Temporary threshold shift, adaptation, and recovery characteristics of frog auditory nerve fibers

While recording from single auditory nerve fibers in a frog, a monaural 3 min pure tone stimulus at CF was used to induce temporary threshold shift (TTS). TTS magnitude was correlated with the exposure tone intensity relative to the pre-exposure best threshold of the neuron, but not with exposure tone absolute intensity. CF and spontaneous spike rate were also uncorrelated with TTS magnitude. Comparison of frequency-threshold curves (FTCs) made before and successively after exposure revealed either a maximum sensitivity loss at the tip of the FTC or an equal shift at all frequencies. Neurons tended to recover from TTS within 3 min post-exposure, regardless of the initial TTS. Thus, recovery from TTS was more rapid for larger shifts. Recovery dynamics followed single or a double negative exponential functions.