Effects of EPJPs in synchronizing direct-current (DC) and TC-induced spikes in FS pairs of barrel cortex layer IV. A) Tonic-spikes without (A1) or with TC stimulus (A2) in FS pairs. B1) TC- spikes in the presence of carbenoxolone (Carb.,) in the same FS pairs. B2) Cross-correlation analysis of the response of A1 (gray), A2 (black solid line) and B1 (black dotted line). Inset: comparison of the degree of synchronization induced by TC with GJ coupling (filled black bar), D.C. with GJ coupling (filled gray bar) and TC without GJ coupling (open bar), respectively. **: p < 0.01 vs. D.C. and carbenoxolone groups, respectively, n = 5. C1) High frequency TC stimulus (4 shock@25 Hz) induced responses in the same two FS cells. Note that the TC stimuli induced an "upstate" in which the membrane potentials of the two FS cells were very close to firing threshold. C2) Cross-correlation analysis of the response traces of C1.