fMRI data analysis
CORTEX
Reaction times for the go trials (either including or excluding rare go trials) were analyzed and those below 100 ms or over 800 ms were excluded. Accuracy rates were estimated as the percentage of “no response” in all no go trials. RTs and accuracy rates were analyzed separately using mixed effect linear model with condition as the fixed factor and subject as random factor. All analysis were done using R statistical software.The full-volume fMRI data were analyzed in SPM12. The whole-brain random effects model was applied using a two-stage process with separate first and second levels. For each subject, first-level GLM was used to predict regional effects of task parameters (no go vs. go signals; go signals including both “go” and “rare go” signals) on BOLD indices of activation and data from both conditions (secretin vs. placebo) were fitted into the same model. Statistical threshold was set at ROIs including the insula and motor area (including the pre-supplementary motor area, pre- and post-central cortex) were selected based on previously validated involvement in response inhibition, for example, [