Featured Research

from universities, journals, and other organizations

Protecting ears from hearing loss: Primary role of olivocochlear efferent system discovered

Date:
March 27, 2013
Source:
Massachusetts Eye and Ear Infirmary
Summary:
New research may have discovered a key piece in the puzzle of how hearing works by identifying the role of the olivocochlear efferent system in protecting ears from hearing loss.

New research from the Massachusetts Eye and Ear, Harvard Medical School and Harvard Program in Speech and Hearing Bioscience and Technology may have discovered a key piece in the puzzle of how hearing works by identifying the role of the olivocochlear efferent system in protecting ears from hearing loss. The findings could eventually lead to screening tests to determine who is most susceptible to hearing loss.

Their paper is published today in the Journal of Neuroscience.

Until recently, it was common knowledge that exposure to a noisy environment (concert, iPod, mechanical tools, firearm, etc.), could lead to permanent or temporary hearing loss. Most audiologists would assess the damage caused by this type of exposure by measuring hearing thresholds, the lowest level at which one starts to detect/sense a sound at a particular frequency (pitch). Drs. Sharon Kujawa and Charles Liberman, both researchers at Mass. Eye and Ear, showed in 2009 that noise exposures leading to a temporary hearing loss in mice (when hearing thresholds return to what they were before exposure) in fact can be associated with cochlear neuropathy, a situation in which, despite having a normal threshold, a portion of auditory nerve fibers is missing).

The inner ear, the organ that converts sounds into messages that will be conveyed to and decoded by the brain, receives in turn fibers from the central nervous system. Those fibers are known as the olivocochlear efferent system. Up to now, the involvement of this efferent system in the protection from acoustic injury -- although clearly demonstrated -- has been a matter of debate because all the previous experiments were probing its protective effects following noise exposures very unlikely to be found in nature.

Stephane Maison, Ph.D., investigator at the Eaton-Peabody Laboratory at Mass. Eye and Ear and lead author, explains. "Humans are currently exposed to the type of noise used in those experiments but it's hard to conceive that some vertebrates, thousands of years ago, were submitted to stimuli similar to those delivered by speakers. So many researchers believed that the protective effects of the efferent system were an epiphenomenon -- not its true function."

Instead of using loud noise exposures evoking a change in hearing threshold, we used a moderate noise exposure at a level similar to those found in restaurants, conferences, malls, and also in nature (some frogs emit vocalizations at similar or higher levels) and instead of looking at thresholds, we looked for signs of cochlear neuropathy, Dr. Maison continued.

The researchers demonstrated that such moderate exposure lead to cochlear neuropathy (loss of auditory nerve fibers), which causes difficulty to hear in noisy environments.

"This is tremendously important because all of us are submitted to such acoustic environments and it takes a lot of auditory nerve fiber loss before it gets to be detected by simply measuring thresholds as it's done when preforming an audiogram," Dr. Maison said. "The second important discovery is that, in mice where the efferent system has been surgically removed, cochlear neuropathy is tremendously exacerbated. That second piece proves that the efferent system does play a very important role in protecting the ear from cochlear neuropathy and we may have found its main function."

The researchers say they are excited about this discovery because the strength of the efferent system can be recorded non-invasively in humans and a non-invasive assay to record the efferent system strength has already been developed and shows that one is able to predict vulnerability to acoustic injury (Maison and Liberman, Predicting vulnerability to acoustic injury with a noninvasive assay of olivocochlear reflex strength, Journal of Neuroscience, 20:4701-4707, 2000).

"One could envision applying this assay or a modified version of it to human populations to screen for individuals most at risk in noise environments," Dr. Maison concluded.

This work was supported by the National Institute on Deafness and Other Communication disorders (Grants RO1 DC 0188 and P30 DC 05209).


Story Source:

The above story is based on materials provided by Massachusetts Eye and Ear Infirmary. Note: Materials may be edited for content and length.


Journal Reference:

  1. S. F. Maison, H. Usubuchi, M. C. Liberman. Efferent Feedback Minimizes Cochlear Neuropathy from Moderate Noise Exposure. Journal of Neuroscience, 2013; 33 (13): 5542 DOI: 10.1523/JNEUROSCI.5027-12.2013

Cite This Page:

Massachusetts Eye and Ear Infirmary. "Protecting ears from hearing loss: Primary role of olivocochlear efferent system discovered." ScienceDaily. ScienceDaily, 27 March 2013. <www.sciencedaily.com/releases/2013/03/130327133521.htm>.
Massachusetts Eye and Ear Infirmary. (2013, March 27). Protecting ears from hearing loss: Primary role of olivocochlear efferent system discovered. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2013/03/130327133521.htm
Massachusetts Eye and Ear Infirmary. "Protecting ears from hearing loss: Primary role of olivocochlear efferent system discovered." ScienceDaily. www.sciencedaily.com/releases/2013/03/130327133521.htm (accessed July 23, 2014).

Share This




More Health & Medicine News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Courts Conflicted Over Healthcare Law

Courts Conflicted Over Healthcare Law

AP (July 22, 2014) Two federal appeals courts issued conflicting rulings Tuesday on the legality of the federally-run healthcare exchange that operates in 36 states. (July 22) Video provided by AP
Powered by NewsLook.com
Why Do People Believe We Only Use 10 Percent Of Our Brains?

Why Do People Believe We Only Use 10 Percent Of Our Brains?

Newsy (July 22, 2014) The new sci-fi thriller "Lucy" is making people question whether we really use all our brainpower. But, as scientists have insisted for years, we do. Video provided by Newsy
Powered by NewsLook.com
Scientists Find New Way To Make Human Platelets

Scientists Find New Way To Make Human Platelets

Newsy (July 22, 2014) Boston scientists have discovered a new way to create fully functioning human platelets using a bioreactor and human stem cells. Video provided by Newsy
Powered by NewsLook.com
Gilead's $1000-a-Pill Drug Could Cure Hep C in HIV-Positive People

Gilead's $1000-a-Pill Drug Could Cure Hep C in HIV-Positive People

TheStreet (July 21, 2014) New research shows Gilead Science's drug Sovaldi helps in curing hepatitis C in those who suffer from HIV. In a medical study, the combination of Gilead's Hep C drug with anti-viral drug Ribavirin cured 76% of HIV-positive patients suffering from the most common hepatitis C strain. Hepatitis C and related complications have been a top cause of death in HIV-positive patients. Typical medication used to treat the disease, including interferon proteins, tended to react badly with HIV drugs. However, Sovaldi's %1,000-a-pill price tag could limit the number of patients able to access the treatment. TheStreet's Keris Lahiff reports from New York. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins