[Analysis of single unit activity evoked by tones amplitude-modulated by low-frequency noise in frog medulla].

A method for the construction of shuffled autocorrelation functions was used to characterize single units located in the cochlear nucleus of grassy frog (Rana temporaria). A continuous characteristic frequency tone modulated by repeating pieces of low-frequency noises was used as a stimulus. This function was calculated as the correlation between the firing discharges evoked by different repeating pieces of the low-frequency noise. This approach allows one to exclude the influence of refractoriness and also considerably increases the repres. A comparison of the shiffled autocorrelation function with the conventional autocorrelation function allows one to estimate the temporal dynamics of changes in the postspike excitability of the neuron. An analysis of several examples demonstrates the possibility of facilitation just after the period of absolute refractoriness in some tonic units. Neurons demonstrating only a phasic response to the onset of unmodulated voice-frequency pieces were capable to selectively respond to special moments of noise amplitude modulation. These cells demonstrate an extremely high synchronism of reaction. In the cochlear nucleus of the frog, we described a neuron characterized by the internal periodicity of firing, which is not connected with the dynamics of arriving stimuli.