June’s paper provides an unprecedented glimpse into the acoustical mechanics of a hearing structure deep within the ear that has been largely inaccessible for measurement.
This research was conducted as part of an investigative collaboration, and includes members of the OHSU Departments of Biomedical Engineering, Department of Dermatology, the Oregon Hearing Research Center, and other institutions.*
The ear is a remarkably sensitive sensory system.
Inside the inner ear, faint sounds cause motions that are as small as the diameter of a hydrogen atom – around 1/10th of a billionth of a meter. These invisible motions have intrigued scientists for decades.
“It’s a puzzle how the ear can detect and encode information from such tiny signals,” said Alfred Nuttall, PhD, director of OHSU's Oregon Hearing Research Center and lead author of the paper. “Within the cochlea, one type of sensory cell, the outer hair cell, is essential for our ability to pick up the faint sounds. These cells have the fastest biological motility known.”
Previously, it has been difficult for scientists to determine how the outer hair cell movements act inside the ear, because the hearing organ, the organ of Corti within the cochlea, is buried deep inside the temporal bone of the skull. In fact, scientists have shown that only the organ’s easily visible first surface, the basilar membrane, has been accessible for measurements of vibration.
In a breakthrough, Dr. Nuttall and his team have developed a new kind of optical measurement system to probe motions inside the structure of the organ. By combining an interferometer with an optical coherence tomography system, they demonstrated that structures deep within the organ can be imaged and their movements measured.
Using this novel optical measurement tool, the team further demonstrated that the outer hair cells, which are sandwiched between the reticular lamina and the basilar membrane, enhance the motions of the reticular lamina, a structure that was formerly invisible and not possible to measure.
“The larger motions of the reticular lamina are important because the structures of the inner hair cells that detect and encode the sound are attached to it,” said Dr. Nuttall. “Therefore, the ear can detect faint sounds largely because the motions of the outer hair cells amplify the sound-evoked motions of the structure close to the detector, the reticular lamina.”
Pictured (Left to Right): Xiaorui Shi, MD, PhD, Fangyi Chen, PhD, Steven Jacques, PhD, and Alfred Nuttall, PhD
ABOUT PAPER AUTHORS*From the Oregon Hearing Research Center, Fangyi Chen, PhD, Dingjun Zha, MD, PhD, Anders Fridberger, MD, PhD, Jiefu Zheng, MD, PhD, Xiaorui Shi, MD, PhD, Alfred Nuttall PhD; From the Department of Biomedical Engineering, Niloy Choudhury, PhD, Steven Jacques, PhD, Alfred Nuttall, PhD; From the Department of Dermatology, Steven Jacques, PhD; From the University of Washington, Seattle, Ruikang Wang, PhD; from the Institute of Microcirculation, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, Xiaorui Shi, MD, PhD
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List of May's published OHSU faculty papers.
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ABOUT THE PAPER OF THE MONTH
The School of Medicine newsletter spotlights a recently published faculty research paper in each issue. The goals are to highlight the great research happening at OHSU and to share this information across departments, institutes and disciplines. The monthly paper summary is selected by Associate Dean for Basic Science Mary Stenzel-Poore, PhD.
June’s paper provides an unprecedented glimpse into the acoustical mechanics of a hearing structure deep within the ear that has been largely inaccessible for measurement. This multi-disciplinary team of investigators came at this problem using sophisticated imaging techniques that led them to a remarkable breakthrough in the physics of sound transmission.