2-B-S37-2 〇任 書晃¹、安部 力¹、堀井 和広¹、森元 伊織¹、小川 博史^1,2、長瀬 典子^1,2、小川 武則² Fumiaki Nin¹, Chikara Abe¹, Kazuhiro Horii¹, Iori Morimoto¹, Bakushi Ogawa^1,2, Noriko Nagase^1,2, Takenori Ogawa^{2 1}岐阜大・院医・生理、²岐阜大・院医・耳鼻咽喉科・頭頸部外科 ¹Dept. of Physiol. Grad. Sch. of Med. Gifu Univ., ²Dept. Otolaryngol. Grad. Sch. of Med. Gifu Univ. 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.