Efferent involvement in neural adaptation to acoustical stimuli: Insights from otoacoustic emissions

Abstract

Neural adaptation to sound level statistics has been demonstrated at various levels of the auditory pathway, including the auditory periphery. Adaptation is thought to improve the efficiency of encoding acoustic stimuli using limited neural resources without compromising accuracy. However, the precise mechanisms underlying the statistical learning of an acoustic environment are not fully understood. This includes the potential contribution to the stimulus-specific modulation of afferent auditory nerve activity by the medial olivocochlear reflex (MOCR), an efferent feedback loop linking the brainstem to the cochlear amplifier. We used otoacoustic emissions (OAEs) to investigate evidence of neural adaptation in the MOCR in response to broadband elicitors of fluctuating intensity whose mean levels were either predictable (alternating low [48 dB SPL] and high [66 dB SPL]) or unpredictable (randomly occurring low and high mean levels). Magnitudes and time-courses of the MOCR obtained in normal-hearing ears were compared for differences based on the presence or absence of an acoustically predictable context. Our findings will provide valuable insights into the role of the efferent auditory system in neural adaptation to acoustical stimuli at the auditory periphery.