Physicists have identified a complex, previously unrecognized set of “modes” in the human ear that influence how it amplifies weak sounds, withstands loud noises, and recognizes a wide variety of sound frequencies. By utilizing established mathematical models on a basic representation of the cochlea, a spiral-shaped structure in the inner ear, the researchers uncovered an additional layer of intricacy in cochlear mechanics. This research provides new perspectives on the incredible ability and precision of human hearing.
Yale physicists have identified a complex, previously unrecognized set of “modes” in the human ear that influence how it amplifies weak sounds, withstands loud noises, and recognizes a wide variety of sound frequencies.
By applying established mathematical models to a basic representation of the cochlea—a spiral-shaped structure in the inner ear—the researchers unveiled an additional layer of complexity within the cochlea. This research sheds new light on the extraordinary capacity and precision of human hearing.
“We aimed to comprehend how the ear adjusts to detect faint sounds while remaining stable and responding even in the absence of external noises,” explained Benjamin Machta, an assistant professor of physics at Yale and co-senior author of a recent study published in the journal PRX Life. “While investigating this, we unexpectedly uncovered a new set of low-frequency mechanical modes that the cochlea likely possesses.”
In humans, sound is transformed into electrical signals in the cochlea, enabling the detection of sounds with frequencies across a vast range and more than a trillion-fold difference in power, down to the slightest air vibrations.
When sound waves enter the cochlea, they convert into surface waves traveling along the hair-lined basilar membrane.
“Each pure tone resonates at a specific point along this spiral organ,” said Asheesh Momi, a physics graduate student at Yale and the study’s lead author. “The hair cells at that location then communicate the tone you are hearing to your brain.”
Additionally, these hair cells function as mechanical amplifiers, injecting energy into sound waves to overcome friction and ensure they reach their intended destinations. Providing the correct amount of energy and making continuous adjustments is vital for accurate hearing, according to the researchers.
However, this represents just one known set of hearing modes within the cochlea; the Yale researchers discovered an additional, more extensive set of modes.
In these extended modes, a significant section of the basilar membrane reacts and moves in unison, even for a single tone. This collective movement affects how hair cells respond to incoming sounds and influence the energy they inject into the basilar membrane.
“Given that these newly found modes display low frequencies, we believe our results could enhance the understanding of low-frequency hearing, which remains an active area of study,” noted Isabella Graf, a former postdoctoral researcher at Yale now at the European Molecular Biology Laboratory in Heidelberg, Germany.
Graf and Machta have worked together on various studies over recent years, applying mathematical models and statistical physics concepts to deepen the understanding of biological systems, including a pit viper’s sensitivity to temperature changes and interactions between different phases of matter within cell membranes.
Michael Abbott from Yale and Julian Rubinfien from Harvard are co-authors of the new study. Machta, Momi, and Abbott are affiliated with Yale’s Quantitative Biology Institute.
This research received funding from the National Institutes of Health, a Simons Investigator award, and the German Research Foundation.
