Enemy soldiers stalk your village. You hide in a cellar with some neighbors and your baby, who starts to cry. Unless you keep his mouth covered, the soldiers will find you and kill everyone. Do you smother him to save yourself and your neighbors?
Joshua D. Greene, a postdoctoral fellow at Princeton University, used fMRI scans to map subjects' brain activity. The "crying baby" question set the wheels turning in two zones: an area associated with emotion and areas linked to abstract reasoning and cognitive control. To referee the fight between incompatible emotional instincts ("Don't kill the baby") and cognitive responses ("Save more people"), an area thought to monitor conflict also kicked into gear.