Researchers have found that the parts of the inner ear that process sounds such as speech and music seem to work differently than other parts of the inner ear. Researchers from Linköping University in Sweden are part of the international team behind the discovery.
“This helps us understand the mechanisms that enable us to perceive speech and music,” said Anders Fridberger, PhD, professor of neuroscience at Linköping University. “We hope that more knowledge about the capabilities of the inner ear will lead to better treatments for the hearing impaired.”
To perceive speech and music, you must be able to hear low-frequency sound. In order to do this, the brain needs information from the receptors that are located deep within the inner ear, or cochlea, close to the top section of this spiral cavity. This part of the inner ear is difficult to study, as it is embedded in thick bone that is hard to reach without causing damage. Now the research team has been able to measure, in an intact inner ear, how the hearing organ reacts to sound. The results have been published in an article in the July 2016 edition of the Proceedings of the National Academy of Sciences (PNAS).
According to the researchers, to make measurements in the inner ear, they used optical coherence tomography, a visualization technology for biological matter that is often used to examine the eye. Using this method, they were able to measure the inner ear response to sound without having to open the surrounding bone structures, and found that the hearing organ responds in a completely different way to sounds in the voice-frequency range.
Specifically, in this study the researchers investigated responses to sound in the low-frequency region of the inner ear to examine its mechanical response to sound in intact preparations. The team used optical coherence tomography to image sound-evoked vibration inside the intact cochlea, and showed that low-frequency sound moves a small portion of the basilar membrane, and that the motion declines in an exponential manner across the basilar membrane. Hence, the response of the hearing organ to speech-frequency sounds is different from the one evident in high-frequency cochlear regions. This finding goes against what was previously thought regarding how the inner ear works, particularly in response to low-frequency sounds. For more details about this finding, see the published article in PNAS.
In addition to Anders Fridberger and Rebecca L. Warren from Linköping University, Alfred Nuttall from the Oregon Health & Science University, and researchers from Imperial College London and the Indian Institute of Technology in Bombay participated in the study.
Article: Minimal basilar membrane motion in low-frequency hearing, Rebecca L. Warren, Sripriya Ramamoorthy, Nikola Ciganovic, Yuan Zhang, Teresa M. Wilson, Tracy Petrie, Ruikang K. Wang, Steven L. Jacques, Tobias Reichenbach, Alfred L. Nuttall and Anders Fridberger, PNAS, July 2016.
Image credits: Anders Fridberger, Linköping University