The persistent sodium (NaP) current is assumed to cause the plateau potentials in the soma described by . The basis for the equations describing NaP current were single-electrode voltage-clamp recordings of NaP current in guinea pig hippocampal neurons . These recordings provided steady-state activation data and we assumed the same number of gates as for the NaF channel . Time constants for activation and deactivation and the threshold of activation for NaP current were obtained from . Note: The NaP current activation follows a slope similar to that of NaF current activation, but with a lower threshold of activation.