Mechanisms of bone‐conducted ultrasonic perception assessed by electrophysiological measurements in human

Abstract

Several studies have reported that bone‐conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf; however, the mechanisms involved remain unclear. We previously reported some unique characteristics of BCU perception: (1) the pitch of BCU is about ten‐odd kHz and is independent of its frequency, (2) the dynamic range of BCU is narrow, less than 20 dB, and (3) BCU mask 10–15‐kHz air‐conducted sounds. In this study, cortical magnetic field (N1m), middle latency (MLRs) and auditory brainstem responses (ABRs) and electrocochleogram (EcochG) evoked by BCU in human were recorded to clarify the neural pathway for BCU. Substantial MLRs and ABRs (wave‐I–V) were evoked by BCU as well as by air‐conducted sound. Although a clear N1m response was elicited by BCU and its equivalent current dipoles (ECDs) were estimated in the auditory cortices, ECD locations for BCU did not follow the tonotopic organization at the cortical level. Both wave I of ABRs and AP of EcochG were observed clearly, indicating that the auditory nerve was substantially activated. These results suggest that BCU goes through the normal auditory pathway—there are no special organs for BCU perception; however, unique processes may exist in the cochlea.