In an effort to better understand how the inner ear can hear the quietest of noises, researchers from Yale University stumbled across a potential new way the human body actively manages sound waves that may help us sift out extremely low frequencies.
“We set out to understand how the ear can tune itself to detect faint sounds without becoming unstable and responding even in the absence of external sounds,” says physicist Benjamin Machta.
“But in getting to the bottom of this we stumbled onto a new set of low frequency mechanical modes that the cochlea likely supports.”
Machta and his team’s mathematical modeling of the snail-like auditory sensing organ known as the cochlea reveals a new layer of complexity in how our hearing actively manages sound waves to find meaning in all that noise.
To become sounds we can hear, vibrations push and pull frequency-specific patches of tiny hairs in the cochlea’s membrane, forcing them to emit nervous signals that are transmitted to the brain.
Those vibrations can easily lose steam as they ripple along the membrane’s surface, dulling tones and decreasing volume. It’s been understood for some time discrete patches of the cochlea’s hairs can amplify surface vibrations with a precise, well-timed ‘kick’ to assist in our hearing of the tones those patches are most sensitive to detecting.
Now it seems the ear has a similar reflex that broadly tunes surface waves regardless of its tone, sensitively striking a balance that cancels unwanted noise without introducing phantom sounds.
The super-sensitive hairs that line the basilar membrane in the cochlea can work in both a localized way, and a more extended, collective way, the models suggested, adapting as needed to manage sound waves as they’re converted into electrical signals.
Key to the new findings is the discovery that large parts of the basilar membrane can join up and act as a single entity for lower frequency sounds. That helps the cochlea better manage incoming vibrations and prevent the ear from being overloaded by sounds at higher volumes.
The findings give us a much more detailed understanding of how the cochlea and the ear work, as well as how problems with hearing might develop and opening up opportunities for future research into ear function.
“Since these newly discovered modes exhibit low frequencies, we believe our findings might also contribute to a better understanding of low-frequency hearing, which is still an active area of research,” says theoretical biophysicist Isabella Graf, previously at Yale and now at the European Molecular Biology Laboratory in Germany.
Low frequency hearing is considered to be in the range of 20–1000 Hz. In line with previous studies, it’s possible that the hair cell behavior noted in this research is crucial in making sure quieter sounds are detected and passed to the brain.
“The exploration of these extended modes and their impact on hearing continues to be an exciting avenue for future research,” write the researchers in their published paper.
The research has been published in PRX Life.
