Physiology of cochlear efferent and afferent neurons: direct comparisons in the same animal

Exposure of the vestibulo-cochlear anastomosis in the cat allows single-unit recording of afferent fibers originating from inner hair cells and olivocochlear efferent fibers to the outer hair cells. Comparison of data obtained from individual animals show similarities in absolute threshold and dynamic range between the efferent fibers and that subset of auditory-nerve afferents with low spontaneous rates and high thresholds [Liberman (1978) J. Acoust. Soc. Am. 63, 442-455]. The afferent-efferent comparisons also show that interanimal variability in efferent excitability (thresholds and maximum discharge rates) is directly correlated with variation in the mean spontaneous discharge rate of the afferent fiber population. It is suggested that interanimal differences in efferent excitability may explain some of the interanimal variability in susceptibility to acoustic trauma.