A neural and behavioral study of auditory habituation in the bullfrog,Rana catesbeiana

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1. Neural activity (single neurons or evoked potentials) in response to repetitive acoustic stimulation was recorded at three different levels of the ascending auditory system in the bullfrog,Rana catesbeiana. 2. Auditory fibers in the eighth nerve did not habituate in response to repeated stimuli. 3. Evoked potentials from the principal nucleus of the torus semicircularis in the midbrain exhibited marked habituation only if the stimulus repetition rate was at least 1/s. 4. Evoked potentials from the central nucleus of the dorsal thalamus, the primary diencephalic target of ascending fibers from the torus semicircularis, habituated in response to stimulation rates as slow as 1 every 10s. Thus there is a pronounced change in habituation to acoustic stimuli in the dorsal thalamus compared to the torus semicircularis. Furthermore, the habituation in the central nucleus was especially effective in response to sounds with amplitude spectra similar to that in the bullfrog's mating call (simultaneous low-frequency and high-frequency energy). 5. Male bullfrogs living in a laboratory environment produced mating calls in response to playbacks of taped bullfrog mating calls. This evoked calling habituated in response to repeated playbacks. 6. Maximal evoked calling occurred at stimulus repetition rates that did not produce neural habituation in the central nucleus. These results suggest that auditory processing in the central nucleus of the dorsal thalamus may be important in mediating the evoked calling behavior of the bullfrog.