Hear Res 2005 Jun 01;2041-2:29-36. doi: 10.1016/j.heares.2004.12.009.

Auditory evoked potentials from medulla and midbrain in the clawed frog, Xenopus laevis laevis.

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Auditory evoked potentials (AEPs) to clicks and tonal pulses were recorded from medulla and midbrain in Xenopus laevis laevis. They comprise three components: an initial peak (I) at 2.2-3 ms latency, a fast series of peaks (F) at 5-15 ms latency, and a slow negative wave (S) at 20-40 ms latency. In medullary recordings, the initial peak was largest, whereas in midbrain recordings typically the two other components prevailed. For all components and animals, response threshold at 4 clicks/s was approximately 69 dB SPL. In response to tonal stimuli, AEP amplitudes were maximal at 1.3-2.0 and 3.5 kHz. Raising the click rate to 100/s gradually reduced the amplitude of the I and the first F peaks, whereas later F peaks and the S wave virtually disappeared at 20-40 clicks/s. On the other hand, extending the plateau duration of tonal stimuli from 4 to 10 ms hardly affected the I and F peaks but doubled the S amplitude. This suggests two systems for stimulus processing, a fast system capable to follow clicks up to high repetition rates and a slow system with longer integration time.

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