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Laser Cochlear Implants
Researchers at Northwestern University are investigating the development of a cochlear implant that uses light, not electrical signals, to stimulate the auditory nerve. The study is part of a five-year, $1.68 million research grant through the National Institute on Deafness and Other Communication Disorders.
Principal investigator Claus-Peter Richter, an assistant professor of otolaryngology, and colleagues suggest that a cochlear implant that uses low-energy infrared light from a laser may provide more precise stimulation of a smaller population of nerve cells, unlike the broad current spread in conventional electrical stimulation. Because the regions of stimulation are more discrete, the laser cochlear implant will better correspond with the tonotopic organization of the cochlea, conveying more accurate sound information to the brain. According to the researchers, increased accuracy in stimulating relevant nerve populations may make it possible to increase the amount of auditory information flowing to the brain, providing greater ability to perceive speech in the presence of background noise. In addition, the optical fibers that would replace the implant electrodes would not need to touch neural tissues for stimulation, minimizing tissue damage.
Research in gerbils has demonstrated that infrared light can stimulate the auditory nerve and that discrete populations of auditory nerve fibers can be stimulated, even for several hours, with no tissue damage. The researchers hypothesize that heat absorbed by water inside the tissue activates nerves.
The research, which began last year, will also attempt to identify the optimal conditions—including wavelength, pulse length, pulse frequency, and optical fiber position—required to selectively stimulate the auditory nerves in several animal models. The team will also study safety issues, such as whether the cochlea can be stimulated with lasers over several months without experiencing damage from overheating.
The eventual goal is to develop a hybrid implant that uses both electrodes and a laser for clinical testing in humans. The development of the laser, also funded by a grant from NIDCD, is being conducted by Aculight Corp. in Bothell, WA.
Visit NIDCD's Web site for more information.
Folic Acid May Slow Hearing Loss
A Dutch study shows that folic acid—a B vitamin already added to flour in the United States—may slow age-related hearing loss.
The study looked at 728 men and women aged 50 to 70, and found that participants had high blood levels of homocysteine. Since folic acid reduces homocysteine levels, the researchers concluded that the participants apparently
consumed little folic acid. Half the study participants received 800 micrograms of folic acid per day, about twice what one would get in a multivitamin pill, while the other half received a placebo. After three years, those who received folic acid supplements had less low-frequency hearing loss than those who received a placebo. No high-frequency hearing loss was observed in either group. Researcher Jane Durga of Wageningen University, Netherlands, and colleagues suggest that by fortifying their flour with folic acid, nations might lessen their citizens' age-related hearing loss. The study was published in the Jan. 2, 2007, issue of Annals of Internal Medicine (Vol. 147, pp. 1-9).
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