Integer multiple spiking in neuronal pacemakers without external periodic stimulation

An integer multiple spiking, whose interspike intervals (ISIs) were mostly located at the integer multiples of a basic ISI, was observed in the experiment on a neuronal pacemaker without external periodic stimulation. It was observed between the period 1 spiking and the subthreshold oscillation when extra-cellular calcium concentration ([Ca++](o)) was changed as a control parameter. A Hopf bifurcation point across which the period 1 spiking changed into the subthreshold oscillation directly was observed in the corresponding parameter region in the deterministic Chay model. In the stochastic Chay model, if the parameter nu (c) (corresponding to [Ca++](o) in the experiment) was changed across the Hopf bifurcation point, the integer multiple spiking, appeared between the period 1 spiking and the subthreshold oscillation, was simulated. It exhibited similar characters to those in the experiment and was verified to be caused by autonomous stochastic resonance (ASR). The result revealed the sequence of firing patterns near the Hopf bifurcation point and indicated that ASR was probably the cause of the generation of the integer multiple spiking in the experiment. (C) 2001 Elsevier Science B.V. All rights reserved.