Shedding light on the cochlea: Two new optical probes for investigating the inner ear

This research program will develop new optical probes that can be used to answer fundamental questions about the inner ear. The hearing part of the inner ear, the cochlea, is the organ responsible for transducing acoustic stimuli into neural impulses. The cochlea is a highly dynamic structure that acts both as a tapered passive acoustic waveguide, and as a nonlinear, compressive electromechanical amplifier. Many fundamental questions remain unanswered about the exact nature of the amplification mechanism, intracochlear hydrodynamics and the etiology of various cochlear disorders such as Meniere's Disease, Sudden Sensorineural Hearing Loss and tinnitus. The proposal is to create two new probes for investigating the cochlea. The first is an imaging probe that makes use of optical coherence tomography (OCT). OCT is an optical interferometric technique that allows depth-resolved imaging of transparent and semitransparent tissues. While it is used extensively for opthalmic, intravascular and gastrointestinal imaging, it has only recently been applied to the auditory system. We will build the first OCT endoscope for imaging the cochlea and develop Doppler techniques to allow us to watch intracochlear organs move in response to sound.The second probe is an interferometric optical probe that will allow us to measure the dynamic pressure of fluids inside the cochlea in response to sound. Used in conjunction with imaging technologies, this probe will allow us to map out the complex hydrodynamics that occur inside the cochlea and, for the first time, to study intracochlear pressure at very low sound level. At low sound levels, the auditory system has to compete with thermal noise and makes strong use of a mechanical amplification mechanism which is still poorly understood. This probe will help to illuminate the cochlea's behaviour at these low signal levels.