Means and standard deviations (n= 8) of short interval intracortical facilitation (SICF) under different experimental conditions. SICF was normalized as a ratio of conditioned MEP to the test MEP. 2C/2A indicates SICF alone. 2G/2E indicates SICF in the presence of short interval intracortical inhibition (SICI) with same test MEP size as 2C/2A. 2Gcon/2E indicates SICF in the presence of SICI, but with adjusted S2 intensity (motor threshold in the presence of CS3). These three ratios are shown in filled columns. They are matched by test MEP size. Open columns indicate 2F/2D (SICF alone, but with adjusted S1 intensity). 2F/2D and 2G/2E used same S1 intensity. A, interaction between SICI and SICF-1. B, interaction between SICI and SICF-2. C, interaction between SICI and SICF-3. *P < 0.05, **P < 0.01, comparing SICF under different experimental conditions. SICF-2 and SICF-3 but not SICF-1 were increased by SICI with matched test MEP amplitude.