Two-tone suppression between the ultrasounds above and within the hearing range in mice.

Hearing range differs among various species. Ultrasound, which is audible to microbats and dolphins, is inaudible to humans through air conduction. However, it can create an auditory sensation when the stimulation is transmitted through the temporal bone. This phenomenon is known as ultrasonic hearing - sounds at frequencies exceeding the normal hearing range participate in audition. Mice are among the animals that possess one of the highest upper limits of the hearing range. Although ultrasonic hearing has been experimentally demonstrated in humans and guinea pigs, its existence in mice and interaction with ultrasound within the hearing range remain unknown. In this study, we found that ultrasound above the hearing range delivered through the temporal bone evokes the cochlear microphonic potential (CM) in mice. The CM synchronized with the applied single-tone ultrasound, and was actively amplified. Furthermore, the amplitudes of the CM were suppressed by sound with subharmonic frequencies of the applied frequencies. The results indicate that hair cells in mice can detect ultrasound stimuli with frequencies over 120 kHz and ultrasounds within and above the hearing range evoked hair cell currents at the close position along the cochlea.