PHASE SENSITIVITY END ENTRAINMENT IN A MODELED BURSTING NEURON

A model of neuron R15 in Aplysia was used to study the mechanisms dete rmining the phase-response curve (PRC) of the cell in response to both extrinsic current pulses and modeled synaptic input and to compare en trainment predictions from PRCs with those from actual simulations. Ov er the range of stimulus parameters studied, the PRCs of the model exh ibited minimal dependence upon stimulus amplitude, and a strong depend ence upon stimulus duration. State-space analysis of the effect of tra nsient current pulses provided several important insights into the rel ationship between the PRC and the underlying dynamics of the model, su ch as a correlation between the prestimulus concentration of Ca2+ and the poststimulus phase of the oscillation. The system nullclines were also found to provide well-defined limits upon the perturbatory extent of a hyperpolarizing input. These results demonstrated that experimen tally applied current pulses are sufficient to determine the shape of the PRC in response to a synaptic input, provided that the duration of the current pulse is of a duration similar to that of the evoked syna ptic current. Furthermore, we found that predictions of phase-locked 1 :m entrainment from PRCs were valid, even when the duration of the per iodically applied pulses were a significant portion of the control lim it cycle.