Basic properties of auditory-nerve responses from a "simple' ear: the basilar papilla of the frog.

Spike discharges initiated by mammalian inner hair cells are produced by a complicated system involving both mechanical and neural components that normally operate in a bi-directional configuration involving multiple feedback loops. In contrast, the frog basilar papilla has the equivalent of inner hair cells, but lacks outer hair cells; it has no efferent system, and no basilar membrane. This suggests that the frog basilar papilla lacks some of the mechanical and neural feedback paths characteristic of the mammalian system. Detailed measurements of tuning curves, spontaneous activity and responses to tones an clicks reveal large parametric differences between frog and mammals in spontaneous rate, absolute refractory time, long-term adaptation and phase locking. Responses to tone bursts are qualitatively similar, but parametrically quite different. More focused examinations of these effects will be able to exploit the differences in adaptation to long- versus short-duration stimuli could be caused by depletion of afferent neurotransmitter or by activation of feedback loops involving the efferent system. In the basilar papilla, any differences in adaptation must result from changes in the afferent pathway alone.