We present a comparison of the intrinsic saturation of firing frequency in four simple neural models: leaky integrate-and-fire model, leaky integrate-and-fire model with reversal potentials, two-point leaky integrate-and-fire model, and a two-point leaky integrate-and-fire model with reversal potentials. "Two-point" means that the equivalent circuit has two nodes (dendritic and somatic) instead of one (somatic only). The results suggest that the reversal potential increases the slope of the "firing rate vs input" curve due to a smaller effective membrane time constant, but does not necessarily induce saturation of the firing rate. The two-point model without the reversal potential does not limit the voltage or the firing rate. In contrast to the previous models, the two-point model with the reversal potential limits the asymptotic voltage and the firing rate, which is the main result of this paper. The case of excitatory inputs is considered first and followed by the case of both excitatory and inhibitory inputs.

Department of Statistics North Carolina State University 2311 Stinson Drive Raleigh NC 27695 8203 United States of America

Institute of Physiology of the Czech Academy of Sciences Videnska 1083 14220 Prague 4 Czech Republic

Institute of Physiology of the Czech Academy of Sciences Videnska 1083 14220 Prague 4 Czech Republic; 2nd Medical Faculty Charles University 5 Uvalu 84 15006 Prague 6 Czech Republic

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