Smad4 mutants showed impaired modulation of inhibitory transmission in CA1. A, There was no significant difference for mIPSC amplitude and frequency between genotypes. B, Representative sweeps from two groups. C, A subtle but significant higher decay constant τ2 from Samd4 KO cells. D, The IPSC input–output curve evoked from the striatum radiatum in Smad4 KO cells was normal. E, Significant PPD was recorded from Smad4 KO cells (for each ISI, *p < 0.05).