Fig. 4. The elevation of intracellular Ca²⁺ raises the V_ts and prolongs the RP of sequential spikes in regular-spiking neurons. (A) The superimposed waves of measuring absolute RP for spike 3 under control (blue traces) and adenophostin-A (red traces) infusion, where the absolute RP is defined as the duration from a complete spike to a subsequent spike evoked with 50% probability. (B) The relationship between the normalized stimuli and the absolute RP of spike 1 (S₁, triangles) or spike 3 (S₃, diamonds) under control (open symbols) and adenophostin-A (filled symbols) infusion, in which linear correlations are shifted upward. Values of the absolute RP-3 relevant to the similar stimulus intensity are statistically different (P<0.01). (C) The difference between V_ts and V_r (V_ts–V_r) for spike 1 to spike 5 under control () and adenophostin-A () infusion, where V_ts values relevant to the same number in sequential spikes are statistically different (P<0.01).