Simulation of phase-dependent pattern changes to perturbations of regular firing in crayfish stretch receptor

A comparison was made of responses of a repetitively firing neuron to perturbations imposed in an ongoing steady firing pattern with those predicted by a model termed the 'active pacemaker model' and by a simpler 'integrate-and-fire' model. The active pacemaker model simulates the kinetics of processes such as active response generation and electrogenic sodium pumping which govern the membrane potential trajectory between a reset-point following an impulse and threshold for the next impulse. Responses of the crayfish stretch receptor neuron (MRO) and of both models were studied for both abrupt steps and square pulses of current, both hyperpolarizing and depolarizing, as a function of phase of the start of the stimulus in the normal interspike interval. Physiological results are consistent with a substantially weaker effect of a perturbation delivered earlier in the interspike interval as compared to the same one given later. The active pacemaker model successfully simulates several of the prominent results of the physiology (though by no means all), while the linear integrate-and-fire model is less successful.