Using sensors tucked inside the ears of live gerbils, researchers from Columbia University are providing critical insights into how the ear processes sound. In particular, the researchers have uncovered new evidence on how the cochlea, a coiled portion of the inner ear, processes and amplifies sound. The findings could lay the initial building blocks for better hearing aids and implants.
The research could also help settle a long-simmering debate: Do the inner workings of the ear function somewhat passively with sound waves traveling into the cochlea, bouncing along sensory tissue, and slowing as they encounter resistance until they are boosted and processed into sound? Or does the cochlea actively amplify sound waves? The study, published in Biophysical Journal, suggests the latter is the case.
The team, led by Elizabeth Olson, a biomedical engineer of Columbia University, used sensors that simultaneously measured small pressure fluctuations and cell-generated voltages within the ear. The sensors allowed the researchers to pick up phase shifts—a change in the alignment of the vibrations of the sound waves within the ear—suggesting that some part of the ear was amplifying sound. What causes that phase shift is still unclear although the researchers think the power behind the phase shift comes from the outer hair cells. Apparently the hair cells’ movement serves to localize and sharpen the frequency region of amplification.