Imaging and vibrometry of the mouse cochlear apex using spectral domain optical coherence tomography
Raphael, Robert M.
Doctor of Philosophy
Hearing loss affects millions of Americans and is of increasing concern to an aging population. It can occur as a result of congenital malformations or damage to the functional soft tissues within the hearing organ, the cochlea. Current clinical imaging modalities such as magnetic resonance imaging and computed tomography do not have the necessary resolution to detect such changes and, furthermore, provide no functional information. As well, research into how the intracochlear tissues vibrate and thus transduce sound pressure waves into neural signals has stagnated because of the limitations inherent to currently available technologies. To address these challenges, we developed a spectral domain optical coherence tomography system to visualize and measure nanoscale vibrations of intracochlear structures. Using this system and mouse models, we first imaged excised cochlea from a transgenic mouse model of human hearing loss with an altered tectorial membrane. The soft tissue structures and expected anatomical variations were visible using OCT, and quantitative measurements confirmed the ability to detect critical changes relevant to hearing. We then compared the vibratory patterns of the intracochlear structures of live and dead normal hearing mice and found that active force generation by outer hair cells produced larger displacements of the tectorial membrane than any other structure, including the basilar membrane. As well, there was a traveling wave that emanated from the point of outer hair cell attachment and moved radially. This presumably propels fluid and drives the stimulation of inner hair cell stereociliary bundles. Because inner hair cells provide the majority of the afferent auditory input, these nanoscale movements thus describe how the forces produced by outer hair cells improve the auditory sensitivity and frequency selectivity of mammalian hearing.
Cochlea; Auditory physiology; Cochlear mechanics; Optical coherence tomography