to improved cochlear implants and the invention of devices to restore vision, maintain balance, and treat movement disorders.

The idea is to talk to the brain with optical infrared pulses instead of electrical pulses, which now are used in cochlear implants to provide deaf people with limited hearing.

The research, funded by the National Institutes of Health (NIH), also raises the possibility of developing cardiac pacemakers and other new devices to aid vision, balance, and movement.

The scientific significance of the studies is the discovery that optical signals—short pulses of an invisible wavelength of infrared laser light delivered via a thin, glass optical fiber—can activate inner-ear cells related to balance and hearing.

Because infrared light can be felt as warmth, it was thought that heart and ear cells were activated by heat rather than the infrared radiation itself. However, this latest research showed that infrared light pulses generated by a light diode were able to activate the cells in the experiment.

The inner-ear cells used came from the inner-ear organ that senses motion of the head. The hair cells came from oyster toadfish, which are well-established models for comparison with human inner ears and the sense of balance.

The scientists believe their research could lead to better cochlear implants that would use optical signals, rather than electrical signals that implants utilize today.

Lead author Richard Rabbitt, professor of bioengineering (pictured), explained, “A healthy adult can hear more than 3,000 different frequencies. With optical stimulation, there’s a possibility of hearing hundreds or thousands of frequencies instead of eight. Perhaps someday an optical cochlear implant will allow deaf people to once again enjoy music and hear all the nuances in sound that a hearing person would enjoy.”

Unlike electrical current, which spreads through tissue and cannot be focused to a point, infrared light can be focused. Thus, numerous wavelengths (corresponding to numerous frequencies of sound) could be aimed at different cells in the inner ear.

Nerve cells that send sound signals from the ears to the brain can fire more than 300 times per second, so ideally, a cochlear implant using infrared light would be able to perform as well. In the University of Utah experiments, the researchers were able to apply laser pulses to hair cells to make the adjacent nerve cells fire up to 100 times per second. For a cochlear implant, the nerve cells would be activated with infrared light instead of the hair cells.

Rabbitt cautioned it may be 5 to 10 years before the development of cochlear implants that run optically. To be practical, they need a smaller power supply and light source, and must be more power efficient to run on small batteries like a hearing aid.

Taste Changes, Childhood Obesity, and Chronic Ear Inflammation

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Are middle ear infections and childhood obesity related to changes in a child’s taste? According to a report in the March issue of Archives of Otolaryngology–Head & Neck Surgery, one of the JAMA/Archives journals, children with chronic inflammation of the middle ear can experience changes in their sense of taste, and these changes may be related to childhood obesity.

Chronic otitis media with effusion (COME) is a persistent inflammation of the middle ear, in which effusion fluid is retained in the middle ear cavity. “Otitis media with effusion (OME) is a disease with a high incidence in childhood and is a common cause of hearing disturbances in children,” the authors write as background information in the article. “Although most children have a good prognosis, 10% of affected children develop recurrent or persistent OME.”

The researchers, at Kyung Hee University and The Catholic University in South Korea, conducted a case-control study to evaluate the association between the taste threshold in patients who have chronic otitis media with effusion, and the body mass index (BMI). The authors hypothesized that changes in taste function may occur in children with COME and that such changes may be associated with body weight.

The authors measured the taste thresholds of 42 children with COME who underwent insertion of a small plastic tube into the eardrum to keep the middle ear aerated, and a control group of 42 children without OME.

Four standard taste solutions—sucrose, sodium chloride, citric acid, and quinine hydrochloride—were used in chemical taste tests.

The results indicated that children who had chronic otitis media with effusion had a significantly higher BMI than those in the control group. Test results also showed that taste thresholds on the anterior part of the tongue were higher in children with COME than in the control group.

Chemical taste tests showed the thresholds of sweet and salty tastes were elevated for children in the COME group. The thresholds of bitter and sour taste were also somewhat higher in the otitis media group, but these differences were not statistically significant.

“These findings suggest an association between changes in taste and increased BMI in pediatric patients with COME,” the authors conclude.

College Students Often Overestimate Their Hearing Sensitivity

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In a University of Florida (UF), Gainesville, study of 56 college students who believed they had normal hearing, 25% did not have normal hearing sensitivity.

The unexpected discovery was made during the early stages of another UF study. Researchers at the College of Public Health and Health Professions were recruiting college students with normal hearing for a study on temporary hearing loss and personal music players.

The resulting findings were derived from 56 college students with an average age of 21 years old. Prospective participants who reported normal hearing in initial phone interviews were asked to visit the lab for hearing tests to determine their study eligibility. The participants completed a health survey and a questionnaire about their previous exposure to loud noise, such as playing a musical instrument, listening to personal music players, using lawn equipment, or attending sporting events or concerts. Participants then received hearing tests in a sound booth at all of the sound frequencies used in a traditional full clinical hearing test.

In 25% of the participants, researchers measured 15 dB or more of hearing loss at one or more test frequencies, an amount that is not severe enough to require a hearing aid, but could disrupt learning.

Of the participants who demonstrated hearing loss, 7% had 25 dB or more of hearing loss, which is clinically diagnosed as mild. The loss occurred in both the range of frequencies identified as “speech frequencies” because of their importance for speech discrimination, as well as the higher frequencies of 6 and 8 kHz.

Lead researcher Colleen Le Prell, PhD, associate professor in the Department of Speech, Language, and Hearing Sciences, said in the press statement, “Several experts have speculated that increased rates of hearing loss in young adults may be related to the popularity of personal music players. The UF study did find that the highest levels of high frequency hearing loss were in male students who reported using personal music players.”

More research is needed with a larger sample size to determine the role of personal music players and gender in noise-induced hearing loss, Le Prell added.

Le Prell is now calling for more thorough hearing tests in schoolchildren and better hearing health education for children and adolescents.

She said, “When you look carefully at hearing loss at specific frequencies or higher frequencies than you would in a traditional school-based hearing test, you find a much, much higher rate of hearing screening failures. The implication is that the current screening protocols are potentially missing a lot of hearing loss, based on the kinds of failure rates that we’ve detected when you broaden the criteria.”

The study findings appeared in a special supplement of the March issue of International Journal of Audiology.