General mechanisms of BPR. (A) The electrical circuit provides a schematic representation of the compartmentalization of the PC model, highlighting the axon initial segment (AIS), soma and dendrites. Membrane potential in the main nodes (VAIS, Vsoma, Vdend) depends on current flow along the internal resistances (Rsoma-AIS, Rdend-soma) and through the membrane of each compartment (including leakage resistances and voltage-dependent ionic channels). Traces on the left show the BPR (enhanced for the purpose of clarity by increasing KCa by 50%) along with the current flowing through the AIS membrane (the action potential current threshold is indicated) and the AIS Na channel states (open, closed, inactivated and blocked). Traces on the bottom show the current flowing through internal resistances from dendrites to soma and AIS. The action potential current threshold is indicated by dotted lines (see “Materials and Methods” Section for details). (B) Effect of ionic channel knock-out from the PC model on BPR. Left, voltage traces. Right, corresponding percent change of the ratio between pause and basal ISI in the different conditions.