Visualization of relative cochlear motions using high resolution optical coherence microscopy.

Despite enormous progress in understanding the electro-mechanical properties of outer hair cells and the molecular basis of these properties, less is known about the relative motion of the organ of Corti and accessory structures that shape cochlear responses to acoustic stimulation. Here, we characterize absolute and relative motions of apical regions of the excised gerbil cochleae using a custom Doppler optical coherence microscopy (DOCM) system. Responses to sinusoidal stimuli show nanometer-scale motions of the tectorial membrane (TM), organ of Corti structures (e.g. outer hair cells, pillar cells), and basilar membrane in the apical turn of the cochlea. Motion-magnified analysis reveals rotations about the inner pillar cells at nearly constant phase, whereas TM motion lags that of the underlying cells by as much as 0.1 radians. Our DOCM results demonstrate a new technique capable of concurrent high resolution anatomical imaging and nanometer-scale motion analysis of cellular and acellular structures in response to stapes stimulation, enabling investigations of relative cochlear motions and feedback mechanisms.