Vocal pathways modulate efferent neurons to the inner ear and lateral line

All sonic vertebrates face the problem of sound production interfering with their ability to detect and process external acoustic signals, including conspecific vocalizations. Direct efferent inputs to the inner ear of all vertebrates, and the lateral line system of some aquatic vertebrates, represent a potential mechanism to adjust peripheral sensitivity during sound production. We recorded from single efferent neurons that innervate the inner ear and lateral line in a sound-producing teleost fish while evoking fictive vocalizations predictive of the temporal features of natural vocalizations. The majority of efferent neurons showed an increase in activity that occurred in-phase with modulations in the fine temporal structure of the fictive vocalizations. Many of these neurons also showed a decrease in activity at fictive vocal offset. Efferents to the sacculus, the main auditory end organ, showed features especially well adapted for maintaining sensitivity to external acoustic signals during sound production. These included robust phase locking of efferent activity to each cycle of a fictive vocalization and a long-duration rebound suppression after each fictive vocalization that could provide a rapid, long-lasting period of sensitization to external acoustic stimuli such as the call of a conspecific. These results suggest that efferent activation by the vocal motor system can directly modulate auditory sensitivity to self-generated sounds and maintain sensitivity to ongoing external sounds. Given the conserved organization of the auditory efferent system across vertebrates, such mechanisms may be operative among all sonic vertebrates.