Freeman lab fine tunes understanding of hearing mechanism in mammalian inner ear

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November 15, 2010

EECS Professor and principal investigator in the Research Laboratory of Electronics, Dennis Freeman, and his RLE associates A.J. Aranyosi and postdoctoral associate Roozbeh Ghaffari, members of the Auditory Physiology Group and the Micromechanics Group, reported in Nature Communications that a mutation in one of three proteins of the inner ear tectorial membrane interferes with the highly refined process of mammalian hearing. This result reinforces the group's report in 2007 on the work of the gel-like tectorial membrane.

The MIT News Office Nov. 10, 2010, article details the work:

It has been known for more than 50 years that sound waves entering the ear travel along the spiral-shaped, fluid-filled cochlea in the inner ear. Hair cells lining the ribbon-like basilar membrane in the cochlea translate those sound waves into electrical impulses that are sent to the brain. As sound waves travel along the basilar membrane, they “break” at different points, much as ocean waves break on the beach. The break location helps the ear to sort sounds of different frequencies.

Until recently, the role of the tectorial membrane in this process was not well understood.

In their 2007 paper, Freeman and Ghaffari showed that the tectorial membrane carries waves that move from side to side, while up-and-down waves travel along the basilar membrane. Together, the two membranes can work to activate enough hair cells so that individual sounds are detected, but not so many that sounds can’t be distinguished from each other.

Made of a special gel-like material not found elsewhere in the body, the entire tectorial membrane could fit inside a one-inch segment of human hair. The tectorial membrane consists of three specialized proteins, making them the ideal targets of genetic studies of hearing.

One of those proteins is called beta-tectorin (encoded by the TectB gene), which was the focus of Ghaffari, Aranyosi and Freeman’s recent Nature Communications paper. The researchers collaborated with biologist Guy Richardson of the University of Sussex and found that in mice with the TectB gene missing, sound waves did not travel as fast or as far along the tectorial membrane as waves in normal tectorial membranes. When the tectorial membrane is not functioning properly in these mice, sounds stimulate a smaller number of hair cells, making the ear less sensitive and overly selective.

Read more:

MIT News Office, Oct. 10, 2007 article by David Chandler: "MIT finds new hearing mechanism. Discovery could lead to improved hearing aids"