A team of scientists led by Joshua Greene put people in an fMRI machine to watch what their brains did while they thought about the trolley problem and its other versions. When people thought about pulling the trolley switch to kill one person instead of five, the parts of the brain that do cool, rational thinking (the prefrontal cortex) lit up. When people thought about pushing a fat man onto the track, the parts of their brain that do emotion (the amygdala) lit up. The people decided not to push the fat man onto the track. Greene and the other scientists said they think human beings are more likely to make moral decisions using intuition when they are feeling emotions, for example the disgust they feel at the thought of killing an innocent fat man. Green and the other scientists said they think human beings are more likely to make decisions using logic when their emotions are not involved.