Feature Of The Week 04/05/15: Noninvasive in vivo Imaging Reveals Differences Between Tectorial Membrane and Basilar Membrane Traveling Waves in the Mouse Cochlea
Sound is encoded within the auditory portion of the inner ear, the cochlea, after propagating down its length as a traveling wave. For over half a century, vibratory measurements to study cochlear traveling waves have been made using invasive approaches such as laser Doppler vibrometry. While these studies have provided critical information regarding the non-linear processes within the living cochlea that increase the amplitude of vibration and sharpen frequency tuning, the data have typically been limited to point measurements of basilar membrane vibration. In addition, opening the cochlea may alter its function and affect the findings. Here we describe volumetric optical coherence tomography vibrometry, a technique that overcomes these limitations by providing depth-resolved displacement measurements at 200 kHz inside a 3D volume of tissue with picometer sensitivity. We studied the mouse cochlea by imaging non-invasively through the surrounding bone to measure sound-induced vibrations of the sensory structures in vivo, and report the first measures of tectorial membrane vibration within the unopened cochlea. We found that the tectorial membrane sustains traveling wave propagation. Compared to basilar membrane traveling waves, tectorial membrane traveling waves have larger dynamic ranges, sharper frequency tuning, and apically-shifted positions of peak vibration. These findings explain discrepancies between previously-published basilar membrane vibration and auditory nerve single unit data. Since the tectorial membrane directly overlies the inner hair cell stereociliary bundles, these data provide the most accurate characterization of the stimulus shaping the afferent auditory response available to date.
For more information see recent Article. Courtesy of Hee Yoon Lee from Stanford University.