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The only available treatment option for most types of hearing loss is a hearing aid. While hearing aids make sounds louder, they do not make speech clearer. Thus, many users of hearing aids are frustrated when they cannot understand what people are saying, particularly in the presence of background noise. This is because, in a hearing-impaired cochlea, auditory nerves are not stimulated in a normal pattern.

Stanford researchers are studying how the normal cochlea first detects and then changes the mechanical sound pressure waves before the auditory nerve is even stimulated. This process is termed “cochlear amplification” and it occurs when outer hair cells selectively amplify and sharpen the frequency response of the cochlea. When outer hair cells are lost, such as in most common causes of hearing loss like age-related and noise-induced hearing loss, the cochlea can still detect sounds but the nuances of speech are not detected. In particular, more neurons are stimulated than should be, which is often noticed by the patient as a severe discomfort to loud sounds.

Developing a treatment for hearing loss that improves speech clarity means that auditory neurons need to be stimulated selectively and in a more targeted fashion. Stanford is studying how outer hair cells are able to accomplish this naturally within the normal cochlea. The research team has pioneered the development of a new technology, Volumetric Optical Coherence Tomography Vibrometry, which permits non-invasive imaging of sound-induced vibrations within the cochlea. These vibrations are extremely small (<1 nm), but critical to normal hearing.

By studying normal-hearing and hearing-impaired animal models, the research team hopes to improve treatments for hearing loss by learning how to recreate a normal vibratory pattern within a hearing-impaired cochlea. This will stimulate the auditory nerve in a more targeted fashion. Furthermore, this technology will be developed for use in humans to guide individualized therapies that can be tailored to a patient’s disability, a principle of Stanford’s mission towards Precision Health.