[Process of adaptation in frog auditory system neurons]

The responses of single neurones located in different parts of the auditory system of amphibians to tone signals of a small death of amplitude modulation were studied. It was shown that the firing rate generally diminished during both the first second of sounding (short-term adaptation) and subsequent several tens of seconds (long-term adaptation). In a considerable proportion of neurones, a sharp improving of the phase-locking of the response to modulation waveform was observed in parallel the drop in firing rate. These effects are expressed much more strongly in higher nucleus of the auditory system. A sharp accentuation of modulation waveform could be seen also in the completely adapted regime. In some cases, this effect was evident only after the addition of a random noise to the modulating function (stochastic resonance effect). These data were compared with physiological results obtained on mammals and with psychophysical observations.