Auditory brainstem response and cochlear microphonic potentials evoked by the bone-conducted ultrasound above the hearing range in guinea pigs.

Abstract

Ultrasound, or sound at frequencies exceeding the conventional range of human hearing, is not only audible to mice, microbats, and dolphins, but also creates an auditory sensation when delivered through bone conduction in humans. Although ultrasound is utilized for brain activation and in hearing aids, the physiological mechanism of ultrasonic hearing remains unknown. In guinea pigs, we found that ultrasound above the hearing range delivered through the temporal bone evokes not only an auditory brainstem response (ABR) but also a mechano-electrical transduction current through hair cells, as shown by the local field potential called the cochlear microphonic potential (CM). The CM synchronizes with ultrasound, and like the response to audible sounds is actively and nonlinearly amplified. The results indicate that the cochlea can detect ultrasound stimuli with frequencies more than two octaves higher than the upper limit of the ordinary hearing range. If hearing thresholds in ultrasonic hearing can capture the pre-symptomatic states of diseases, they could be used for prevention, prognostic prediction, and the development of treatments.