Mechanisms of interaction of transient EPJP and EPSPs. A1) EPSP underlying ICapand INa in soma of a simulated FS cell. The ICap precedes the onset of INa. A2) In a GJ coupled pair, a suprathreshold current induced an AP in a presynaptic FS cell (not shown), and post-junctional responses (not shown). The ICap and INa of the postsynaptic (via GJ coupling) cell was plotted. The two transient ICap precedes the onset of INa . B1-3) A critical time window for TC and EPJP interactions. Two TC inputs arriving at the GJ coupled FS pairs, respectively. A weak, subthreshold TC input arrives at FS1 (gray trace) at different time point in reference to the time of a strong, suprathreshold TC input to FS0 (black trace C1) The ICap of FS1 in B2 and B1 was aligned at the onset of the two TC inputs. Note that the initial ICap transients are the same (because TC input maintains the same). However, the second transient ICap arriving 3 ms earlier (4.1 ms vs. 7.2 ms) and resulted in larger INa (suprathreshold) in FS1 (solid line). C2) The effective coupling (number of spikes/number of TC inputs) between the two transient TC inputs was plotted as a function of interval of the two TC transients in a FS cell with EPJP of 0.2 nS.